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Wettability and floatability of coal macerals as derived from flotations in methanol solutions Holuszko, Maria Ewelina 1991

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WETTABILITY AND FLOATABILITY OF COAL MACERALS AS DERIVED FROM FLOTATIONS IN METHANOL SOLUTIONS. BY MARIA EWELINA HOLUSZKO B.A.Sc., Technical University of S i l e s i a , Mining and Mineral Process Engineering, Poland, 1979 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Mining and Mineral Process Engineering) We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June 1991 * Maria Ewelina Holuszko In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of HW(A)6 MfA/B/&*£. Tfi-GCBSS '6tN£B4tA)g-The University of British Columbia Vancouver, Canada Date fht/G. /<?<?/ DE-6 (2/88) ABSTRACT In t h i s study w e t t a b i l i t y and f l o a t a b i l i t y o f c o a l p e t r o g r a p h i c components were examined u s i n g the concept of c r i t i c a l s u r f a c e t e n s i o n . Two te c h n i q u e s were s t u d i e d ; f i l m f l o t a t i o n and s m a l l - s c a l e f l o t a t i o n t e s t s . Both t e s t s use Zisman xs concept of c r i t i c a l s u r f a c e t e n s i o n of s o l i d s . In these t e s t s p a r t i c l e s are se p a r a t e d a c c o r d i n g t o t h e i r r e s p e c t i v e c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y ( f i l m f l o t a t i o n ) or c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y ( s m a l l - s c a l e f l o t a t i o n ) . S u r f a c e h e t e r o g e n e i t y of c o a l p a r t i c l e s a r i s e s from the chemica l composition of c o a l s u r f a c e . The c o a l macerals are known t o have d i f f e r e n t chemical composition and s u r f a c e p r o p e r t i e s . S u r f a c e p r o p e r t i e s of macerals and t h e i r f l o t a t i o n response have u s u a l l y been e v a l u a t e d w i t h the c o n t a c t angle o r d i r e c t f l o t a t i o n t e s t s . In t h i s study, the e s t i m a t i o n of s u r f a c e p r o p e r t i e s of c o a l macerals was accomplished by s t u d y i n g t h e i r c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y and f l o a t a b i l i t y . The w e t t a b i l i t y d i s t r i b u t i o n s of c o a l samples of v a r i o u s p e t r o g r a p h i c composition were ob t a i n e d from f i l m f l o t a t i o n . W e t t a b i l i t y of p e t r o g r a p h i c components was e v a l u a t e d i n terms of an average c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y . In s m a l l - s c a l e f l o t a t i o n experiments, c o a l p a r t i c l e s were se p a r a t e d a c c o r d i n g t o t h e i r c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y . D i f f e r e n c e s i n f l o a t a b i l i t y and w e t t a b i l i t y d i s t r i b u -t i o n s of c o a l l i t h o t y p e s and maceral c o n c e n t r a t e s a re d i s c u s s e d . M i c r o s c o p i c examination of the products from f i l m and s m a l l - s c a l e f l o t a t i o n s was used t o f u r t h e r study the e f f e c t of c o a l p e t r o g r a p h i c composition on the w e t t a b i l i t y and f l o a t a b i l i t y . i i TABLE OF CONTENTS ABSTRACT i i TABLE OF CONTENTS i i i LIST OF FIGURES v i LIST OF TABLES x i v AKNOWLEDGEMENT x v i i CHAPTER 1 INTRODUCTION 1 CHAPTER 2 HYDROPHOBICITY AND FLOATABILITY 5 2.1 W e t t a b i l i t y of s o l i d s 5 2.1.1 Theory of the w e t t a b i l i t y o f s o l i d s by l i q u i d s 5 2.1.2 C r i t i c a l s u r f a c e t e n s i o n of w e t t i n g 9 2.1.3 C r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y . 20 2.2. H y d r o p h o b i c i t y and f l o a t a b i l i t y 24 2.2.1 H y d r o p h o b i c i t y t h e o r i e s 24 2.2.2 F l o a t a b i l i t y 26 CHAPTER 3 COAL 28 3.1 Co a l p r o p e r t i e s 28 3.1.1 Chemical composition of c o a l 28 3.1.2 Rank 30 3.1.3 Type of c o a l 35 3.1.4 M i n e r a l matter 37 3.2 P e t r o g r a p h i c composition o f c o a l 40 3.2.1 O r i g i n of macerals 41 3.2.2 Chemical and p h y s i c a l p r o p e r t i e s o f macerals 44 3.2.3 M i c r o l i t h o t y p e s 45 3.2.4 L i t h o t y p e s 47 CHAPTER 4 HYDROPHOBICITY AND FLOATABILITY OF COAL . . . 50 4.1 Hydrophobic c h a r a c t e r of c o a l 50 4.1.1 Rank 51 4.1.2 O x i d a t i o n 56 4.1.3 E l e c t r i c a l charge 58 4.1.4 P e t r o g r a p h i c composition 61 i i i 4.1.5 M i n e r a l matter 63 4.2 F l o a t a b i l i t y o f c o a l 65 4.2.1 F l o a t a b i l i t y o f c o a l as a f u n c t i o n o f rank 65 4.2.2 F l o a t a b i l i t y o f l i t h o t y p e s 66 4.2.3 F l o a t a b i l i t y o f macerals 69 CHAPTER 5 OBJECTIVES AND SCOPE 73 CHAPTER 6 MATERIALS - METHODS OF PREPARATION . . 75 6.1 Glassware 75 6.2 S o l u t i o n s 75 6.3 Coa l Samples 77 6.3.1 Sample D e s c r i p t i o n 77 6.3.2 Sample p r e p a r a t i o n 78 6.3.2.1 Composite sample 79 6.3.2.2 D e n s i t y f r a c t i o n s 80 6.3.2.3 L i t h o t y p e s 80 6.3.3 Proximate and U l t i m a t e A n a l y s e s 81 6.3.4 P e t r o g r a p h i c Analyses 83 CHAPTER 7 METHODS - EXPERIMENTAL PROCEDURES 7.1 F i l m F l o t a t i o n T e s t s 7.2 S m a l l - S c a l e F l o t a t i o n T e s t s 7.2.1 Apparatus 7.2.2 Procedure 7.3 M i c r o s c o p i c Examination 7.3.1 Maceral A n a l y s i s 7.3.2 G r a i n Type A n a l y s i s CHAPTER 8 RESULTS AND DISCUSSION 108 8.1 F i l m F l o t a t i o n R e s u l t s 108 8.1.1 Composite sample 109 8.1.2 D e n s i t y f r a c t i o n s I l l 8.1.3 L i t h o t y p e s 114 8.1.4 D i f f e r e n t s i z e f r a c t i o n s . . 117 8.2 R e s u l t s of S m a l l - S c a l e F l o t a t i o n T e s t s 119 8.2.1 C o n d i t i o n s o f f l o t a t i o n 119 8.2.1.1 F l o t a t i o n time 119 8.2.1.2 C o n d i t i o n i n g time 121 8.2.2 F l o a t a b i l i t y d i s t r i b u t i o n o f c o a l p a r t i c l e s 124 8.2.2.1 Composite sample 124 8.2.2.2 D e n s i t y f r a c t i o n s 128 i v 94 94 96 96 98 101 101 103 8.2.3 Cumulative ash versus cumulative y i e l d . . 133 8.2.4 F l o a t a b i l i t y - w a s h a b i l i t y c h a r a c t e r i s t i c s . 139 8.2.5 M i c r o s c o p i c examination o f f l o t a t i o n p r o d u c t s 150 8.3 D i s c u s s i o n o f the w e t t a b i l i t y and f l o a t a b i l i t y -d i s t r i b u t i o n s r e s u l t s 154 8.3.1 W e t t a b i l i t y d i s t r i b u t i o n s o f d i f f e r e n t c o a l samples 154 8.3.2 F l o a t a b i l i t y d i s t r i b u t i o n s of d i f f e r e n t c o a l samples 157 8.3.3 S u r f a c e p r o p e r t i e s of c o a l p a r t i c l e s . . 163 8.3.4 M i n e r a l matter c h a r a c t e r i s t i c s 168 8.3.5 P e t r o g r a p h i c composition 170 8.4 Comparison o f the w e t t a b i l i t y and f l o a t a b i l i t y d i s t r i b u t i o n s 173 CHAPTER 9 CONCLUSIONS 178 9.1 Gener a l 178 9.2 W e t t a b i l i t y d i s t r i b u t i o n of v a r i o u s c o a l p a r t i c l e s 179 9.3 F l o a t a b i l i t y d i s t r i b u t i o n s o f v a r i o u s c o a l p a r t i c l e s 180 CHAPTER 10 RECOMMENDATIONS 183 REFERENCES 184 APPENDIX A PETROGRAPHIC DATA 198 A. l P e t r o g r a p h i c a n a l y s e s 198 APPENDIX B SURFACE TENSION MEASUREMENT 204 B. l Du Nouy r i n g method 204 APPENDIX C OXIDATION DETECTION - PROCEDURES 209 C. l S t a i n t e s t f o r d e t e c t i o n o f o x i d i z e d p a r t i c l e s . . 209 C.2 A l k a l i - e x t r a c t i o n t e s t f o r o x i d i z e d c o a l p a r t i c l e s 210 C.3 A d i f f u s e r e f l e c t a n c e FTIR technique 212 APPENDIX D STATISTICAL ANALYSIS 216 APPENDIX E SMALL-SCALE FLOTATION TESTS 218 APPENDIX F FILM FLOTATION TESTS 223 APPENDIX G GENERAL 227 v LIST OF FIGURES F i g u r e Page 2.1.1 Contact angle formed by water, vapor (gas), and s o l i d phases. 11 2.1.2. Zisman diagram f o r l i q u i d s and aqueous s o l u t i o n s on hydrophobic s o l i d s . (Hornsby and L e j a , 1983). 12 2.1.3 W e t t a b i l i t y diagram i l l u s t r a t i n g adhesion t e n s i o n of v a r i o u s specimens; s t i b n i t e , t a l c and p a r a f f i n wax as a f u n c t i o n of s u r f a c e t e n s i o n (Kelebek, 1987) . 14 2.1.4 Adhesion t e n s i o n diagram i l l u s t r a t i n g w e t t a b i l i t y l i n e s f o r t h r e e hydrophobic s o l i d s i n aqueous s o l u t i o n s of a s h o r t - c h a i n n - a l c o h o l , and s e l e c t i v e w e t t i n g r e g i o n (shaded area) s o l i d s A and B. (Hornsby and L e j a , 1983). 15 2.1.5 F i l m f l o t a t i o n w e t t a b i l i t y d i s t r i b u t i o n curve f o r Cambria No. 33 bituminous c o a l (a) frequency h i s t o -gram f o r l y o p h o b i c i t y of Cambria No. 33 c o a l (b) p a r t i t i o n curve (Fuerstenau e t a l . , 1988b). 18 2.1.6 Adhesion t e n s i o n diagram; the concept of c r i t i c a l s u r f a c e t e n s i o n of adhesion, Y Ca' ^ o r a hydrophobic s o l i d w i t h w e t t a b i l i t y l i n e B, (Hornsby and L e j a , 1983). 22 2.1.7 E f f e c t of the s u r f a c e t e n s i o n of methanol/water s o l u t i o n s on f l o a t a b i l i t y and w e t t a b i l i t y of molyb-d e n i t e , s u lphur and t e f l o n (Yarar and Kaoma, v i 1984). 23 3.1.1 Carbon d i s t r i b u t i o n i n c o a l s of d i f f e r e n t ranks. (Whitehurst e t a l . , 1980) 29 3.1.2 The Wiser model of s t r u c t u r a l groups and c o n n e c t i n g b r i d g e s i n bituminous c o a l s (Wiser, 1975) 31 3.1.3 P h y s i c a l and m o l e c u l a r changes of v i t r i t e d u r i n g the c o a l i f i c a t i o n of bituminous c o a l s and a n t h r a c i t e s , ( T e i c h m u l l e r , 1982). 34 3.2.1 The c o a l i f i c a t i o n t r a c k s of main maceral groups, -( T e i c h m u l l e r , 1982). 46 4.1.1 Contact angle f o r c o a l s of d i f f e r e n t ranks measured by c a p t i v e bubble and s e s s i l e drop t e c h n i q u e ; (a) c o n t a c t angles versus % Carbon, (b) c o n t a c t angles v e r s u s v i t r i n i t e r e f l e c t a n c e . 53 4.1.2 D i s t r i b u t i o n of Oxygen groups i n c o a l s of d i f f e r e n t ranks; (a) adapted from Ihnatowicz, (1952), (b) from Blom, (1957). 55 4.1.3 G e n e r a l i z e d z e t a - p o t e n t i a l v e r s u s pH diagram f o r c o a l s of v a r i o u s ranks (Laskowski and P a r f i t t , 1989) . 59 4.1.4 I s o e l e c t r i c p o i n t s f o r c o a l s o f v a r y i n g rank (Laskowski, 1968). 60 6.2.1 S u r f a c e t e n s i o n of methanol s o l u t i o n s (temp. 20+/-2 ° C ) . 76 6.3.1 D i s t r i b u t i o n of macerals i n the d e n s i t y f r a c t i o n s of -212+149 nm composite sample (mineral m a t t e r - f r e e -v i i b a s i s , o b t a i n e d from p o i n t c o u n t i n g t e c h -nique) . 85 6.3.2 D i s t r i b u t i o n of c o a l g r a i n s i n d e n s i t y f r a c t i o n s (a) ; d i s t r i b u t i o n of g r a i n s a s s o c i a t e d w i t h m i n e r a l matter and those w i t h o x i d i z e d s u r f a c e (b). 88 6.3.3 Examples of c o a l l i t h o t y p e s found i n Bullmoose c o a l seams, (Lamberson, 1989). A - d u l l c o a l ; B - banded d u l l ; C - banded c o a l ; D - banded b r i g h t ; E -b r i g h t ; F - f i b r o u s ; G,H - sheared. 90 6.3.4 Maceral a n a l y s e s of l i t h o t y p e s of Bullmoose seam A ( m i n e r a l - f r e e - b a s i s , o b t a i n e d from p o i n t c o u n t i n g t e c h n i q u e ) . 91 6.3.5 M i n e r a l matter p r e s e n t i n composite sample (a) massive c l a y on the v i t r i n i t e p a r t i c l e ; (b) s m a l l q u a r t z g r a i n s i n v i t r i n i t e ; (c) c l a y f i l l i n g the c r a c k s ; (d) c l a y s intergrown w i t h the v i t r i n i t e . 92 7.1.1 F i l m f l o t a t i o n set-up. (a) s e a p a r a t o r y f u n n e l s used f o r the f l o t a t i o n procedure; (b) f i l m f l o t a t i o n t e s t w i t h the methanol s o l u t i o n s , i n c r e a s i n g methanol c o n c e n t r a t i o n f r o m l e f t t o r i g h t . 95 7.2.1 The p l e x i g l a s s " f r o t h l e s s " P a r t r i d g e - S m i t h f l o t a t i o n c e l l used f o r the f l o a t a b i l i t y s t u d i e s ; (a) assembled; (b) b a s i c o p e r a t i o n , (Hornsby, 1981). 97 7.3.1 G r a i n s found i n the examined samples; (a),(b) f r e e v i i i v i t r i n i t e ; (c) p s e u d o v i t r i n i t e ; (d),(e) v i t r + i n e r t , V>I; i n e r t + v i t r , I>V; ( f ) , ( g ) f u s i n i t e , f r e e ; (h) v i t r + m i n e r a l matter. 104 7.3.2 D i f f e r e n t degrees of o x i d a t i o n . A,B - e x t e n s i v e o x i d a t i o n of v i t r i n i t e ; C,D o x i d a t i o n on the edges of g r a i n s ; E,F p h y s i c a l changes appearing i n g r a i n s ; c r a c k s and f i s s u r i n g . 104 8.1.1 F i l m f l o t a t i o n . The cumulative y i e l d p l o t t e d as a f u n c t i o n of s u r f a c e t e n s i o n (methanol c o n c e n t r a t i o n , volume %) f o r the composite samples: (a) high-ash; (b) low-ash. 110 8.1.2 F i l m f l o t a t i o n . The w e t t a b i l i t y d i s t r i b u t i o n s of p a r t i c l e s from v a r i o u s d e n s i t y f r a c t i o n s . 112 8.1.3 F i l m f l o t a t i o n . The cumulative w e t t a b i l i t y d i s t r i b u -t i o n f o r d i f f e r e n t l i t h o t y p e s (a) w e t t a b i l i t y d i s t r i b u t i o n ; (b) ash c ontent i n the f l o a t i n g f r a c -t i o n s . 115 8.1.4 The e f f e c t of s i z e on the w e t t a b i l i t y . F i l m f l o t a t i o n of d i f f e r e n t s i z e f r a c t i o n s of v i t r a i n (Bullmoose seam A). 118 8.2.1 The e f f e c t of f l o t a t i o n time on y i e l d and on ash of f l o a t s : (a) cumulative y i e l d of f l o a t s v e r s u s f l o t a t i o n time; (b) cumulative ash % i n f l o a t s v e r s u s f l o t a t i o n time. 120 8.2.2 The e f f e c t of c o n d i t i o n i n g time on f l o t a t i o n , (a) Cumulative y i e l d of f l o a t s v e r s u s p r e c o n d i t i o n i n g i x time; (b) Cumulative ash i n f l o a t s v e r s u s p r e c o n d i t i o n i n g time. 122 8.2.3 The e f f e c t of s i z e on f l o a t a b i l i t y . S m a l l - s c a l e f l o t a t i o n c a r r i e d out i n P/S f l o t a t i o n c e l l o f v i t r a i n (Bullmoose seam A) . 123 8.2.4 The cumulative y i e l d v e r s u s s u r f a c e t e n s i o n f o r two composite samples: (a) high-ash composite sample; (b) low-ash composite sample. 125 8.2.5 Ash content i n f l o a t s and r e j e c t s f o r the high-ash composite sample: (a) f l o a t s ; (b) r e j e c t s . 125 8.2.6 Ash content i n f l o a t s and r e j e c t s f o r the low-ash composite sample: (a) f l o a t s ; (b) r e j e c t s 125 8.2.7 The cumulative y i e l d vs s u r f a c e t e n s i o n curves f o r v a r i o u s d e n s i t y f r a c t i o n s as o b t a i n e d from P/S s m a l l - s c a l e f l o t a t i o n t e s t s . 129 8.2.8 Ash content i n the f l o a t s of the t h r e e d e n s i t y f r a c -t i o n s : (a) < 1.30 s p e c i f i c g r a v i t y ; (b) 1.30 - 1.35 s p e c i f i c g r a v i t y ; (c) 1.35 - 1.40 s p e c i f i c g r a v i t y . 131 8.2.9 Ash content i n the r e j e c t s of t h e t h r e e d e n s i t y f r a c t i o n s : (a) < 1.30 s p e c i f i c g r a v i t y ; (b) 1.30 -1.35 s p e c i f i c g r a v i t y ; (c) 1.35 - 1.40 s p e c i f i c g r a v i t y . 131 8.2.10 The cumulative y i e l d v ersus cumulative ash f o r the f l o a t s and r e j e c t s f o r the high-ash composite sample, (a) f l o a t s ; (b) r e j e c t s . 134 8.2.11 The cumulative y i e l d v e r s u s cumulative ash curves f o r the f l o a t s and r e j e c t s f o r the low-ash composite sample, (a) f l o a t s ; (b) r e j e c t s . 134 8.2.12 The cumulative y i e l d v e r s u s cumulative ash f o r the f l o a t s and r e j e c t s f o r the < 1.3 0 s p e c i f i c g r a v i t y f r a c t i o n : (a) f l o a t s ; (b) r e j e c t s . 137 8.2.13 The cumulative y i e l d v e r s u s cumulative ash curves f o r the f l o a t s and r e j e c t s f o r the 1.30 - 1.35 s p e c i f i c g r a v i t y f r a c t i o n : (a) f l o a t s ; (b) r e j e c t s . 138 8.2.14 The cumulative y i e l d v e r s u s cumulative ash curves f o r the f l o a t s and r e j e c t s f o r t h e 1.35 - 1.40 s p e c i f i c g r a v i t y f r a c t i o n : (a) f l o a t s ; (b) r e j e c t s . 140 8.2.15 The cumulative y i e l d v ersus cumulative ash curves f o r the high-ash composite sample (from w a s h a b i l i -t y ) : ( a) f l o a t s ; (b) r e j e c t s . 143 8.2.16 The in c r e m e n t a l y i e l d and ash f o r the high-ash composite sample: (a) in c r e m e n t a l y i e l d histogram; (b) i n c r e m e n t a l ash p l o t . 143 8.2.17 The i n c r e m e n t a l y i e l d and ash data f o r the low-ash composite sample: (a) in c r e m e n t a l y i e l d histogram; (b) i n c r e m e n t a l ash p l o t . 143 8.2.18 The i n c r e m e n t a l y i e l d and ash f o r t h e < 1.30 s p e c i f i c g r a v i t y f r a c t i o n : (a) i n c r e m e n t a l y i e l d h istogram; (b) i n c r e m e n t a l ash p l o t . 143 x i 8.2.19 The i n c r e m e n t a l y i e l d and ash f o r the 1.30 - 1.35 s p e c i f i c g r a v i t y f r a c t i o n : (a) i n c r e m e n t a l y i e l d histogram; (b) in c r e m e n t a l ash p l o t . 143 8.2.20 The i n c r e m e n t a l y i e l d and ash f o r the 1.35 - 1.40 s p e c i f i c g r a v i t y f r a c t i o n : (a) i n c r e m e n t a l y i e l d histogram; (b) in c r e m e n t a l ash p l o t . 149 8.2.21 F l o a t a b i l i t y of the p a r t i c l e s from the < 1.3 d e n s i t y f r a c t i o n i n methanol s o l u t i o n s . P e t r o g r a p h i c composition o f the f l o a t s . 161 8.2.22 F l o a t a b i l i t y o f p a r t i c l e s from the 1.30 - 1.35 d e n s i t y f r a c t i o n i n methanol s o l u t i o n s . P e t r o g r a p h i c composition o f the f l o a t s . 161 8.3.1 The e f f e c t of o x i d a t i o n on the f l o a t a b i l i t y of the composite sample a t v a r i o u s o x i d a t i o n temperatures. (a) n o n - o x i d i z e d ; (b) o x i d i z e d a t 120 C; (c) o x i d i z e d a t 200 C. 165 8.4.1 The t h e o r e t i c a l adhesion t e n s i o n diagram f o r the examined c o a l . L i m i t s f o r w e t t a b i l i t y and f l o a t a b i l i t y f o r : (a) the <1.30 d e n s i t y f r a c t i o n ; (b) the 1.30-1.35 d e n s i t y f r a c t i o n . 175 B. l D i s t e n t i o n of s u r f a c e f i l m d u r i n g s u r f a c e t e n s i o n measurement ( a ) ; c o n d i t i o n of s u r f a c e f i l m a t b r e a k i n g p o i n t (b). 205 C. l The FTIR s p e c t r a f o r two samples; composite and 1.3 0 s p e c i f i c g r a v i t y f r a c t i o n . 213 C.2 The FTIR s p e c t r a of the samples l a b e l e d B u l l A x i i u n o x i d i z e d (low-ash composite) and B u l l A o x i d i z e d (at 200°C). x i i i LIST OF TABLES T a b l e Page 3.1.1 D i f f e r e n t p h y s i c a l and chemical rank parameters and t h e i r a p p l i c a b i l i t y t o the d i f f e r e n t c o a l i f i c a t i o n s tages (adapted from Stach, 1982). 31 3.1.2 The dependency of the t r a n s f o r m a t i o n of o r g a n i c substances on oxygen supply ( T e i c h m u l l e r , 1982). 36 3.1.3 Common c o a l m i n e r a l s and t h e i r o r i g i n (adapted from Mackowsky, 1982). 38 3.2.1 Macerals and groups of macerals i n bituminous c o a l s (ICCP Handbook, 1963). 41 3.2.2 D e s c r i p t i o n of m i c r o l i t h o t y p e s a c c o r d i n g t o the ICCP (ICCP Handbook, 1963). 42 3.2.3 Comparison of two l i t h o t y p e c l a s s i f i c a t i o n s : S t o p e x s and A u s t r a l i a n , ( B u s t i n e t a l . , 1983). 48 6.3.1 The proximate and u l t i m a t e a n a l y s e s of l i t h o t y p e s . The r e s u l t s are presented on a d r y and ash f r e e b a s i s . 78 6.3.2 The u l t i m a t e and proximate a n a l y s e s r e s u l t s of the composite samples and the c o r r e s p o n d i n g d e n s i t y f r a c t i o n s . 82 6.3.3 Maceral a n a l y s i s of the composite and t h e 212+149 um s i z e f r a c t i o n from the composite sample. 84 7.3.1 Summary of g r a i n - t y p e a n a l y s i s . 104 A . l Maceral a n a l y s e s of f i v e l i t h o t y p e samples, (from p o i n t - c o u n t i n g t e c h n i q u e ) . 199 x i v A. 2 Maceral composition of d e n s i t y f r a c t i o n s (from p o i n t - c o u n t i n g t e c h n i q u e ) . 200 A. 3 D i s t r i b u t i o n of g r a i n s i n d e n s i t y f r a c t i o n s . D e s c r i p t i o n i n terms of a s s o c i a t i o n w i t h m i n e r a l matter and v i s i b l e o x i d a t i o n . 201 A.4 G r a i n - t y p e a n a l y s i s of the f l o a t s and r e j e c t s f o r 1.30 s p e c i f i c g r a v i t y , a t d i f f e r e n t methanol con-c e n t r a t i o n s . 202 A. 5 G r a i n - t y p e a n a l y s i s of the f l o a t s and r e j e c t s f o r 1.30-1.35 s p e c i f i c g r a v i t y , a t d i f f e r e n t methanol c o n c e n t r a t i o n s . 203 B. l The s u r f a c e t e n s i o n v a l u e s f o r methanol s o l u t i o n s used i n experiments. 207 C. 6 The t r a n s m i t t a n c e v a l u e s f o r composite sample and d e n s i t y f r a c t i o n s (%T, p e r c e n t l i g h t t r a n s m i t t e d ) . 211 D. l Comparison of the c a l c u l a t e d f e e d ash v a l u e s w i t h the measured ash v a l u e s . T e s t i n g the c o n f i d e n c e i n t e r v a l f o r f e e d ash content data. 217 E. l S m a l l - s c a l e f l o t a t i o n r e s u l t s (from t e s t s w i t h P/S c e l l ) . The y i e l d vs f l o t a t i o n time and y i e l d vs c o n d i t i o n i n g time, f o r the high-ash composite sample. 219 E.2 S m a l l - s c a l e f l o t a t i o n r e s u l t s (from t e s t s w i t h P/S c e l l ) . The y i e l d vs s u r f a c e t e n s i o n , f o r h i g h and low-ash composite sample. 220 xv E.3 S m a l l - s c a l e f l o t a t i o n r e s u l t s (from t e s t s w i t h P/S c e l l ) . The y i e l d vs s u r f a c e t e n s i o n f o r the d e n s i t y f r a c t i o n s . 221 E. 4 S m a l l - s c a l e f l o t a t i o n r e s u l t s (from t e s t s w i t h P/S c e l l ) . The y i e l d vs s u r f a c e t e n s i o n f o r the d e n s i t y f r a c t i o n s ( c o n t i n u a t i o n ) . 222 F. l F i l m f l o t a t i o n r e s u l t s o f the two composite samples and the d e n s i t y f r a c t i o n s . 224 F.2 F i l m f l o t a t i o n r e s u l t s o f l i t h o t y p e s samples. 225 F. 3 F i l m f l o t a t i o n r e s u l t s of l i t h o t y p e s samples (con-t i n u a t i o n ) . 226 G. l W a s h a b i l i t y data o f composite (+149-212 jim) Bullmoose seam A. 228 x v i AKNOWLEDGEMENT The author wishes t o express her s i n c e r e g r a t i t u d e t o her r e s e a r c h s u p e r v i s o r Dr. Janusz S. Laskowski f o r h i s guidance and support over the course of her graduate study. Thanks are a l s o extended t o the t e c h n i c a l s t a f f of the Min i n g and M i n e r a l Process E n g i n e e r i n g f o r t h e i r a s s i s t a n c e , e s p e c i a l l y t o Mrs. S. F i n o r a and Mr. F. Schmidiger. The author wishes t o express her a p p r e c i a t i o n t o P r o f e s s o r s A.L Mular, G. W. P o l i n g and M.R. B u s t i n f o r t e a c h i n g i n t e r e s t i n g c o u r s e s . S p e c i a l thanks a re extended t o P r o f e s s o r J . L e j a f o r many v a l u a b l e d i s c u s s i o n s , and t o a l l f e l l o w students i n Department o f Mining and M i n e r a l Process E n g i n e e r i n g (UBC), with whom the author had a p l e a s u r e t o work and cooperate. A s p e c i a l g r a t i t u d e i s due t o M i c h e l l e Lamberson of the Department of G e o l o g i c a l S c i e n c e s f o r p r o v i d i n g l i t h o t y p e samples and v e r y h e l p f u l comments and sugg e s t i o n s r e g a r d i n g p e t r o g r a p h i c a n a l y s i s . In p a r t i c u l a r , the author wishes t o express her thanks t o Dr. Dave Lefebure of M i n i s t r y o f Energy, Mines and Petroleum Resources f o r s i g n i f i c a n t support i n the f i n a l stages of t h e s i s p r e p a r a t i o n , and a l l c o l l e g u e s from C o a l S e c t i o n f o r t h e i r moral x v i i support. Mr. Dave A. G r i e v e and John Cunningham re a d an e a r l y d r a f t of t h i s t h e s i s and c o n t r i b u t e d t o the improvement of the t e x t f o r which the author i s the most g r a t e f u l . A v e r y s p e c i a l thanks are g i v e n t o my mother, f o r her enduring support, t o my l o v i n g husband and wonderful daughter f o r t h e i r u nderstanding, and s h a r i n g h a r d s h i p of t h e p a s t y e a r s . x v i i i CHAPTER 1 INTRODUCTION Coa l i s by f a r the w o r l d x s l a r g e s t source of energy. The economic d e p o s i t s may however be exhausted sooner than a n t i c i p a t e d i f they a r e not p r o p e r l y e x p l o i t e d and proc e s s e d . The s a y i n g , t h a t " t a i l i n g s o f today may be the p l a n t f e e d of tomorrow", suggests t h a t we might be c o n s t r a i n e d t o process s i g n i f i c a n t l y lower grade c o a l s i n the f u t u r e . In t h a t case, the understanding of the f u l l p o t e n t i a l o f c o a l may become im p e r a t i v e . In the p r o c e s s i n g of any ore i t i s c r i t i c a l t o understand the mineralogy of ore a t the e a r l i e s t p o s s i b l e o p p o r t u n i t y , whereas w i t h c o a l , the mineralogy and petrography are u s u a l l y c o n s i d e r e d as a supplementary e v a l u a t i o n . T r a d i t i o n a l l y , c o a l q u a l i t y has been as s e s s e d through parameters such as ash content, v o l a t i l e matter, s i z e and s u i t e of p h y s i c o - c h e m i c a l p r o p e r t i e s , w i t h s i g n i f i c a n t n e g l e c t o f the p e t r o g r a p h i c composition of c o a l . The o n l y area where petrography has gained a p p r e c i a t i o n i s i n the p r e d i c t i o n of c o k i n g p r o p e r t i e s of c o a l s , s i n c e a c e r t a i n r a t i o of r e a c t i v e p e t r o g r a p h i c components t o the i n e r t ones i s r e q u i r e d t o produce a c c e p t a b l e q u a l i t y coke (Ammosov e t a l . , 1957; Shapiro e t a l . , 1964; B e n e d i c t e t al.,1973; Gray e t a l . , 1978). A more d i v e r s e use of c o a l d i c t a t e s i n c r e a s i n g l y complex s p e c i f i c a t i o n s f o r the c o a l q u a l i t y . These uses i n c l u d e : c o a l as a 1 primary energy source f o r power g e n e r a t i o n ; c o n v e r s i o n of c o a l t o gaseous l i q u i d s or s o l i d f u e l s ; m e t a l l u r g i c a l uses i n p r o d u c t i o n of s t e e l ; and, f i n a l l y , c o a l as a source of hydrocarbons i n the p r o d u c t i o n of a v a r i e t y of chemical p r o d u c t s . I t i s becoming apparent t h a t most of these t e c h n o l o g i c a l uses r e q u i r e c o a l w i t h s p e c i f i c p r o p e r t i e s , and, i n many i n s t a n c e s c o a l s e n r i c h e d i n c e r t a i n p e t r o g r a p h i c components are needed. From the p o l l u t i o n c o n t r o l p o i n t of view, some of the p r o c e s s e s r e q u i r e s t r i c t l i m i t s on the q u a n t i t y of m i n e r a l matter and o t h e r d e l e t e r i o u s elements i n c o a l . To meet these s p e c i f i c a t i o n s more e f f i c i e n t and more r e f i n e d c o a l c l e a n i n g t e c h n i q u e s are necessary. For more e f f e c t i v e c l e a n i n g , the l i b e r a t i o n of combustible components of c o a l from m i n e r a l matter and l i b e r a t i o n of macerals from each ot h e r must r e s u l t . T h i s w i l l i n v o l v e a g r e a t e r degree of comminution of c o a l , f o l l o w e d by v e r y e f f i c i e n t treatment of f i n e s . The p r o c e s s i n g of f i n e c o a l has always been more p r o b l e m a t i c than the c l e a n i n g of coarse c o a l , and t h e r e f o r e more expensive. P r e s e n t l y , o n l y f i n e s produced from m e t a l l u r g i c a l c o a l s r e c e i v e adequate treatment, because o n l y f o r these c o a l s , can the c l e a n i n g c o s t be j u s t i f i e d . For the p r o c e s s i n g of f i n e c o a l , f r o t h f l o t a t i o n remains the most e f f e c t i v e method, although o t h e r methods r e l y i n g on the s u r f a c e p r o p e r t i e s of c o a l , such as o i l agglomera-t i o n , have r e c e i v e d a t t e n t i o n i n r e c e n t y e a r s . In B r i t i s h Columbia the p r o d u c t i o n of m e t a l l u r g i c a l c o a l i n 1991 exceeded 22 m i l l i o n m e t r i c tones. T h i s comprises more than 2 85 % of the t o t a l c o a l p r o d u c t i o n i n the p r o v i n c e ( M i n e r a l S t a t i s t i c s , EMPR, 1991). Due t o the g e o l o g i c a l c o n d i t i o n s , the i n t e n s i v e mechanization and n o n - s e l e c t i v e mining, the amount of f i n e s ( m a t e r i a l below .50 mm i n s i z e ) i n the run-of-mine c o a l i n m a j o r i t y o f seams exceeds 35 %, and f o r some reaches 60 %. On average, 15 t o 20 % of the t o t a l c l e a n c o a l product comes from the c l e a n i n g by f r o t h f l o t a t i o n . The e f f e c t i v e n e s s of f l o t a t i o n r e l i e s on the n a t u r a l h y d r o p h o b i c i t y o f c o a l p a r t i c l e s . The h y d r o p h o b i c i t y o f c o a l changes w i t h the rank, p e t r o g r a p h i c composition, degree of o x i d a t i o n and the amount of m i n e r a l matter a s s o c i a t e d w i t h the c o a l . For each g r a i n s u b j e c t e d t o the f l o t a t i o n , the average s u r f a c e p r o p e r t i e s determine i t s f l o a t a b i l i t y . The s e p a r a t i o n o f an assembly of p a r t i c l e s i n t o f r a c t i o n s of equal c r i t i c a l s u r f a c e t e n s i o n s o f w e t t a b i l i t y and f l o a t a b i l i t y , as developed i n r e c e n t y e a r s (Hornsby and L e j a , 1980; Hornsby, 1981; Fuerstenau e t a l . , 1985), i s an e l e g a n t way of o b t a i n i n g the d i s t r i b u t i o n of p a r t i c l e s a c c o r d i n g t o t h e i r s u r f a c e p r o p e r t i e s . The w e t t a b i l i t y and f l o a t a b i l i t y o f p e t r o g r a p h i c components have been a s u b j e c t o f a number of s t u d i e s . Two approaches were u s u a l l y used: t e s t i n g f l o a t a b i l i t y o f p e t r o g r a p h i c components under r e a l f l o t a t i o n c o n d i t i o n s (Horsley and Smith, 1951; K l a s s e n , 1966; Hower e t a l . , 1984; Sarkar e t a l . , 1984; Bujnowska, 1985) or r e l a t i n g w e t t a b i l i t y parameters such as c o n t a c t angle of v a r i o u s macerals t o the f l o t a t i o n (Brown, 1961; Kl a s s e n , 1966; Parekh and Apian, 1978; S o b i e r a j and Myrcha, 1980; A r n o l d and 3 Apian, 1989) . I t i s of s p e c i a l i n t e r e s t , however, t o examine n a t u r a l s u r f a c e p r o p e r t i e s of c o a l g r a i n s of v a r i o u s p e t r o g r a p h i c composi-t i o n i n terms of t h e i r c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y and f l o a t a b i l i t y . Consequently, t h i s w i l l show the i n f l u e n c e of the p e t r o g r a p h i c composition of i n d i v i d u a l p a r t i c l e s on t h e i r average s u r f a c e p r o p e r t i e s , and perhaps h e l p i n u n derstanding the nature of s u r f a c e h e t e r o g e n e i t y of c o a l . The p o s s i b i l i t y of s e l e c t i v e s e p a r a t i o n of p e t r o g r a p h i c components i s important i n both the l a b o r a t o r y and the i n d u s t r i a l a p p l i c a t i o n s . I t i s not necessary t o o b t a i n complete s e p a r a t i o n of p e t r o g r a p h i c components, as long as t h e p r o p o r t i o n of c e r t a i n components i n c o n c e n t r a t e i s achieved. The f i r s t t h r e e c h a p t e r s c o n s i s t of a l i t e r a t u r e review of w e t t a b i l i t y and f l o a t a b i l i t y , the r e l a t i o n s h i p between hydropho-b i c i t y and f l o a t a b i l i t y , f o l l o w e d by an a n a l y s i s of c o a l s u r f a c e p r o p e r t i e s . The experimental t e s t i n g and d i s c u s s i o n of w e t t a b i l i t y and f l o a t a b i l i t y of c o a l p a r t i c l e s of d i f f e r e n t p e t r o g r a p h i c composition, as d e r i v e d from two methods: f i l m f l o t a t i o n and s m a l l -s c a l e f l o t a t i o n are d i s c u s s e d i n the f o l l o w i n g c h a p t e r s . 4 CHAPTER 2 HYDROPHOBICITY AND FLOATABILITY 2.1 W e t t a b i l i t y of s o l i d s 2.1.1 Theory of the w e t t a b i l i t y of s o l i d s by l i q u i d s When a drop of l i q u i d i s p l a c e d on a s o l i d , t he l i q u i d e i t h e r spreads t o form a t h i n , more or l e s s u niform f i l m or remains on t h e s u r f a c e as a d i s c r e t e drop. The former b e h a v i o r i s g e n e r a l l y d e s c r i b e d as a complete w e t t i n g , the l a t t e r as incomplete or p a r t i a l w e t t i n g . A s o l i d can be c l a s s i f i e d as l y o p h i l i c i f the l i q u i d c o m p letely wets i t , or l y o p h o b i c i f i t i s o n l y p a r t i a l l y wetted. Hydrophobic and h y d r o p h i l i c are the terms which s p e c i f i c a l -l y a p p l y t o w e t t i n g by aqueous s o l u t i o n s . Thomas Young (1805) i n h i s e q u a t i o n d e s c r i b e d w e t t i n g c o n d i t i o n s i n terms of s u r f a c e t e n s i o n s . He viewed s u r f a c e t e n s i o n s as the f o r c e s a c t i n g a l o n g the pe r i m e t e r of a drop o f l i q u i d p l a c e d on an i d e a l l y smooth s o l i d s u r f a c e . Both phases were c o n s i d e r e d t o be i n e q u i l i b r i u m w i t h the surrounding vapor phase. He d e r i v e d the f o l l o w i n g e q u a t i o n known as Young^s eq u a t i o n : Ysv " Y s l = Y i v c o s e 2.1.1 Y s v , Y s i / Y i v a r e t h e s o l i d / v a p o r , s o l i d / l i q u i d , l i q u i d / v a p o r 5 i n t e r f a c i a l s u r f a c e t e n s i o n s and 8 i s the angle of c o n t a c t measured a c r o s s the l i q u i d phase ( F i g u r e 2.1.1). T h i s e q u a t i o n may a l s o be d e r i v e d from thermodynamic c o n d i t i o n s (Gibbs, 1928; Johnson, 1959). Young xs equ a t i o n p r o v i d e s a p r e c i s e thermodynamic d e f i n i t i o n of the c o n t a c t angle, but s u f f e r s from the l a c k of d i r e c t measurement of s o l i d s u r f a c e t e n s i o n s . Hence, i t cannot be e x p e r i m e n t a l l y v e r i f i e d . There are a number of other o b j e c t i o n s t o Young*s eq u a t i o n . The most obvious one i s the assumption t h a t the s u r f a c e of the s o l i d i s an i d e a l one. Real s o l i d s u r f a c e s are u s u a l l y c h a r a c t e r i z e d by i m p e r f e c t i o n s such as roughness, and heterogene-i t y . I f the s u r f a c e i s rough, a c o r r e c t i o n f a c t o r has t o be i n t r o d u c e d as a weighing f a c t o r f o r cos6 t o compensate f o r the roughness (Wenzel, 1936),the h e t e r o g e n e i t y can t o be c o r r e c t e d i n a s i m i l a r way ( C a s s i e and Baxter, 1944; C a s s i e , 1948). Usi n g thermodynamics, Dupre (1869) d e f i n e d the work of adhesion, Wa, as the r e v e r s i b l e work necessary t o separate u n i t area of the i n t e r f a c e between two i m m i s c i b l e l i q u i d s i n e q u i l i b r i -um, i n t o two u n i t areas of l i q u i d / v a p o r i n t e r f a c e s of these l i q u i d s . T h i s was f u r t h e r extended t o the l i q u i d / s o l i d i n t e r f a c e s . Work of cohesion, Wc, i s the work necessary t o form two u n i t area s u r f a c e s from one l i q u i d . The c ohesion of the g i v e n l i q u i d and i t s adhesion t o the g i v e n s o l i d , are the two parameters t h a t determine w e t t i n g or non-w e t t i n g c o n d i t i o n s . Harkins (1952) d e f i n e d the phenomenon of w e t t i n g as the d i f f e r e n c e between the work of adhesion (Wa) of the 6 l i q u i d t o the s o l i d (or o t h e r s u b s t r a t e ) and the work of cohesion Wc of the l i q u i d . I f the d i f f e r e n c e (S) i s g r e a t e r than zero the l i q u i d s h o u l d spread (or wet) the s o l i d ( s u b s t r a t e ) , i f S i s l e s s than zero the non-wetting should occur. S i n c e Wa = Y S V + Y l v ~ Y s l a n d u s i n " ? Young xs e q u a t i o n 2.1.2 Wa = Y i v (1+cosO) 2.1.3 Wc = 2 Y l v 2.1.4 S = Wa - Wc 2.1.5 Hence S = Y S V - Y i v ~ Y s i > 0 denotes w e t t i n g 2.1.6 and S = y s v - Y ] _ v ~ Y s i < 0 denotes non-wetting 2.1.7 For S = Y i v c o s ® ~ Y i v < 0 t n e n Y i v c o s ^ < Y i v 2.1.8 In these e x p r e s s i o n s o n l y the i n t e r f a c i a l t e n s i o n s p e r t a i n i n g t o f l u i d phases can be r e l i a b l y determined. The i n t e r f a c i a l t e n s i o n s of s o l i d phases cannot be measured, o n l y t h e i r d i f f e r e n c e i s measurable, by Y i v C O S 8 . T h i s q u a n t i t y i s c a l l e d the adhesion t e n s i o n . For the non-wetting c o n d i t i o n s , the adhesion t e n s i o n s h o u l d be l e s s than Y i v * 7 A l s o , Wa/Wc = Y i v < x + cos8)/2 Y i v 2.1.9 and then cos8 = 2 Wa/Wc - 1 2.1.10 For p a r t i c l e - t o - b u b b l e c o n t a c t t o be p o s s i b l e , the f r e e energy change (AG) d u r i n g the attachment has t o be n e g a t i v e 0.G < 0 (Laskowski, 1974; 1986a; 1989) and i s g i v e n by e q u a t i o n 2.1.11 6G = Y i v ( c o s d " 1) 2.1.11 as a r e s u l t the attachment i s p o s s i b l e o n l y when 8 > 0 (cos8 < 1). F u r t h e r , f o r cos8 t o be s m a l l e r than 1, (equation 2.1.10) Wa must be s m a l l e r than Wc, Wa < Wc and S < 0. Young*s e q u a t i o n and the s p r e a d i n g c o e f f i c i e n t e quation are of g r e a t importance i n f r o t h f l o t a t i o n , because they d e s c r i b e the thermodynamic c o n d i t i o n s f o r w e t t a b i l i t y and f l o a t a b i l i t y of a s o l i d . One o f the measurable thermodynamic parameters i n f l o t a t i o n systems i s c o n t a c t angle, 8. The c o n t a c t angle measured a t e q u i l i b r i u m i s a unique f u n c t i o n of the t h r e e i n t e r f a c i a l t e n s i o n s . Whenever a p a r t i c l e i s a t t a c h e d t o an a i r bubble, t h e r e i s always a d e f i n i t e angle formed a t the border of i n t e r f a c e s . T h i s angle i s assumed t o be d i r e c t l y r e l a t e d t o the f l o t a t i o n of a p a r t i c l e . The major problem w i t h i n t e r r e l a t i n g f l o a t a b i l i t y w i t h c o n t a c t angle l i e s i n the f a c t t h a t , i t does not r e f l e c t the k i n e t i c c o n d i t i o n s o f the f l o t a t i o n p r o c e s s (Laskowski, 1974; Laskowski, 1989). D e s p i t e a l l the drawbacks caused by h e t e r o g e n e i t y 8 (Wenzel, 1949; Neuman and Good, 1972) and roughness of the measured s u r f a c e (Good, 1973) and r e s u l t i n g h y s t e r e s i s , the c o n t a c t angle i s s t i l l an extremely u s e f u l i n d i c a t o r of the w e t t a b i l i t y of s o l i d s . 2.1.2 C r i t i c a l s u r f a c e t e n s i o n of w e t t i n g Young xs equ a t i o n p r o v i d e s s e m i - e m p i r i c a l e s t i m a t e s o f the s u r f a c e t e n s i o n of hydrophobic s o l i d s , by u s i n g the c o n t a c t angle and l i q u i d s u r f a c e t e n s i o n data. An experimental method f o r e v a l u a t i n g the s u r f a c e t e n s i o n o f hydrophobic s o l i d s was developed by Zisman (1964). He found t h a t the c o n t a c t angle, measured by s e s s i l e drop on a hydrophobic s o l i d , i s a f u n c t i o n o f Y i v a n c * d e c r e a s e s e v e n t u a l l y t o zero, when Y i v i s reduced. The v a l u e of Y i v a t which the c o n t a c t angle j u s t reaches zero was d e f i n e d as the c r i t i c a l s u r f a c e t e n s i o n of wet t i n g , yc. In other words, y c i s t h a t v a l u e o f Y i v b e l o w which l i q u i d spreads on a p a r t i c u l a r s u r f a c e and wets i t completely. From an e x t e n s i v e study of the c o n t a c t angles o f a homologous s e r i e s o f o r g a n i c l i q u i d s ( l a t e r s t u d i e s by Zisman showed t h a t i t was not e s s e n t i a l t o use homologous l i q u i d s ) on a hydrophobic s o l i d , cos8 was found t o be a l i n e a r f u n c t i o n of Y i v (Fox and Zisman, 1950). E x t r a p o l a t i o n t o cos© = 1 g i v e s the va l u e o f Y c * M a t h e m a t i c a l l y , cos8 i s r e l a t e d t o Y i v by: cos8 = 1 + b ( Y C - Y i v ) 2.1.12 9 T h i s p l o t i s f r e q u e n t l y r e f e r r e d t o as the Zisman p l o t . The c o n s t a n t b was shown t o be r e l a t e d t o the degree of the h y d r o p h o b i c i t y of the s o l i d s u r f a c e , and found t o be a f u n c t i o n of Y C / b = 1 / Y C (Good and G i r i f a l c o , 1960). Parekh and Apian (1974; 1978) t e s t e d Y C of a number of m i n e r a l s and c o a l , and found t h a t the i n c r e a s i n g s l o p e of the l i n e was a s s o c i a t e d e i t h e r w i t h h i g h e r a d s o r p t i o n of s u r f a c t a n t onto the m i n e r a l s u r f a c e ( i n c r e a s e d h y d r o p h o b i c i t y ) , or w i t h i n c r e a s i n g rank i n the case of c o a l . The s l o p e c o r r e l a t e s w i t h the rank i n a v e r y s i m i l a r manner as does the c o n t a c t angle. To some extent, the v a l u e of yc depends on the s e t of l i q u i d s used t o measure i t . T h i s i s p a r t i c u l a r l y t r u e i f t h e r e are p o l a r i n t e r a c t i o n s . Zisman d e s c r i b e d yc as a u s e f u l e m p i r i c a l parameter whose r e l a t i v e v a l u e a c t s as one would expect of s u r f a c e t e n s i o n of s o l i d , Y S ' ( Y s r e p r e s e n t s the v a l u e of y i n a vacuum, without any a d s o r p t i o n of v a p o r ) , an i n d i c a t o r of s p e c i f i c energy of the s o l i d . Many attempts have been made t o i d e n t i f y Y c w i t h Y S or Y S D (Yg^' c r i t i c a l s u r f a c e t e n s i o n a r i s e n from the d i s p e r s i v e f o r c e s ) . Good and G i r i f a l c o (1960) i m p l i e d t h a t f o r nonpolar l i q u i d s and s o l i d s , the c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y i s equal t o the s u r f a c e t e n s i o n of the s o l i d Y c = Y s « S i m i l a r l y , Fowkes (1963) showed t h a t Y c = Ys^* T h e i r experimental r e s u l t s appear t o support t h e s e p r e d i c t i o n s . One might t h e r e f o r e expect t h a t f o r non-polar s o l i d s , Y c = Y s / p r o v i d e d t h e r e i s no s i g n i f i c a n t a d s o r p t i o n a t the s o l i d / a i r or s o l i d / l i q u i d i n t e r f a c e 10 Another common way of e x p r e s s i n g the w e t t a b i l i t y of i n h e r e n t l y hydrophobic m i n e r a l s i n s o l u t i o n s of changing s u r f a c e t e n s i o n s i s through the adhesion t e n s i o n diagram, Y i v c o s ® versus y-^v' ( F i g u r e 2.1.3), on such a diagram the c o n t a c t angles p l o t g i v e s a s t r a i g h t l i n e , and i s r e p r e s e n t e d by the e q u a t i o n : Y l v cose = A Y i v + ( 1 - A ) Y c 2.1.13 water solid F i g u r e 2.1.1 Contact angle formed by water, vapor (gas), and s o l i d phases. The maximum s l o p e occurs when A=l, and t h e r e f o r e cosO = 1 (0=0), and r e p r e s e n t s the maximum p o l a r i t y ( h y d r o p h i l i c i t y ) o f the s o l i d . A g r a d u a l decrease i n the magnitude of A below u n i t y i s i n t e r p r e t e d as an i n c r e a s e i n n o n p o l a r i t y . Once the w e t t a b i l i t y l i n e becomes p a r a l l e l t o the cos(180°) l i n e , t h e r e i s p r a c t i c a l l y no adhesion of COMPLETE WETTING Yz PARTIAL WETTING (LYOPHILIC) I I (LYOPHOBIC) 11 i l -" 11 — cos 8 0 0 2 0 4 0 6 0 SURFACE TENSION , y dyne/cm Iv Figure 2.1.2. Zisman diagram f o r l i q u i d s and aqueous solutions on hydrophobic s o l i d s (Hornsby and Leja, 1983). l i q u i d to the s o l i d . This represents a highly non-polar s o l i d surface (maximum hydrophobicity), (Kelebek, 1987). Further, the p o l a r i t y was found to be r e l a t e d to the slope of the adhesion tension l i n e , by the expression A = 1.7 X h l - 0.7 2.1.14 where X h^ i s the f r a c t i o n of the hydrophilic portion of the mineral surface as calculated from C a s s i e x s equation (Cassie, 1948). Figure 2.1.3 from Kelebek (1987) shows that the increase i n p o l a r i t y i s accompanied by a regular increase i n the slope of the adhesion tension l i n e of these s o l i d s . P a r a f f i n i s shown to be completely non-polar, while s t i b n i t e has the highest p o l a r i t y , since the slope of i t s adhesion l i n e i s almost p o s i t i v e . For non-12 p o l a r s o l i d s , t h e parameter which r e f l e c t s t h e d i f f e r e n c e i n w e t t a b i l i t y p r o p e r t i e s i s y c « However, when the s o l i d becomes more p o l a r , the s l o p e of the adhesion t e n s i o n l i n e becomes a more s e n s i t i v e parameter of w e t t a b i l i t y . For two s o l i d s w i t h s i g n i f i c a n t l y d i f f e r e n t v a l u e s of y c (determined i n s o l u t i o n s o f the same a l c o h o l ) a s e l e c t i v e w e t t i n g r e g i o n w i l l e x i s t i f y c a < Y i v < Ye*3/ a s i n d i c a t e d i n F i g u r e 2.1.4 by the shaded a r e a . In t h i s case, s o l i d B w i l l be wetted, w h i l e s o l i d A w i l l be o n l y p a r t i a l l y wetted. The w e t t a b i l i t y r e g i o n f o r s o l i d B and D w i l l be the same, even though t h e i r p o l a r i t y i s d i f f e r e n t . The concept of c r i t i c a l s u r f a c e t e n s i o n o f w e t t a b i l i t y , i r r e s p e c t i v e o f i t s many l i m i t a t i o n s , i s s t i l l a u s e f u l parameter i n the c h a r a c t e r i z a t i o n of the r e l a t i v e w e t t a b i l i t y o f a s o l i d s u r f a c e . W e t t a b i l i t y of a number of low-energy ( i n h e r e n t l y hydrophobic) s o l i d s was t e s t e d u s i n g t h i s method ( Fox and Zisman,1950; Hornsby, 1981). The f i r s t v a l u e s o f the c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y f o r c o a l s o f d i f f e r e n t ranks and l i t h o t y p e s were r e p o r t e d by E i s s l e r and Van Holde (1962). They found the c r i t i c a l s u r f a c e t e n s i o n , Yc' f o r a n t h r a c i t e equal t o 39.8 dyne/cm, f o r f u s a i n t o 54 dyne/cm, and f o r v i t r a i n from c o a l s of v a r i o u s ranks, were estimated t o range from 41 t o 56 dyne/cm. The h i g h e s t v a l u e of y c corresponded t o the v i t r a i n of the hig h v o l a t i l e and the lowest t o the low v o l a t i l e rank of c o a l . Parekh and Apian (1978) found c r i t i c a l s u r f a c e t e n s i o n of w e t t i n g y c f o r g r a p h i t e and c o a l t o be a t 45 dyne/cm ( i r r e s p e c t i v e of r a n k ) . 13 The most common way of a s s e s s i n g c r i t i c a l s u r f a c e t e n s i o n s has been based on o b t a i n i n g r e l i a b l e c o n t a c t angle v a l u e s and then p l o t t i n g the adhesion t e n s i o n diagram such as the one i n F i g u r e 2.1.4. The v a l u e o f c r i t i c a l s u r f a c e t e n s i o n i s o b t a i n e d as the i n t e r c e p t o f Y i v c o s ® w i t h the 0=0, l i n e and r e p r e s e n t e d by y^ v . Because many problems are u s u a l l y a s s o c i a t e d w i t h c o n t a c t angle measurements e s p e c i a l l y o f powder samples, o t h e r a l t e r n a t i v e methods of c r i t i c a l s u r f a c e t e n s i o n e s t i m a t i o n have become more a t t r a c t i v e . 30 -10 0St1bn1te(l) AStibnite(2) • Talc o Stibnite 9 10 • Paraffin • /&-90* \ 20 30 40 K50 60 70 \» F i g u r e 2.1.3 W e t t a b i l i t y diagram i l l u s t r a t i n g adhesion t e n s i o n of v a r i o u s specimens; s t i b n i t e , t a l c and p a r a f f i n wax as a f u n c t i o n of s u r f a c e t e n s i o n (Kelebek, 1987). Garshva e t a l . , (1976) used a m o d i f i e d Walker (1952) procedure t o measure immersion time o f the disappearance of powder i n t o s o l u t i o n s of d e c r e a s i n g s u r f a c e t e n s i o n t o d e f i n e YC* I N another procedure (Yarar, 1985), s m a l l - s c a l e f l o t a t i o n t e s t s were 14 F i g u r e 2.1.4 Adhesion t e n s i o n diagram i l l u s t r a t i n g w e t t a b i l i t y l i n e s f o r t h r e e hydrophobic s o l i d s i n aqueous s o l u t i o n s of a s h o r t -c h a i n n - a l c o h o l , and s e l e c t i v e w e t t i n g r e g i o n (shaded area) between s o l i d s A and B, (Hornsby and L e j a , 1983). performed on a number of hydrophobic s o l i d s , u s i n g methanol s o l u t i o n s t o v a r y s u r f a c e t e n s i o n . The weight p e r c e n t o f r e c o v e r y of the hydrophobic f r a c t i o n v e r s u s s u r f a c e t e n s i o n y i e l d e d a f l o a t a b i l i t y t e n s i o n d i s t r i b u t i o n w i t h a minimum and maximum. The va l u e o f Y c °^ w e t t i n g was determined by e x t r a p o l a t i o n t o zero f l o t a t i o n r e c o v e r y . In the same study i t was shown t h a t t h e r e i s a v e r y good agreement wi t h c r i t i c a l s u r f a c e t e n s i o n o f w e t t a b i l i t y o f t h r e e d i f f e r e n t s o l i d s e s t i m a t e d by t h i s t e c h n i q u e and c o n t a c t angle method ( F i g u r e 2.1.7). For the heterogeneous s o l i d s the r e c o v e r y o f f l o a t i n g f r a c t i o n v e r s u s s u r f a c e t e n s i o n o f s o l u t i o n was r e p r e s e n t e d by a wider cumulative d i s t r i b u t i o n curve, w i t h a more obvious minimum and maximum. Homogeneous s o l i d s form an almost s t r a i g h t l i n e , i n d i c a t i n g o n l y one v a l u e of y c f o r a l l p a r t i c l e s 15 within the sample. Marmur et a l . , (1986) c a l l e d the highest surface tension at which a l l p a r t i c l e s were imbibed " t o t a l f l o a t i n g concentration", TFC, and the lowest methanol concentration at which a l l p a r t i c l e s are wetted, the " t o t a l sinking concentration" (TSC). He argued that one should not use the term c r i t i c a l surface tension, because the measurement of yc depends on the r e l a t i v e adsorption of solutes to the s o l i d - l i q u i d and liquid-vapor interfaces. Reported y c values should be supplemented by some estimate of the r e l a t i v e adsorption of the solute to the various interfaces. He used the term " c r i t i c a l spreading concentration" to characterize the lowest concentration of the l e a s t polar components (methanol and ethanol) i n a binary s o l u t i o n leading to complete spreading. On the other hand he concluded that Y s calculated at TSC i s i n good agreement with the Y C calculated from the contact angle. The difference between TFC and TSC i s due to either a v a r i a t i o n i n surface energies of p a r t i c l e s or contact angle hysteresis. The l a t t e r i s associated with possible roughness and chemical heterogeneity of the p a r t i c l e . S i m i l a r l y , a modified Walker t e s t was used by Fuerstenau et a l . , (1985; 1986; 1987a; 1988b) to t e s t surface properties of an assembly of coal p a r t i c l e s . Fuerstenau used the term f i l m f l o t a t i o n to describe t h i s technique. Coal p a r t i c l e s were placed onto the surface of solutions of decreasing surface tension, forming a monolayer i d e n t i f i e d as the f i l m . Three parameters were defined: Y cmin, the surface tension of the solution that wets a l l p a r t i c l e s , Y ~ C , the mean c r i t i c a l wetting surface tension of p a r t i c l e s i n the 16 d i s t r i b u t i o n ; and Y c m a x » the s u r f a c e t e n s i o n of the s o l u t i o n above which none of the p a r t i c l e s are wetted, ( F i g u r e 2.1.5). An average w e t t i n g s u r f a c e t e n s i o n was proposed as an index f o r c o r r e l a t i n g the w e t t i n g b e h a v i o r of c o a l s w i t h t h e i r composition and degree of s u r f a c e o x i d a t i o n . I t was shown t h a t an average w e t t i n g s u r f a c e t e n s i o n of c o a l s i n c r e a s e s upon s u r f a c e o x i d a t i o n . The i n c r e a s e i n Y c , a q u a n t i t i v e measure of t h e c o a l s u r f a c e energy, was found t o be caused by the i n c r e a s e i n oxygen f u n c t i o n a l groups. A marked change i n y c w i t h o x i d a t i o n i s mainly a r e s u l t of an i n c r e a s e i n the v a l u e of Y c m a x / s i n c e the Y c m i n d i d not s h i f t a p p r e c i a b l y . The competence of f i l m f l o t a t i o n f o r c h a r a c t e r i z i n g the h y d r o p h o b i c / h y d r o p h i l i c nature of s o l i d p a r t i c l e s was e s t a b l i s h e d through t e s t s w i t h p a r t i c l e s of d i f f e r e n t d e n s i t i e s and shapes t h a t have homogeneous hydrophobic s u r f a c e s (Fuerstenau e t a l . , 1988a). M a t e r i a l s such as sulphur, s i l a n a t e d g l a s s beads and q u a r t z , and p a r a f f i n coated c o a l , g r a p h i t e , c a l c i t e , magnesite and p y r i t e p a r t i c l e s were f l o a t e d u s i n g the f i l m f l o t a t i o n t e c h n i q u e . I t was concluded t h a t the t echnique i s n e a r l y independent of p a r t i c l e shape, s i z e , and d e n s i t y over f a i r l y wide range. These r e s u l t s c o nfirmed t h a t the p r o c e s s i n v o l v e d i n f i l m f l o t a t i o n i s predomi-n a n t l y c o n t r o l l e d by i n t e r f a c i a l f o r c e s . Another important c o n c l u s i o n was reached i n r e g a r d t o the e f f e c t s of p r e f e r e n t i a l a d s o r p t i o n on i n v o l v e d i n t e r f a c e s . I t was shown t h a t the v a l u e of y c , determined from f i l m f l o t a t i o n u s i n g d i f f e r e n t p o l a r reagents (to v a r y s u r f a c e t e n s i o n ) , of the g r a p h i t e p a r t i c l e s was the same. A more comprehensive study on the w e t t i n g b e h a v i o r and r e l a t e d 17 25 20 • 15-10 • CAMBRIA • 33 C O A L 4»x«5 MESH I 1 i i d \ \ IkJ "20 30 40 50 60 70 LIQUID SURFACE TENSION, mN/m 80 F i g u r e 2.1.5 F i l m f l o t a t i o n w e t t a b i l i t y d i s t r i b u t i o n curve f o r Cambria No. 33 bituminous c o a l (a) frequency histogram f o r l y o p h o b i c i t y of Cambria No. 33 c o a l (b) p a r t i t i o n curve, (Fuerstenau e t a l . , 1988b). 18 p r o p e r t i e s o f methanol s o l u t i o n s was r e p o r t e d by Kelebek (1987). He showed t h a t the r e l a t i v e a d s o r p t i o n d e n s i t y of methanol a t the aqueous s o l u t i o n - g a s i n t e r f a c e reaches a maximum v a l u e when the s u r f a c e t e n s i o n i s between 40 and 30 dyne/cm (35 and 65 methanol c o n c e n t r a t i o n ) . Complete w e t t i n g due t o a d s o r p t i o n of methanol a t s o l i d s u r f a c e may occur when the a d s o r p t i o n of methanol a t the s o l u t i o n - g a s and/or s o l i d - s o l u t i o n i n t e r f a c e s r e a c h a maximum v a l u e . Hornsby and L e j a (1980) showed t h a t the s e l e c t i v e s e p a r a t i o n of two s o l i d s o f d i f f e r e n t y c w a s achieved by simple m a n i p u l a t i o n o f the s u r f a c e t e n s i o n o f the w e t t i n g s o l u t i o n . In t h e i r method, they used a mixture of two s o l i d s , each wi t h known Y c , and c a r r i e d out s e p a r a t i o n i n t e s t tubes w i t h v a r y i n g methanol s o l u t i o n s . S i m i l a r r e s u l t s were r e p o r t e d by o t h e r s (Kelebek and Smith, 1985; F i n c h and Smith, 1975). S e p a r a t i o n of two s o l i d s by f l o t a t i o n depends on the r e l a t i v e w e t t a b i l i t y o f p a r t i c l e s . The s e l e c t i v e s e p a r a t i o n of two hydrophobic s o l i d s w i t h d i f f e r e n t y c of w e t t a b i l i t y , f u l f i l l i n g the s e l e c t i v e w e t t a b i l i t y c o n d i t i o n s , was found p o s s i b l e and q u i t e p r a c t i c a l . In view of t h i s r e l a t i o n between f l o t a t i o n and s e l e c t i v e w e t t a b i l i t y , the concept of c r i t i c a l s u r f a c e t e n s i o n i s d i r e c t l y r e l e v a n t t o f l o t a t i o n . 19 2.1.3 C r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y In s e c t i o n 2.1.2 i t was shown t h a t a s e l e c t i v e w e t t i n g r e g i o n e x i s t s between s o l i d s w i t h d i f f e r e n t Y c v a l u e s . The Y c determined from w e t t a b i l i t y r e p r e s e n t s , however, o n l y the s t a t i c w e t t i n g b e h a v i o r of p a r t i c l e s . I t i s obvious t h a t , under the a c t u a l f l o t a t i o n c o n d i t i o n s , p a r t i c l e s are s u b j e c t e d t o dynamic non-e q u i l i b r i u m c o n d i t i o n s . T h e r e f o r e i t may be expected t h a t f l o a t -a b i l i t y cannot be unambiguously p r e d i c t e d from w e t t a b i l i t y a n a l y s e s . The development of the concept of a c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y , as proposed by Hornsby (Hornsby, 1980; Hornsby and L e j a , 1983) , i n d i c a t e d t h a t a s i g n i f i c a n t d i f f e r e n c e i n c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y , Y c f ' v a l u e s may e x i s t between two s o l i d s , even though t h e r e may be l i t t l e or no d i f f e r -ence i n t h e i r Y c v a l u e s . Such a d i f f e r e n c e would p r o v i d e a s e l e c -t i v e f l o a t a b i l i t y r e g i o n , where s e p a r a t i o n of the two s o l i d s should be p o s s i b l e . The d i f f e r e n c e s i n the c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y between p a r t i c l e s of the same Y c a r i s e from the d i f f e r e n c e s i n c r i t i c a l s u r f a c e t e n s i o n of adhesion, Y C a ( Y C a > Y c ) , below which adhesion of a bubble t o the p a r t i c l e i s not p o s s i b l e , and c r i t i c a l s u r f a c e t e n s i o n of p a r t i c l e - b u b b l e s t a b i l i t y , below which a p a r t i c l e - b u b b l e aggregate becomes u n s t a b l e . These two parameters, and the hydrodynamic c o n d i t i o n s i n the f l o t a t i o n c e l l , d e c i d e whether a p a r t i c l e w i l l s u c c e s s f u l l y a t t a c h t o an a i r bubble and s e p a r a t e from the f l o t a t i o n s l u r r y . For f l o t a t i o n t o occur, the c o l l i s i o n between a p a r t i c l e and a bubble 20 i n the f l o t a t i o n system i s necessary. T h i s c o n d i t i o n i s u s u a l l y f u l f i l l e d by adequate hydrodynamic f l o t a t i o n c r i t e r i a , and was shown t o be independent of a p a r t i c l e s h y d r o p h o b i c i t y . The adhesion of a bubble t o a p a r t i c l e i n c r e a s e s as the i n d u c t i o n time decreases (Laskowski, 1974). I n d u c t i o n time was a l s o found t o decrease as the p a r t i c l e s i z e and the v i s c o s i t y of the s o l u t i o n i n the d i s j o i n i n g f i l m decreases (Laskowski, 1974). As the Y ^ v approaches the l i m i t of y c , the i n d u c t i o n time i n c r e a s e s a t some p o i n t and i t becomes l a r g e r than the time of c o n t a c t between bubble and p a r t i c l e . T h i s i n d i c a t e s the p r o x i m i t y of c r i t i c a l s u r f a c e t e n s i o n of adhesion, Y C a * T ^ e c o n t a c t angle a s s o c i a t e d with t h i s v a l u e i s r e f e r r e d t o as © c a . The c r i t i c a l c o n t a c t angle of adhesion i s always l a r g e r than zero. F i g u r e 2.1.6 i l l u s t r a t e s the concept of the c r i t i c a l s u r f a c e t e n s i o n of adhesion f o r h y p o t h e t i c a l s o l i d B. Assuming c o l l i s i o n and adhesion have taken p l a c e , t h e r e w i l l be l i m i t i n g v a l u e s of Y i v a n c * ® below which a p a r t i c l e of a g i v e n s i z e and d e n s i t y w i l l not f l o a t due t o u n s t a b l e p a r t i c l e -bubble aggregate, even though © has a f i n i t e v a l u e . The p a r t i c l e -bubble aggregate s t a b i l i t y depends on the s i z e , d e n s i t y and w e t t a b i l i t y of f l o a t e d p a r t i c l e s . For p a r t i c l e s w i t h i d e n t i c a l s u r f a c e p r o p e r t i e s (same w e t t a b i l i t y c h a r a c t e r i s t i c s , y c a n d s l o p e b of l i n e B) , but d i f f e r e n t s i z e s , the f l o a t a b i l i t y w i l l be d i f f e r e n t . The l a t t e r would be d e s c r i b e d by d i f f e r e n t v a l u e s of c r i t i c a l s u r f a c e t e n s i o n of p a r t i c l e - b u b b l e s t a b i l i t y , Yes o r d i f f e r e n t v a l u e s of c o r r e s p o n d i n g c o n t a c t angle, 8 C S , as shown i n 21 F i g u r e 2.1.6. Two p a r t i c l e s of d i f f e r e n t s i z e s , where d* < d* x would have the r e l e v a n t ^ c s < ^ c s a n c i Y C s < cs' T h e r e f o r e , i f the Y i v w e r e s u c h t h a t Y * C s < Y i v < Y * C s ' t h e s m a H e r p a r t i c l e would be f l o a t e d , whereas the l a r g e r p a r t i c l e would be non-f l o a t a b l e , due t o i n s u f f i c i e n t p a r t i c l e - b u b b l e aggregate i n s o l u t i o n of Y i v * F i g u r e 2.1.6 Adhesion t e n s i o n diagram; the concept of c r i t i c a l s u r f a c e t e n s i o n of adhesion, Ypa' ^ o r a hydrophobic s o l i d w i t h w e t t a b i l i t y l i n e B, (Hornsby and L e j a , 1983). The v a l u e s Y c s °r Yea c o u ^ D e the l i m i t i n g f l o a t a b i l i t y parameters f o r p a r t i c l e s , depending on which i s g r e a t e r . For example, f o r t h e two p a r t i c l e s of s o l i d B i n F i g u r e 2.1.6, the y ^ c s v a l u e i s t h e l i m i t i n g v a l u e f o r f l o t a t i o n of t h e l a r g e r p a r t i c l e , whereas Y C a becomes t h e c r i t i c a l v a l u e i n the f l o a t a b i l i t y of the s m a l l e r one. In g e n e r a l , a p a r t i c l e w i l l be f l o a t a b l e i f Y i v > Y C f / where Ycf r e p r e s e n t s e i t h e r Yes o r Y C a 22 F i g u r e 2.1.7 E f f e c t of the s u r f a c e t e n s i o n o f methanol/water s o l u t i o n s on f l o a t a b i l i t y and w e t t a b i l i t y of molybdenite, sulphur and t e f l o n , (Yarar and Kaoma, 1984). (whichever i s l a r g e r ) , and i s the c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y . I f the two s o l i d s t o be sepa r a t e d have a wide v a r i e t y of p a r t i c l e s i z e d i s t r i b u t i o n s , t h e r e may be a range of y C f va l u e s i n s t e a d o f one d i s c r e t e v a l u e . The same may be t r u e f o r the systems w i t h the heterogeneous p a r t i c l e s , where broad bands of w e t t a b i l i t y r e p r e s e n t s t h e i r s u r f a c e p r o p e r t i e s . 23 2.2. H y d r o p h o b i c i t y and f l o a t a b i l i t y 2.2.1 H y d r o p h o b i c i t y t h e o r i e s The hydrophobic s o l i d s are those which d i s p l a y p a r t i a l or incomplete w e t t a b i l i t y by water. A number of s o l i d s e x h i b i t v a r y i n g degrees of h y d r o p h o b i c i t y when t h e i r s u r f a c e s a re f r e s h l y formed ( L e j a , 1983). These s o l i d s may be e i t h e r o r g a n i c , such as hydrocar-bons, waxes, g r a p h i t e , t a r s , bitumen and c o a l s , or i n o r g a n i c , such as s u l p h u r , t a l c and molybdenite. H y d r o p h o b i c i t y i s of paramount importance i n many s u r f a c e based p r o c e s s e s . The success of f r o t h f l o t a t i o n p r i m a r i l y depends on the h y d r o p h o b i c i t y o f the f l o a t e d p a r t i c l e s . The h y d r o p h o b i c i t y c o n t r o l s not o n l y the thermodynamics of f l o t a t i o n but a l s o the k i n e t i c s o f the p r o c e s s . To e x p l a i n h y d r o p h o b i c i t y , Gaudin (1957) showed t h a t d u r i n g t h e pro c e s s of s u r f a c e f o r m a t i o n s o l i d s remain n a t u r a l l y hydrophobic o n l y i f t h e i r f r a c t u r e or cleava g e o c c u r s without r u p t u r e of i n t e r a t o m i c bonds other than r e s i d u a l ones. These s u r f a c e s can o n l y i n t e r a c t w i t h the aqueous environment through d i s p e r s i o n f o r c e s . Breakage of c o v a l e n t o r i o n i c bonds lead s t o h y d r o x y l a t i o n or i o n i z a t i o n of the s u r f a c e , which i n t u r n renders the s o l i d s u r f a c e h y d r o p h i l i c . The h y d r o p h o b i c i t y o f a s o l i d (water r e j e c t i o n ) decreases w i t h an i n c r e a s e i n the amount of p o l a r s i t e s ( h y d r o x y l o r i o n i c ) on the m i n e r a l s u r f a c e . Through these p o l a r s i t e s water becomes a t t r a c t e d t o the s u r f a c e . 24 A c c o r d i n g t o Frumkin and D i e r i a g i n ( i n K l a s s e n , 1966) h y d r o p h o b i c i t y can be e x p l a i n e d u s i n g a water h y d r a t i o n l a y e r concept. Low h y d r a t i o n of a m i n e r a l s u r f a c e i n d i c a t e s s t r o n g h y d r o p h o b i c i t y , whereas h i g h h y d r a t i o n i n d i c a t e s h y d r o p h i l i c i t y . In view of t h i s t h e o r y , t h r e e types of f i l m s , d i s j o i n i n g p a r t i c l e and bubble, may be c r e a t e d as a r e s u l t of s u r f a c e h y d r a t i o n : s t a b l e , m e t a s t a b l e and u n s t a b l e . A s t a b l e w e t t i n g f i l m i s c h a r a c t e r i s t i c of a s t r o n g l y hydrated s u r f a c e , w h i l e an u n s t a b l e f i l m i s t y p i c a l of a hydrophobic s o l i d . A metastable w e t t i n g f i l m becomes u n s t a b l e below a c r i t i c a l t h i c k n e s s of the d i s j o i n i n g f i l m ; t h i s i s t y p i c a l f o r f l o t a t i o n w i t h c o l l e c t o r systems. An i n s t a b i l i t y of water f i l m s on hydrophobic s o l i d s i s due t o the l a c k of hydrogen bonding i n t h e s e f i l m s as compared t o the bulk water. In o t h e r words, the p r o x i m i t y of a nonpolar s u r f a c e imposes on the n e i g h b o r i n g water molecule an u n f a v o r a b l e c o n f i g u r a t i o n (Laskowski and K i t c h e n e r , 1969). Laskowski and K i t c h e n e r (1969) used Fowkes concept of i n t e r f a c i a l e n e r g i e s t o e x p l a i n the h y d r o p h o b i c - h y d r o p h i l i c t r a n s i t i o n of the s o l i d s u r f a c e . They concluded t h a t the work of adhesion of water t o a s o l i d depends on d i s p e r s i o n f o r c e s , h y d r a t i o n of n o n - i o n i c p o l a r s i t e s , and e l e c t r i c a l charge. H y d r o p h o b i c i t y a r i s e s whenever the two l a t t e r terms are s m a l l , because d i s p e r s i o n e n e r g i e s are always s m a l l e r (except f o r f l u o r o c a r b o n s ) than the ( e x c e p t i o n a l l y large) work of c o h e s i o n of water. The s o l i d i s hydrophobic whenever i t i n t e r a c t s w i t h water through d i s p e r s i o n f o r c e s o n l y . H y d r o p h o b i c i t y a r i s e s e s s e n t i a l l y 25 from the weakness of adhesion of water t o the s o l i d (Fowkes, 1963; Laskowski and K i t c h e n e r , 1969). 2.2.2 F l o a t a b i l i t y As d i s c u s s e d i n s e c t i o n 2.1.3, f o r a p a r t i c l e t o be f l o a t a b l e , not o n l y dewetting of the p a r t i c l e s u r f a c e have t o be thermodynamically f a v o r a b l e , by f u l f i l l i n g 0 > 0 or Y i v > Yc c o n d i t i o n s , but s e v e r a l o t h e r c r i t e r i a a l s o have t o be s a t i s f i e d (Laskowski, 1974; Trahar and Warren, 1976; Laskowski, 1986; Laskowski, 1989): a) the p a r t i c l e must c o l l i d e w i t h a bubble; b) the d i s j o i n i n g f i l m s e p a r a t i n g the p a r t i c l e and bubble must t h i n , r u p t u r e and recede w i t h i n the c o l l i s i o n time; c) the p a r t i c l e - b u b b l e aggregate formed must be of s u f f i c i e n t s t r e n g t h t o w i t h s t a n d d i s r u p t i v e f o r c e s i n the f l o t a t i o n c e l l . The c r i t e r i a d e s c r i b e d above can be expressed i n terms of p r o b a b i l i t i e s as proposed by Tomlinson and Fleming, (1963;) and l a t e r d i s c u s s e d by Laskowski (1974) p f = P c * P a * P s 2' 2- 1 26 where P c, P a, P s are the p r o b a b i l i t i e s of c o l l i s i o n , attachment, and p a r t i c l e - b u b b l e aggregate s t a b i l i t y , r e s p e c t i v e l y . The p r o b a b i l i t y of c o l l i s i o n as d i s c u s s e d by many (Tomlinson and Fleming, 1963; Reay and R a t c l i f f , 1973; Anfrus and K i t h c h e n e r , 1977; Jameson e t a l . , 1977, Yoon and L u t t r e l l , 1989) was found t o be independent of p a r t i c l e h y d r o p h o b i c i t y . I t mainly depends on the hydrodynamic c o n d i t i o n s of f l o t a t i o n , and p a r t i c l e as w e l l as bubble s i z e . The p r o b a b i l i t y of adhesion, or p r o b a b i l i t y of attachment i s d i f f i c u l t t o q u a n t i f y i n terms of s o l i d h y d r o p h o b i c i t y , because the c o n t a c t angle does not c h a r a c t e r i z e the k i n e t i c e f f e c t s d u r i n g f l o t a t i o n c o n t r i b u t i n g t o r e s i s t a n c e t o the attachment. For a p a r t i c l e t o be a t t a c h e d s u c c e s s f u l l y t o a bubble, not o n l y a f i n i t e c o n t a c t angle has t o be formed, but a l s o the i n d u c t i o n time, the time r e q u i r e d f o r t h i n n i n g , r u p t u r e and r e c e s s i o n of the d i s j o i n i n g f i l m , has t o be s m a l l e r than the c o n t a c t time. A s m a l l i n d u c t i o n time has g e n e r a l l y been found f o r s o l i d s which form l a r g e c o n t a c t a n g l e s . The adhesion depends, as d i s c u s s e d i n s e c t i o n 2.1.3, on the magnitude of the c o n t a c t angle r e l a t e d t o the c r i t i c a l s u r f a c e t e n s i o n of adhesion. The s t a b i l i t y of the p a r t i c l e - b u b b l e aggregate i s d i r e c t l y r e l a t e d t o the c o n t a c t angle. The l a r g e r the c o n t a c t angle, the s t r o n g e r the p a r t i c l e - b u b b l e aggregate, and, as a r e s u l t , the l a r g e r the v a l u e of P g. 27 CHAPTER 3 COAL Coa l i s an o r g a n i c sedimentary rock composed of two b a s i c m a t e r i a l s : i n o r g a n i c c r y s t a l l i n e m i n e r a l s and o r g a n i c carbonaceous components r e c o g n i z e d as macerals. The o r g a n i c p a r t of c o a l i s formed from peat d e p o s i t s produced i n swamps through the accumulation of p l a n t m a t e r i a l , and has undergone f u r t h e r b i o c h e m i c a l and metamorphic changes, r e f e r r e d t o as c o a l i f i c a t i o n . C o a l i f i c a t i o n i s the p r o g r e s s i v e enrichment of the c o a l m a t r i x i n o r g a n i c a l l y bound carbon. In g e n e r a l , h i g h e r carbon c o n t e n t i n d i c a t e s h i g h e r rank of c o a l . Many p h y s i c a l and chemica l p r o p e r t i e s of c o a l vary w i t h rank. Macerals form the o r g a n i c p a r t of c o a l and are d i v i d e d i n t o t h r e e groups - v i t r i n i t e , l i p t i n i t e and i n e r t i n i t e . There are t h r e e important c o m p o s i t i o n a l p r o p e r t i e s which determine c o a l q u a l i t y : rank, type and grade. While rank and type r e f l e c t p r o p e r t i e s o f the o r g a n i c p a r t of c o a l , the grade r e f e r s t o the cont e n t o f m i n e r a l matter a s s o c i a t e d w i t h c o a l . 3.1 Co a l p r o p e r t i e s 3.1.1 Chemical composition of c o a l In a chemical sense, c o a l i s a substance o f h i g h m o l e c u l a r weight and non-uniform s t r u c t u r e . C o a l as a whole i s 28 s t r o n g l y aromatic; i t s a r o m a t i c i t y i n c r e a s e s more or l e s s s t e a d i l y w i t h rank, r e a c h i n g i t s maximum a t about 94% carbon i n v i t r i n i t e s . C o a l has a p o l y m e r i c s t r u c t u r e . The average s t r u c t u r a l u n i t i n c o a l s from l i g n i t e t o the l o w - v o l a t i l e bituminous stage c o n t a i n s about 20 C atoms and about 4-5 aromatic r i n g s . In t h e a n t h r a c i t e stage the s i z e of c l u s t e r s and number of r i n g s p e r c l u s t e r i n c r e a s e s r a p i d l y (van Kr e v e l e n , 1961; Lowry, 1963; Ig n a s i a k , 1975; Ignasiak, 1977; Larsen, 1978; Given, 1984). The d i s t r i b u t i o n of carbon i n t o d i f f e r e n t hydrocarbon forms as a f u n c t i o n o f rank i s shown i n F i g u r e 3.1.1 45 50 55 60 65 70 75 80 85 90 95 CARBON, % dmmf F i g u r e 3.1.1 Carbon d i s t r i b u t i o n i n c o a l s o f d i f f e r e n t ranks, (Whitehurst e t a l . , 1980). 29 One of the e a r l i e s t proposed c o a l s t r u c t u r e s was t h a t of van K r e v e l e n i n 1954. Another model of c o a l s t r u c t u r e was suggested by Given (1960) . The most commonly r e f e r r e d t o i s the model proposed by Wiser (1975). In h i s model hydroaromatic s t r u c t u r e i s predominant, w i t h weak bonding between aromatic u n i t s ( F i g u r e 3.1.2). Oxygen f u n c t i o n a l groups are i n c o r p o r a t e d i n the carbon s k e l e t o n . C o a l c o m p o s i t i o n a l p r o p e r t i e s change w i t h the changing c h e m i c a l s t r u c t u r e of c o a l a s s o c i a t e d w i t h the rank. 3.1.2 Rank Rank of c o a l i s not a d i r e c t l y measurable q u a n t i t y . To d e f i n e i t , i t i s necessary t o r e f e r t o a s p e c i f i c p h y s i c a l or ch e m i c a l p r o p e r t y which e x h i b i t s adequate change i n the course of c o a l i f i c a t i o n . Rank r e p r e s e n t s the degree of chemical and p h y s i c a l changes which occur i n the o r g a n i c p a r t of c o a l as a r e s u l t of c o a l i f i c a t i o n . C o a l i f i c a t i o n i s the p r o g r e s s i v e t r a n s f o r m a t i o n of peat through l i g n i t e , subbituminous, bituminous, a n t h r a c i t e t o m e t a - a n t h r a c i t e c o a l , a s s o c i a t e d w i t h the p r o g r e s s i v e enrichment i n o r g a n i c carbon. Rank of c o a l can be estimated by chemical parameters, f o r example, moisture content, c a l o r i f i c v a l u e , v o l a t i l e matter content (ASTM D 388-77) or carbon, oxygen and hydrogen (ISO, S e y l e r ) . An I n t e r n a t i o n a l Committee on Coal P e t r o l o g y (ICCP) uses o p t i c a l p r o p e r t i e s , e.g. v i t r i n i t e r e f l e c t a n c e . The new c l a s s i f i c a t i o n proposed by A l p e r n (1983), i n c o r p o r a t e s a l l parameters w i t h i n t h e i r 30 F i g u r e 3.1.2 The Wiser model of s t r u c t u r a l groups and c o n n e c t i n g b r i d g e s i n bituminous c o a l s (Wiser, 1975) . Rank German USA Refl. Rmoit Vol. M. d. a. f. % Carbon d.a.f. Vitrite Bed Moisture Cal. Value Btu/lb (kcal/kg) Applicability of Different Rank Parameters — 0.2 Torf Peat - 68 a) Weich- ~ Lignite — 0.3 - 64 - 60 - 56 — ca. 60 — ca. 75 - c a . 35 7200 CU ro 5 'a -C= re IS) 0 J= ai re Matt-3 140001 -0 cu re u Sub-Bit 8 - O . i - 52 - c a . 71 — ca. 25 9900 to - 48 15500) Gianz- - 0 . 5 - 0 . 6 - 44 - c a . 77 — ca. 8-10 12600 Flamm-B i - 0 . 7 - 40 - 36 ~ 170001 re Gasflamm-Qi E •5 "0 A * -o.e 3 . 0 - O re 0 Gas- ~ :£ -1,0 - 32 . 1 o Medium - 1.2 - 28 - 24 - ca. 87 15500 Fett-Volatile Bituminous - 1.4 186501 • CU cu re Low - 1.6 - 20 >~ 53 Ess-Volatile Bituminous - 1.8 - 16 ro C OJ JS a = Mager- Semi-Anthracite — 2.0 - 12 >• u re t j V *S _ D ca. 91 15600 — • Anthrazit Anthracite - 3.0 0 18650) re TD Meta-Anthr. -4 .0 — 4 CT O " O » » re ' Meta-A. I >C "5 T a b l e 3.1.1 D i f f e r e n t p h y s i c a l and chemical rank parameters and t h e i r a p p l i c a b i l i t y t o the d i f f e r e n t c o a l i f i c a t i o n s t a g e s (adapted from Stach, 1982). 32 range of a p p l i c a b i l i t y and r e c o g n i z e s p e t r o g r a p h i c composition as t h e important element i n c o a l c l a s s i f i c a t i o n . The chemical changes of c o a l s t r u c t u r e v a r y d u r i n g d i f f e r e n t stages of c o a l i f i c a t i o n , and t h e r e f o r e some rank i n d i c a t o r s are more a p p r o p r i a t e than o t h e r s i n p a r t i c u l a r rank s t a g e s . T a b l e 3.1.1 compares d i f f e r e n t p h y s i c a l and chemical rank parameters and shows t h e i r a p p l i c a b i l i t y t o the d i f f e r e n t c o a l i -f i c a t i o n s t a g e s . For the c o a l s from peat t o m e d i u m - v o l a t i l e bituminous, m o i s t u r e and c a l o r i f i c v a l u e s (dry, a s h - f r e e b a s i s ) are v e r y good i n d i c a t o r s of rank. V i t r i n i t e r e f l e c t a n c e and v o l a t i l e matter (dry, a s h - f r e e b a s i s ) are the accepted rank parameters f o r medium t o high-rank c o a l s , w i t h r e f l e c t a n c e of v i t r i n i t e i n c r e a s i n g w i t h c o a l i f i c a t i o n , and v o l a t i l e matter content d e c r e a s i n g as rank i n c r e a s e s . R e f l e c t a n c e appears t o be the most w i d e l y a p p l i c a b l e and the most c o n s i s t e n t rank parameter, as i t i s g e n e r a l l y independent of p e t r o g r a p h i c composition, the e x c e p t i o n may be c o a l s w i t h h i g h l i p t i n i t e content, where s u p p r e s s i o n of r e f l e c t a n c e of v i t r i n i t e was found t o be s i g n i f i c a n t (Raymond and Murchison, 1991). D i f f e r e n t macerals undergo change a t d i f f e r e n t r a t e s d u r i n g c o a l i f i c a t i o n , and t h e r e f o r e comparative rank s t u d i e s should be determined on v i t r i n i t e or a c o n c e n t r a t e of t h i s maceral. V i t r i n i t e i s t h e maceral which r e f l e c t s c o a l i f i c a t i o n changes most r e l i a b l y , i r r e s p e c t i v e of the f a c t t h a t i t i s the most abundant component of humic c o a l s . P r o g r e s s i v e rank i n c r e a s e i s c l o s e l y r e l a t e d t o changes 33 0,1 ft? 0.0 0,8 1,0 0.1 Oj i s » aromacity ring condensation dimension of aromatic clusters Icrystatllfes 1 0 JO 40 10 00 W 0 o y n n "I* - increasing —»- -increasing—— \ hardness density mai. internal moisture heat of wetting In methanol) (infernal surface, porosity) first row: molecular structure second row - o - = hydrogen bonding — = molecular bonding third row: fourth row grindability liecipr. strength I » n » u> \ s  \ \ free radicals fluidity during carbonisation solubility in ethylenediamine t ] i i k } i 0,1 0 t 4 I refractive absorption indei indei reflectance orientation of molecules perpendicular to the bedding plane lenses = aromatic clusters lines = non-aromatic elements development of chemical properties in relation to carbon content (daf) development of physical properties in relation to carbon content (daf) F i g u r e 3.1.3 P h y s i c a l and molecular changes of v i t r i t e d u r i n g the c o a l i f i c a t i o n of bituminous c o a l s and a n t h r a c i t e s , ( T e i c h m u l l e r , 1982) . i n c h e m i c a l s t r u c t u r e of c o a l . A steady decrease i n moisture c o n t e n t from l i g n i t e t o h i g h - v o l a t i l e bituminous c o a l i s due t o a decrease i n the p o r o s i t y , and oxygen f u n c t i o n a l groups. As a r e s u l t , the carbon content g r a d u a l l y r i s e s . F i g u r e 3.1.3 i l l u s -t r a t e s p h y s i c a l and chemical changes o c c u r r i n g d u r i n g the c o a l i -f i c a t i o n of bituminous c o a l s as adopted from T e i c h m u l l e r (1982). As c o a l i f i c a t i o n p r o g r e s s e s from h i g h - v o l a t i l e b i t u m i -nous t o m e d i u m - v o l a t i l e c o a l s , t h e r e i s a c o n t i n u e d f a l l of m o i s t u r e c o n t e n t and a c o r r e s p o n d i n g r i s e i n the c a l o r i f i c v a l u e . In bituminous c o a l s v o l a t i l e matter f a l l s due t o t h e removal of a l i p h a t i c groups and the i n c r e a s e i n a r o m a t i z a t i o n of c o a l . In the a n t h r a c i t e stage t h e r e i s a r a p i d f a l l i n the hydrogen content a l o n g w i t h an i n c r e a s e i n a r o m a t i c i t y and a s t r o n g i n c r e a s e i n r e f l e c t i v i t y (Mackowsky, 1982) 3.1.3 Type of c o a l Type of c o a l r e f l e c t s d i f f e r e n t p l a n t and d e p o s i t i o n a l c o n d i t i o n s and the e x t e n t of the change o c c u r r e d d u r i n g the b i o c h e m i c a l and geochemical p r o c e s s e s of c o a l f o r m a t i o n . Two major types o f c o a l are r e c o g n i z e d , humic or banded c o a l s which are formed i n s i t u (autochthonous), and s a p r o p e l i c or non-banded which are formed from d r i f t e d d e b r i s of m a t e r i a l s such as spores, p o l l e n , and degraded peat, and are d e p o s i t e d i n s t a n d i n g waters ( a l l o c h t h o -nous) . S a p r o p e l i c c o a l s d i f f e r from humic c o a l s i n t h e i r uniform 35 t e x t u r e , g r e a t s t r e n g t h and c o n c h o i d a l f r a c t u r e . S a p r o p e l i c c o a l s a r e d i s t i n g u i s h e d c h e m i c a l l y by h i g h hydrogen content and a h i g h y i e l d o f v o l a t i l e matter. They can be d i v i d e d i n t o c a n n e l and boghead c o a l . Cannel c o a l s are composed of peat d e g r a d a t i o n p r o d u c t s , mainly r e s i s t a n t p l a n t p a r t s such as waxy and r e s i n o u s substances which were c o n c e n t r a t e d d u r i n g the d e g r a d a t i o n of peat. Cannel c o a l s a l s o c o n t a i n h i g h amounts of v i t r i n i t e , but i n very comminuted form. Boghead c o a l s are d e r i v e d mainly from a l g a l m a t e r i a l t h a t grows i n s i t u ( B u s t i n e t a l . , 1983). Humic c o a l s a re predominant. They o r i g i n a t e from o r g a n i c matter which has undergone change by h u m i f i c a t i o n , the process of peat f o r m a t i o n w i t h r e s t r i c t e d oxygen supply. The scheme i n the Ta b l e 3.1.2 shows the dependency of the t r a n s f o r m a t i o n of o r g a n i c substances on oxygen supply ( T e i c h m u l l e r , 1982). Process Product a. a . 3 O 5 I disinregracion mouldering peatification putrefaction usually ho solid residue, possibly liptobioliths TJ 3 l i d peat sapropel humic coals >^ sapropelic coals \ sapropelites petroleum £ . 3 a . 3 2 n _ n Z. o 3 r r 3" 3 -I q 3 3 a . T a b l e 3.1.2 The dependency of the t r a n s f o r m a t i o n of o r g a n i c substances on oxygen supply, ( T e i c h m u l l e r , 1982) 36 Humic c o a l s u s u a l l y c o n s i s t of m a c r o s c o p i c a l l y r e c o g n i z -a b l e bands of c o a l . These d i f f e r e n t types of c o a l w i t h i n the seam are c a l l e d " l i t h o t y p e s " . The composition of l i t h o t y p e s i s s t r o n g l y dependant on t h e maceral composition and the a s s o c i a t i o n of macerals w i t h d i f f e r e n t p r o p o r t i o n s of m i n e r a l matter (e.g. D i e s e l , 1985 a,b). L i t h o t y p e s and macerals, as w e l l as t h e i r d e f i n i t i o n s , are d i s c u s s e d i n s e c t i o n 3.2. 3.1.4 M i n e r a l matter The m i n e r a l matter i n c o a l occurs as i n o r g a n i c matter from t h e o r i g i n a l p l a n t m a t e r i a l , d e t r i t a l p a r t i c l e s and a u t h i g e n i c d e p o s i t s a s s o c i a t e d w i t h the f i r s t stage of c o a l i f i c a t i o n , or as d e p o s i t s a s s o c i a t e d w i t h the second stage of c o a l i f i c a t i o n , a f t e r c o n s o l i d a t i o n of c o a l (Rao and G l u s k o t e r , 1973; Renton, 1978; Stach e t a l . , 1982; Finkelman, 1982;). Ta b l e 3.1.3 shows the common c o a l m i n e r a l s and t h e i r o r i g i n as adapted from Mackowsky (1982). A u t h i g e n i c and d e t r i t a l m i n e r a l s are termed s y n g e n e t i c , whereas m i n e r a l s formed l a t e r are r e f e r r e d t o as e p i g e n e t i c . The s y n g e n e t i c m i n e r a l s tend t o be f i n e and i n t i m a t e l y intergrown w i t h the c o a l o r g a n i c p a r t , w h i l e e p i g e n e t i c are u s u a l l y d e p o s i t e d i n t h e c r a c k s and f i s s u r e s of macerals. The terms extraneous and i n h e r e n t m i n e r a l matter are a l s o f r e q u e n t l y used t o d e s c r i b e p h y s i c a l l y s e p a r a t a b l e m i n e r a l matter from i n s e p a r a t a b l e . These t e c h n i c a l terms may be r a t h e r m i s l e a d i n g , 37 First stage of coalification Second stage of coalification Mineral Group Syngenetic formation synsedimentary-early diagenetic (intimately intergrown) Epigenetic formation Transported by water or wind Newly formed Deposited in fissures, cleats and cavities (coarsely intergrown) Transformation of syngenetic minerals (intimately intergrown) Clay Minerals Kaolinite, Ulite, Sericite, Clay Minerals with mixed-layer structure Montmorillonite, Tonstein Mite, Chlorite Carbonates Siderite-AnkeriteAnkerite concretions, Calcite Dolomite, Dolomite Calcite, Ankerite Siderite, Calcite Ankerite in Fusite Pyrite Pyrite Pyrite from the concretions Marcasite transformation Melnikovite- Zinc Sulphide of syngenetic Pyrite (Sphalerite) concretions of - , , . , Coarse Pyrite S u , P h , d e s (Marcasite) Lead Sulphide (Galena) FeC03 Concretions of Copper FeS2—CuFeSo— Sulphide ZnS (Chalcopyrite) Pyrite in Fusite Oxides Hematite Goethite, Lepidocrocite ('Needle-Iron Ore') Quartz Quartz grains Chalcedony and Quartz from the weathering of Feldspar and Mica Quartz Phosphates Apatite Phosphorite, Apatite Heavy minerals and accessory minerals Zircon, Rutile, Tourmaline, Orthoclase, Biotite Chlorides, Sulphates and Nitrates T a b l e 3.1.3 Common c o a l m i n e r a l s and t h e i r o r i g i n , (adapted from Mackowsky, 1982). 38 s i n c e they are o p e r a t i o n a l r a t h e r than g e n e t i c . T y p i c a l s y n g e n e t i c m i n e r a l s are p y r i t e and s i d e r i t e , and i n some c o a l s c l a y s and q u a r t z , e t c . (Cook, 1981). Syngenetic m i n e r a l s are u s u a l l y d i s p e r s e d through the c o a l o r g a n i c p a r t and p r e s e n t a g r e a t e r c l e a n i n g problems, u n l e s s i n massive occu r r e n c e s . E p i g e n e t i c m i n e r a l s form i n c o a l c l e a t s and f r a c t u r e s as t h e m i n e r a l - f o r m i n g i o n s migrate i n t o the c o a l seams. The major e p i g e n e t i c m i n e r a l s are p y r i t e , c a l c i t e and o t h e r carbonates, and a v a r i e t y of r a r e m i n e r a l s (Cook, 1981). P h y s i c a l s e p a r a t i o n of e p i g e n e t i c m i n e r a l s i s more e f f i c i e n t because of t h e i r nature of a s s o c i a t i o n i n the c o a l . The p r e f e r e n t i a l a s s o c i a t i o n of m i n e r a l matter w i t h c o a l macerals has been shown i n many s t u d i e s (Gaudin, 1957; K l a s s e n , -1966; O^Gorman, 1971; Jowett, 1980;). F u s i n i t e s , due t o t h e i r c e l l u l a r s t r u c t u r e , are b e l i e v e d t o have the h i g h e s t p o t e n t i a l f o r secondary m i n e r a l emplacement, whereas v i t r i n i t e s are c o n s i d e r e d t o have the lowest m i n e r a l matter content. As a r e s u l t , the a s s o c i a -t i o n of m i n e r a l matter w i t h l i t h o t y p e s i n c r e a s e s i n the order v i t r a i n - c l a r a i n - d u r a i n - f u s a i n (Klassen, 1966) The m i n e r a l s a s s o c i a t e d w i t h c o a l have s i g n i f i c a n t l y d i f f e r e n t p h y s i c a l and chemical p r o p e r t i e s than the c o a l macerals. T h e r e f o r e , i n many cases knowledge of the type and d i s t r i b u t i o n of t h e s e m i n e r a l s i n c o a l has u s e f u l a p p l i c a t i o n . In a g e o l o g i c a l sense, presence of some m i n e r a l s may p r o v i d e v a l u a b l e i n f o r m a t i o n on the c o n d i t i o n s of c o a l f o r m a t i o n , or as i n the case of t o n s t -e i n s , may a l l o w the seam i d e n t i f i c a t i o n and c o r r e l a t i o n ( B u s t i n e t 39 a l . , 1983). Many p h y s i c a l and chemical c o a l u t i l i z a t i o n p r ocesses are g r e a t l y i n f l u e n c e d by the m i n e r a l matter content. The type and occu r r e n c e o f m i n e r a l matter i n c o a l i s p a r t i c u l a r l y important t o w a s h a b i l i t y c h a r a c t e r i s t i c s (Mackowsky and Hoffman, 1960; Fal c o n , 1983) and t o the s i z i n g or even c r u s h i n g of the c o a l (Hower e t a l . , 1986; Hower e t a l . , 1987) The i n t e r g r o w t h of m i n e r a l matter w i t h c o a l p l a y s a s i g n i f i c a n t r o l e i n deter m i n i n g p h y s i c a l p r o p e r t i e s of c o a l g r a i n s . In thermal c o a l s , m i n e r a l matter content a f f e c t s the h e a t i n g v a l u e of c o a l , and i t s ash f u s i o n p o i n t , which i n t u r n i n f l u e n c e s i t s tendency t o form d e p o s i t s or cause c o r r o s i o n on s u r f a c e s o f h e a t i n g chambers ( B u s t i n e t a l . , 1983). P y r i t e i n thermal c o a l i s a p o t e n t i a l source o f s u l f u r d i o x i d e i n the atmosphere. Presence o f m i n e r a l matter a l s o l e a d s t o problems i n f i l t r a t i o n and c a t a l y s t p o i s o n i n g i n l i q u e f a c t i o n (Handbook of Coal P e t r o l o g y , 1963; T s a i , 1982), and a f f e c t s q u a l i t y o f coke. D e s p i t e a l l t he d e t r i m e n t a l e f f e c t s of m i n e r a l matter i n c o a l , t h e r e are some b e n e f i c i a l e f f e c t s . For example, p y r i t e may a c t as a c a t a l y s t (Gorbaty, 1983) i n c o a l c o n v e r s i o n p r o c e s s e s such as h y d r o l i q u e -f a c t i o n . Moreover, some amount of m i n e r a l matter i s r e q u i r e d f o r optimum coke s t r e n g t h (Davis, 1976; Gray, 1978; T s a i , 1982). 3.2 P e t r o g r a p h i c composition of c o a l M acerals are the s m a l l e s t m i c r o s c o p i c a l l y d i s t i n g u i s h a b l e components of c o a l , and are analogous t o m i n e r a l s i n rock. There a r e t h r e e maceral groups i n c o a l , v i t r i n i t e , i n e r t i n i t e and 40 l i p t i n i t e . The i n d i v i d u a l macerals are grouped a c c o r d i n g t o t h e i r s i m i l a r p e t r o g r a p h i c p r o p e r t i e s , such as morphology, r e f l e c t a n c e , r e l i e f and c o l o r i n r e f l e c t e d or t r a n s m i t t e d l i g h t . The p r o p e r t i e s of c o a l macerals change i n the course of c o a l i f i c a t i o n . T a b l e 3.2.1 p r e s e n t s macerals and groups o f macerals i n bituminous c o a l s (ICCP handbook). D E T A I L E D N O M E N C L A T U R E SIMPLIFIED N O M E N C L A T U R E (for technical use) Maceral Group Symbol Collinite Telinite Vitrinite V Sporinite Cutinite Alginite Resinite Exinite or Liptinite E w . . . 1 fine-grained micrinite Micrimte j . . . . { massive micrinite Sclerotinite Semifusinite Fusinite lnertinite 1 T a b l e 3.2.1 Macerals and groups of macerals i n bituminous c o a l s (ICCP Handbook, 1963). The v a r i o u s a s s o c i a t i o n s of macerals w i t h each o t h e r , as observed under the microscope, are d e f i n e d as m i c r o l i t h o t y p e s . On a macroscopic s c a l e , the v a r i a t i o n i n appearance o f d i f f e r e n t bands of c o a l , due t o maceral c o n c e n t r a t i o n s , a re c a l l e d l i t h o t y p e s . 3.2.1 O r i g i n of macerals C o a l macerals o r i g i n a t e from c o a l i f i e d p l a n t remains. 41 Microlithotype Maceral-Group composition mineral-free Monomaceralic Vitrite Liptite Inertite V > 95% L > 95% I > 95% Bimaceralic Clarite Vitrinertite Durite V • L > 95% V f I > 9S% L + I > 95% * Trimacerite Duroclarite Clarodurite VitTinertoliptite V > L and I I > V and L E > V and I V = v i t r i n i t e , L = l i p t i n i t e , I = i n e r t i n i t e . * in t r imacer i tes at least 5% of each maceral must be present. T a b l e 3.2.2 D e s c r i p t i o n of micro l i t h o t y p e s a c c o r d i n g t o the ICCP (ICCP Handbook, 1963). Some of them s t i l l have p r e s e r v e d p l a n t s t r u c t u r e , w h i l e o t h e r s are p r o d u c t s of d e g r a d a t i o n of p l a n t s , i n which case p l a n t s t r u c t u r e can no l o n g e r be r e c o g n i z e d . V i t r i n i t e s are c o a l i f i c a t i o n p r o d u c t s of humic a c i d s which o r i g i n a t e from decomposition of l i g n i n and c e l l u l o s e of wood c e l l s . The humic a c i d s are formed through moldering and p e a t i f i c a -t i o n . As d i g e n e s i s proceeds, humic a c i d s l o s e t h e i r a c i d c h a r a c t e r and a r e changed i n t o humins. F u r t h e r g e l i f i c a t i o n of humins takes p l a c e w i t h i n c r e a s i n g rank, which leads t o v i t r i n i t e f o r m a t i o n . The p r e c u r s o r s of v i t r i n i t e i n peat and subbitumous stage are r e f e r r e d t o as huminite macerals. The i n i t i a l d i f f e r e n c e s between p l a n t remains g r a d u a l l y d i s a p p e a r as c o a l rank i n c r e a s e s ; t h e r e f o r e 42 huminite macerals outnumber v i t r i n i t e macerals. L i p t i n i t e s (or e x i n i t e s ) are d e r i v e d from h y d r o g e n - r i c h p l a n t remains such as r e s i n s , c u t i n s , waxes and f a t s . L i p t i n i t e s c o n t a i n l a r g e amounts of a l i p h a t i c c o n s t i t u e n t s ( p a r a f f i n s ) as compared t o the humic macerals. In low-rank c o a l s , l i p t i n i t e macerals a r e c h a r a c t e r i z e d by lower r e f l e c t a n c e than v i t r i n i t e . At the h i g h e r rank l i p t i n i t e assumes the chemical and o p t i c a l p r o p e r t i e s of v i t r i n i t e . Thus, as c o a l rank i n c r e a s e s , the r e f l e c t a n c e of l i p t i n i t e i n c r e a s e s t o r e a c h t h a t of v i t r i n i t e , a t t h e l o w - v o l a t i l e bituminous c o a l stage. I n e r t i n i t e macerals are d e r i v e d from the same o r i g i n a l p l a n t m a t e r i a l as v i t r i n i t e or l i p t i n i t e , but they are s u b j e c t e d t o a d i f f e r e n t p r o c e s s of primary decomposition ( T e i c h m u l l e r , 1982). I n e r t i n i t e macerals are produced by c h a r r i n g ( f o r e s t f i r e s ) or m o l d e r i n g of the wood t i s s u e s or other o r i g i n a l substances. In g e n e r a l , i n e r t i n i t e macerals are c h a r a c t e r i z e d by r e l a t i v e l y h i g h carbon content, v e r y low hydrogen, and are e n r i c h e d i n oxygen as compared t o v i t r i n i t e or l i p t i n i t e . They are a l s o c h a r a c t e r i z e d by an i n c r e a s e d l e v e l of a r o m a t i z a t i o n of hydrocarbons. I n e r t i n i t e macerals are the ones which e x p e r i e n c e the l e a s t s t r u c t u r a l changes d u r i n g the p r o c e s s of c o a l i f i c a t i o n . In terms of o p t i c a l p r o p e r t i e s , i n e r t i n i t e i s c h a r a c t e r i z e d by h i g h e r r e f l e c t a n c e than v i t r i n i t e of t h e same rank. The c o a l i f i c a t i o n t r a c k s of t h r e e main maceral groups are shown i n F i g u r e 3.2.1. Each maceral undergoes a p a r t i c u l a r e v o l u t i o n d u r i n g c o a l i f i c a t i o n . V i t r i n i t e s changes i n the most 43 u n i f o r m way and i s the maceral which r e f l e c t s most p r e d i c t a b l y the rank of c o a l . 3.2.2 Chemical and p h y s i c a l p r o p e r t i e s o f macerals. The t h r e e maceral groups are not o n l y p e t r o g r a p h i c a l l y d i s t i n c t but a l s o are c h a r a c t e r i z e d by d i f f e r e n t p h y s i c a l and chemic a l p r o p e r t i e s . These d i f f e r e n c e s i n chemical and p h y s i c a l p r o p e r t i e s a re r e f l e c t e d i n the t e c h n o l o g i c a l b e h a v i o r o f c o a l macerals. V i t r i n i t e macerals are the most d e s i r e d components i n co k i n g c o a l , where they c o n t r i b u t e t o p l a s t i c i t y of c o a l . The r e a c t i v i t y i n low rank c o a l s means they are r e a d i l y hydrogenated. In c o a l p r o c e s s i n g , v i t r i n t e s c o n c e n t r a t e i n f i n e s due t o b r i t t l e -ness and f i s s u r i n g (T. Laskowski, 1948). The range f o r d e n s i t y of v i t r i n i t e i s from 1.3 t o 1.45 g/cm 3. D e n s i t y changes w i t h rank, the minimum d e n s i t y o c c u r r i n g i n the medium v o l a t i l e bituminous rank range. L i p t i n i t e macerals are p a r t i c u l a r l y r i c h i n hydrogen, and as a r e s u l t y i e l d h i g h amounts of gas and t a r when c a r b o n i z e d ( F a l c o n , 1978) . For the same reason, c o a l s w i t h h i g h l i p t i n i t e c o n t e n t a r e the most s u i t a b l e f o r hydrogenation. An i n c r e a s e d l i p t i n i t e c o n t e n t i n c r e a s e s the s t r e n g t h of c o a l ( F a l c o n , 1978). The d e n s i t y o f l i p t i n i t e range from 1.0 t o 1.25 g/cm 3 (Kroger and Bade, 1961; Dyrkacz e t a l . , 1981; T s a i , 1982; C r e l l i n g , 1983; Dyrkacz e t a l . , 1984a and 1984b). 44 I n e r t i n i t e macerals are g e n e r a l l y v e r y i n e r t i n carbon-i z a t i o n and hydrogenation p r o c e s s e s . The s p e c i f i c g r a v i t y of i n e r t i n i t e s i s i n the range of 1.45 t o 1.50. I n e r t i n i t e s , e s p e c i a l -l y f u s i n i t e , can be v e r y f r i a b l e and c o n t r i b u t e s i g n i f i c a n t l y t o dust f o r m a t i o n (T. Laskowski, 1948; Hower e t a l . , 1987) Many of these p h y s i c a l p r o p e r t i e s have been e x p l o i t e d t o s e p a r a t e macerals, sometimes q u i t e s u c c e s s f u l l y (Golouskin, 1959, Kroger 1961, Dyrkacz e t a l . , 1981). The e a r l y s t u d i e s on the s e p a r a t e d macerals were done by many d i s t i n g u i s h e d s c i e n t i s t s (vanKrevelen, 1961; Given, 1984). A s i g n i f i c a n t amount of modern fundamental r e s e a r c h i n t o maceral c h a r a c t e r i z a t i o n was accomplished a f t e r i n t r o d u c t i o n of the d e n s i t y g r a d i e n t c e n t r i f u g a t i o n method f o r maceral s e p a r a t i o n by Gary Dyrkacz i n 1981 (Dyrkacz e t a l . , 1981; Winans and C r e l l i n g , 1984; Pugmuire e t a l . , 1984; S i l b e r -n a g e l e t a l . , 1984). 3.2.3 M i c r o l i t h o t y p e s Macerals do not always occur as d i s c r e t e or l i b e r a t e d p a r t i c l e s . Most o f t e n they are i n a s s o c i a t i o n w i t h each o t h e r and v a r i e d amounts of m i n e r a l matter. A s s o c i a t i o n s of macerals w i t h each o t h e r , as observed m i c r o s c o p i c a l l y , are c a l l e d m i c r o l i t h o -t y p e s . M i c r o l i t h o t y p e s are arranged i n t o t h r e e main groups; monomaceralic, b i m a c e r a l i c , and t r i m a c e r a l i c , depending on whether they are composed of macerals from one, two or t h r e e maceral groups. D e s c r i p t i o n of m i c r o l i t h o t y p e s a c c o r d i n g t o the ICCP 45 °/c F i g u r e 3.2.1 The c o a l i f i c a t i o n t r a c k s of main maceral groups, ( T e i c h m u l l e r , 1982) Handbook i s p r e s e n t e d i n T a b l e 3.2.2. A c c o r d i n g t o e s t a b l i s h e d procedure (ICCP, 1963; B u s t i n e t a l . , 1983; Stach e t a l , 1982; Ward, 1984) minimum band widths are 50 microns, and macerals which account f o r l e s s than 5% by volume o f a p a r t i c l e a r e d i s r e g a r d e d . In p r a c t i c e , a t w e n t y - p o i n t r e t i c u l e i s used t o count macerals on the examined c o a l p a r t i c l e . The a s s o c i a t i o n of macerals w i t h m i n e r a l matter (20 t o 60 % by volume) p l a c e s a p a r t i c l e i n t o the c a r b o m i n e r i t e category. When the c o a l p a r t i c l e i s a s s o c i a t e d w i t h c l a y m i n e r a l s i t i s r e f e r r e d t o as c a r b a r g i l l i t e , and when a s s o c i a t e d w i t h p y r i t e , c a r b o p y r i t e (Stach, 1982). In many c o a l u t i l i z a t i o n p r o c e s s e s maceral a n a l y s i s i s 46 not adequate t o p r e d i c t c o a l behavior. M i c r o l i t h o t y p e a n a l y s i s p r o v i d e s more d e t a i l e d i n f o r m a t i o n on the i n t i m a t e a s s o c i a t i o n of macerals and intergrown m i n e r a l s . M i c r o l i t h o t y p e a n a l y s i s can be v e r y e f f e c t i v e i n p r e d i c t i n g the c o a l p r e p a r a t i o n c h a r a c t e r i s t i c s , f o r example, g r i n d a b i l i t y of c o a l (Hower e t a l . , 1987), w a s h a b i l i t y c h a r a c t e r i s t i c s ( F a l c o n and F a l c o n , 1983; Hower e t a l . , 1986), and even s e l e c t i v i t y i n f l o t a t i o n (Cudmore e t a l . , 1986). Another important a p p l i c a t i o n of m i c r o l i t h o t y p e a n a l y s i s i s i n c h a r a c t e r -i z a t i o n of c o k i n g c o a l s (Brown e t al.,1964; R e n t e l , 1987). 3.2.4 L i t h o t y p e s L i t h o t y p e s are m a c r o s c o p i c a l l y r e c o g n i z a b l e bands of c o a l s , and are c a t e g o r i z e d i n t o f o u r t y p e s : v i t r a i n , c l a r a i n , d u r a i n , and f u s a i n (ICCP, 1963). These f o u r d i f f e r e n t types of c o a l are mainly r e c o g n i z e d and d i s t i n g u i s h e d from each ot h e r on the b a s i s of t h e i r l u s t e r , t e x t u r e , s t r a t i f i c a t i o n and degree of homogeneity. L i t h o t y p e s , as d e s c r i b e d by Stopes (1919), are p r e f e r r e d a s s o c i a t i o n s of macerals i n humic c o a l s . V i t r a i n i s c o n s i d e r e d t o be a n a t u r a l c o n c e n t r a t e of v i t r i n i t e ; f u s a i n i s e n r i c h e d i n f u s i n i t e and i n e r t i n i t e ; c l a r a i n has a v a r i a b l e composition of v i t r i n i t e , e x i n i t e and i n e r t i n i t e ; d u r a i n i s shown t o be r i c h i n l i p t i n i t e and i n e r t i n i t e . An a l t e r n a t i v e , s i m p l e r method f o r l i t h o t y p e c l a s s i f i c a -t i o n was developed i n A u s t r a l i a ( D i e s s e l , 1965a). In t h i s approach c o a l i s regarded as a mixture of two b a s i c components, b r i g h t and 47 d u l l . L i t h o t y p e s are d e f i n e d a c c o r d i n g t o the p r o p o r t i o n s of these two components ( B u s t i n e t a l . , 1983). The advantage of t h i s method i s t h a t bands of c o a l are more e a s i l y r e c o g n i z e d on the b a s i s of v a r y i n g p r o p o r t i o n s of two components. In terms of nomenclature, t h e r e i s no c o m p o s i t i o n a l i m p l i c a t i o n as i n the ICCP-Stopes system. The comparison between both l i t h o t y p e c l a s s i f i c a t i o n s i s g i v e n i n T a b l e 3.2.3 ( B u s t i n e t a l . , 1983). A s u c c e s s f u l attempt was made t o c o r r e l a t e m i c r o s c o p i c composition of D i e s s e l x s l i t h o t y p e c l a s s i f i -c a t i o n by Lamberson and B u s t i n (1989) u s i n g Lower Cretaceous c o a l s of B r i t i s h Columbia. The abundance of v i t r i n i t e macerals was shown t o decrease from b r i g h t t o d u l l e r l i t h o t y p e s , w h i l e the o p p o s i t e t r e n d was observed f o r i n e r t i n i t e . Stope^s C l a s -s i f i c a t i o n A u s t r a l i a n C l a s s i f i c a t i o n D e s c r i p t i o n V i t r a i n B r i g h t c o a l S u b v i t r o u s t o v i t r o u s l u s t r e , or c o n c h o i d a l f r a c t u r e <10 % d u l l C l a r a i n Banded b r i g h t Banded c o a l Banded d u l l B r i g h t c o a l , d u l l bands 10-40 % d u l l B r i g h t and d u l l i n equal p r o -p o r t i o n s , 40-60 % d u l l D u l l c o a l w i t h some b r i g h t bands 10-40 % b r i g h t D u r a i n D u l l c o a l Matt l u s t r e , uneven f r a c t u r e 10 % b r i g h t F u s a i n F i b r o u s c o a l S a t i n l u s t r e , f r i a b l e T a b l e 3.2.3 Comparison of two l i t h o t y p e c l a s s i f i c a t i o n s : Stope^s and A u s t r a l i a n , ( B u s t i n e t a l . , 1983). 48 L i t h o t y p e s a r e the p e t r o g r a p h i c components which are handled on a macroscopic s c a l e . Many of the p h y s i c a l p r o p e r t i e s of c o a l have been f r e q u e n t l y l i n k e d t o the l i t h o t y p e composition (Jeremic, 1980; Stach, 1982; T s a i , 1982; Hower, 1987 and 1988;). L i t h o t y p e s can be u s e f u l i n d i c a t o r s not o n l y o f the o r i g i n a l environment of c o a l f o r m a t i o n but a l s o o f p h y s i c a l and chemical p r o p e r t i e s o f c o a l . The d e n s i t y of l i t h o t y p e s v a r i e s q u i t e s i g n i f i c a n t l y , w i t h the v i t r a i n h a v ing the lowest d e n s i t y , c l a r a i n i n t e r m e d i a t e and the f u s a i n the h i g h e s t . The p o r o s i t y o f l i t h o t y p e s d i f f e r s ; i n v i t r a i n micropores are predominant, w h i l e i n f u s a i n mesopores predominate. Mechanical p r o p e r t i e s such as s t r e n g t h , hardness, and f r i a b i l i t y a re s t r o n g l y dependant on l i t h o t y p e composition (Hower e t a l . , 1986; F a l c o n , and F a l c o n , 1987; Hower, 1988; Hower and L i n b e r r y , 1988; Hower e t a l . , 1990). Apart from p h y s i c a l p r o p e r t i e s , l i t h o t y p e s have been shown t o have d i f f e r e n t c a r b o n i z a t i o n responses, due t o t h e i r d i s t i n c t p l a s t i c c h a r a c t e r i s t i c s . Coking t e s t s show t h a t s t r o n g e r cokes were produced from the b r i g h t e r l i t h o t y p e s (Gray e t a l . , 1976; B u r s t l e i n i n Hower e t a l . , 1986). 49 CHAPTER 4 HYDROPHOBICITY AND FLOATABILITY OF COAL 4.1 Hydrophobic c h a r a c t e r o f c o a l C o a l i s c o n s i d e r e d t o be n a t u r a l l y hydrophobic. T h i s i s a r e s u l t o f i t s hydrocarbon s t r u c t u r e . I t i s the s u r f a c e of c o a l which c o n t r o l s the mechanism of water a t t r a c t i o n , and t h e r e f o r e the h y d r o p h i l i c - h y d r o p h o b i c c h a r a c t e r o f c o a l . The s u r f a c e p r o p e r t i e s of c o a l may be q u i t e d i f f e r e n t than the p r o p e r t i e s o f the bulk s o l i d , as i n the case of s u r f a c e o x i d a t i o n , or s e l e c t i v e adsorp-t i o n . A c c o r d i n g t o Gaudin (1957), h y d r o p h o b i c i t y i s onl y p o s s i b l e f o r s o l i d s i n which f r a c t u r e or cleavage occurs without r u p t u r e o f i n t e r a t o m i c bonds oth e r than r e s i d u a l ones. Whenever r u p t u r e o c c u r s i n i o n i c l i n k a g e s i t leads t o the h y d r o x y l a t i o n or i o n i z a t i o n o f the s u r f a c e , and c r e a t i o n of the h y d r o p h i l i c s u r f a c e . The thermodynamic c o n d i t i o n f o r h y d r o p h i l i c i t y , as d i s c u s s e d i n s e c t i o n 2.2.1, i m p l i e s t h a t the main f o r c e s of water a t t r a c t i o n t o the s o l i d s u r f a c e are hydrogen bonding (through the s u r f a c e h y d r o x y l groups), o r the f o r c e s a r i s i n g from the e l e c t r i c a l charge of the i n t e r f a c e . In c o a l , oxygen f u n c t i o n a l groups such as h y d r o x y l , c a r b o n y l o r c a r b o x y l occur e i t h e r as a r e s u l t of o x i d a t i o n or as a p a r t of the c o a l s t r u c t u r e . The amount and type o f these groups 50 change w i t h the rank of c o a l , as do many oth e r p r o p e r t i e s . The oxygen f u n c t i o n a l groups content, and t h e i r type, were f r e q u e n t l y used t o s t r e s s the change of c o a l s u r f a c e p r o p e r t i e s w i t h rank (Ihnatowicz, 1952; Blom, 1957). The h y d r o p h o b i c i t y of c o a l was shown t o be a f u n c t i o n of rank. For a g i v e n rank of c o a l and c o n t r o l l e d l e v e l of o x i d a t i o n , h y d r o p h o b i c i t y i s p r i m a r i l y dependant on the s u r f a c e h e t e r o g e n e i t y a r i s i n g from the p e t r o g r a p h -i c composition, as the macerals are known t o have v a r y i n g s u r f a c e p r o p e r t i e s . The important f a c t o r i n e s t i m a t i o n of h y d r o p h o b i c i t y of c o a l i s the a s s o c i a t e d m i n e r a l matter. S i n c e c o a l m i n e r a l s are h y d r o p h i l i c , i n t i m a t e a s s o c i a t i o n of m i n e r a l matter has a s t r o n g e f f e c t on the h y d r o p h o b i c i t y of c o a l p a r t i c l e s . 4.1.1 Rank The c o n t a c t angle has long been the o n l y measure of h y d r o p h o b i c i t y of c o a l . The e a r l i e s t r e s u l t s on c o n t a c t angle of d i f f e r e n t rank of c o a l s were r e p o r t e d by Brady and Gauger (1940) and E l y a s h e v i t c h (1941). T h e i r r e s u l t s showed t h a t bituminous c o a l s had a h i g h e r c o n t a c t angle than e i t h e r a n t h r a c i t e or l i g n i t e . In subsequent s t u d i e s by H o r s l e y and Smith (1951), Sun (1954) v e r y s i m i l a r r e s u l t s were o b t a i n e d . The most r e c e n t work by Apian (1983), G u t i e r r e z - R o d r i g u e z e t a l . (1984), O n l i n and Apian (1984) r e l a t e d h y d r o p h o b i c i t y of c o a l t o v a r i o u s rank parameters, such as p e r c e n t of u l t i m a t e carbon content, f i x e d carbon, oxygen, 51 OH/carbon r a t i o , and v i t r i n i t e r e f l e c t a n c e . Contact angles are u s u a l l y determined u s i n g e i t h e r : c a p t i v e bubble or s e s s i l e drop method. In the former technique an a i r bubble i s d e p o s i t e d on the c o a l s u r f a c e i n s o l u t i o n , whereas i n the l a t t e r the drop of water i s p l a c e d on the dry c o a l s u r f a c e . In both methods c o n t a c t angle i s measured through the water phase; the h i g h e r t h e c o n t a c t angle, the more hydrophobic t h e s u r f a c e . The r e s u l t s of c o n t a c t angle v a l u e s f o r c o a l s of d i f f e r e n t ranks are d e p i c t e d i n F i g u r e 4.1.1 a f t e r Apian (1984), O n l i n and Apian (1987) and A r n o l d and Apian (1988). A c c o r d i n g t o O n l i n and Apian (1987) and A r n o l d and Apian (1988), the c a p t i v e bubble technique can o n l y c h a r a c t e r i z e the h y d r o p h o b i c i t y of h i g h e r rank c o a l s , t h a t i s when the carbon content i s h i g h e r than 80%, w h i l e the s e s s i l e drop t e c h n i q u e may be used t o assess h y d r o p h o b i c i t y over the whole range of c o a l ranks (Parekh and Apian, 1978; G u t t i e r e z - R o d r i g u e z e t a l . , 1984) . The s e s s i l e drop r e s u l t s , however, show v e r y s i g n i f i c a n t s c a t t e r . I t was concluded (Arnold and Apian, 1988) t h a t a g r e a t d e a l of t h i s s c a t t e r i s caused by d i f f e r e n c e s i n the o r i g i n of the s t u d i e d c o a l s , and f u r t h e r t h a t s c a t t e r was reduced when v i t r i n i t e r e f l e c t a n c e was used as the rank parameter ( F i g u r e 4.1.2). C o a l i s porous and depending on whether the pores are f i l l e d w i t h a i r or water, the c o n t a c t angle may d i s p l a y q u i t e d i f f e r e n t v a l u e s ( K e l l e r , 1987; He and Laskowski, 1991). A c c o r d i n g t o t h i s t h e o r y , f o r lower rank or l e s s hydrophobic c o a l s , the pores are f i l l e d w i t h water and t h e r e f o r e the c o n t a c t angle measured on such a s u r f a c e may assume v e r y s m a l l v a l u e s , ( t h i s i s e s p e c i a l l y t r u e f o r c a p t i v e bubble t e c h n i q u e ) . F i g u r e 4.1.1 Contact angle f o r c o a l s of d i f f e r e n t ranks measured by c a p t i v e bubble and s e s s i l e drop t e c h n i q u e ; (a) c o n t a c t angles v e r s u s % Carbon, (b) c o n t a c t angles v e r s u s v i t r i n i t e r e f l e c t a n c e . 53 Over the y e a r s o t h e r i n d i r e c t t e c h n i q u e s of c h a r a c t e r i z -i n g the h y d r o p h o b i c i t y have been s u c c e s s f u l l y a p p l i e d . These i n c l u d e : r a t e o f disappearance of c o a l p a r t i c l e s d e p o s i t e d on the s u r f a c t a n t s o l u t i o n s (Garshva e t a l . , 1978; G l a n v i l l e and Wightman; 1980), a measure of immersion time f o r p a r t i c l e s t o s i n k i n t o the l i q u i d s o f d i f f e r e n t s u r f a c e t e n s i o n s (Fuerstenau, e t a l . , 1986; Fuerstenau, e t a l . , 1987), i n d u c t i o n time (time r e q u i r e d f o r p a r t i c l e t o a t t a c h t o an a i r bubble), (Ye and M i l l e r , 1988). They a l l have shown a c o r r e l a t i o n o f h y d r o p h o b i c i t y of c o a l t o rank, i n the same manner as the c o n t a c t angle. A decreased h y d r o p h o b i c i t y i n low rank c o a l s i s mainly due t o the presence of a h i g h amount of oxygen f u n c t i o n a l groups i n the c o a l s t r u c t u r e . Through those groups water i s a t t r a c t e d t o the c o a l s u r f a c e (Laskowski, 1964; Fuerstenau e t a l . , 1983). In the t r a n s i t i o n from l i g n i t e t o h i g h e r rank c o a l s (80% C) , the c o a l s t r u c t u r e l o s e s a s i g n i f i c a n t p o r t i o n of the oxygen groups, and a t the same time aromatic carbon i s i n c r e a s e d . The diagram presented by Ihnatowicz (1952), and by Blom (1957), shows the d i s t r i b u t i o n of oxygen groups i n c o a l s of d i f f e r e n t ranks as shown i n F i g u r e 4.1.2. The decrease i n h y d r o p h o b i c i t y as the a n t h r a c i t e rank i s reached i s o f t e n r e l a t e d t o i t s g r a p h i t e - l i k e s t r u c t u r e , aromatic hydrocarbons b e i n g l e s s hydrophobic than p a r a f f i n i c hydrocarbons, ( K e l l e r , 1986), (Zismans c r i t i c a l s u r f a c e t e n s i o n v a l u e s f o r g r a p h i t e and aromatic hydrocarbons, are h i g h e r than f o r p a r a f f i n hydrocarbons i n d i c a t i n g lower h y d r o p h o b i c i t y ) . 54 F i g u r e 4.1.2 D i s t r i b u t i o n of Oxygen groups i n c o a l s o f d i f f e r e n t ranks; (a) adapted from Ihnatowicz, (1952); (b) from Blom, (1957). 4.1.2 O x i d a t i o n O x i d a t i o n i s a chemical p r o c e s s l e a d i n g t o t h e a l t e r a t i o n o f many m i n e r a l s d u r i n g weathering (Gray and Lowenhaupt, 1989) . The o x i d a t i o n o f c o a l can occur i n - s i t u , d u r i n g mining and p r o c e s s i n g , or i n t h e s t o c k - p i l e s . Coal o x i d a t i o n a d v e r s e l y a f f e c t s many t e c h n o l o g i c a l p r o p e r t i e s o f c o a l . Coking q u a l i t y and p l a s t i c p r o p e r t i e s o f bituminous c o a l s , f l o t a t i o n r e c o v e r y , and c a l o r i f i c v a l u e s a re a l l s i g n i f i c a n t l y i n f l u e n c e d , and, i n many cases, some of t h e s e p r o p e r t i e s a re l o s t , when c o a l i s o x i d i z e d (Ignasiak e t a l . , 1974; Gray e t a l . , 1976; Berkowitz, 1979; C r e l l i n g e t a l . , 1979; Mezularaar e t a l . , 1987). When c o a l i s exposed t o the atmosphere, a d s o r p t i o n of oxygen t o the c o a l s u r f a c e occurs which i s f o l l o w e d by chemical r e a c t i o n s . As a r e s u l t , oxygen f u n c t i o n a l groups, such as -OH, -CO, -COOH and -0CH3, are formed on the s u r f a c e . The low-rank c o a l s are more s u s c e p t i b l e t o o x i d a t i o n than h i g h e r rank c o a l s (Berkowitz, 1979; Meuzelaar e t a l . , 1987), as t h e i r s t r u c t u r e a l r e a d y possesses h i g h amounts of oxygen f u n c t i o n a l groups, which i n t u r n are s i t e s f o r p r e f e r e n t i a l oxygen a d s o r p t i o n . The h i g h e r rank c o a l s are the l e a s t s u s c e p t i b l e t o o x i d a t i o n . The oxygen f u n c t i o n a l groups which are produced on the c o a l s u r f a c e as a r e s u l t of o x i d a t i o n c o n t r o l c o a l w e t t a b i l i t y through the balance of h y d r o p h o b i c / h y d r o p h i l i c s i t e s (Fuerstenau e t a l . , 1986), and f l o t a t i o n k i n e t i c s by i n f l u e n c i n g the s u r f a c e charge ( I s k r a and Laskowski, 1967; Wen, 1977; Fuerstenau e t a l . , 56 1983; Laskowski and P a r f i t t , 1989; Fuerstenau e t a l . , 1988c). The presence of t h e s e p o l a r groups le a d s t o i n t e r a c t i o n w i t h water molecules, which makes c o a l s h y d r o p h i l i c . H y d r o p h o b i c i t y of c o a l w i l l t h e r e f o r e be s i g n i f i c a n t l y i n f l u e n c e d by the degree of o x i d a t i o n . Numerous s o p h i s t i c a t e d methods and t e c h n i q u e s have been employed t o study o x i d a t i o n of c o a l and i t s e f f e c t on t e c h n o l o g i -c a l b e h a v i o r . Among these are p y r o l y s i s , mass spectrometry, gas chromatography, thermogravimetry/mass spectroscopy, FTIR technique (Meuzelaar, 1987), a l o n g w i t h s i m p l e r t e s t i n g procedures such as c h e m i c a l t i t r a t i o n s of a c i d i c groups (Schafer, 1970; Ignasiak and I g n a s i a k , 1970), Free S w e l l i n g Index, f l o t a t i o n response (Sun, 1954; Y a r a r and L e j a , 1982), s a l t f l o t a t i o n method f l o t a t i o n of o x i d i z e d c o a l s ( I s k r a and Laskowski, 1967), a l k a l i s o l u b i l i t y (Gray e t a l . , 1976), e l e c t r o s t a t i c charge, p e t r o g r a p h i c examinations (Chandra, 1962; M a r c h i o n i , 1983) and many o t h e r s (Gray e t a l . , 1976; Gray and Lowenhaupt, 1980) . U n f o r t u n a t e l y some of these methods f a i l t o d e t e c t o x i d a t i o n on the s u r f a c e of c o a l , as they can o n l y measure the change i n bulk p r o p e r t i e s . The s u c c e s s f u l methods t o t e s t s u r f a c e o x i d a t i o n are those which i n v o l v e d i r e c t measurement of h y d r o p h o b i c i t y , or b e h a v i o r of o x i d i z e d c o a l i n r e l a t e d p r o c e s s e s . Meaningful c o r r e l a t i o n s were found between degree of s u r f a c e o x i d a t i o n and the v a l u e of c o n t a c t angle (Horsley and Smith, 1951; I s k r a and Laskowski, 1967), immersion time (Garshva e t a l . , 1978; Widyani and Wightman, 1982; Fuerstenau e t a l . , 1986), e l e c t r o k i n e t i c poten-57 t i a l s , and parameters r e l a t e d t o the change i n the c r i t i c a l s u r f a c e of w e t t i n g and f l o a t a b i l i t y (Fuerstenau e t a l . , 1985; 1987a; Hornsby and L e j a , 1980; Hornsby and L e j a , 1983). As n a t u r a l o x i d a t i o n proceeds, oxygen r e a c t s w i t h the c o a l s u r f a c e and as a r e s u l t i t a f f e c t s s u r f a c e p r o p e r t i e s of c o a l . I t has been shown t h a t the aromatic c o a l s t r u c t u r e s are the most r e s i s t a n t t o o x i d a t i o n , because they are f r e e of f u n c t i o n a l groups. The a l i p h a t i c hydrocarbons are more prone t o the o x i d a t i o n as they a r e c h a r a c t e r i z e d by h i g h content of s i d e f u n c t i o n a l groups. For the same reasons, i t was concluded t h a t v i t r i n i t e macerals are the most s u s c e p t i b l e t o o x i d a t i o n , as compared t o i n e r t i n i t e or l i p t i n i t e macerals (Mackowsky, 1982; K l a s s e n , 1966; Mazeluraar, 1987). R e c e n t l y , a f l o t a t i o n technique was developed which i n v o l v e s ozone o x i d a t i o n of c o a l macerals t o s e l e c t i v e l y f l o a t the r e s i n substances from c o a l ( M i l l e r and Ye, 1988) . Due t o the p r e f e r e n t i a l o x i d a t i o n of c o a l macerals, s e p a r a t i o n of r e s i n from c o a l was p o s s i b l e t o a c h i e v e . From a chemical p o i n t of view, the r e s i n i s c o n s i d e r e d t o have s i m i l a r composition t o some of the l i p t i n i t e macerals (e.g. r e s i n i t e ) , hence t h i s may i n d i c a t e some r e s i s t a n c e t o o x i d a t i o n of l i p t i n i t e macerals. 4.1.3 E l e c t r i c a l charge The e l e c t r o k i n e t i c b e h a v i o r of c o a l i s d i f f i c u l t t o d e l i n e a t e due t o c o a l complex h e t e r o g e n e i t y , and i t s tendency t o a l t e r d u r i n g the exposure t o atmosphere (Fuerstenau e t a l . , 1988c; 58 Laskowski and P a r f i t t , 1989). A v a r i o u s heteroatoms and f u n c t i o n a l groups a l t o g e t h e r w i t h m i n e r a l matter c o n s i s t s u r f a c e of c o a l . These s i t e s d i s p l a y d i f f e r e n t e l e c t r o c h e m i c a l c h a r a c t e r i s t i c s , and c o n t r i b u t e t o the s u r f a c e charge of i n d i v i d u a l p a r t i c l e s . The m i n e r a l s a s s o c i a t e d w i t h c o a l can have v e r y d i f f e r e n t e l e c t r o k i n e t i c c h a r a c t e r i s t i c s . For example, a l u m i n o s i l i c a t e s are known t o have n e g a t i v e charge a t the b a s a l p l a n e s and t h e i r edges ar e c h a r a c t e r i z e d by i s o e l e c t r i c p o i n t ( i . e . p ) a t pH = 9.1, ( A l 2 0 3 ) . Quartz i s n e g a t i v e l y charged over e n t i r e range of pH, w h i l e the carbonates have t h e i r i . e . p i n the s l i g h t l y a l k a l i n e pH (Laskowski, 1987). Anthracites F i g u r e 4.1.3 G e n e r a l i z e d z e t a - p o t e n t i a l v e r s u s Ph diagram f o r c o a l s of v a r i o u s ranks, (Laskowski and P a r f i t t , 1989). 59 8" 7Y + _1 I I 10 20 30 VOLATILE MATTER, % DRY BASIS F i g u r e 4.1.4 I s o e l e c t r i c p o i n t s f o r c o a l s of v a r y i n g rank, (Laskowski, 1968) . Type and v a r y i n g amounts of m i n e r a l matter were shown t o s i g n i f i c a n t l y a l t e r e l e c t r o k i n e t i c p r o p e r t i e s of c o a l (Fuerstenau, 1988; Laskowski, 1989). A h i g h c o n t e n t of m i n e r a l matter was found t o change the e l e c t r o k i n e t i c b e h a v i o r of c o a l t o resemble t h a t of a s s o c i a t e d m i n e r a l s , and u s u a l l y was r e p o r t e d t o move i . e . p towards lower pH v a l u e s (Fuerstenau e t a l . 1988c). The e l e c t r i c charge on c o a l s u r f a c e i s developed by d i s s o c i a t i o n of f u n c t i o n a l groups, such as -COOH and -OH or by a d s o r p t i o n of i o n s from the s o l u t i o n (Fuerstenau, 1988; Laskowski, 1989) . For the c a r b o x y l i c and p h e n o l i c groups, the s i g n of the charge on the c o a l s u r f a c e depends on the pH of the s o l u t i o n , and H+ and OH- are p o t e n t i a l d e t e r m i n i n g i o n s (Campbell and Sun, 1970) . The i s o e l e c t r i c p o i n t s (i.e.p) f o r v i t r a i n s from a n t h r a c i t e and bituminous c o a l s were found t o l i e between 4.5 and 7 pH, w h i l e f o r l i g n i t e a t 2.3 pH. The maximum i . e . p v a l u e s were found between 6 and 7 f o r low v o l a t i l e bituminous c o a l s (Laskowski, 1968; Campbell and Sun, 1970). The data r e p o r t e d by S o b i e r a j and Myrcha ( S o b i e r a j and Myrcha, 1980), showed t h a t , the i . e . p v a l u e s f o r low rank and o x i d i z e d c o a l s were moved towards more a c i d i c pH ranges. A g e n e r a l i z e d z e t a p o t e n t i a l v e r s u s pH v a l u e s diagram f o r v a r i o u s ranks o f c o a l and o x i d i z e d c o a l i s shown i n F i g u r e 4.1.3. The i . e . p v a l u e s were a l s o found t o change w i t h rank, as d e s c r i b e d by Laskowski (Laskowski, 1968; Laskowski and P a r f i t t , 1989) and shown i n F i g u r e 4.1.4. A good c o r r e l a t i o n was found between maximum f l o t a t i o n r a t e and i s o e l e c t r i c p o i n t f o r c o a l s o f d i f f e r e n t ranks (Laskowski and Lupa, 1966; Fuerstenau e t a l . , 1983). T h i s maximum f l o a t a b i l i t y and h y d r o p h o b i c i t y u s u a l l y c o i n c i d e s w i t h the n e u t r a l pH range f o r the u n o x i d i z e d c o a l s . 4.1.4 P e t r o g r a p h i c composition U n f o r t u n a t e l y , v e r y l i t t l e i s known about the hydropho-b i c i t y of pure macerals, mainly because of the d i f f i c u l t y i n o b t a i n i n g pure maceral c o n c e n t r a t e s . The o n l y study o f s u r f a c e p r o p e r t i e s o f pure macerals was r e c e n t l y r e p o r t e d by Chol-yoo (1988). The macerals were o b t a i n e d by the d e n s i t y g r a d i e n t s e p a r a t i o n technique, as i n t r o d u c e d by Dyrkacz (Dyrkacz and Bloomquist, 1981). In t h i s study on a d s o r p t i o n of s u r f a c t a n t s on c o a l macerals, i t was found t h a t the change i n the s u r f a c e 61 p r o p e r t i e s o f i n e r t i n i t e w i t h rank i s s i g n i f i c a n t l y l e s s dramatic than f o r v i t r i n i t e and l i p t i n i t e . A comprehensive study of the s t r u c t u r e of macerals ( C r e l l i n g , 1979; Winans and C r e l l i n g , 1984; Winans e t a l . , 1984) showed t h a t the i n e r t i n i t e have the most aromatic s t r u c t u r e (lowest H/C r a t i o ) , w i t h v i t r i n i t e b e i n g next but w i t h much h i g h e r contents of p o l a r groups (oxygen f u n c t i o n a l groups). L i p t i n i t e c o n t a i n s much h i g h e r amounts of a l i p h a t i c hydrocarbons ( p a r a f f i n i c ) i n i t s s t r u c t u r e . Based on t h i s i n f o r m a t i o n one may expect t h a t l i p t i n i t e w i l l be the most hydrophobic maceral, s i n c e a l i p h a t i c hydrocarbons are more hydrophobic than aromatic hydrocarbons, v i t r i n i t e l e s s so, and i n e r t i n i t e l e a s t so. In most of the humic c o a l s , e s p e c i a l l y a t the rank where they d i s p l a y h i g h e s t h y d r o p h o b i c i t y (hvb-mvb), l i p t i n i t e c o ntent i s u s u a l l y v e r y s m a l l , and the v i t r i n i t e maceral i s t he most abundant. T h e r e f o r e , the s u r f a c e p r o p e r t i e s of l i p t i n i t e a re not so d i s t i n c t . Most of the s t u d i e s a s s e s s i n g h y d r o p h o b i c i t y of p e t r o -g r a p h i c components were u s u a l l y l i m i t e d t o l i t h o t y p e samples, r e p r e s e n t i n g n a t u r a l c o n c e n t r a t e s of macerals. The ve r y f i r s t c o n t a c t angle measurements were performed on l i t h o t y p e s (Horsley and Smith, 1951), f o l l o w e d by many oth e r r e s e a r c h e r s (Sun, 1954; K l a s s e n , 1966). H o r s l e y and Smith (1951) showed t h a t the n a t u r a l c o n t a c t angles of d i f f e r e n t l i t h o t y p e s d i f f e r e d by n e a r l y 50 degrees, w i t h v i t r a i n b e i n g the most hydrophobic, f o l l o w e d by c l a r a i n , d u r a i n and f u s a i n . Sun (1954) suggested t h a t the order of h y d r o p h o b i c i t y , based on the c a l c u l a t i o n of s u r f a c e p r o p e r t i e s from 62 t h e e l e m e n t a l a n a l y s e s ( f l o a t a b i l i t y i n d e x ) , decreases as f o l l o w s : c l a r a i n > v i t r a i n > f u s a i n > d u r a i n Frequent d i s c r e p a n c i e s i n the assessment of h y d r o p h o b i c i -t y o f c o a l l i t h o t y p e s a re a t t r i b u t e d t o fundamental d i f f e r e n c e s between c o a l s , as w e l l as v a r i a t i o n s i n maceral and m i n e r a l matter c o m p o s i t i o n of l i t h o t y p e s from one c o a l t o another. A r n o l d and Apian (1989) determined h y d r o p h o b i c i t y of macerals from v a r i o u s ranks of c o a l by measuring the c o n t a c t angle on m i c r o s c o p i c a l l y i d e n t i f i e d macerals. They concluded t h a t the l i p t i n i t e i s c h a r a c t e r i z e d by the h i g h e s t h y d r o p h o b i c i t y among a l l macerals, w i t h c o n t a c t angles as h i g h as 114-132° f o r r e s i n i t e from hvb c o a l , and approximately 90° f o r s p o r i n i t e (hvA). V i t r i n i t e i s somewhat l e s s hydrophobic than l i p t i n i t e and appears t o be s i g n i f i c a n t l y more hydrophobic than f u s i n i t e . The c o n t a c t angle of 1 p s e u d o v i t r i n i t e i s g e n e r a l l y s l i g h t l y h i g h e r than f o r the c o r r e -sponding v i t r i n i t e , i m p l y i n g h i g h e r h y d r o p h o b i c i t y of t h i s maceral. 4.1.5 M i n e r a l matter The m i n e r a l s t h a t a r e a s s o c i a t e d w i t h c o a l are, as d i s c u s s e d i n s e c t i o n 3.1.3, n a t u r a l l y h y d r o p h i l i c . Consequently, any i n c l u s i o n s o f m i n e r a l matter on the c o a l s u r f a c e w i l l have an 1 P s e u d o v i t r i n i t e i s a type of v i t r i n i t e which u s u a l l y has h i g h e r r e f l e c t a n c e than c o r r e s p o n d i n g v i t r i n i t e s . I t appears as v e r y smooth w i t h c h a r a c t e r i s t i c s s l i t s i n the s t r u c t u r e , and occurs w i t h fewer a s s o c i a t i o n s w i t h o t h e r macerals. The term pseudo-v i t r i n i t e was i n t r o d u c e d by B e n e d i c t (1968) ; t h i s maceral was found t o be l e s s r e a c t i v e i n the c o k i n g p r o c e s s . 63 i n f l u e n c e on i t s h y d r o p h o b i c i t y . Depending on the type o f m i n e r a l matter and i t s form of a s s o c i a t i o n w i t h i n a p a r t i c u l a r c o a l , i t s t e x t u r e and l i b e r a t i o n c h a r a c t e r i s t i c s d i f f e r . Syngenetic m i n e r a l s are u s u a l l y p a r t of the c o a l p a r t i c l e s , whereas e p i g e n e t i c m i n e r a l s a re the e a s i e s t t o se p a r a t e from macerals. In terms of h y d r o p h o b i c i t y , the s y n g e n e t i c m i n e r a l matter w i l l i n f l u e n c e the s u r f a c e p r o p e r t i e s of c o a l p a r t i c l e s the most. E p i g e n e t i c m i n e r a l s , which are t y p i c a l l y c o n c e n t r a t e d a l o n g c l e a t s , are u s u a l l y l i b e r a t e d d u r i n g breakage, and are not p a r t of the c o a l p a r t i c l e s u r f a c e . C a u t i o n has t o be used when c o r r e l a t i n g the c o n t a c t angle r e s u l t s w i t h the f l o a t a b i l i t y of c o a l p a r t i c l e s , s i n c e the s u r f a c e examined might not n e c e s s a r i l y be the one which would be r e s p o n s i b l e f o r p a r t i c l e b ehavior i n the f l o t a t i o n p r o c e s s . Apart from f r a c t u r e p l a n e s and pores, m i n e r a l matter i n c l u s i o n s w i l l g r e a t l y i n f l u e n c e the f i n a l v a l u e of the c o n t a c t angle. I t was observed by Gaudin (1957) t h a t an i n c r e a s e i n the ash content of c o a l r e s u l t e d i n r e d u c t i o n o f c o n t a c t angle, and hence, i n the h y d r o p h o b i c i t y . Dramatic change i n the s u r f a c e p r o p e r t i e s of g r a p h i t e was noted w i t h an i n c r e a s e i n ash content (Parekh and Apian 1978). In the work of Bustamante and Warren (1983) some c o n c l u s i o n s were reached as t o the d i r e c t i n f l u e n c e o f m i n e r a l matter content and f l o t a t i o n r e c o v e r y of c o a l g r a i n s . In t h e i r study, r e l a t i v e l y s m a l l amounts of m i n e r a l matter i n the c o a l g r a i n s depressed the f l o t a t i o n of low rank c o a l , but when the c o a l 64 was of h i g h e r rank r e l a t i v e l y l a r g e p r o p o r t i o n s o f m i n e r a l matter had l i t t l e e f f e c t on f l o a t a b i l i t y . The low-rank c o a l i n t h e i r study was hvb, and was regarded as being l e s s hydrophobic, whereas the h i g h rank c o a l was mvb, and was c o n s i d e r e d t o be h i g h l y hydropho-b i c . The v e r y f a c t t h a t l a r g e amounts of m i n e r a l matter are u s u a l l y a s s o c i a t e d w i t h f u s i n i t e has o f t e n been used t o e x p l a i n v e r y low h y d r o p h o b i c i t y o f t h i s maceral (Brown, 1962; Kla s s e n , 1966; Bujnowska, 1985a). 4.2 F l o a t a b i l i t y o f c o a l 4.2.1. F l o a t a b i l i t y o f c o a l as a f u n c t i o n o f rank An i n h e r e n t h y d r o p h o b i c i t y of c o a l i s the p r e r e q u i s i t e c o n d i t i o n f o r n a t u r a l f l o a t a b i l i t y of c o a l . For t h i s reason the c o n t a c t angle i s ve r y f r e q u e n t l y used t o assess f l o a t a b i l i t y of c o a l s (Brown, 1962; Sun, 1954; H o r s l e y and Smith, 1951; Apian, 1983) . High c o n t a c t angles are always a s s o c i a t e d w i t h h i g h f l o a t a b i l i t y . I t has long been known t h a t c o a l f l o a t a b i l i t y changes w i t h rank. Many hypotheses have been put forward t o e x p l a i n t h i s phenomenon. Taggart (1939 i n Sun, 1954a) suggested t h a t the d i f f e r e n c e between f l o a t a b i l i t y of bituminous c o a l and a n t h r a c i t e was due t o the v a r i a t i o n i n the hydrogen-carbon r a t i o . W i l k i n s (1947 i n Sun, 1954a) i m p l i e d t h a t f l o a t a b i l i t y i n c r e a s e s w i t h 65 carbon content, t h a t i s wi t h the rank. The t h e o r y based on the change i n chemical s t r u c t u r e of c o a l s w i t h the rank, and t a k i n g i n t o account the i n f l u e n c e of oxygen f u n c t i o n a l groups on o v e r a l l h y d r o p h o b i c i t y of c o a l was proposed by K l a s s e n (1953). In 1954 Sun developed the s u r f a c e component theory, where he used an e m p i r i c a l formula t o c o r r e l a t e f l o a t a b i l i t y w i t h u l t i m a t e a n a l y s i s o f c o a l . A c c o r d i n g t o t h i s theory, h i g h carbon and hydrogen contents are r e s p o n s i b l e f o r h i g h h y d r o p h o b i c i t y , and t h e r e f o r e h i g h f l o a t a b i l -i t y , whereas oxygen, n i t r o g e n and water c o n t r i b u t e t o a h y d r o p h i l i c c h a r a c t e r . Based on h i s c a l c u l a t i o n s of f l o a t a b i l i t y i n d i c e s , medium or l o w - v o l a t i l e bituminous c o a l s c o n t a i n more f l o a t a b l e components than a n t h r a c i t e . T h i s was shown t o be i n a v e r y good agreement w i t h the minimum amount of f u e l o i l used as a c o l l e c t o r f o r f l o t a t i o n of medium and l o w - v o l a t i l e bituminous c o a l s (Brown, 1962; K l a s s e n , 1966, Apian, 1989). The s t r o n g l y hydrophobic c o a l s may even be f l o a t e d w i t h a f r o t h e r alone. In p r a c t i c e , up t o 0.5 kg/tone of f u e l o i l i s added t o the c o a l f l o t a t i o n . The q u a n t i t y of c o l l e c t o r i n c r e a s e s f o r lower rank c o a l s . Subbituminous c o a l s r e q u i r e not o n l y more c o l l e c t o r f o r f l o t a t i o n but a l s o r i g h t combination of an o i l y c o l l e c t o r and a f r o t h e r (Klassen, 1966). 4.2.2. F l o a t a b i l i t y o f l i t h o t y p e s The f l o t a t i o n response of c o a l l i t h o t y p e s was u s u a l l y observed as v a r i a t i o n s i n composition of c o n c e n t r a t e s from d i f f e r e n t p o i n t s of the f l o t a t i o n c i r c u i t . The f i r s t r e s u l t s on 66 l i t h o t y p e f l o t a t i o n on commercial s c a l e were o b t a i n e d i n 1954 and r e p o r t e d by K l a s s e n (1966). He showed e x p l i c i t l y t h a t v i t r a i n had h i g h e r f l o t a t i o n r a t e s . Almost a l l v i t r a i n was r e c o v e r e d i n the v e r y f i r s t f l o t a t i o n c e l l s , w h i l e o n l y h a l f of the f u s a i n was r e c o v e r e d i n the same c e l l s . The b u l k of the c l a r a i n and d u r a i n was r e c o v e r e d i n t h e middle c e l l s . A number of s t u d i e s i n t o the f l o a t a b i l i t y of l i t h o t y p e s on the l a b o r a t o r y s c a l e were r e p o r t e d by H o r s l e y and Smith (1951), and Sun (1954a). In one study (Horsley and Smith, 1951) an order of d e c r e a s i n g f l o a t a b i l i t y was found as f o l l o w s : v i t r a i n > c l a r a i n > d u r a i n > f u s a i n . A c c o r d i n g t o Sun (1954a), the order of f l o a t a b i l i -t y was e s t a b l i s h e d i n d e c r e a s i n g order as c l a r a i n > v i t r a i n > f u s a i n > d u r a i n . In both cases the order of f l o a t a b i l i t y was i n v e r y good agreement w i t h the c o n t a c t angle v a l u e s f o r l i t h o t y p e s . The d i s c r e p a n c i e s between r e s u l t s may be due t o the v a r y i n g amount of m i n e r a l matter content i n l i t h o t y p e s or most p r o b a b l y o r i g i n of c o a l s and t h e r e f o r e v a r i a t i o n i n macroscopic appearance of l i t h o t y p e s . The s e l e c t i v e f l o t a t i o n of c o a l p e t r o g r a p h i c components may s i g n i f i c a n t l y improve the q u a l i t y of c o a l f o r c o k i n g p r o c e s s . A number of f l o t a t i o n s t u d i e s i n s e l e c t i v e f l o t a t i o n of l i t h o t y p e s were summarized by K l a s s e n (1966), and dated as e a r l y as 1922. I t was observed t h a t t h e r e i s c e r t a i n s e l e c t i v i t y i n f l o t a t i o n when d i f f e r e n t c o l l e c t o r s are used. For example, l i g h t o i l s were more e f f e c t i v e i n f u s a i n f l o t a t i o n , w h i l e c r e s o l i n f l o t a t i o n of v i t r a i n and d u r a i n (Majer and Cukierman, 1934). Other s t u d i e s (Barysz-67 nikow, 1940) confirmed t h a t phenol promotes f l o t a t i o n of b r i g h t ( v i t r a i n ) components of c o a l , and then was concluded (Deminowa, 1957) t h a t i n f l o t a t i o n without c o l l e c t o r s v i t r a i n has the h i g h e s t f l o a t a b i l i t y , w h i l e f u s a i n the lowest. The s a l t f l o t a t i o n (2% NaCl) was shown t o boost f l o t a t i o n of v i t r a i n and somehow depress f l o t a t i o n of f u s a i n . On the o t h e r hand, p i n e o i l i n s a l t f l o t a t i o n induced f l o a t a b i l i t y o f f u s a i n and d u r a i n . Chapman (1922) claimed t o s e p a r a t e d u r a i n from v i t r a i n and c l a r a i n w i t h the use of phenol and kerosene as the c o l l e c t o r s . In h i s study, c o n t r a r y t o other r e s u l t s o b t a i n e d l a t e r on, phenol promoted f l o t a t i o n of d u r a i n and kerosene a i d e d r e c o v e r y of c l a r a i n and v i t r a i n . Very i n t e r e s t i n g r e s u l t s were o b t a i n e d on the f l o a t -a b i l i t y of low rank l i t h o t y p e s by Roznowa (1963). She showed t h a t i n f l o t a t i o n of low rank c o a l s o n l y f u s a i n i s c h a r a c t e r i z e d by n a t u r a l f l o a t a b i l i t y . The h i g h e r f l o a t a b i l i t y of f u s a i n as compared t o v i t r a i n was a t t r i b u t e d t o the h i g h e r degree of a r o m a t i z a t i o n of t h e f u s i n i t e maceral ( f u s a i n b e i n g a n a t u r a l c o n c e n t r a t e of f u s i n i t e ) a t t h i s rank. V i t r i n i t e s t r u c t u r e i s c h a r a c t e r i z e d by v e r y h i g h content of h y d r o p h i l i c oxygen f u n c t i o n a l groups, r e n d e r i n g v i t r a i n ( n a t u r a l c o n c e n t r a t e of v i t r i n i t e ) l e s s f l o a t -a b l e . The l a y o u t f o r s e l e c t i v e f l o t a t i o n of l i t h o t y p e s was proposed and t e s t e d on i n d u s t r i a l s c a l e (Roznowa, 1963). With the c a r e f u l s e l e c t i o n of f l o t a t i o n reagents and f l o t a t i o n c o n d i t i o n s t h r e e d i f f e r e n t p roducts were o b t a i n e d : low-ash v i t r a i n concen-t r a t e , low-ash and high-ash f u s a i n c o n c e n t r a t e s . 68 c A comprehensive study on s e l e c t i v i t y o f c o l l e c t o r s i n f l o t a t i o n of l i t h o t y p e s was c a r r i e d out by Kroger and Bade (1961). They showed t h a t t h e r e i s s e l e c t i v i t y i n a d s o r p t i o n of d i f f e r e n t c o l l e c t o r s onto the d i f f e r e n t l i t h o t y p e s as a r e s u l t of t h e i r s u r f a c e p r o p e r t i e s . V i t r a i n was c h a r a c t e r i z e d by the h i g h e s t h y d r o p h o b i c i t y i n h i g h t o medium-volatile c o a l s and the best i n t e r a c t i o n w i t h c o l l e c t i n g r eagents. 4.2.3 F l o a t a b i l i t y of macerals Brown (1962) i n h i s review of f r o t h f l o t a t i o n suggested t h a t d i s t i n c t i o n s between the f l o a t a b i l i t y of the major maceral groups can be made. Si n c e t h a t time, v e r y l i m i t e d r e s e a r c h was done on f l o a t a b i l i t y o f d i f f e r e n t macerals. The o n l y c o a l s which r e c e i v e d adequate a t t e n t i o n were the medium and low v o l a t i l e bituminous c o a l s . As a r e s u l t , v i t r i n i t e macerals were i d e n t i f i e d as the most f l o a t a b l e f o r a l l rank of c o a l s (Brown, 1962; K l a s s e n , 1966; Hower, 1984). In the more r e c e n t study by Sarkar (1984), s e l e c t i v i t y of c o a l macerals d u r i n g f l o t a t i o n and o i l agglomeration was examined. The f l o t a t i o n t e s t s were c a r r i e d out w i t h the use of standard f l o t a t i o n r e agents ( d i e s e l o i l as c o l l e c t o r and p i n e o i l as a f r o t h e r ) i n the commercial f l o t a t i o n c e l l . From the m i c r o s c o p i c a n a l y s i s i t was concluded t h a t v i t r i n i t e has s u p e r i o r response t o f l o t a t i o n over o t h e r macerals. 69 V i t r i n i t e was found t o be s e l e c t i v e l y c o n c e n t r a t e d i n the c l e a n c o a l f l o t a t i o n p r o d u c t s . The c l e a n c o a l c o n c e n t r a t e s , c o l l e c t e d a t d i f f e r e n t time i n t e r v a l s d u r i n g f l o t a t i o n , r e v e a l e d t h a t f r e e v i t r i n i t e g r a i n s responded i n the i n i t i a l stage, w h i l e o t h e r g r a i n s were c o l l e c t e d a t a l a t e r stage of f l o t a t i o n . F u s i n i t e was shown t o be s i g n i f i c a n t l y l e s s amenable t o f l o t a t i o n . T h i s i s i n a v e r y good agreement w i t h the e a r l i e r s t u d i e s on the m e d i u m - v o l a t i l e b i t u m i -nous c o a l s . A somewhat c o n t r o v e r s i a l r e s u l t s on f l o a t a b i l i t y of c o a l macerals of d i f f e r e n t ranks were o b t a i n e d by Bennett e t a l . , (1983). A c c o r d i n g t o t h i s study, c o a l p a r t i c l e s of v a r y i n g m i c r o l i t h o t y p e composition; v i t r i n i t e , c l a r i t e , v i t r i n e r t i t e or t r i m a c e r i t e , w i t h no v i s i b l e m i n e r a l matter had s i m i l a r f l o a t a -b i l i t i e s when r e c o v e r e d by batch f l o t a t i o n i n the presence of f r o t h e r . I n e r t i n i t e p a r t i c l e s were found t o be a slower f l o a t i n g than g r a i n s of o t h e r macerals group, r e g a r d l e s s of rank of c o a l . The most r e c e n t and p r o b a b l y the most comprehensive study on f l o a t a b i l i t y of p e t r o g r a p h i c components of low rank c o a l s was conducted by Bujnowska (1985b). In t h i s study v a r i o u s reagents were used t o promote f l o a t a b i l i t y of d i f f e r e n t macerals, which are o t h e r w i s e nonf l o a t a b l e . The reagents were chosen i n such a way t h a t they promoted the f l o t a t i o n of one maceral a t a time. The mecha-nisms of i n t e r a c t i o n between the reagents and the s u r f a c e of c o a l was e x p l a i n e d on the b a s i s of d i f f e r e n t s u r f a c e p r o p e r t i e s of macerals. In subbituminous c o a l , i n e r t i n i t e (mainly f u s i n i t e ) was 70 shown t o be more hydrophobic than o t h e r macerals. The chemical s t r u c t u r e of f u s i n i t e i n t h i s rank i s c o n s i d e r e d t o have s m a l l amounts of s i d e groups ( a l i c y c l i c and a l i p h a t i c s t r u c t u r e s , b r i d g e s , f u n c t i o n a l groups) as compared t o the v i t r i n i t e o f the same rank. F u s i n i t e aromatic s t r u c t u r e i s a r e s u l t of i t s h i g h degree of a r o m a t i z a t i o n and condensation i n the e a r l y stages of c o a l i f i c a t i o n (van K r e v e l e n , 1961; Stach e t a l . , 1982). The h i g h content of oxygen f u n c t i o n a l groups i n the s t r u c t u r e of v i t r i n i t e of the lower rank c o a l has a d e c i s i v e r o l e i n d e c r e a s i n g i t s f l o a t a b i l i t y . Low f l o a t a b i l i t y o f l i p t i n i t e ( e x i n i t e ) can be e x p l a i n e d by i t s l e s s aromatic and more d i s o r d e r e d s t r u c t u r e , w i t h low content of f u n c t i o n a l groups. R e l a t i v e l y s m a l l c o n t e n t of oxygen groups i n l i p t i n i t e macerals may i n d i c a t e a l e s s h y d r o p h i l i c s u r f a c e . In the case of n o n f l o a t a b l e low rank c o a l , however, the f l o a t a b i l i t y has t o be induced by a d s o r p t i o n of c h e m i c a l reagents ( u s u a l l y p o l a r ) , and t h i s means, i n the case of l i p t i n i t e , weaker i n t e r a c t i o n s i t e s f o r the f l o t a t i o n r eagents. As a r e s u l t f l o a t a b i l i t y of l i p t i n i t e i n lower rank c o a l s was shown t o be decreased (Bujnowska, 1985b). For v i t r i n i t e , the l a r g e content of f u n c t i o n a l groups was shown t o f a c i l i t a t e a d s o r p t i o n of p o l a r r e a g e n t s , but not enough t o i n c r e a s e h y d r o p h o b i c i t y of v i t r i n i t e t o exceed t h a t of f u s i n i t e . The f l o a t a b i l i t y of macerals of subbituminous c o a l were found t o be i n the f o l l o w i n g order (Bujnowska, 1985b): i n e r t i n i t e > v i t r i n i t e > l i p t i n i t e 71 more p r e c i s e l y : f u s i n i t e > m i c r i n i t e > v i t r i n i t e > l i p t i n i t e The f l o a t a b i l i t y of p e t r o g r a p h i c components was shown t o change w i t h the rank, and f o r medium and h i g h rank c o a l s the f o l l o w i n g d e c r e a s i n g o r der was observed by s e v e r a l r e s e a r c h e r s (Brown, 1962; K l a s s e n , 1966; Hower, 1984; Sarkar, 1984; Bujnowska, 1985a): v i t r i n i t e > i n e r t i n i t e > l i p t i n i t e The s t r u c t u r e of v i t r i n i t e changes w i t h t h e rank, the con t e n t of aromatic hydrocarbons i n c r e a s e s d r a s t i c a l l y w i t h the s u b s t a n t i a l decrease i n number of h y d r o p h i l i c groups, whereas the s t r u c t u r e o f f u s i n i t e changes i n s i g n i f i c a n t l y throughout the c o a l i f i c a t i o n range. For t h i s reason, f l o a t a b i l i t y o f v i t r i n i t e i n h i g h rank c o a l s exceeds t h a t of f u s i n i t e . 72 CHAPTER 5 OBJECTIVES AND SCOPE The o b j e c t i v e of t h i s study was t o i n v e s t i g a t e wetta-b i l i t y and f l o a t a b i l i t y of c o a l p a r t i c l e s of d i f f e r e n t p e t r o g r a p h i c c o m p o s i t i o n . F i l m f l o t a t i o n was used t o e v a l u a t e w e t t a b i l i t y and a P a r t r i d g e - S m i t h c e l l f l o t a t i o n was used t o determine f l o a t a b i l i t y of macerals and l i t h o t y p e s . The f i l m f l o t a t i o n technique, as proposed by Fuerstenau (1985) , u t i l i z e s concept of c r i t i c a l s u r f a c e t e n s i o n o f w e t t a b i l i t y t o a s s e s s h y d r o p h o b i c i t y of an assembly of c o a l p a r t i c l e s . In t h i s t e s t c o a l p a r t i c l e s a re separated i n t o f r a c t i o n s a c c o r d i n g t o t h e i r c r i t i c a l s u r f a c e t e n s i o n as d e f i n e d by Zisman (1964). The f l o t a t i o n t e s t s a re c a r r i e d out by p l a c i n g c o a l p a r t i c l e s on the s u r f a c e of the s o l u t i o n . Aqueous methanol s o l u t i o n s a re used t o c r e a t e d i f f e r e n t s u r f a c e t e n s i o n s . The cumulative w e t t a b i l i t y d i s t r i b u t i o n of p a r t i c l e s v e r s u s t h e i r c r i t i c a l s u r f a c e t e n s i o n o f w e t t i n g i s o b t a i n e d . In s m a l l - s c a l e f l o t a t i o n t e s t s , the concept of c r i t i c a l s u r f a c e t e n s i o n has been extended t o the dynamic f l o t a t i o n t e s t s (Hornsby and L e j a , 1980; Hornsby, 1981; Hornsby and L e j a , 1983). S i n c e w e t t a b i l i t y and f l o a t a b i l i t y are not n e c e s s a r i l y synonymous, the term c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y was proposed 73 (Hornsby, 1981). In f l o t a t i o n , the s e l e c t i v e s e p a r a t i o n of two hydrophobic s o l i d s may occur even though they may have the same c r i t i c a l s u r f a c e t e n s i o n , yc, but d i f f e r e n t Y cf# the c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y . Cumulative f l o a t a b i l i t y d i s t r i b u -t i o n of p a r t i c l e s a c c o r d i n g t o t h e i r c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y was o b t a i n e d from the s m a l l - s c a l e f l o t a t i o n t e s t s i n methanol s o l u t i o n s . Maceral c o n c e n t r a t e s o b t a i n e d from d e n s i t y f r a c t i o n a t i o n o f m e d i u m - v o l a t i l e c o a l , as w e l l as hand-picked l i t h o t y p e s of the same c o a l , were used f o r the f i l m f l o t a t i o n and the s m a l l - s c a l e f l o t a t i o n t e s t s . Cumulative d i s t r i b u t i o n s of w e t t a b i l i t y and f l o a t a b i l i t y f o r maceral c o n c e n t r a t e s and l i t h o t y p e s were compared. Furthermore, m i c r o s c o p i c a n a l y s e s of the f l o t a t i o n p r o d u c t s were performed i n o r d e r t o determine f l o t a t i o n response of c o a l g r a i n s of v a r i o u s p e t r o g r a p h i c composition i n s o l u t i o n s of changing s u r f a c e t e n s i o n s . The c o a l sample p r o p e r t i e s were c h a r a c t e r i z e d by proximate and u l t i m a t e a n a l y s e s , p e t r o g r a p h i c examination and Free S w e l l i n g Index. The narrow s i z e f r a c t i o n of c o a l was used t o minimize the e f f e c t s of p a r t i c l e s i z e on f l o a t a b i l i t y . The s i z e -210+149 jim, (65x100 mesh, T y l e r ) was chosen f o l l o w i n g Hornsby (1981). 74 CHAPTER 6 MATERIALS - METHODS OF PREPARATION 6.1 Glassware A l l glassware used f o r experiments was washed i n d e t e r g e n t s o l u t i o n o f E x t r a n MN-1 ( l g per 1 l i t e r of water), then c l e a n e d w i t h acetone and i n chromic a c i d s o l u t i o n s ( K 2 C r 2 0 7 / H 2S0 4) when necessary, and t h o r o u g h l y r i n s e d i n s i n g l e d i s t i l l e d water. 6.2 S o l u t i o n s A s i n g l e d i s t i l l e d water used i n expe r i m e n t a t i o n , was o b t a i n e d from a Barnstead s t i l l \ d i s t i l l a t i o n u n i t . F r e s h d i s t i l l e d water was s t o r e d i n l a r g e Pyrex g l a s s c o n t a i n e r s . The methanol s o l u t i o n s were prepared from F i s h e r C e r t i f i e d ACS grade methanol, Cat. No. A-412-4 UN 1230. S o l u t i o n s of d i f f e r e n t s u r f a c e t e n s i o n s were prepared by p i p e t t i n g the r e q u i r e d volume of methanol i n t o v o l u m e t r i c f l a s k s w i t h d i s t i l l e d water a t room temperature (20 -/+ 3° C) . The s u r f a c e t e n s i o n of methanol s o l u t i o n s was measured by the DuNouy r i n g method. The measurements were c a r r i e d out a t 20 +/-2° C. The mean experimental 75 so 0 20 40 60 80 100 Methanol concentration, vol % F i g u r e 6.2.1 S u r f a c e t e n s i o n of methanol s o l u t i o n s (temp. 20+/-2° C). v a l u e s of s u r f a c e t e n s i o n s are p l o t t e d i n F i g u r e 6.2.1 and Table B . l The d e s c r i p t i o n of apparatus and procedure are g i v e n i n Appendix B. 6.3 C o a l Samples 6.3.1 Sample D e s c r i p t i o n The c o a l samples used i n the study were from the raid A l b i a n (Lower Cretaceous) Gates Formation from n o r t h e a s t e r n B r i t i s h Columbia. The main run-of-mine sample was o b t a i n e d from Bullmoose O p e r a t i n g C o r p o r a t i o n . A c c o r d i n g t o the ASTM D 3888-66 (1972) t h i s c o a l can be c l a s s i f i e d as medium v o l a t i l e bituminous ( F i x e d Carbon, d.a.f. of the composite sample was 69.51%). Complete g e o l o g i c a l d e s c r i p t i o n s of Bullmoose seams are a v a i l a b l e from p u b l i c a t i o n s by K a l k r e u t h and L e c k i e (1989) and Drozd (1985). The r e f l e c t a n c e ( R o m a x ) of the seams v a r i e s from 1.14% i n seam A, c o n s i d e r e d as the o l d e s t , t o 1.02% of Seam E, the youngest ( K a l k r e u t h and L e c k i e , 1989) . Seam A l i t h o t y p e samples were a v a i l a b l e thanks t o M i c h e l l e Lamberson and Marc B u s t i n of G e o l o g i c a l S c i e n c e s of the U n i v e r s i t y of B r i t i s h Columbia. L i t h o t y p e s were c o l l e c t e d as d e s c r i b e d by Lamberson (Lamberson e t a l . , 1989) a c c o r d i n g t o a m o d i f i e d A u s t r a l i a n c l a s s i f i c a t i o n scheme as d i s c u s s e d i n s e c t i o n 3.2.4. A minimum t h i c k n e s s of one c e n t i m e t e r was used t o d e l i n e a t e a l i t h o t y p e i n the f i e l d . A r e p r e s e n t a t i v e sample of approximately 77 T a b l e 6.3.1 The proximate and u l t i m a t e a n a l y s e s o f l i t h o t y p e s . The r e s u l t s a re pre s e n t e d on a dry and ash f r e e b a s i s . L i t h o t y p e sample B BB BD BC FIBROUS Mo i s t u r e , % . . 0.92 1.23 0.50 1.97 2.07 Ash, % . . . 4.20 5.23 6.12 8. 00 3.46 V o l a t i l e M a t t e r 30.41 27.07 29.46 26.73 26.99 (d.a.f) F i x e d Carbon . . 69.59 72.93 70.54 73.27 73.01 (d.a.f) F • S * X 8.5 6.5 4 1.5 0 U l t i m a t e T o t a l Sulphur . .42 .55 .29 .37 .24 (d.a.f) Carbon . . . 87.37 88.56 87.57 86.3 87.06 (d.a.f) Hydrogen . . . 5.43 4.86 4 .84 4.69 3.44 (d.a.f) N i t r o g e n . . . 1. 04 1.20 1.18 1.12 .60 (d.a.f) Oxygen . . . 5.74 4.84 6.12 7.52 8.66 ( c l i f f ) Atomic R a t i o s H/C . . . . .75 .66 .66 .65 .47 0/C . . . .004 .03 .05 .05 .06 B - b r i g h t ; BB - banded b r i g h t ; BD - banded d u l l ; BC - bande( c o a l d.a.f - r e p o r t e d on dry ash f r e e b a s i s 50 grams (whenever a v a i l a b l e ) was taken, s e a l e d i n p l a s t i c bags and s t o r e d i n t h e r e f r i g e r a t o r . The complete s e t of proximate and u l t i m a t e a n a l y s e s of l i t h o t y p e s i s i n c l u d e d i n T a b l e 6.3.1. 78 6.3.2 Sample p r e p a r a t i o n 6.3.2.1 Composite sample A 100 kg b a r r e l of run-of-mine Bullmoose seam A c o a l was spread out on the d r y i n g f l o o r . The sample was d r i e d f o r 48 hours t o e q u i l i b r a t e w i t h the l a b o r a t o r y atmosphere, and then reduced t o 37.5 mm (1/2 inch) s i z e . A f t e r c r u s h i n g , the t o t a l sample was s p l i t a c c o r d i n g t o the s t a n d a r d p r e p a r a t i o n procedure, ASTM D 2013-72 i n o r d e r t o o b t a i n r e p r e s e n t a t i v e 12.5 kg sample. A f u r t h e r l / 8 t h of t o t a l sample was s p l i t by r i f f l i n g i n t o 6 l o t s of approximately 2 kg each. Then each sample was ground i n a r o d m i l l i n water suspension a t approximately 40 % s o l i d c o n c e n t r a t i o n f o r 20 minutes. A f t e r g r i n d i n g , samples were wet screened on v i b r a t i n g s c r e e n s . A l l s i z e f r a c t i o n s were s t o r e d s e p a r a t e l y i n s e a l e d p l a s t i c bags. The -212+149 jim (65x100 mesh) s i z e f r a c t i o n was chosen f o r experimental work. T h i s s i z e f r a c t i o n was found t o be p a r t i c u l a r l y h i g h i n ash content (28.34%). High d e n s i t y m i n e r a l p a r t i c l e s were removed wit h the use of "gold-pan" washing t e c h -nique. Both samples were used i n experiments; high-ash composite sample was the i n i t i a l -212+149 jim s i z e f r a c t i o n , whereas the " c l e a n e d " sample was the low-ash composite. For u l t i m a t e and proximate as w e l l as o t h e r bulk a n a l y s e s l / 8 t h of the head sample was s p l i t a g a i n t o o b t a i n 125 grams of composite r e p r e s e n t a t i v e sample. 79 6.3.2.2 D e n s i t y f r a c t i o n s To o b t a i n maceral c o n c e n t r a t e s from the composite sample, a f l o a t - a n d - s i n k t echnique was used. Macerals are known t o have d i f f e r e n t d e n s i t i e s . The d e n s i t y f r a c t i o n a t i o n was c a r r i e d out i n aqueous Z n C l 2 s o l u t i o n s ( Z n C l 2 , F i s h e r C e r t i f i e d ACS, Cat. Z33-500) . In each run 50 grams of -212+149 jim s i z e f r a c t i o n of composite sample was i n t r o d u c e d i n t o 1 l i t e r s e p a r a t o r y f u n n e l w i t h d e n s i t y s o l u t i o n . The lowest d e n s i t y s o l u t i o n was 1.3 g/cm 3 and i t was subsequently i n c r e a s e d by .5 g/cm 3 up t o 1.5 g/cm 3. A f t e r the s i n k and f l o a t were completed, samples were washed w i t h 20% methanol s o l u t i o n and w i t h warm d i s t i l l e d water t o remove t r a c e s of Z n C l 2 . The f r a c t i o n s were d r i e d and s t o r e d under N 2 i n s e a l e d g l a s s c o n t a i n e r s . 6.3.2.3 L i t h o t y p e s L i t h o t y p e s were r e c e i v e d as f r e s h samples i n s e a l e d p l a s t i c bags. To o b t a i n a -212+149 jim s i z e f r a c t i o n , each sample was reduced i n p e s t l e and mortar under n i t r o g e n atmosphere, t o 100% p a s s i n g .50 mm (28 mesh) s i z e and r e q u i r e d s i z e f r a c t i o n was i s o l a t e d . The l i t h o t y p e samples were s e a l e d under vacuum i n t i g h t p l a s t i c bags and s t o r e d i n the r e f r i g e r a t o r . 80 6.3.3 Proximate and U l t i m a t e Analyses The proximate a n a l y s e s of the composite Bullmoose seam A, l i t h o t y p e samples and d e n s i t y f r a c t i o n s were o b t a i n e d i n the a n a l y t i c a l l a b o r a t o r y of the Department of M i n i n g and M i n e r a l Process E n g i n e e r i n g i n accordance w i t h the ASTM procedures. The r e s u l t s a r e p r e s e n t e d i n T a b l e s 6.3.1 and 6.3.2 on a dry and ash f r e e b a s i s . T o t a l s u lphur and FSI were a l s o o b t a i n e d i n the same l a b o r a t o r y and r e p o r t e d w i t h proximate a n a l y s i s . The u l t i m a t e a n a l y s e s of c o a l samples used i n the experimental work were o b t a i n e d from the Canadian M i c r o a n a l y t i c a l S e r v i c e L t d . , Delta,B.C. and A n a l y t i c a l L a b o r a t o r y of the A l b e r t a Research C o u n c i l , Edmonton. The u l t i m a t e a n a l y s i s data are the mean of the s e t of a n a l y s e s performed i n d u p l i c a t e by A l b e r t a Research C o u n c i l and one s e t o f a n a l y s i s by Canadian M i c r o a n a l y t i c a l S e r v i c e s , D e l t a . T a b l e 6.3.1 p r e s e n t s u l t i m a t e and proximate a n a l y s e s of l i t h o t y p e s . The proximate and u l t i m a t e a n a l y s e s of the composite Bullmoose A, -212+149 um s i z e f r a c t i o n ( i s o l a t e d from the composite) and the c o r r e s p o n d i n g d e n s i t y f r a c t i o n s of the -212+149 u,m s i z e f r a c t i o n a re g i v e n i n Tab l e 6.3.2. The u l t i m a t e analyses are r e p o r t e d on dry, a s h - f r e e b a s i s ; the Oxygen i s c a l c u l a t e d by d i f f e r e n c e . A comparison of the a n a l y t i c a l data of the composite sample w i t h the a n a l y t i c a l data f o r d e n s i t y f r a c t i o n s has not r e v e a l e d any s i g n i f i c a n t d i f f e r e n c e s i n ele m e n t a l composition except f o r the h e a v i e s t d e n s i t y f r a c t i o n , where carbon content i s decreased. The elemental composition of l i t h o t y p e s e x h i b i t s expected v a r i a t i o n o f C,H,N and 0. 81 D e n s i t y f r a c . <1.30 1.30 1.35 1.40 >1.50 Compo Hi-ash Lo-ash -1.35 -1.40 -1.45 - s i t e Moisture, % . . . 0.65 0.48 0.48 0.72 0.51 0.75 0.61 0.55 Ash, % 3.01 7.87 14.89 20.89 62.74 35.25 28.34 16.03 V o l a t i l e Matter 24.94 24.21 23.02 22.56 32.76 30.49 27.60 26.16 (d.a.f) F i x e d Carbon . 75.06 75.79 76.98 77.44 67.39 69.51 72.40 73.84 (d.a.f) F.S.I 9.0 4.0 3.0 1.5 1.0 4.5 6.0 8.0 U l t i m a t e T o t a l Sulphur . . 0.45 0.55 0.50 0.51 1.07 0.70 0.78 0.56 (d.a.f) Carbon . . . . 87.51 86.94 88.00 88.96 85.74 83.89 82.54 89.29 (d.a.f) Hydrogen . . . . 5.05 4.76 4.71 4.86 5.58 4.80 5.12 5.11 (d.a.f) N i t r o g e n . . . . 1.25 1.10 1.06 1.05 1.28 1.14 1.04 1.22 (d.a.f) Oxygen 5.74 6.65 5.73 4.62 6.33 9.47 9.56 3.83 ( d i f f y Atomic R a t i o s H/C 0.69 0.68 0.66 0.68 0.78 0.69 0.74 0.71 O/C 0.043 0.042 0.045 0.037 .042 0.043 0.080 0.090 d.a.f - r e p o r t e d on dry ash f r e e b a s i s T a b l e 6.3.2 The u l t i m a t e and proximate a n a l y s e s r e s u l t s of the composite samples and the corres p o n d i n g d e n s i t y f r a c t i o n s . 6.3.4 P e t r o g r a p h i c Analyses P e t r o g r a p h i c a n a l y s e s i n c l u d e d t h r e e type of examina-t i o n s : maceral a n a l y s i s , R Q (random) r e f l e c t a n c e measurement and g r a i n type a n a l y s e s . A d d i t i o n a l l y , m i c r o s c o p i c examination of the m i n e r a l matter has been performed on the composite seam A sample. Maceral a n a l y s e s were performed on the r e p r e s e n t a t i v e composite sample of Bullmoose A seam, the -212+149 um s i z e f r a c t i o n from the composite sample, d e n s i t y f r a c t i o n s o b t a i n e d from g r a v i t y s e p a r a t i o n s of the -212+149 um composite sample, and the hand-p i c k e d l i t h o t y p e s from the same seam. R e f l e c t a n c e (R Q) was o b t a i n e d on the v i t r i n i t e maceral o f t h e Bullmoose A composite sample and hand-picked l i t h o t y p e s . R e f l e c t a n c e data are i n c l u d e d w i t h the p e t r o g r a p h i c a n a l y s e s of composite and l i t h o t y p e s samples. The examination of f l o t a t i o n p r o d u c t s r e q u i r e d a more e f f i c i e n t method t o determine f l o a t a b i l i t y of c o a l p a r t i c l e s . T h e r e f o r e g r a i n type a n a l y s e s were used i n s t e a d of t r a d i t i o n a l maceral c o u n t i n g . Every counted p a r t i c l e has been d e s c r i b e d on the b a s i s of i t s maceral composition, a s s o c i a t i o n w i t h the m i n e r a l matter and observed o x i d a t i o n . D e t a i l e d d e s c r i p t i o n of the g r a i n a n a l y s i s i s g i v e n i n s e c t i o n 7.3.2. The maceral a n a l y s e s of the Bullmoose seam A and -212+149 um s i z e f r a c t i o n o b t a i n e d from the same seam are r e a s o n a b l y s i m i l a r i n t h e i r p e t r o g r a p h i c composition, w i t h the e x c e p t i o n of the s e m i f u s i n i t e c o n t e n t . The -212+149 um s i z e f r a c t i o n has almost h a l f 83 T a b l e 6.3.3 Maceral a n a l y s i s of the composite and t h e -212+149 um s i z e f r a c t i o n from the composite sample. Maceral Composite Composite Composite Composite Run 1 Run 2 Average (149-212Mm) V i t r i n i t e 81 78 80 85 L i p t i n i t e 0 0 0 0 S e m i f u s i n i t e 9 11 10 6 F u s i n i t e 4 4 4 3 I n e r t o d e t r 6 7 6 6 T o t a l I n e r t s 19 22 20 21 R0,mean 1.10 of the s e m i f u s i n i t e o f the composite sample. T a b l e 6.3.3 p r e s e n t s p e t r o g r a p h i c a n a l y s e s of the t o t a l composite sample and s i z e f r a c t i o n (-212+149 um) from the composite. P e t r o g r a p h i c examination o f the d e n s i t y f r a c t i o n s showed s i g n i f i c a n t d i s t r i b u t i o n of macerals i n t o d i f f e r e n t d e n s i t y ranges. I t was found t h a t v i t r i n i t e (volume p e r c e n t on m i n e r a l - m a t t e r - f r e e b a s i s ) was c o n c e n t r a t e d i n the < 1.3 s p e c i f i c g r a v i t y f r a c t i o n and t h a t i t s volume reached a minimum i n the range of 1.40-1.50 s p e c i f i c g r a v i t y , and p r o g r e s s i v e l y i n c r e a s e d a g a i n i n t h e f r a c t i o n w i t h d e n s i t y h i g h e r than 1.50. S i m i l a r changes i n r e l a t i v e abundance of macerals from s i n k - a n d - f l o a t a n a l y s i s were r e p o r t e d by B u s t i n (1982). D i s t r i b u t i o n o f macerals i n d e n s i t y f r a c t i o n s , as ob t a i n e d from maceral p o i n t c o u n t i n g , i s shown i n F i g u r e 6.3.1. A l l of the samples c o n t a i n e d v e r y s m a l l amounts of the r e c o g n i z a b l e 84 Maceral, volume % 100 V 80 60 40 20 iliWSSSSSiiiiiS:: mm Jies I . : m < 1.30 1.30-1.35 1.35-1.40 1.40-1.45 1.45-1.50 >1.50 Density Vitrinite HI Liptinite H Semifusinite • Fusinite ^ Inertodetrinite F i g u r e 6.3.1 D i s t r i b u t i o n of macerals i n the d e n s i t y f r a c t i o n s of +149-212 um composite sample, ( m i n e r a l m a t t e r - f r e e - b a s i s , o b t a i n e d from p o i n t c o u n t i n g t e c h n i q u e ) . l i p t i n i t e . The reasons f o r the low l e v e l of l i p t i n i t e may be the d i f f i c u l t y i n i t s r e c o g n i t i o n a t h i g h e r rank, or a combination of o r i g i n a l v e g e t a t i o n and peat chemistry (Lamberson, 1990). From g r a i n type a n a l y s i s i t i s e v i d e n t t h a t mainly homogeneous c l e a n v i t r i n i t e and p s e u d o v i t r i n i t e p a r t i c l e s occur i n the l i g h t e s t d e n s i t y f r a c t i o n s . A t o t a l o f 63% of the f r e e v i t r i n i t e p a r t i c l e s and 24% of the p s e u d o v i t r i n i t e a re p r e s e n t i n the 1.3 s p e c i f i c g r a v i t y f r a c t i o n . P s e u d o v i t r i n i t e s mostly occur as s e p a r a t e p a r t i c l e s . F u r t h e r , o n l y 4% of the t o t a l accountable v i t r i n i t e s a re a s s o c i a t e d w i t h the m i n e r a l matter. The number of f r e e v i t r i n i t e p a r t i c l e s decreases as the d e n s i t y i n c r e a s e s . The minimum oc c u r s a t 1.45 s p e c i f i c g r a v i t y , where f r e e v i t r i n i t e accounts f o r o n l y 36% of the t o t a l volume of v i t r i n i t e . However, a t the same time 100% of those v i t r i n i t e p a r t i c l e s a re i n a s s o c i a t i o n w i t h m i n e r a l matter. With the i n c r e a s e i n d e n s i t y , the number of v i t r i n i t e p a r t i c l e s i n a s s o c i a t i o n w i t h i n e r t i n i t e s r a p i d l y i n c r e a s e s . At 1.3 s p e c i f i c g r a v i t y , v i t r i n i t e i n a s s o c i a t i o n with the i n e r t i n i t e accounts f o r o n l y 13% by volume. In the next d e n s i t y f r a c t i o n , 1.30-1.35, the number i n c r e a s e s d r a m a t i c a l l y t o 35% and then i n c r e a s e s s t e a d i l y u n t i l i t reaches 63% i n the 1.45-1.50 d e n s i t y range. In the h e a v i e s t , 1.50 s p e c i f i c g r a v i t y , the amount of v i t r i n i t e i n a s s o c i a t i o n w i t h i n e r t i n i t e s h a r p l y d e c l i n e s t o 39%, and a t the same time the amount of f r e e v i t r i n i t e w i t h m i n e r a l matter i n c r e a s e s t o 61 % of t o t a l v i t r i n i t e . I t i s noteworthy t h a t the 1.30 s p e c i f i c g r a v i t y f r a c t i o n i s e n r i c h e d i n p s e u d o v i t r i n i t e , 86 which may be of p r a c t i c a l use when m e t a l l u r g i c a l c o a l s are c o n s i d e r e d . The presence of p s e u d o v i t r i n i t e l e a d s t o the d e t e r i o r a -t i o n of coke q u a l i t y (Benedict e t a l . , 1968). D i s t r i b u t i o n of g r a i n s i n d e n s i t y f r a c t i o n s and t h e i r d e s c r i p t i o n i n terms of a s s o c i a t i o n w i t h m i n e r a l matter as w e l l as the v i s i b l e o x i d a t i o n i s p r e s e n t e d i n F i g u r e s 6.3.2 a and b, and i s summarized i n T a b l e A.4 (Appendix A ) . L i t h o t y p e s of Bullmoose seam A were d e s c r i b e d u s i n g the A u s t r a l i a n c l a s s i f i c a t i o n scheme ( D i e s s e l , 1965; M a r c h i o n i , 1980). The examples of c o a l l i t h o t y p e s found i n Bullmoose c o a l seams are shown i n F i g u r e 6.3.3. Seam A, as d e s c r i b e d by Lamberson (1989) i s p r i m a r i l y composed of banded c o a l and banded d u l l l a y e r s . Maceral a n a l y s e s of t h e l i t h o t y p e s (Lamberson, u n p u b l i s h e d data) shows t h a t t h e r e i s a s i g n i f i c a n t decrease i n v i t r i n i t e , a l o n g w i t h an i n c r e a s e i n i n e r t i n i t e , from b r i g h t t o d u l l e r l i t h o t y p e s . There i s a l s o an i n c r e a s e d abundance of p s e u d o v i t r i n i t e s i n the b r i g h t l i t h o t y p e . Among the i n e r t i n i t e maceral group, s e m i f u s i n i t e i s the most abundant. The maceral a n a l y s e s of l i t h o t y p e s of the Bullmoose seam A on the m i n e r a l - m a t t e r - f r e e b a s i s are g i v e n i n T a b l e A . l (Appendix A) and i l l u s t r a t e d i n F i g u r e 6.3.4. The r e f l e c t a n c e data f o r Bullmoose seam A l i t h o t y p e s , as w e l l as the composite sample, were a g a i n made a v a i l a b l e by M i c h e l l e Lamberson and M a ria M a s t a l e r z of the Department of G e o l o g i c a l S c i e n c e s , U n i v e r s i t y of B r i t i s h Columbia. The random r e f l e c t a n c e ( R Q j of the v i t r i n i t e p a r t i c l e s was determined by measuring r e f l e c t a n c e of a t l e a s t 50 r e l i e f - f r e e v i t r i n i t e p a r t i c l e s u s i n g 87 Volume % 100 80 m 60 -40 -20 -WL i i i : n l l l l l l i l i i i i 111111 H i :.: ; 9. . I  i ; • 1 IE. <1.30 1.30-1.35 1.35-1.40 1.40-1.45 1.45-1.50 >1.50 Density fractions (H Free vitrinite | | Pseudovitrinte | | Vitr> Inert I | lnertod,lnert>Vitr^ Fusinite 0 Semrfusinte Volume % 100 80 60 40 20 l i l t i i l l <1.30 1.30-1.35 1.35-1.40 1.40-1.45 1.45-1.50 Density fractions [U Oxy vitrinite|| Vrbinite-rMM >1.50 F i g u r e 6.3.2 D i s t r i b u t i o n of c o a l g r a i n s i n d e n s i t y f r a c t i o n s (a) ; d i s t r i b u t i o n of g r a i n s a s s o c i a t e d w i t h m i n e r a l matter and those w i t h o x i d i z e d s u r f a c e (b). 88 e s t a b l i s h e d t e c h n i q u e s (ICCP, 1971). A L e i t z O r thoplan r e f l e c t i n g l i g h t microscope equipped w i t h a MPV2 p h o t o m u l t i p l i e r was used f o r r e f l e c t a n c e measurements. The mean random r e f l e c t a n c e R Q, of l i t h o t y p e s v a r i e d from 0.88 % f o r banded d u l l t o 1.06% f o r b r i g h t , w i t h the v a l u e s of 1.0% and 1.04% f o r banded b r i g h t and banded c o a l , r e s p e c t i v e l y . The composite sample was found t o have the mean random r e f l e c t a n c e R Q = 1.10%. The r e f l e c t a n c e v a l u e s f o r l i t h o -t y p e s are i n c l u d e d i n Tab l e A . l (Appendix A ) . 89 F i g u r e 6.3.3 Examples of c o a l l i t h o t y p e s found i n Bullmoose c o a l seams, (Lamberson, 1989). A - d u l l c o a l ; B - banded d u l l ; C -banded c o a l ; D - banded b r i g h t ; E - b r i g h t ; F - f i b r o u s ; G,H -sheared. 90 Volume % Lithotypes • TelocollinitH PseudovitrinlH DesmocollinUl Vitrodetrinite M SemifusiniG] Fusinite • Other Inerts E2 Total Liptinite F i g u r e 6.3.4 Maceral a n a l y s e s of l i t h o t y p e s of Bullmoose seam A. ( m i n e r a l - f r e e - b a s i s , o b t a i n e d from p o i n t c o u n t i n g technique) F i g u r e 6.3.5 M i n e r a l matter p r e s e n t i n composite sample (a) massive c l a y on the v i t r i n i t e p a r t i c l e ; (b) s m a l l q u a r t z g r a i n s i n v i t r i n i t e ; (c) c l a y f i l l i n g the c r a c k s ; (d) c l a y s intergrown w i t h the v i t r i n i t e . 92 M i c r o s c o p i c examination of the m i n e r a l matter i n the composite sample of the Bullmoose seam A r e v e a l e d an abundance of c l a y - t y p e m i n e r a l s and r e l a t i v e l y s m a l l amounts of q u a r t z . The c l a y s were mainly i n two forms: as f i n e l y d i s p e r s e d i n c l u s i o n s i n c o a l p a r t i c l e s , o r as c l a y bands. The f i n e i n c l u s i o n s were mostly c o n f i n e d t o the v i t r i n i t e o r i n the c a v i t i e s of f u s i n i t e . Photo-graphs of the m i n e r a l matter i n composite sample are i n c l u d e d i n F i g u r e 6 .3 .5 . 93 CHAPTER 7 METHODS - EXPERIMENTAL PROCEDURES 7.1 F i l m F l o t a t i o n T e s t s A sample of 0.2 t o 0.3 gram of c o a l was p l a c e d on the s u r f a c e of a l i q u i d t o form monolayer of p a r t i c l e s . These t e s t s were c a r r i e d out i n s m a l l 150 ml s e p a r a t o r y f u n n e l s . The f u n n e l s were used i n s t e a d of shallow e v a p o r a t i n g d i s h e s as recommended i n o r i g i n a l f i l m f l o t a t i o n procedure (Fuerstenau e t al.1985). I n i t i a l t e s t s were c a r r i e d out f o l l o w i n g the above procedure, but s i n c e i t was d i f f i c u l t t o c o l l e c t f l o a t i n g m a t e r i a l and t o o b t a i n reproduc-i b l e r e s u l t s , s e p a r a t o r y f u n n e l s were chosen t o c a r r y out the t e s t s . For each complete run, s i x d i f f e r e n t s o l u t i o n s of d e c r e a s i n g s u r f a c e t e n s i o n were prepared and t r a n s f e r r e d u s i n g b u r e t t e , i n t o the s e p a r a t o r y f u n n e l s . The h i g h e s t s u r f a c e t e n s i o n corresponded t o the 2% by volume of methanol i n d i s t i l l e d water, and the lowest t o the 30% by volume. A f t e r a c o a l sample was p l a c e d onto the s u r f a c e of the s o l u t i o n two minutes was allowed f o r the immersion. There was no s i g n i f i c a n t change i n amount of f l o a t i n g m a t e r i a l a f t e r prolonged immersion time. Two minutes time was the s h o r t e s t immersion time f o r the amount of c o a l used. The c o a l which sank was removed from the f u n n e l by opening the t h r e e way stopcock, and c o l l e c t e d i n the e v a p o r a t i n g d i s h w i t h a minimum of f l o t a t i o n 94 F i g u r e 7.1.1 F i l m f l o t a t i o n set-up. (a) s e a p a r a t o r y f u n n e l s used f o r the f l o t a t i o n procedure; (b) f i l m f l o t a t i o n t e s t w i t h the methanol s o l u t i o n s , i n c r e a s i n g methanol c o n c e n t r a t i o n from l e f t t o r i g h t . 95 (b) s o l u t i o n . The f l o a t i n g m a t e r i a l was r e c o v e r e d by vacuum f i l t r a t i o n i n a M i l l i p o r e f i l t r a t i o n u n i t . The f l o a t s and r e j e c t s from f i l m f l o t a t i o n t e s t s were d r i e d i n the oven a t about 105° C, c o o l e d and e q u i l i b r a t e d w i t h l a b o r a t o r y atmosphere b e f o r e they were weighed. F i g u r e 7.1.1 shows the f i l m f l o t a t i o n set-up. 7.2 S m a l l - S c a l e F l o t a t i o n T e s t s 7.2.1 Apparatus The s m a l l - s c a l e f l o t a t i o n experiments were c a r r i e d out i n a p l e x i g l a s s P a r t r i d g e and Smith f l o t a t i o n c e l l u s u a l l y r e f e r r e d t o as P/S c e l l ( P a r t r i d g e and Smith, 1971). The dimensions of the c e n t r a l f l o t a t i o n column were as f o l l o w s : diameter, 30 mm; h e i g h t 200 mm. The c o l l e c t i o n chamber was 60 mm i n diameter, 125 mm i n h e i g h t and the c e n t r a l column p r o j e c t e d about 42 mm i n t o i t . The t o t a l h e i g h t of the f l o t a t i o n column was 335 mm, and the volume was about 950 ml. The p l e x i g l a s s P/S f l o t a t i o n c e l l i s sketched i n F i g u r e 7.2.1. The d e s i g n of the column was such t h a t hydrophobic m i n e r a l s (or i n t h i s case, hydrophobic c o a l p a r t i c l e s ) , a f t e r being c o n d i t i o n e d w i t h the f l o t a t i o n s o l u t i o n and gas bubbles by the i m p e l l e r , were brought t o the top of the c e n t r a l column. When the p a r t i c l e s reached.the top of the column they were c o l l e c t e d i n the c o l l e c t i o n chamber. The c e n t r a l column was long enough t o a v o i d mechanical c a r r y over of f i n e p a r t i c l e s . The o n l y p a r t i c l e s which 96 F i g u r e 7.2.1 The p l e x i g l a s s " f r o t h l e s s " P a r t r i d g e - S m i t h f l o t a t i o n c e l l used f o r the f l o a t a b i l i t y s t u d i e s ; (a) assembled; (b) b a s i c o p e r a t i o n , (Hornsby, 1981). 97 1 stirrer collection chamber Irs floated material 11 bubble deflector solution level path of floated material fritted g lass d i s c f lotation column gas ( a ) (b) reached t h e top of the column, under the g i v e n t e s t c o n d i t i o n s , were the most hydrophobic ones. In i t s o r i g i n a l d e s i g n , t h e P a r t r i d g e - S m i t h f l o t a t i o n c e l l was equipped w i t h a bubble d e f l e c t o r , as shown i n F i g u r e 7.2.1, t o d e f l e c t f low of bubbles a t the end of the f l o t a t i o n column. However, as i n d i c a t e d by Hornsby (1980), b e t t e r ash r e j e c t i o n and h i g h e r f l o t a t i o n r a t e s were a c h i e v e d without a bubble d e f l e c t o r . T h e r e f o r e a bubble d e f l e c t o r was not used i n the f l o t a t i o n t e s t s . The c o a l samples and f l o t a t i o n s o l u t i o n s were t r a n s f e r r e d through the g l a s s f u n n e l i n t o the f l o t a t i o n c e l l . The f l o t a t i o n gas was grade K n i t r o g e n s u p p l i e d by L i n d e . The n i t r o g e n was d e l i v e r e d a t a p r e s s u r e of 10 p . s . i . g . by Tygon t u b i n g . The gas flow was r e g u l a t e d by a Dwyer rotameter, which has a c a p a c i t y of 20-250cm 3/min. From the rotameter n i t r o g e n was d i r e c t e d t o the f l o t a t i o n c e l l . 7.2.2 Procedure The procedure f o r f l o t a t i o n t e s t s i n P/S c e l l was based on t h a t d e s c r i b e d by Hornsby (1981) w i t h a few m o d i f i c a t i o n s . For each f l o t a t i o n t e s t , 2 grams of c o a l was p l a c e d i n a s m a l l weighing boat and allowed t o e q u i l i b r a t e w i t h the l a b o r a t o r y atmosphere. Before each t e s t , the f l o t a t i o n c e l l was taken a p a r t and a l l t h e p a r t s were washed w i t h d i s t i l l e d water and then w i t h the a p p r o p r i a t e methanol s o l u t i o n used i n the t e s t . P r i o r t o the 98 f l o t a t i o n t e s t , n i t r o g e n under p r e s s u r e was passed through the f r i t t e d d i s c t o make sure t h a t pores i n the d i s c were f r e e of s o l i d p a r t i c l e s . The f o l l o w i n g f l o t a t i o n procedure was used f o r a l l the f l o t a t i o n t e s t s , u n l e s s s p e c i f i e d o therwise. 1. C l e a n p a r t s o f the P/S c e l l were assembled and checked f o r a p p r o p r i a t e f u n c t i o n i n g . S p e c i a l a t t e n t i o n had t o be p a i d t o the s t i r r e r alignment and i t s c l e a r a n c e (1 t o 2 mm) from the f r i t t e d d i s c . 2. Each c o a l sample was p r e c o n d i t i o n e d i n 100 ml of d i s t i l l e d water f o r 10 minutes by mechanical mixing. The speed of the s t i r r e r was s e t a t 1100 rpm. T h i s speed was necessary t o break down c o a l p a r t i c l e aggregates. The t o t a l volume of s o l u t i o n used f o r f l o t a t i o n was 750 ml, t h e r e f o r e the remaining 650 ml was used t o prepare an adequate c o n c e n t r a t i o n of the methanol. 3. A f t e r c o n d i t i o n i n g , the c o a l sample was c a r e f u l l y t r a n s -f e r r e d i n t o the column u s i n g a g l a s s f u n n e l , and r i n s e d u s i n g as l i t t l e o f the f l o t a t i o n s o l u t i o n as p o s s i b l e . The c o a l suspension was allowed t o s e t t l e f o r 5 t o 10 minutes. 4. A f t e r c o a l p a r t i c l e s s e t t l e d i n the column, the c e l l was f i l l e d v e r y s l o w l y , t o prevent any c a r r y - o v e r o f p a r t i c l e s i n t o the c o l l e c t i o n chamber, w i t h the remaining methanol s o l u t i o n 5. The f l o t a t i o n c e l l was c a r e f u l l y f i t t e d onto the r o t o r s t i r r e r , as the f r i t t e d d i s c a t the bottom of the c e l l was very f r a g i l e , and the s t i r r e r s h ould not touch i t . 6. The n i t r o g e n supply tube was connected t o the bottom 99 s e c t i o n o f the c e l l and c o n t r o l l e d by the t h r e e way stopcock. 7. The c o a l s l u r r y was c o n d i t i o n e d f o r a d d i t i o n a l 5 minutes, without n i t r o g e n flow, a t 1100 r.p.m. 8. S h o r t l y b e f o r e c o n d i t i o n i n g was completed the s t i r r e r speed was reduced t o the s e t t i n g r e q u i r e d f o r f l o t a t i o n (300 r.p.m) and the N 2 was i n t r o d u c e d a t the r a t e of 3 0 ml/min. T h i s flow r a t e g enerated a s u f f i c i e n t number of bubbles but d i d not cause s i g n i f i c a n t t u r b u l e n c e t o c a r r y over n o n - f l o a t i n g p a r t i c l e s . 9. Time of f l o t a t i o n was counted from the moment the f i r s t bubbles reached the top of the f l o t a t i o n c e l l . 10. A f t e r the f l o t a t i o n time e x p i r e d , the s t i r r e r was stopped and the gas supply d i s c o n n e c t e d . 11. F l o a t i n g c o a l p a r t i c l e s were removed from the c o l l e c t i o n chamber by r e l e a s i n g the clamp on the t e f l o n hose from the chamber o u t l e t , and l e t t i n g i t d r a i n i n t o the c l e a n beaker. S i m i l a r l y , the n o n - f l o a t i n g " r e j e c t s " were c o l l e c t e d i n t o another beaker. Any remaining m a t e r i a l i n the c e n t r a l column or a t the bottom of the c e l l was r i n s e d i n t o the " r e j e c t s " beaker, and remaining m a t e r i a l from the c o l l e c t i o n chamber was washed i n t o the " f l o a t s " . 12. The f l o a t s and r e j e c t s were f i l t e r e d u s i n g the micropore vacuum f i l t r a t i o n u n i t and then d r i e d i n an oven a t about 105° C. F l o t a t i o n p r o d u c t s which had c o o l e d and e q u i l i b r a t e d w i t h the l a b o r a t o r y atmosphere were weighed and submitted f o r ash a n a l y s i s . 100 7.3 M i c r o s c o p i c Examination For a l l m i c r o s c o p i c examinations r e p r e s e n t a t i v e samples were used t o prepare standard 2.54 cm (1 inch) c o a l p e l l e t s . In most cases c o a l samples were crushed t o -850 microns (ASTM D 2797-75) , s p l i t and mixed wi t h p o l y e s t e r r e s i n t o make a p e l l e t . In i n s t a n c e s where the -212+149 i»m s i z e f r a c t i o n was used, no c r u s h i n g was nec e s s a r y p r i o r t o p e l l e t p r e p a r a t i o n . C o a l p e l l e t s were prepared u s i n g a h y d r a u l i c p r e s s w i t h e l e v a t e d temperature (110° C) t o melt p o l y e s t e r r e s i n i n t o t r a n s o p t i c powder, and c o a l p a r t i c l e s were mounted i n i t . F o l l o w i n g t h a t , p e l l e t s were p l a c e d i n a h o l d e r f o r g r i n d i n g and p o l i s h i n g w i t h an automated g r i n d e r / p o l i -s h er. D e t a i l e d procedures are i n ASTM D 2797-75. A Zeiss-2 r e f l e c t i n g l i g h t microscope, w i t h t o t a l 640 X m a g n i f i c a t i o n , one ey e p i e c e c r o s s - h a i r , and a S w i f t mechanical stage and r e g i s t e r i n g c ounter, was used t o c a r r y out maceral c o u n t i n g . The mechanical stage was capable of advancing the specimen l a t e r a l l y by equal s t e p s . The p o i n t counts were r e c o r d e d on the counter i n s i x d i f f e r e n t c a t e g o r i e s . The m i c r o s c o p i c equipment used was i n accordance w i t h the ASTM D 2799-72 (reproved 1976) standard procedure as w e l l as w i t h the ICCP standards (ICCP, Handbook, 1963). 7.3.1 Maceral A n a l y s i s Macerals are m i c r o s c o p i c a l l y r e c o g n i z a b l e o r g a n i c c o n s i s t u e n t s of c o a l and can be c a t e g o r i z e d i n t o t h r e e groups: 101 v i t r i n i t e , l i p t i n i t e ( e x i n i t e ) and i n e r t i n i t e . I t i s p o s s i b l e t o d i s t i n g u i s h one maceral from another based on t h e i r appearance under the microscope. The macerals can be i d e n t i f i e d mainly by t h e i r d i f f e r e n c e s i n r e f l e c t a n c e , c o l o r , morphology and other o p t i c a l p r o p e r t i e s , which are p a r t i c u l a r l y s t r i k i n g i n low rank c o a l s . The p r o p o r t i o n s of these p e t r o g r a p h i c components i n a l l c o a l samples used i n the study were determined by p o i n t c o u n t i n g a s t a t i s t i c a l l y adequate number of p o i n t s , and summing those r e p r e s e n t a t i v e of each component. Three hundred p o i n t s were counted ( m i n e r a l matter f r e e , i . e . m i n e r a l matter p a r t i c l e s were not counted) u s i n g the e s t a b l i s h e d maceral c o u n t i n g procedure f o r bituminous c o a l s ( B u s t i n e t a l . , 1983). A maceral was counted when i t appeared d i r e c t l y under the c r o s s h a i r s . The specimen was advanced by mechanical stage i n s t e p s of 0.1mm. The p o i n t - t o - p o i n t d i s t a n c e was chosen a c c o r d i n g t o the ASTM D 2799-72 procedure, which recommends t h a t s t e p p i n g d i s t a n c e be h a l f of the diameter of the l a r g e s t g r a i n . The maximum s i z e o f the p a r t i c l e i n most cases was 0.20 mm, as i n a l l the experimental work the p a r t i c l e s i z e range was -212+149 um, except where otherwise s p e c i f i e d . The number of p o i n t s counted f o r each i n d i v i d u a l maceral or maceral group were c a l c u l a t -ed as a percentage of the t o t a l of a l l p o i n t s r e c orded. The v a l u e s were expressed as volume perc e n t , and r e s u l t s were r e c o r d e d as an i n t e g e r , because maceral a n a l y s e s may be i n e r r o r of a t l e a s t +/-1 p e r c e n t (Hevia-Rodriguez and Prado, 1961). The accuracy of the 102 a n a l y s e s are u s u a l l y g i v e n by the r e p r o d u c i b i l i t y of the r e s u l t s . For t h i s type of a n a l y s i s i t i s r e q u i r e d t h a t accuracy of two a n a l y s e s made by one o p e r a t o r on the same p o l i s h e d s u r f a c e should be +/- 1.5 %. The r e s u l t s must not d i f f e r by more than 3% by volume f o r any maceral or maceral group i f they are t o meet ICCP s t a n -dards . 7.3.2 G r a i n Type A n a l y s i s F l o t a t i o n p r o d u c t s of the s t u d i e d c o a l , the c o n c e n t r a t e s and the t a i l i n g s were analyzed f o r maceral and g r a i n type composi-t i o n s i m u l t a n e o u s l y . The e f f i c i e n c y of the f l o t a t i o n p rocess depends p r i m a r i l y on the s u r f a c e p r o p e r t i e s of the s e p a r a t e g r a i n s . The s u r f a c e p r o p e r t y and t h e r e f o r e behavior of a c o a l g r a i n i n f l o t a t i o n can be g r e a t l y i n f l u e n c e d by the presence of m i n e r a l matter, and, t o a l e s s e r extent, by i t s maceral make-up. I t was important t o know how the m i n e r a l matter was d i s t r i b u t e d among c o a l g r a i n s and i n what p r o p o r t i o n s , and a l s o how the macerals were a s s o c i a t e d w i t h each other, and whether these p a r t i c u l a r a s s o c i a -t i o n and the presence of m i n e r a l matter would have an e f f e c t on f l o t a t i o n . However, t h i s type of i n f o r m a t i o n c o u l d not be s u p p l i e d by simple maceral a n a l y s i s . An a n a l y s i s d e s c r i b i n g each g r a i n s e p a r a t e l y i n terms of i t s a s s o c i a t i o n w i t h o t h e r macerals as w e l l as w i t h m i n e r a l matter was r e q u i r e d . The g r a i n - t y p e a n a l y s i s was performed f o l l o w i n g the m o d i f i e d maceral a n a l y s i s procedure (Cudmore e t a l . , 1986). D e f i n i t i o n s of the examined g r a i n types are 103 F i g u r e 7.3.1 G r a i n s found i n the examined samples; (a),(b) f r e e v i t r i n i t e ; (c) p s e u d o v i t r i n i t e ; (d) , (e) v i t r + i n e r t , V>I; i n e r t -+ v i t r , I>V; ( f ) , ( g ) f u s i n i t e , f r e e ; (h) v i t r + m i n e r a l matter. 104 F i g u r e 7.3.2 D i f f e r e n t degrees of o x i d a t i o n . A,B - e x t e n s i v e o x i d a t i o n of v i t r i n i t e ; C,D o x i d a t i o n on the edges of g r a i n s ; E,F p h y s i c a l changes appearing i n g r a i n s ; c r a c k s and f i s s u r i n g . 105 B D T a b l e 7.3.1 Summary of g r a i n - t y p e a n a l y s i s . G r a i n type P r o p o r t i o n of maceral groups Free v i t r i n i t e 100 % v i t r i n i t e P s e u d o v i t r i n i t e 100 % p s e u d o v i t r i n i t e V i t r i n i t e + I n e r t i n i t e V>I V > 50 %, I < 50 % I n e r t o d e t r i n i t e I, I>V 100 % I, ot h e r i n e r t s , and V + I, where I > 50 % F u s i n i t e f r e e f u s i n i t e o r F > 50 % i f a s s o c i a t -ed w i t h o t h e r macerals S e m i f u s i n i t e f r e e s e m i f u s i n i t e or SF > 50 % i f a s s o c i a t e d w i t h other macerals O x i d i z e d v i t r i n i t e observed as o x i d i z e d p a r t i c l e s under the microscope, and r e p o r t e d on the t o t a l v i t r i n i t e b a s i s V i t r i n i t e w i t h M i n e r a l V + MM, where MM > 30 % Matter i n T a b l e 7.3.1. and i l l u s t r a t e d i n F i g u r e 7.3.1. In g e n e r a l , the g r a i n type was determined on the same p a r t i c l e " , on which the maceral had been i d e n t i f i e d . For example, i f the maceral under the c r o s s - h a i r was i d e n t i f i e d as v i t r i n i t e , but the g r a i n was a l s o composed of l e s s e r amounts of i n e r t i n i t e maceral, the g r a i n would be r e c o r d e d as v i t r i n i t e + i n e r t i n i t e (V+I) and a t t h e same time was a l s o i d e n t i f i e d i n terms of m i n e r a l matter c o n t e n t . In terms of m i n e r a l matter content, o n l y those g r a i n s which had an area more than 30% o c c u p i e d by m i n e r a l matter were r e c o r d e d . Under the 106 i n e r t o d e t r i n i t e c a t e g o r y f r e e i n e r t o d e t r i n i t e and g r a i n s of v i t r i n i t e w i t h i n e r t i n i t e a s s o c i a t i o n , where I>V, were counted, w h i l e f r e e s e m i f u s i n i t e and f u s i n i t e were a s s i g n e d t o separate c a t e g o r i e s . A s i m i l a r approach was used by Cudmore (Cudmore e t a l . , 1986) when p e t r o g r a p h i c a l l y c h a r a c t e r i z i n g samples from f r o t h f l o t a t i o n c i r c u i t s . The o x i d a t i o n i s an important f a c t o r i n r e n d e r i n g c o a l p a r t i c l e s n o n - f l o a t a b l e . T h e r e f o r e , the number of o x i d i z e d p a r t i c l e s was a l s o determined i n the f l o t a t i o n f e e d and the product samples. To d i s t i n g u i s h between o x i d i z e d and non-o x i d i z e d p a r t i c l e s , c o a l p e l l e t s were soaked f o r 20 minutes i n s t a i n s o l u t i o n prepared from KOH + H 20 and s a f r i n i n "O" mixed i n adequate p r o p o r t i o n s (Gray e t a l . , 1976; Gray and Lowenhaupt, 1989). S t a i n e d p a r t i c l e s were counted as o x i d i z e d and u n s t a i n e d were c o n s i d e r e d t o r e p r e s e n t f r e s h c o a l g r a i n s . The examples of o x i d i z e d g r a i n s as observed under the microscope ( s t a i n i n g procedure) are i n F i g u r e 7.3.2. 107 CHAPTER 8 RESULTS AND DISCUSSION 8.1 F i l m F l o t a t i o n R e s u l t s In the f i l m f l o t a t i o n experiments as d e s c r i b e d i n s e c t i o n 7.1, c o a l p a r t i c l e s were separated a c c o r d i n g t o t h e i r c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y . At each s u r f a c e t e n s i o n of the s o l u t i o n , p a r t i c l e s were p a r t i t i o n e d i n t o hydrophobic and hydro-p h i l i c f r a c t i o n s . The weight p e r c e n t of the hydrophobic f r a c t i o n was p l o t t e d as a f u n c t i o n of s o l u t i o n s u r f a c e t e n s i o n and as a r e s u l t the w e t t i n g t e n s i o n d i s t r i b u t i o n diagram was o b t a i n e d . The p l o t r e p r e s e n t s cumulative d i s t r i b u t i o n of p a r t i c l e s i n r e l a t i o n t o t h e i r h y d r o p h o b i c i t y . At the h i g h e s t s u r f a c e t e n s i o n (2 % methanol c o n c e n t r a t i o n ) , the s u r f a c e t e n s i o n i s i n s i g n i f i c a n t l y lower than t h a t of water, and the p a r t i t i o n i s between hydrophobic and very h y d r o p h i l i c p a r t i c l e s ; a t the lowest s u r f a c e t e n s i o n o n l y the most hydrophobic p a r t i c l e s f l o a t . The w e t t a b i l i t y d i s t r i b u t i o n i s very s e n s i t i v e t o the s u r f a c e p r o p e r t i e s of p a r t i c l e s , t h e r e f o r e p a r t i c l e s of d i f f e r e n t s u r f a c e c h a r a c t e r i s t i c s w i l l have d i f f e r e n t w e t t a b i l i t y d i s t r i b u t i o n c urves. The f i l m f l o t a t i o n technique was used t o o b t a i n the w e t t a b i l i t y d i s t r i b u t i o n of c o a l p a r t i c l e s from a narrow s i z e range (-212+149 um) of Bullmoose seam A samples. In a d d i t i o n , w e t t a b i l i t y 108 d i s t r i b u t i o n s were o b t a i n e d f o r l i t h o t y p e s and d i f f e r e n t d e n s i t y f r a c t i o n s . To c o n f i r m t h a t the technique i s independent of p a r t i c l e s i z e , d i f f e r e n t s i z e f r a c t i o n s were a l s o used. 8.1.1 Composite sample The composite samples were r e p r e s e n t e d by the -212+149 jim s i z e f r a c t i o n s of low-ash and high-ash c o a l samples. The low-ash sample was the "cleaned" sample, w h i l e the high-ash was the i n i t i a l composite sample r e c e i v e d by s i e v i n g out the chosen s i z e f r a c t i o n from the t o t a l sample, as d e s c r i b e d i n s e c t i o n 6.3.1. The wetta-b i l i t y d i s t r i b u t i o n was o b t a i n e d f o r both composite samples by f i l m f l o t a t i o n . The cumulative y i e l d was p l o t t e d as a f u n c t i o n of s u r f a c e t e n s i o n (methanol c o n c e n t r a t i o n , volume %) f o r the composite samples as shown i n F i g u r e s 8.1.1. Three parameters can be determined from the w e t t a b i l i t y diagram: Y m i n ' rainimum/ t n e s u r f a c e t e n s i o n of the s o l u t i o n t h a t wets a l l p a r t i c l e s , Y m a x ' maximum, which r e p r e s e n t s the s u r f a c e t e n s i o n of the s o l u t i o n above which none of the p a r t i c l e s are wetted; and the mean c r i t i c a l s u r f a c e t e n s i o n of w e t t i n g , Y c * F o r the high-ash composite sample the minimum i s a t 39 dyne/cm, which corresponds t o approximately 30 % by volume of methanol c o n c e n t r a t i o n , and the maximum y i e l d of f l o a t i n g m a t e r i a l , 73.58%, i s observed a t a s u r f a c e t e n s i o n of 68 dyne/cm (2 % by volume methanol c o n c e n t r a t i o n ) . The mean v a l u e of the c r i t i c a l s u r f a c e t e n s i o n i s c a l c u l a t e d as 54 dyne/cm f o r the high-ash sample, w h i l e s i m i l a r v a l u e of 52 dyne/cm i s found f o r the 109 54 45 39 35 Surface tension dyne/cm F i g u r e 8.1.1 F i l m f l o t a t i o n . The cumulative y i e l d p l o t t e d as a f u n c t i o n o f s u r f a c e t e n s i o n (methanol c o n c e n t r a t i o n , volume %) f o r the composite samples: (a) high-ash; (b) low-ash. 110 low-ash composite sample. The amount of n o n - f l o a t a b l e m a t e r i a l a t the h i g h e s t s u r f a c e t e n s i o n (2% methanol c o n c e n t r a t i o n by volume) f o r the low-ash composite sample was about 20 % wt. and f o r the high-ash sample almost 40 % wt. M i c r o s c o p i c a n a l y s i s of the r e j e c t s i n d i c a t e s t h a t most of the c o a l p a r t i c l e s h e a v i l y contaminated w i t h m i n e r a l matter, as w e l l as o x i d i z e d p a r t i c l e s are p r e s e n t i n the non-f l o a t i n g f r a c t i o n . Due t o the s m a l l amounts of c o a l used f o r f i l m f l o t a t i o n , and even s m a l l e r amounts r e p o r t i n g t o f l o a t s and r e j e c t s , t h e p o i n t c o u n t i n g technique c o u l d not be a p p l i e d t o determine volume p e r c e n t of d i f f e r e n t p a r t i c l e s as the number of counted p a r t i c l e s has t o be a t l e a s t 300 t o be s t a t i s t i c a l l y v a l i d . T h e r e f o r e , o n l y q u a l i t a t i v e o b s e r v a t i o n s were made. 8.1.2 D e n s i t y f r a c t i o n s The f i l m f l o t a t i o n experiments were conducted on the d e n s i t y f r a c t i o n s o b t a i n e d from g r a v i t y f r a c t i o n a t i o n of the narrow s i z e f r a c t i o n , -212+149 jim, (65x100 mesh T y l e r ) of the high-ash composite sample. A t o t a l of f i v e d e n s i t y f r a c t i o n s were used f o r f i l m f l o t a t i o n t e s t s . The l i g h t e s t d e n s i t y f r a c t i o n was the <1.3 s p e c i f i c g r a v i t y , which has the l e a s t amount of ash, and as d e s c r i b e d i n s e c t i o n 6.3.4, i s the most e n r i c h e d i n v i t r i n i t e m aceral. The abundance of v i t r i n i t e decreases w i t h i n c r e a s i n g d e n s i t y and f o r i n e r t i n i t e the o p p o s i t e t r e n d i s observed ( s e c t i o n 6.3.4) . I l l Methanol concentration, vol.% 5 10 15 20 25 30 35 (/) 80 i 1 o 62 54 50 45 42 39 Surface tension dyne/cm F i g u r e 8.1.2 F i l m f l o t a t i o n . The w e t t a b i l i t y d i s t r i b u t i o n s p a r t i c l e s from v a r i o u s d e n s i t y f r a c t i o n s . The cumulative d i s t r i b u t i o n of p a r t i c l e s a c c o r d i n g t o t h e i r c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y was o b t a i n e d f o r a l l d e n s i t y f r a c t i o n s . These p l o t s are shown i n F i g u r e 8.1.2. The w e t t a b i l i t y d i s t r i b u t i o n of the l i g h t e s t f r a c t i o n i n d i c a t e s the b e s t response t o the f i l m f l o t a t i o n . The h i g h e s t r e c o v e r y of c o a l p a r t i c l e s i n t h i s f r a c t i o n , 70 % by weight, i s observed a t 2 % by volume of methanol c o n c e n t r a t i o n , and the lowest i s observed a t approximately 30 % by volume of methanol c o n c e n t r a t i o n , correspond-i n g t o 39 dyne/cm. About 30 % (by weight) of the m a t e r i a l remained non-f l o a t i n g a t 2 % methanol by volume, most of which, as i n the composite, c o n s i s t e d of o x i d i z e d v i t r i n i t e p a r t i c l e s , h e a v i l y contaminated w i t h the m i n e r a l matter or r e l a t i v e l y s m a l l amounts of f u l l y l i b e r a t e d i n o r g a n i c p a r t i c l e s . The 1.30-1.35 s p e c i f i c g r a v i t y f r a c t i o n shows d i f f e r e n t w e t t a b i l i t y c h a r a c t e r i s t i c s i n terms of the cumulative d i s t r i b u t i o n of p a r t i c l e s v e r s u s t h e i r c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y . The shape of the d i s t r i b u t i o n curve i s q u i t e d i f f e r e n t as compared t o t h e 1.30 s p e c i f i c g r a v i t y f r a c t i o n . The samples of h i g h e r d e n s i t y , such as 1.40-1.45 and > 1.50 g/cm 3 show no response t o the f i l m f l o t a t i o n , w i t h the e x c e p t i o n of the 1.35-1.40 f r a c t i o n , which has low y i e l d a t 2 % methanol c o n c e n t r a t i o n . The primary reason f o r t h i s b ehavior i s t h a t most of the p a r t i c l e s , as examined under the microscope, are v e r y h e a v i l y contaminated w i t h m i n e r a l matter. Furthermore, a l l of the i n o r g a n i c matter i s a s s o c i a t e d w i t h the c o a l p a r t i c l e s 113 ( u n l i b e r a t e d ) . As a r e s u l t of s i n k and f l o a t s e p a r a t i o n , the o n l y f r a c t i o n which c o n t a i n s l i b e r a t e d m i n e r a l matter i s the h e a v i e s t , > 1.50 d e n s i t y f r a c t i o n . 8.1.3 L i t h o t y p e s Hand p i c k e d samples of f i v e l i t h o t y p e s from Bullmoose seam A, as d e s c r i b e d i n s e c t i o n 6.3.2, were used i n the f i l m f l o t a t i o n t e s t s u s i n g methanol s o l u t i o n s . The w e t t a b i l i t y d i s t r i b u -t i o n s were o b t a i n e d f o r a l l f i v e samples. F i g u r e 8.1.3 p r e s e n t s cumulative w e t t a b i l i t y d i s t r i b u t i o n f o r d i f f e r e n t l i t h o t y p e s , and ash c o n t e n t i n f l o a t i n g f r a c t i o n s . The w e t t a b i l i t y of " b r i g h t " and "banded b r i g h t " l i t h o -t y p e s ( A u s t r a l i a n c l a s s i f i c a t i o n ) appears t o be v e r y s i m i l a r . The maximum f l o a t a b i l i t y of p a r t i c l e s occurs f o r both samples a t 2 % by volume of methanol (68 dyne/cm), w i t h y i e l d s of 98.62 % by weight f o r b r i g h t , and 97.18 % f o r banded b r i g h t l i t h o t y p e . The lowest y i e l d s of f l o a t i n g p a r t i c l e s , 29.51 % f o r b r i g h t and 21.99 wt % f o r banded b r i g h t , are found a t the l e v e l of 30 % by volume of methanol c o n c e n t r a t i o n (39 dyne/cm) f o r both l i t h o t y p e s . The ash content ( b r i g h t , 4.20 % ash; banded b r i g h t , 5.23 % ash) and maceral c o m p o s i t i o n of these l i t h o t y p e s are v e r y s i m i l a r (Table 6.3.1 and F i g u r e 6.3.4). W e t t a b i l i t y d i s t r i b u t i o n s of "banded c o a l " and "banded d u l l " are v e r y s i m i l a r . Maceral a n a l y s e s of both l i t h o t y p e s are a g a i n v e r y s i m i l a r . The m i n e r a l matter content f o r both samples i s 114 Methanol concentration, volume % 62 54 50 45 42 39 Surface tension dyne/cm Fibrous Banded Dull Banded Bright Banded Coal Bright — a — •••••A- •© — -c — — « — a Methanol concentration, volume % 0 5 10 15 20 25 30 35 10 | ' ' ' ' ' ' ' 1 2 54 50 45 42 39 Surface tension dyne/cm Ffcreus Banded DuO Banded Bright Banded Coal Bright —3 ••••A ©•••• — *- - —••— F i g u r e 8.1.3 F i l m f l o t a t i o n . The cumulative w e t t a b i l i t y d i s t r i b u -t i o n f o r d i f f e r e n t l i t h o t y p e s (a) w e t t a b i l i t y d i s t r i b u t i o n ; (b) ash content m the f l o a t i n g f r a c t i o n s . 115 v e r y low. The maximum y i e l d of f l o a t i n g p a r t i c l e s i s almost the same and o c c u r r e d f o r banded c o a l and banded d u l l a t 2 % by volume methanol c o n c e n t r a t i o n , and the lowest y i e l d of f l o a t i n g p a r t i c l e s i s a t 30 % by volume, methanol c o n c e n t r a t i o n . F u s a i n ( f i b r o u s ) shows the lowest response t o the f i l m f l o t a t i o n . The maximum y i e l d o f f l o a t i n g p a r t i c l e s a t 2% by volume of methanol c o n c e n t r a t i o n i s 18 % by weight, and t h e minimum y i e l d i s observed a t 10 % by volume of methanol c o n c e n t r a t i o n and corresponds t o a s u r f a c e t e n s i o n of 54 dyne/cm. I t i s e v i d e n t from p e t r o g r a p h i c a n a l y s i s , t h a t f u s a i n i s e n r i c h e d i n i n e r t i n i t e macerals. The i n e r t i n i t e macerals a t t h i s c o a l rank (medium v o l a t i l e bituminous) are known t o have s i g n i f i -c a n t l y lower h y d r o p h o b i c i t y (Brown, 1962; K l a s s e n , 1966; Hower, 1984; Sarkar, 1984; Bujnowska, 1985; Apian, 1989) and t h e r e f o r e much lower f l o t a t i o n response, as compared w i t h t h e v i t r i n i t e m acerals. An a d d i t i o n a l reason f o r h i g h w e t t a b i l i t y o f f u s a i n , i s t h a t t h i s p a r t i c u l a r l i t h o t y p e c o n t a i n s e x c e p t i o n a l l y h i g h amounts of e l e m e n t a l oxygen. From the H/C, O/C or 0/H, atomic r a t i o s i t i s n o t i c e a b l e , t h a t f u s a i n i s the most aromatic (lowest H/C r a t i o ) of a l l l i t h o t y p e s and has the h i g h e s t content of carbon, a l o n g with h i g h c o n t e n t of oxygen. T h i s might have a l s o c o n t r i b u t e d , t o i t s low f l o a t a b i l i t y . Low f l o a t a b i l i t y of f u s a i n , which i s u s u a l l y composed of f u s i n i t e , has been f r e q u e n t l y l i n k e d t o the f a c t t h a t c a v i t i e s i n f u s i n i t e a re u s u a l l y f i l l e d w i t h m i n e r a l matter. M i n e r a l matter 116 r e p r e s e n t s s t r o n g l y h y d r o p h i l i c s i t e s on c o a l p a r t i c l e s , which consequently r e s u l t s i n the lower f l o t a t i o n response. In the f u s a i n s t u d i e d here m i n e r a l matter content i s v e r y low and i t s e f f e c t on the f l o a t a b i l i t y i s p r o b a b l y n e g l i g i b l e . 8.1.4 D i f f e r e n t s i z e f r a c t i o n s F i l m f l o t a t i o n technique i s predominantly c o n t r o l l e d by i n t e r f a c i a l f o r c e s . The e f f e c t of p a r t i c l e s d e n s i t y , shape and s i z e was s t u d i e d by Fuerstenau e t a l . , (1988a). They concluded t h a t the t e c h n i q u e i s n e a r l y independent of a l l f a c t o r s o t h e r than the s u r f a c e p r o p e r t i e s of the p a r t i c l e s . The hand-picked v i t r a i n p a r t i c l e s were sep a r a t e d i n t o the f o u r d i f f e r e n t s i z e f r a c t i o n s (35x48, 48x65, 65x100,and 100x200 mesh) and used i n f i l m f l o t a t i o n experiments. W e t t a b i l i t y d i s t r i b u t i o n s of d i f f e r e n t s i z e f r a c t i o n s were o b t a i n e d . The w e t t a b i l i t y d i s t r i b u t i o n s of a l l d i f f e r e n t s i z e f r a c t i o n s are n e a r l y i d e n t i c a l . F i g u r e 8.1.4 p r e s e n t s w e t t a b i l i t y of d i f f e r e n t s i z e f r a c t i o n s of v i t r a i n . The v i t r a i n l i t h o t y p e was chosen t o m a i n t a i n the same p e t r o g r a p h i c composition f o r a l l the s i z e f r a c t i o n s . The s e g r e g a t i o n of macerals i n t o d i f f e r e n t s i z e f r a c t i o n s was r e p o r t e d p r e v i o u s l y i n the s i z i n g p r o c e s s (T. Laskowski, 1948; Hower e t a l . , 1987; F a l c o n and F a l c o n , 1987). 117 F i g u r e 8.1.4 The e f f e c t of s i z e on the w e t t a b i l i t y . F i l m f l o t a t i o n of d i f f e r e n t s i z e f r a c t i o n s of v i t r a i n (Bullmoose seam A) . 8.2 R e s u l t s of S m a l l - S c a l e F l o t a t i o n T e s t s The s m a l l - S c a l e f l o t a t i o n as d e s c r i b e d i n s e c t i o n 7.2 was used t o e v a l u a t e f l o a t a b i l i t y o f c o a l samples of d i f f e r e n t p e t r o g r a p h i c composition. F l o t a t i o n t e s t s were c a r r i e d out i n a P a r t r i d g e - S m i t h f l o t a t i o n c e l l without u s i n g r e a g e n t s . D i f f e r e n t methanol c o n c e n t r a t i o n s were used t o va r y s u r f a c e t e n s i o n . The r e l a t i v e f l o a t a b i l i t y of c o a l samples of d i f f e r e n t p e t r o g r a p h i c composition was analyzed i n terms of the c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y , Y C f T ^ e f l o a t a b i l i t y d i s t r i b u t i o n s of c o a l p a r t i c l e s a c c o r d i n g t o t h e i r r e s p e c t i v e c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y were o b t a i n e d . The cumulative y i e l d % (weight p e r c e n t of f l o a t e d f r a c t i o n s ) v e r s u s s u r f a c e t e n s i o n (methanol c o n c e n t r a t i o n ) was p l o t t e d f o r each sample. 8.2.1 C o n d i t i o n s of f l o t a t i o n The parameters such as f l o t a t i o n time and c o n d i t i o n i n g time were kept c o n s t a n t f o r a l l f l o a t a b i l i t y t e s t s . A p r e l i m i n a r y s e r i e s o f t e s t s was c a r r i e d out t o determine o p t i m a l f l o t a t i o n c o n d i t i o n s . 8.2.1.1 F l o t a t i o n time The s m a l l - s c a l e f l o t a t i o n t e s t s were performed w i t h the 119 F i g u r e 8.2.1 The e f f e c t of f l o t a t i o n time on y i e l d and on ash of f l o a t s : (a) cumulative y i e l d of f l o a t s v e r s u s f l o t a t i o n time; (b) cumulative ash % i n f l o a t s versus f l o t a t i o n time. -212+149 jim high-ash composite sample i n o r d e r t o e s t a b l i s h the o p t i m a l f l o t a t i o n time. F l o t a t i o n t e s t s were c a r r i e d out i n 2 % methanol s o l u t i o n , keeping a l l the o t h e r f l o t a t i o n parameters unchanged except the f l o t a t i o n time, which v a r i e d over the range from .50, 1, 2, 3, t o 4 minutes. Cumulative y i e l d of f l o a t i n g c o a l p a r t i c l e s becomes e s s e n t i a l l y c o n s t a n t a f t e r 3 minutes of f l o t a -t i o n . An a d d i t i o n a l i n c r e a s e i n f l o t a t i o n y i e l d , beyond the 3 minutes f l o t a t i o n time, was found t o i n c r e a s e ash content of the f l o a t i n g f r a c t i o n ( F i g u r e 8.2.1). The f l o t a t i o n time of 3 minutes was t h e r e f o r e used f o r a l l experiments. 8.2.1.2 C o n d i t i o n i n g time C o n d i t i o n i n g i s needed t o wet a c o a l sample w i t h water. C o n d i t i o n i n g i s a l s o a p p l i e d t o mix the f l o t a t i o n p u l p a f t e r the reagent a d d i t i o n . The most common p r a c t i c e i s t o use 10 t o 15 minutes c o n d i t i o n i n g t o wet c o a l p a r t i c l e s w i t h water p r i o r t o the a d d i t i o n of reagents (Hornsby, 1981). F o l l o w i n g the a d d i t i o n of methanol, o n l y a s h o r t c o n d i t i o n i n g time (3 t o 5 minutes) was used t o mix c o a l w i t h the reagents. The e f f e c t of c o n d i t i o n i n g time i n water on the y i e l d and ash of f l o a t s i s d e p i c t e d i n F i g u r e 8.2.2. The c o n d i t i o n i n g times p r i o r t o the reagent a d d i t i o n were 0, 3, 5 and 10 minutes. The o p t i m a l c o n d i t i o n i n g time f o r a l l f l o a t a b i l i t y experiments was s e t a t 10 minutes. 121 Cumulative % yield, floats Cumulative ash %, floats F i g u r e 8.2.2 The e f f e c t of c o n d i t i o n i n g time on f l o t a t i o n , (a) Cumulative y i e l d of f l o a t s versus p r e c o n d i t i o n i n g time; (b) Cumulative ash i n f l o a t s versus p r e c o n d i t i o n i n g time. F i g u r e 8.2.3 The e f f e c t of s i z e on f l o a t a b i l i t y S m a l l - s c a l e f l o t a t i o n t e s t s i n P/S f l o t a t i o n c e l l . o f v i t r a i n . 8.2.2 F l o a t a b i l i t y d i s t r i b u t i o n o f c o a l p a r t i c l e s The cumulative y i e l d was p l o t t e d as a f u n c t i o n of s u r f a c e t e n s i o n (methanol c o n c e n t r a t i o n ) f o r a number of Bullmoose A-seam c o a l samples. The f l o t a t i o n t e s t s were c a r r i e d out under standard f l o t a t i o n c o n d i t i o n s : 10 minutes c o n d i t i o n i n g i n water time, 3 minutes f l o t a t i o n time, no bubble d e f l e c t o r . The curves have been f i t t e d through the r e p l i c a t e d ata p o i n t s whenever r e p l i c a t e s were a v a i l a b l e . D e n s i t y f r a c t i o n s of the composite sample (as d e s c r i b e d i n s e c t i o n 6.3.1) were a l s o used i n the f l o a t a b i l i t y t e s t s . Since f l o t a t i o n i s s i z e dependant, d i f f e r e n t s i z e f r a c t i o n s were used t o examine the e f f e c t o f s i z e on f l o a t a b i l i t y ( F i g u r e 8.2.3). 8.2.2.1 Composite sample The cumulative y i e l d v e rsus s u r f a c e t e n s i o n (methanol c o n c e n t r a t i o n , volume %) p l o t s were o b t a i n e d f o r the two composite samples. F i g u r e 8.2.4 p r e s e n t s f l o a t a b i l i t y d i s t r i b u t i o n s f o r these samples. The i n i t i a l composite sample has an ash content of 28.34%, and the low-ash composite sample r e f e r r e d t o as "cleaned" has 16.03% ash; both were used i n the f l o t a t i o n t e s t s . Both composite samples appear t o be r e a d i l y f l o a t a b l e . The cumulative y i e l d s f o r the c l e a n e r sample are much h i g h e r a t any g i v e n methanol c o n c e n t r a t i o n . The minimum y i e l d of f l o a t i n g p a r t i c l e s i n both cases i s a t about 30 % methanol c o n c e n t r a t i o n . At methanol c o n c e n t r a t i o n s g r e a t e r than 30 %, a c o n s t a n t amount of p a r t i c l e s was r e p o r t i n g t o the f l o a t i n g f r a c t i o n . 124 F i g u r e 8.2.4 The cumulative y i e l d v e rsus s u r f a c e t e n s i o n f o r two composite samples: (a) high-ash composite sample; (b) low-ash composite sample. Methanol concentration vol. % 25 CO fc o L i - 15 c CO < 10 -5 -10 54 45 X 40 50 Ash=28.34 % 32 100 10 20 to "o '<F 60 rr c v O x: to < 40 20 54 45 30 —I— 40 50 Ash=28.34 % 39 35 Surface tension dyne/cm 32 b F i g u r e 8.2.5 Ash content i n f l o a t s and r e j e c t s f o r the high-ash composite sample: (a) f l o a t s ; (b) r e j e c t s . 126 25 § 15 SZ tn < 10 70 80 o si tn < 20 70 Methanol concentration, vol. % 10 _i 54 20 _J 45 20 30 40 Ash= 16.03 % 39 30 35 32 50 Ash=16.03% 54 45 39 35 Surface tension dyne/cm 32 F i g u r e 8.2.6 Ash content i n f l o a t s and r e j e c t s f o r the low-ash composite sample: (a) f l o a t s ; (b) r e j e c t s 127 The ash con t e n t o f the f l o a t e d f r a c t i o n s decreases w i t h an i n c r e a s e i n methanol c o n c e n t r a t i o n and reaches a minimum a t 20 % methanol, and then tends t o i n c r e a s e as the c o n c e n t r a t i o n of methanol i s f u r t h e r i n c r e a s e d . The h i g h e r ash content of f l o a t s a t h i g h e r methanol c o n c e n t r a t i o n may i n d i c a t e the presence of c l a y s i n the sample. T h i s e f f e c t i s e s p e c i a l l y v i s i b l e i n the high-ash composite sample. A reason f o r c l a y p a r t i c l e s r e p o r t i n g t o the f l o a t i n g f r a c t i o n i s the p e p t i z a t i o n of c l a y s i n h i g h c o n c e n t r a t i o n s of methanol (Hornsby, 1981). S i m i l a r e f f e c t s were observed i n the f l o a t a b i l i t y experiments by Hornsby (1981). F i g u r e 8.2.5 and F i g u r e 8.2.6 p r e s e n t ash content i n f l o a t s and r e j e c t s f o r both composite samples. 8.2.2.2 D e n s i t y f r a c t i o n s F i v e d e n s i t y f r a c t i o n s were a l s o used i n the f l o t a t i o n t e s t s . F l o a t a b i l i t y d i s t r i b u t i o n s were o b t a i n e d f o r each of the d e n s i t y f r a c t i o n s ( F i g u r e 8.2.7). The t h r e e l i g h t e s t d e n s i t y f r a c t i o n s show p o s i t i v e response t o f l o t a t i o n i n methanol s o l u -t i o n s . The t h r e e h e a v i e s t have a con s t a n t amount of p a r t i c l e s f l o a t i n g a t each methanol c o n c e n t r a t i o n , w i t h no e v i d e n t f l o a t a b i l -i t y d i s t r i b u t i o n s . The h i g h e s t cumulative y i e l d s were o b t a i n e d f o r the l i g h t e s t f r a c t i o n (<1.30 s p e c i f i c g r a v i t y ) , w i t h the maximum y i e l d a t s u r f a c e t e n s i o n of 68 dyne/cm (2 % methanol c o n c e n t r a t i o n ) , and the lowest y i e l d a t about 39 dyne/cm of s u r f a c e t e n s i o n (30 % 128 Methanol concentration, vol. % 10 20 30 40 100 OH 1 1 1 1 1 1 1 1 70 54 45 39 35 Surface tension, dyne/cm F i g u r e 8.2.7 The cumulative y i e l d vs s u r f a c e t e n s i o n c u rves f o r v a r i o u s d e n s i t y f r a c t i o n s as ob t a i n e d from P/S s m a l l - s c a l e f l o t a t i o n t e s t s . methanol c o n c e n t r a t i o n ) . The second l i g h t e s t f r a c t i o n (1.30-1.35 s p e c i f i c g r a v i t y ) i s c h a r a c t e r i z e d by a d i f f e r e n t f l o a t a b i l i t y d i s t r i b u t i o n , w i t h much lower y i e l d s and a sharper change i n shape of the d i s t r i b u t i o n curve. The t h i r d l i g h t e s t f r a c t i o n (1.35-1.40 s p e c i f i c g r a v i t y ) shows c o n s i d e r a b l y lower f l o t a t i o n response when compared t o the two l i g h t e r f r a c t i o n s d i s c u s s e d above. The low y i e l d s a t low methanol c o n c e n t r a t i o n s (high s u r f a c e t e n s i o n s ) are mainly due t o the f a c t t h a t most of the c o a l p a r t i c l e s w i t h i n t h i s f r a c t i o n are h e a v i l y contaminated w i t h m i n e r a l matter. The t r e n d s i n ash content of f l o a t s and r e j e c t s f o r the t h r e e d e n s i t y f r a c t i o n s under d i s c u s s i o n are d e p i c t e d i n F i g u r e s 8.2.8 and 8.2.9. The ash content of f l o a t i n g c o a l p a r t i c l e s f o r the two l i g h t e s t f r a c t i o n s seem t o be independent of methanol c o n c e n t r a t i o n ( s u r f a c e t e n s i o n ) , w h i l e the ash content of r e j e c t s decreases as t h e methanol c o n c e n t r a t i o n i n c r e a s e s ; the minimum ash content o c c u r s a t about 10 % methanol c o n c e n t r a t i o n f o r both f r a c t i o n s . F u r t h e r , the ash content of r e j e c t s becomes co n s t a n t w i t h decrease i n s u r f a c e t e n s i o n . The h i g h ash content of r e j e c t s a t low methanol c o n c e n t r a t i o n (high s u r f a c e t e n s i o n ) c o n f i r m s t h a t a t t h a t s u r f a c e t e n s i o n the s e p a r a t i o n i s between a l l hydrophobic c o a l p a r t i c l e s and o n l y v e r y h y d r o p h i l i c m i n e r a l matter (or h e a v i l y contaminated c o a l p a r t i c l e s ) . The ash p a t t e r n f o r the f l o a t s of the t h i r d d e n s i t y f r a c t i o n (1.35-1.40 s p e c i f i c g r a v i t y ) i s d i f f e r e n t from the p a t t e r n f o r the d e n s i t y f r a c t i o n s d i s c u s s e d above. The m a j o r i t y of the 130 Methanol concentration, vol.% 54 45 39 35 1.30 S.g Methanol concentration! vol. % 32 10 10 20 10 20 30 40 50 0 Surface tension, dyne/cm a B — B - B -3 0 —I _1_ Methanol concentration vol.% JL 50 1.35 s.g. 20 10 _ i 54 45 38 35 Surface tension, dyne/cm 32 b 20 30 40 50 1.40 s g 54 45 39 35 Surface tension, dyne/cm 32 c F i g u r e 8.2.8 Ash content i n the f l o a t s of the t h r e e d e n s i t y f r a c -t i o n s : (a) < 1.30 s p e c i f i c g r a v i t y ; (b) 1.30 - 1.35 s p e c i f i c g r a v i t y ; (c) 1 . 3 5 - 1 . 4 0 s p e c i f i c g r a v i t y 14 12 -« 10 O SI rr g 8 # u> to Methanol concentration, vol. % 10 20 - I 30 _ l 40 I 50 0 1.30 s g 54 45 39 35 Surface tension, dyne/cm (a) 12 10 2 -32 Methanol concentration vol % _i_ 20 30 40 1.35 a g o n i „ i „ - , „ , M „ e i a 50 0 20 Methanol concentration vol. % 10 20 30 40 SO 54 45 39 Surface tension, dyne/cm (b) 10 35 32 1.40 sg. —Q 54 45 39 Surface tension, dyne/cm (c) 35 32 F i g u r e 8.2.9 Ash content i n the r e j e c t s of the t h r e e d e n s i t y f r a c t i o n s : (a) < 1.30 s p e c i f i c g r a v i t y ; (b) 1.30 - 1.35 s p e c i f i c g r a v i t y ; (c) 1.35 - 1.40 s p e c i f i c g r a v i t y p a r t i c l e s , however, w i t h i n ^ t h i s d e n s i t y f r a c t i o n are contaminated w i t h m i n e r a l matter, and o n l y a few p a r t i c l e s f l o a t , and t h e r e f o r e the d i s t r i b u t i o n o b t a i n e d from f l o a t a b i l i t y runs i s o n l y f o r those p a r t i c l e s which are hydrophobic enough t o be f l o a t e d . The ash c o n t e n t of t h e r e j e c t s appears t o be c o n s t a n t over the s t u d i e d methanol c o n c e n t r a t i o n range. S i n c e o n l y a s m a l l amount of c o a l p a r t i c l e s f l o a t a t h i g h methanol c o n c e n t r a t i o n , i t i s d i f f i c u l t t o observe s i g n i f i c a n t changes i n the ash content of r e j e c t s . 8.2.3 Cumulative ash versus cumulative y i e l d The cumulative ash v e r s u s cumulative y i e l d of the f l o a t s and r e j e c t s were p l o t t e d t o c h a r a c t e r i z e the f l o a t a b i l i t y . The data i n F i g u r e s 8.2.10 and F i g u r e 8.2.11 r e p r e s e n t two composite samples; r e s u l t s are p l o t t e d as cumulative ash versus cumulative y i e l d of the f l o a t s and r e j e c t s . For the high-ash composite sample, as the cumulative y i e l d of f l o a t s decreases below 30 %, the ash content i n c r e a s e s r a p i d l y f o r t h e high-ash composite sample. The y i e l d of 30 % of f l o a t s c o i n c i d e s w i t h 20 % methanol c o n c e n t r a t i o n . T h i s t r e n d p r o v i d e s an a d d i t i o n a l evidence t h a t c l a y s l i m e s are r e l e a s e d d u r i n g prolonged c o n d i t i o n i n g i n the more c o n c e n t r a t e d methanol s o l u t i o n s (over 20 % methanol c o n c e n t r a t i o n ) . A c c o r d i n g t o Hornsby (1981), t h e r e i s a s t r o n g p e p t i z i n g e f f e c t of a l c o h o l s o l u t i o n s on c l a y m i n e r a l s a s s o c i a t e d w i t h c o a l . The p e p t i z a t i o n e f f e c t i s minimized a t s h o r t c o n d i t i o n i n g times. The shape of the c l e a n c o a l 133 F i g u r e 8.2.10 The cumulative y i e l d v e r s u s c u m u l a t i v e ash f o r the f l o a t s and r e j e c t s f o r the high-ash composite sample, (a) f l o a t s ; (b) r e j e c t s . F i g u r e 8.2.11 The cumulative y i e l d v ersus cumulative ash curves f o r the f l o a t s and r e j e c t s f o r the low-ash composite sample, (a) f l o a t s ; (b) r e j e c t s curve f o r the low-ash composite sample i n d i c a t e s t h a t , even though c o n d i t i o n i n g time f o r both samples was the same, the p e p t i z i n g e f f e c t appears t o be minimal when t h e ash content i s lower. 136 F i g u r e 8.2.12 The cumulative y i e l d v e r s u s c u m u l a t i v e ash f o r the f l o a t s and r e j e c t s f o r the < 1.30 s p e c i f i c g r a v i t y f r a c t i o n : (a) f l o a t s ; (b) r e j e c t s . F i g u r e 8.2.13 The cumulative y i e l d v ersus cumulative ash curves f o r the f l o a t s and r e j e c t s f o r the 1.30 - 1.35 s p e c i f i c g r a v i t y f r a c t i o n : (a) f l o a t s ; (b) r e j e c t s . The cumulative ash p l o t t e d versus cumulative y i e l d of f l o a t s and r e j e c t s f o r d e n s i t y f r a c t i o n s are g i v e n i n the F i g u r e s 8.2.12 - 8.2.14. For the two lowest d e n s i t y f r a c t i o n s , the p l o t s i n d i c a t e no change i n ash content as the y i e l d of f l o a t s i s decreased. T h i s c l e a r l y i m p l i e s t h a t f o r these samples the s e p a r a t i o n p r o c e s s does not depend on the ash content of p a r t i c l e s . In o t h e r words, once the ash content becomes n e g l i g i b l e , the other f a c t o r s which c o n t r i b u t e towards s u r f a c e p r o p e r t i e s of a g i v e n p a r t i c l e become predominant. The t h i r d d e n s i t y f r a c t i o n under c o n s i d e r a t i o n showed a d i f f e r e n t t r e n d i n the ash d i s t r i b u t i o n . A p p a r e n t l y the e f f e c t of c l a y p e p t i z a t i o n becomes pronounced again, as the ash content i n t h i s f r a c t i o n i s much h i g h e r than i n the o t h e r two d e n s i t y f r a c t i o n s . The p l o t s of cumulative ash versus y i e l d of r e j e c t s r e f l e c t the change i n the q u a l i t y of the n o n - f l o a t i n g m a t e r i a l . The c a l c u l a t e d f e e d ash c o n t e n t o b t a i n e d from f l o a t and r e j e c t f r a c t i o n s f o r a l l f l o t a t i o n t e s t s has been s t a t i s t i c a l l y compared w i t h t h e measured f e e d ash v a l u e s f o r the c o r r e s p o n d i n g samples and i s p r e s e n t e d i n the Appendix D. 8.2.4 F l o a t a b i l i t y - w a s h a b i l i t y c h a r a c t e r i s t i c s The cumulative ash-cumulative y i e l d curves d e r i v e d from the f l o t a t i o n i n methanol s o l u t i o n s can be c o n s i d e r e d , by analogy t o the w a s h a b i l i t y curves, as f l o a t a b i l i t y - w a s h a b i l i t y curves (Hornsby, 1981; Laskowski, 1986b). 139 1.40» g i O OJ >-I E o 40 60 80 100 5 10 15 Cumulative % Ash, Floats 20 100 eo € <a o> DC 33 eo > JS 40 E o 20 1.40 » g 5 10 15 Cumulative % Ash, Rejects 20 Figure 8.2.14 The cumulative y i e l d versus cumulative ash curves for the f l o a t s and re j e c t s for the 1.35 - 1.40 s p e c i f i c gravity f r a c t i o n : (a) f l o a t s ; (b) r e j e c t s . In g r a v i t y w a s h a b i l i t y t e s t s , c o a l p a r t i c l e s are se p a r a t e d a c c o r d i n g t o t h e i r r e s p e c t i v e d e n s i t i e s , and the r e l a t i o n s h i p between the y i e l d and ash i s d e r i v e d t o p r e d i c t the q u a l i t y o f the pro d u c t s from the g r a v i t y based p r o c e s s e s . In the f l o t a t i o n t e s t s c a r r i e d out a t v a r y i n g methanol c o n c e n t r a t i o n s , the aim i s t o sepa r a t e p a r t i c l e s a c c o r d i n g t o t h e i r s u r f a c e p r o p e r t i e s , namely t h e i r Y C f c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y , t o p r e d i c t t h e i r f l o t a t i o n response. In g r a v i t y s e p a r a t i o n the d e n s i t y of a s i n g l e p a r t i c l e p l a y s a d e c i s i v e r o l e . In g e n e r a l , d e n s i t y i s d i r e c t l y p r o p o r t i o n a l t o the m i n e r a l matter content ( d e n s i t y of m i n e r a l s a s s o c i a t e d w i t h c o a l s range from 2.5 t o 5 s.g.; d e n s i t y of macerals i s w i t h i n 1.1 t o 1.45 s . g . ) . T h e r e f o r e , the y i e l d - a s h r e l a t i o n s h i p predominately depends on the m i n e r a l matter content and i t s a s s o c i a t i o n w i t h c o a l p a r t i c l e s . In f l o a t a b i l i t y t e s t s , p a r t i c l e s are sepa r a t e d a c c o r d i n g t o t h e i r s u r f a c e p r o p e r t i e s . S u r f a c e p r o p e r t i e s of each p a r t i c l e a r e b e l i e v e d t o be an average v a l u e o f f a c t o r s such as: m i n e r a l matter co n t e n t ( s t r o n g l y h y d r o p h i l i c s i t e s ) ; o x i d a t i o n degree ( s l i g h t l y t o h i g h l y h y d r o p h i l i c s i t e s depending on the exte n t of o x i d a t i o n ) and f i n a l l y p e t r o g r a p h i c composition (which r e p r e s e n t s s i t e s o f d i f f e r e n t degree of h y d r o p h o b i c i t y ) . M i n e r a l matter and the degree of o x i d a t i o n have the g r e a t e s t e f f e c t on the average s u r f a c e p r o p e r t i e s because they p r e s e n t the h i g h l y h y d r o p h i l i c s i t e s on a g i v e n c o a l p a r t i c l e . In some cases (e.g. medium v o l a t i l e c o a l ) , f l o t a t i o n 141 response may be p r e d i c t a b l e from the g r a v i t y - w a s h a b i l i t y c h a r a c t e r -i s t i c s because the o n l y f a c t o r c o n t r i b u t i n g t o h y d r o p h i l i c i t y i s the presence o f m i n e r a l matter. However, t h i s does not n e c e s s a r i l y mean t h a t even i n such a case the w a s h a b i l i t y w i l l be equal t o f l o a t a b i l i t y . A comparison between the f l o a t a b i l i t y - w a s h a b i l i t y and the w a s h a b i l i t y curves f o r the same composite sample can be made, F i g u r e s 8.2.10 and 8.2.15. The cumulative ash v e r s u s y i e l d curve of high-ash composite sample o b t a i n e d from the w a s h a b i l i t y t e s t shows more y i e l d dependance on ash content than the same curve from the f l o a t a b i 1 i t y - w a s h a b i 1 i t y . The cumulative f l o a t a b i l i t y curves were r e c a l c u l a t e d i n t o the i n c r e m e n t a l f l o a t a b i l i t y d i s t r i b u t i o n s f o r the s t u d i e d samples. The i n c r e m e n t a l ash content was c a l c u l a t e d f o r composite and d e n s i t y samples. F i g u r e s 8.2.16 and 8.2.17 p r e s e n t the inc r e m e n t a l d a t a f o r two composite samples. F i g u r e s 8.2.18 t o 8.2.20 show s i m i l a r histograms and ash l i n e s f o r the d e n s i t y f r a c t i o n s . The i n t e r v a l s c o r r e s p o n d i n g t o the methanol c o n c e n t r a t i o n s i n f l o t a t i o n t e s t s (2, 5, 10, 15, 20, 30 and 40 %) were used f o r in c r e m e n t a l d a t a c a l c u l a t i o n . The f l o t a t i o n f r a c t i o n w i t h i n each of the methanol c o n c e n t r a t i o n s can be d e f i n e d by i t s mean c r i t i c a l s u r f a c e t e n s i o n o f f l o a t a b i l i t y , Y c f The approach u s i n g the in c r e m e n t a l y i e l d s and ash co n t e n t s of each f l o a t a b i l i t y f r a c t i o n was i n t r o d u c e d by Hornsby (1981). He used 2% i n t e r v a l s of methanol c o n c e n t r a t i o n t o c r e a t e i n c r e m e n t a l y i e l d s from the f l o a t a b i l i t y d i s t r i b u t i o n s . The average 142 F i g u r e 8.2.15 The cumulative y i e l d versus cumulative ash curves f o r the high-ash composite sample (from w a s h a b i l i t y ) : (a) f l o a t s ; (b) r e j e c t s . Surface tension dyne/cm 5 10 20 Methanol concentration, vol.% Incremental ash % 25 -20 -15 -10 10 15 20 25 X 35 Methanol concentration, vol.% 40 45 50 F i g u r e 8.2.16 The i n c r e m e n t a l y i e l d and ash f o r the high-ash composite sample: (a) i n c r e m e n t a l y i e l d histogram; (b) incremental ash p l o t . 144 68 60 c E v_ O C 50 -40 * S 30 20 10 Surface tension dyne/cm 62 54 _L 2 5 10 Methanol concentration, vol.% 45 t / 20 Incremental ash % 40 X 20 10 10 1 5 20 25 X 35 Methanol concentration, vol.% 40 F i g u r e 8.2.17 The i n c r e m e n t a l y i e l d and ash da t a f o r the low-ash composite sample: (a) i n c r e m e n t a l y i e l d histogram; (b) incremental ash p l o t . 145 Surface tension dyne/cm 33 C <D E <D o c 5 10 20 Methanol concentration, vol.% Incremental ash % 15 20 25 30 35 Methanol concentration, vol.% Figure 8.2.18 The incremental y i e l d and ash f o r the < 1.30 s p e c i f i c gravity f r a c t i o n : (a) incremental y i e l d histogram; (b) incremental ash p l o t . 146 •a c <9 E <D & C 60 50 40 2 30 20 10 Surface tension dyne/cm 82 45 JZ. 5 10, Methanol concentration, vol.% 20 Incremental ash % 10 15 20 25 30 35 Methanol concentration, vol.% 45 50 F i g u r e 8.2.19 The i n c r e m e n t a l y i e l d and ash f o r the 1.30 - 1.35 s p e c i f i c g r a v i t y f r a c t i o n : (a) i n c r e m e n t a l y i e l d histogram; (b) i n c r e m e n t a l ash p l o t . 147 f l o a t a b i l i t y o f each f r a c t i o n was c h a r a c t e r i z e d by the " f l o a t a b i l i -t y number", FN, which i s the a r i t h m e t i c mean of the two boundaries d e f i n e d by the methanol c o n c e n t r a t i o n s . A c c o r d i n g l y , the h i g h e r the f l o a t a b i l i t y number of a f r a c t i o n the more f l o a t a b l e m a t e r i a l i s i n the f r a c t i o n . F o l l o w i n g the same rea s o n i n g , histogram d i s t r i b u t i o n s of each of the examined samples can be separated i n t o low and h i g h " f l o a t a b i l i t y " r e g i o n s . The ash content and f l o a t a b i l i t y are i n v e r s e l y i n t e r r e -l a t e d f o r the low f l o a t a b i l i t y r e g i o n s of a l l samples. The i n c r e m e n t a l ash reaches minimum v a l u e s a t v a r i o u s methanol c o n c e n t r a t i o n s f o r d i f f e r e n t samples. For the two composite samples and the lowest d e n s i t y f r a c t i o n , the minimum i s reached a t 10 % methanol c o n c e n t r a t i o n , the minimum ash content f o r the lowest d e n s i t y f r a c t i o n (< 1.30) i s a t 20 % methanol c o n c e n t r a t i o n , f o r the next l i g h t e s t (1.30 - 1.35 s p e c i f i c g r a v i t y ) appears t o be a t 5 %, and f o r the 1.35 - 1.40 s p e c i f i c g r a v i t y f r a c t i o n , the ash cont e n t i s u s u a l l y c o n s t a n t over the range of methanol c o n c e n t r a -t i o n s up t o 20 %. For a l l the samples, ash content i n c r e a s e s d r a s t i c a l l y f o r the f l o a t a b i l i t y f r a c t i o n s over 20 % methanol c o n c e n t r a t i o n w i t h the e x c e p t i o n o f the 1.30 d e n s i t y f r a c t i o n , where t h e ash content has the lowest v a l u e . T h i s sudden i n c r e a s e i n ash c o n t e n t i n the h i g h f l o a t a b i l i t y r e g i o n i s a t t r i b u t e d t o the s l i m e s c a r r y - o v e r i n t o the f l o a t s , as d i s c u s s e d i n s e c t i o n 8.2.3. The i n c r e m e n t a l d i s t r i b u t i o n s of the y i e l d versus methanol c o n c e n t r a t i o n are the d i s t r i b u t i o n s of h y d r o p h o b i c i t y f o r a g i v e n sample. Depending on the s u r f a c e c h a r a c t e r i s t i c s of 148 so CO-T3 <D c <D E (D i _ O c 30 -20 10 •ZZ7I Surface tension dyne/cm 62 54 JL 1 4 5 39 5 10 20 Methanol concentration, vol.% 30 Incremental ash % 20 15 15 20 25 30 35 Methanol concentration, vol.% 40 45 50 F i g u r e 8.2.20 The i n c r e m e n t a l y i e l d and ash f o r the 1.35 - 1 s p e c i f i c g r a v i t y f r a c t i o n : (a) in c r e m e n t a l y i e l d histogram; i n c r e m e n t a l ash p l o t . 149 p a r t i c l e s w i t h i n the sample, the d i s t r i b u t i o n of f l o a t i n g p a r t i c l e s may v a r y a c c o r d i n g t o t h e i r i n d i v i d u a l average s u r f a c e p r o p e r t i e s . For example, the d i s t r i b u t i o n of h y d r o p h o b i c i t y of one sample may be c o n s i d e r a b l y d i f f e r e n t i f the average s u r f a c e p r o p e r t i e s of the p a r t i c l e s are s i g n i f i c a n t l y d i f f e r e n t . In t h i s approach, the average s u r f a c e p r o p e r t i e s are c h a r a c t e r i z e d by t h e average c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y , Y c f The m a j o r i t y of the p a r t i c l e s i n the composite samples were found t o be f l o a t i n g a t 10 % methanol c o n c e n t r a t i o n , and the average Y cf» corresponds t o 54 dyne/cm. In the 1.30 s p e c i f i c g r a v i t y f r a c t i o n , the maximum of f l o a t i n g p a r t i c l e s appears t o be a t 10 % and an abundance of f l o a t i n g p a r t i c l e s a l s o occurs a t 20 % methanol c o n c e n t r a t i o n (45 dyne/cm). Most of the p a r t i c l e s w i t h i n t h e 1.30-1.35 s p e c i f i c g r a v i t y f r a c t i o n are found t o be f l o a t i n g a t 5 % methanol c o n c e n t r a t i o n , and t h e i r average Y C f ' w a s 6 2 dyne/cm, w h i l e f o r the 1.35-1.40 s p e c i f i c g r a v i t y f r a c t i o n , the m a j o r i t y of p a r t i c l e s f l o a t a t 2 % methanol c o n c e n t r a t i o n , w i t h average y c f = 68 dyne/cm. 8.2.5 M i c r o s c o p i c examination of f l o t a t i o n products M i c r o s c o p i c a n a l y s e s were c a r r i e d out on f l o t a t i o n p r o d u c t s o b t a i n e d from the P/S s m a l l - s c a l e f l o t a t i o n t e s t s . I n i t i a l l y maceral counts were performed on the f l o a t s and r e j e c t s f o l l o w i n g the standard p e t r o g r a p h i c procedures ( B u s t i n e t a l . , 1983). From maceral a n a l y s e s alone i t was d i f f i c u l t t o observe 150 s i g n i f i c a n t changes i n maceral composition i n the f l o a t s and r e j e c t s a t d i f f e r e n t l e v e l s of methanol c o n c e n t r a t i o n . The maceral c o u n t i n g technique, as d e f i n e d i n I n t e r n a -t i o n a l Handbook of C o a l P e t r o l o g y (1971) i s f r e q u e n t l y used t o e s t i m a t e q u a n t i t i v e l y the r e l a t i v e abundance of macerals. T h i s type of a n a l y s i s i s u s u a l l y s a t i s f a c t o r y f o r p e t r o g r a p h i c p r e d i c t i o n s , where r e l a t i v e abundance of macerals p r o v i d e adequate i n f o r m a t i o n . P e t r o g r a p h i c a n a l y s e s have been s u c c e s s f u l l y used i n p r e d i c t i o n s f o r c a r b o n i z a t i o n p r o c e s s e s . The f l o t a t i o n p r o c e s s , however, r e l i e s on the s u r f a c e p r o p e r t i e s of s e p a r a t e p a r t i c l e s . T h e r e f o r e , the nature of s i n g l e p a r t i c l e i s more important than the abundance of macerals. However, as each p a r t i c l e i s composed of i n t i m a t e l y intergrown macerals, g r a i n - t y p e a n a l y s i s d e s c r i b i n g composition of each p a r t i c l e i s more a p p r o p r i a t e . For the d e t a i l e d m i c r o s c o p i c a n a l y s i s of f l o t a t i o n p r o d u c t s , d e n s i t y f r a c t i o n s were chosen. The maceral counts were performed s i m u l t a n e o u s l y , w i t h f u l l d e s c r i p t i o n of each encountered p a r t i c l e . The p a r t i c l e s were r e c o r d e d i n the set-up g r a i n - t y p e c a t e g o r i e s . The important p a r t of the a n a l y s i s was t o d e s c r i b e i n t h e b e s t p o s s i b l e way the a s s o c i a t i o n of macerals w i t h each other as w e l l as w i t h the m i n e r a l matter. G r a i n - a n a l y s e s of d e n s i t y f r a c t i o n s were d i s c u s s e d i n s e c t i o n 6.3.4. T a b l e s A.5 and A.6 (Appendix A) p r e s e n t g r a i n - t y p e a n a l y s i s of the f l o a t s and r e j e c t s f o r 1.30 s.g. and 1.30-1.35 s.g. a t d i f f e r e n t methanol c o n c e n t r a t i o n s . The t r e n d s i n r e c o v e r y were 151 observed by comparing the volume p e r c e n t of f l o a t i n g p a r t i c l e s t o t h e i r c o n t e n t i n the f e e d sample. F i g u r e s 8.2.21 and 8.2.22 compare f l o a t a b i l i t y of c o a l g r a i n s f o r two d e n s i t y f r a c t i o n s . D e t a i l e d g r a i n a n a l y s i s of the f l o t a t i o n p roducts as o b t a i n e d from f l o t a t i o n s i n methanol s o l u t i o n s , shows the segrega-t i o n of c o a l g r a i n s i n t o f r a c t i o n s of d i f f e r e n t c r i t i c a l s u r f a c e t e n s i o n s . The f l o t a t i o n p roducts of the two l i g h t e s t d e n s i t y f r a c t i o n s were i n t e n t i o n a l l y chosen f o r p e t r o g r a p h i c a n a l y s i s , because both samples are low i n ash content and r e p r e s e n t s p e c i f i c maceral c o n c e n t r a t e s . The l i g h t e s t (1.30 s p e c i f i c g r a v i t y ) f r a c t i o n i s e n r i c h e d i n v i t r i n i t e and p s e u d o v i t r i n i t e , whereas the 1.30-1.35 s p e c i f i c g r a v i t y f r a c t i o n has g r e a t e r abundance of v i t r i n i t e i n a s s o c i a t i o n w i t h i n e r t i n i t e . The number of v i t r i n i t e p a r t i c l e s contaminated w i t h m i n e r a l matter i n c r e a s e s w i t h the d e n s i t y . As the m i n e r a l matter l e v e l i s reduced i n low d e n s i t y f r a c t i o n s , the other f a c t o r s such as p e t r o g r a p h i c composition become more important. The g r a i n - t y p e a n a l y s i s of the f l o t a t i o n p r o d u c t s of the 1.30 s p e c i f i c g r a v i t y f r a c t i o n ( F i g u r e 8.2.21), shows t h a t t h e r e i s s i g n i f i c a n t r e c o v e r y of f r e e v i t r i n i t e p a r t i c l e s i n the f l o a t s , a t 10 % methanol c o n c e n t r a t i o n . The volume p e r c e n t of f r e e v i t r i n i t e p a r t i c l e s r o s e from 60 % by volume i n the f e e d sample t o 81 % by volume i n the f l o a t s , a t 10 % methanol c o n c e n t r a t i o n . The v i t r i n i t e p a r t i c l e s i n t h i s f r a c t i o n appear v e r y l i t t l e contaminated with m i n e r a l matter. The f l o a t a b i l i t y t r e n d s f o r p s e u d o v i t r i n i t e i n d i c a t e t h a t a minimum of f l o a t a b i l i t y o ccurs a t 10 % methanol c o n c e n t r a t i o n and a maximum a t 20 % methanol c o n c e n t r a t i o n . In 152 g e n e r a l , p s e u d o v i t r i n i t e l e v e l s are r e p o r t e d not t o exceed the l e v e l i n the fe e d sample. The f l o t a t i o n of the 1.30-1.35 s p e c i f i c g r a v i t y f r a c t i o n ( F i g u r e 8.2.22), shows l e s s pronounced t r e n d s i n f l o a t a b i l i t y of p e t r o g r a p h i c g r a i n s , as the p a r t i c l e s i n t h i s f r a c t i o n have a more composite nature, more v i t r i n i t e a s s o c i a t e d w i t h i n e r t i n i t e (V > I) and i n e r t i n i t e w i t h v i t r i n i t e (I > V) . F l o a t a b i l i t y o f f r e e v i t r i n i t e p a r t i c l e s remains a t the same l e v e l throughout methanol c o n c e n t r a t i o n s from 2% t o 20 %. The maximum of f l o a t a b i l i t y f o r f r e e v i t r i n i t e i s a t 30 % of methanol c o n c e n t r a t i o n . V i t r i n i t e p a r t i c l e s w i t h m i n e r a l matter were found t o have t h e i r maximum f l o a t a b i l i t y a t 5 % and 30 % methanol c o n c e n t r a t i o n s , and t h e i r minimum a t 10% methanol c o n c e n t r a t i o n (Table A.1.6). Free v i t r i n i t e g r a i n s i n c l u d e d v i t r i n i t e p a r t i c l e s which were f r e e o f a s s o c i a t i o n w i t h o t h e r macerals, but not f r e e o f m i n e r a l matter. T h e r e f o r e , f r e e v i t r i n i t e p a r t i c l e s f l o a t i n g a t 10 % methanol c o n c e n t r a t i o n are t h e l e a s t contaminated w i t h m i n e r a l matter. The h i g h e r f l o a t a b i l i t y o f v i t r i n i t e w i t h m i n e r a l matter a t h i g h e r methanol c o n c e n t r a t i o n s may be the e f f e c t o f c l a y p e p t i z a t i o n a t hig h methanol c o n c e n t r a t i o n s , as d i s c u s s e d e a r l i e r . The i n c r e m e n t a l ash f o r t h i s f r a c t i o n was found t o be q u i t e h i g h , i n d i c a t i n g e x c e s s i v e presence of m i n e r a l matter (8.2.19.b). V i t r i n i t e w i t h i n e r t i n i t e g r a i n s (V > I) were found t o have t h e i r i n c r e a s e d f l o a t a b i l i t y a t low methanol c o n c e n t r a t i o n s i n the range from 2 t o 10 % methanol c o n c e n t r a t i o n s , and show some drop i n f l o a t a b i l i t y a t the 20 t o 30 % methanol c o n c e n t r a t i o n range. I n e r t i n i t e , i n e r t i n i t e w i t h 153 v i t r i n i t e g r a i n s (I > V) , and s e m i f u s i n i t e were found t o f l o a t b e t t e r a t 5 % methanol c o n c e n t r a t i o n . 8.3 D i s c u s s i o n o f the w e t t a b i l i t y and f l o a t a b i l i t y d i s t r i b u t i o n s r e s u l t s 8.3.1 W e t t a b i l i t y d i s t r i b u t i o n s of d i f f e r e n t c o a l samples W e t t a b i l i t y d i s t r i b u t i o n , as d e r i v e d from f i l m f l o t a t i o n i n methanol s o l u t i o n s , i s a v e r y convenient way of d e s c r i b i n g the range o f c r i t i c a l s u r f a c e t e n s i o n s o f an assembly of p a r t i c l e s . Three parameters d e r i v e d from the w e t t a b i l i t y d i s t r i b u t i o n , as d i s c u s s e d i n s e c t i o n 2.1.2., Y C m i n ' Y Cmax a n < * Y c c h a r a c t e r i z e p a r t i c l e s i n r e l a t i o n t o t h e i r h y d r o p h o b i c i t y . The v a l u e o f Y Cmin' (^ n e s u r f a c e t e n s i o n of the s o l u t i o n , t h a t wets a l l p a r t i c l e s ) , i s found f o r both composite samples, two d e n s i t y f r a c t i o n s and l i t h o t y p e s , a t the same s u r f a c e t e n s i o n of 39 dyne/cm ( F i g u r e s 8.1.1, 8.1.2 and 8.1.3). The Y Cmax' w a s f o u n d t o be c o n s t a n t f o r these samples as w e l l , and had a v a l u e o f 68 dyne/cm. The Y Cmin' a n d Y Cmax' a s d i s c u s s e d i n s e c t i o n 2.1.2, r e f l e c t s t h e range of s u r f a c e p r o p e r t i e s of p a r t i c l e s w i t h i n an assembly. For p a r t i c u l a t e c o a l sample, a band on adhesion t e n s i o n diagram,(see F i g u r e 2.1.4) r e p r e s e n t s w e t t a b i l i t y i n s t e a d of a d i s c r e t e l i n e (Hornsby, 1981), r e s u l t i n g i n d i s t i n c t Y max a n d Ycmin* T h e P r e v i ° u s l y quoted work by Fuerstenau (1988) i n d i c a t e d 154 t h a t , the Y C m i n ^ o r c o a ^ - p a r t i c l e s ranged from a t l e a s t 3 0 t o 40 dyne/cm. The d i f f e r e n c e between Y Cmax a n d Y Cmin' ^ s a r o u c J n i n d i c a t o r o f the s u r f a c e h e t e r o g e n e i t y of the sample. For homogeneous p a r t i c l e s , Y c m a x * s a l m o s t equal Y Cmin* These two v a l u e s a l s o d e s c r i b e boundaries f o r w e t t a b i l i t y o f p a r t i c l e s f o r a g i v e n assembly. For a l l examined samples, these l i m i t i n g boundaries of w e t t a b i l i t y were the same. The average c r i t i c a l s u r f a c e t e n s i o n of w e t t i n g , y~C' w a s t h e o n l y parameter changing markedly f o r these d i f f e r e n t samples. For both composite samples was estimated a t 54-56 dyne/cm, f o r lowest d e n s i t y f r a c t i o n was found a t 52 dyne/cm; and f o r the 1.30 -1.35 s p e c i f i c g r a v i t y f r a c t i o n a t 56 dyne/cm. The v a l u e s of average c r i t i c a l s u r f a c e t e n s i o n f o r l i t h o t y p e s Y~c, were as f o l l o w s : b r i g h t and banded b r i g h t , y~c = 48 dyne/cm; f o r banded d u l l and banded c o a l ~y~c = 54 dyne/cm, and 58 dyne/cm f o r f i b r o u s ( f u s a i n ) . The mean v a l u e of Y~c i s an important parameter d e s c r i b i n g each d i s t r i b u t i o n . For the s t u d i e d samples, even though the boundaries of w e t t a b i l i t y were the same, each of the sample had d i s t i n c t w e t t a b i l i t y d i s t r i b u t i o n . A c c o r d i n g t o Fuerstenau (1988), the d i f f e r e n c e i n Y c f o r c o a l p a r t i c l e s , can be a q u a n t i t i v e measure of v a r i a t i o n i n s u r f a c e p r o p e r t i e s , and was found t o be u s e f u l index i n d e t e c t i n g o x i d a t i o n . The y~c v a l u e s of f r e s h and o x i d i z e d c o a l s were c o r r e l a t e d w i t h the decrease i n h y d r o p h o b i c i t y . Consequently, u s i n g the y~c, as a parameter, we can d e f i n e the order of h y d r o p h o b i c i t y as f o l l o w s ; among l i t h o t y p e s the most hydrophobic 155 a r e b r i g h t and banded b r i g h t , then banded d u l l and banded c o a l and the l e a s t hydrophobic f i b r o u s ( f u s a i n ) . The lowest d e n s i t y f r a c t i o n (< 1.30 s p e c i f i c g r a v i t y ) was found more hydrophobic than the next l i g h t e s t g r a v i t y f r a c t i o n (1.30 - 1.35 s p e c i f i c g r a v i t y ) . Three o t h e r f r a c t i o n s were found t o be g e n e r a l l y h y d r o p h i l i c over the s t u d i e d range of s u r f a c e t e n s i o n s . The average c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y of two composite samples, w i t h s i g n i f i c a n t l y d i f f e r e n t ash contents (28.34% and 16.03%), i s q u i t e s i m i l a r . Comparing w e t t a b i l i t y d i s t r i b u t i o n s o f these two samples ( F i g u r e 8.2.4 a,b and F i g u r e 8.1.1), one can n o t i c e the d i f f e r e n c e i n the y i e l d s a t any g i v e n methanol c o n c e n t r a t i o n . T h i s i s l o g i c a l , s i n c e the y i e l d of f l o a t i n g p a r t i c l e s depends on the amount of m i n e r a l p a r t i c l e s p r e s e n t i n the fe e d sample. The h i g h e r the amount of m i n e r a l p a r t i c l e s , o r c o a l p a r t i c l e s h e a v i l y contaminated w i t h m i n e r a l matter, the lower the r e l a t i v e y i e l d of the f l o a t i n g f r a c t i o n s . E v i d e n t l y , the h i g h e r amount of m i n e r a l matter i n the high-ash composite sample does not have a s i g n i f i c a n t e f f e c t on the e s t i m a t i o n o f t h e average c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y f o r t h e s e p a r t i c l e s . The reason f o r t h i s i s a good l i b e r a t i o n of m i n e r a l matter i n the high-ash sample, as observed under the microscope. A l l l i t h o t y p e samples as d e s c r i b e d i n s e c t i o n 6.3.1, are c h a r a c t e r i z e d by r a t h e r low ash content (Table 6.3.1), the o n l y c o m p o s i t i o n a l d i f f e r e n c e are i n t h e i r p e t r o g r a p h i c make-up. The l i t h o t y p e s w i t h i n c r e a s e d v i t r i n i t e c o n t e n t s , b r i g h t and banded 156 b r i g h t , d i s p l a y e d the h i g h e s t h y d r o p h o b i c i t y as compared t o those e n r i c h e d i n i n e r t i n i t e macerals (Table 6.3.4, F i g u r e 6.3.4). S i m i l a r t r e n d s are observed f o r the two d e n s i t y f r a c -t i o n s . The lowest d e n s i t y f r a c t i o n b e i n g a c o n c e n t r a t e of f r e e v i t r i n i t e macerals, i s found t o be more hydrophobic than the one which i s composed of p a r t i c l e s more composite i n nature. The second d e n s i t y f r a c t i o n (1.30 -1.35), i s mainly composed of v i t r i n i t e w i t h i n e r t i n i t e . In the remaining d e n s i t y f r a c t i o n s , as d e p i c t e d i n F i g u r e 6.3.2 b, p a r t i c l e s are h e a v i l y contaminated w i t h m i n e r a l matter. 8.3.2 F l o a t a b i l i t y d i s t r i b u t i o n s o f d i f f e r e n t c o a l samples For an assembly of c o a l p a r t i c l e s w i t h a g i v e n range of w e t t a b i l i t y and oth e r p h y s i c a l c h a r a c t e r i s t i c s ( s i z e , shape, and d e n s i t y ) , a range of y c f v a l u e s e x i s t , as d e s c r i b e d i n s e c t i o n 2.1.3. From the s m a l l - s c a l e f l o t a t i o n s , i n s o l u t i o n s o f v a r y i n g s u r f a c e t e n s i o n , the d i s t r i b u t i o n of p a r t i c l e s a c c o r d i n g t o t h e i r c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y can be obt a i n e d . By analogy t o the w e t t a b i l i t y (see s e c t i o n 8.3.1), the d i s t r i b u t i o n of the c r i t i c a l s u r f a c e t e n s i o n s o f f l o a t a b i l i t y of a range of p a r t i c l e s c h a r a c t e r i z e s each sample. The mean v a l u e of c r i t i c a l s u r f a c e t e n s i o n o f f l o a t a b i l i t y , Y c f c a l c u l a t e d from the f l o a t a b i l i t y frequency d i s t r i b u t i o n , i s the a c t u a l measure of the average f l o t a t i o n response of a g i v e n assembly of p a r t i c l e s . An 157 adjustment of the s u r f a c e t e n s i o n of aqueous f l o t a t i o n s o l u t i o n s , p r o v i d e s c o n d i t i o n s f o r the s e p a r a t i o n of p a r t i c l e s i n t o f r a c t i o n s o f d i f f e r e n t f l o a t a b i l i t y . The average c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y , y C f , f o r both composite samples ( F i g u r e 8.2.4) i s found a t 48 dyne/cm, w h i l e f o r the < 1.30 and 1.30 - 1.35 d e n s i t y f r a c t i o n s ( F i g u r e 8.2.7), a t 50 and 54 dyne/cm, r e s p e c t i v e l y . M i c r o s c o p i c and ash a n a l y s e s of the f l o a t i n g f r a c t i o n a t 30 % methanol c o n c e n t r a t i o n , of 1.30 s p e c i f i c g r a v i t y f r a c t i o n , r e v e a l s t h a t the p a r t i c l e s f l o a t i n g a t t h i s s u r f a c e t e n s i o n should be c o n s i d e r e d as c a r r i e d - o v e r s l i m e s , as d i s c u s s e d e a r l i e r . As a r e s u l t , the minimum c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y i s c o n s i d e r e d t o be a t 45 dyne/cm - (20 % methanol c o n c e n t r a t i o n ) and an average c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y f o r the 1.30 s p e c i f i c g r a v i t y f r a c t i o n i s r e e s t a b l i s h e d a t 45 dyne/cm. A c c o r d i n g l y , the f l o a t -a b i l i t y of the two composite samples appears t o be the same, wh i l e the f l o a t a b i l i t y of the lowest d e n s i t y f r a c t i o n has s u p e r i o r f l o a t a b i l i t y t o t h a t of o t h e r samples. As quoted i n the l i t e r a t u r e (Hornsby and L e j a , 1983; Y a r a r and Kaoma, 1984; Kelebek and Smith, 1985), the a c t u a l shape of the f l o a t a b i l i t y d i s t r i b u t i o n curve i n d i c a t e s the nature of the p a r t i c l e s . H i g h l y homogeneous p a r t i c l e s can produce almost a s t r a i g h t l i n e , whereas heterogeneous p a r t i c l e s w i l l have much broader d i s t r i b u t i o n s , w i t h the d i s t i n c t v a l u e s of Y Cfmax a n < * Ycfmin- D i f f e r e n c e between Y c f m a x and Y c f m i n c a n a l s o b e i n d i c a t i v e of r e l a t i v e h e t e r o g e n e i t y of p a r t i c l e s w i t h i n the 158 sample. For the s t u d i e d composite samples and d e n s i t y f r a c t i o n s , the w i d e s t spread between minimum and maximum of c r i t i c a l s u r f a c e t e n s i o n o f f l o a t a b i l i t y , i s found f o r the lowest d e n s i t y f r a c t i o n , and the l e a s t f o r the 1.30 - 1.35 s p e c i f i c g r a v i t y f r a c t i o n . Y arar and Kaoma (1984) r e l a t e d the c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y of hydrophobic s o l i d s , d e r i v e d from t e s t s i n a s m a l l - s c a l e f l o t a t i o n c e l l , t o the c r i t i c a l s u r f a c e t e n s i o n o b t a i n e d from c o n t a c t angle measurements. They found v e r y good agreement between the c r i t i c a l s u r f a c e t e n s i o n v a l u e s o b t a i n e d by e x t r a p o l a t i o n of the l i n e a r p a r t of the r e c o v e r y curve t o the zero r e c o v e r y , and the y c from the c o n t a c t angle measurements. The same e x t r a p o l a t i o n t e c h n i q u e as d e s c r i b e d above i s used t o estimate the v a l u e s of yc f o r composite samples and d e n s i t y f r a c t i o n s . These are as f o l l o w s : 43 dyne/cm f o r composite samples; 39 dyne/cm f o r the < 1.30 s p e c i f i c g r a v i t y ; and 50 dyne/cm f o r the 1.30 - 1.35 s p e c i f i c g r a v i t y f r a c t i o n . The e v a l u a t i o n of f l o a t a b i l i t y u s i n g the average v a l u e of c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y and c r i t i c a l s u r f a c e t e n s i o n r e v e a l s t h a t the f l o a t a b i l i t y of p a r t i c l e s decreases w i t h i n c r e a s e i n d e n s i t y . However, the f l o a t a b i l i t y of the 1.30 - 1.35 s p e c i f i c g r a v i t y f r a c t i o n i s by f a r i n f e r i o r t o t h a t of the < 1.30 d e n s i t y f r a c t i o n , than one might expect from the i n c r e a s e d ash c o n t e n t of t h i s f r a c t i o n . The ash content of the < 1.30 and 1.30 -1.35 s p e c i f i c g r a v i t y was 3.01% and 7.87%, whereas f o r the composite sample 16.03 %. The lower f l o a t a b i l i t y of the 1.30 - 1.35 f r a c t i o n i s r a t h e r a t t r i b u t e d t o the i n c r e a s e d content of i n e r t i -159 n i t e maceral than t o the i n c r e a s e d m i n e r a l matter content. The frequency d i s t r i b u t i o n s of f l o a t a b i l i t y f o r v a r i o u s d e n s i t y f r a c t i o n s i n d i c a t e v a r i a t i o n s i n the s u r f a c e p r o p e r t i e s of p a r t i c l e s w i t h i n these f r a c t i o n s . For the 1.3 0 s.g. f r a c t i o n ( F i g u r e 8.2.18), most of the p a r t i c l e s f l o a t a t 10 % methanol c o n c e n t r a t i o n , fewer are f l o a t a b l e a t 20 % and 5 % and the l e a s t a t 2 % methanol c o n c e n t r a t i o n . Minimum ash content i s found f o r p a r t i c l e s f l o a t i n g i n the range from 5 t o 20 % methanol c o n c e n t r a -t i o n . From a f l o a t a b i l i t y - w a s h a b i l i t y p o i n t of view, t h i s d e n s i t y f r a c t i o n i s composed of p a r t i c l e s whose s u r f a c e p r o p e r t i e s are d e f i n e d by the boundary of 5 t o 20 % methanol c o n c e n t r a t i o n . The most hydrophobic p a r t i c l e s are found a t 20 % methanol c o n c e n t r a -t i o n , (45 dyne/cm), whereas the l e a s t hydrophobic a t 5 % methanol c o n c e n t r a t i o n (62 dyne/cm). For the next lowest d e n s i t y f r a c t i o n , (1.30 -1.35 s p e c i f i c g r a v i t y ) , the m a j o r i t y of p a r t i c l e s are f l o a t a b l e w i t h i n a 5 % methanol c o n c e n t r a t i o n range, c o r r e s p o n d i n g t o 62 dyne/cm, the lowest i n c r e m e n t a l ash content corresponds t o the most abundant f r a c t i o n ( F i g u r e 8.2.19 a,b). The m i c r o s c o p i c a n a l y s i s of the f l o t a t i o n products ( F i g u r e 8.2.21 and 8.2.22), r e v e a l s t h a t i n e r t i n i t e p a r t i c l e s , or those which are i n a s s o c i a t i o n w i t h i n e r t i n i t e , appears t o have maximum f l o a t a b i l i t y a t low methanol c o n c e n t r a t i o n s (high s u r f a c e t e n s i o n s ) and t o have the lowest f l o a t a b i l i t y a t h i g h methanol c o n c e n t r a t i o n s . The sudden drop i n f l o t a t i o n of i n e r t i n i t e or p a r t i c l e s c o n t a i n i n g i n e r t i n i t e a t h i g h methanol c o n c e n t r a t i o n , f o r 160 Volume % 100 80 60 40 20 ilBlil 7 V m mm y composite 5 10 20 Methanol concentration, vol.% ] Free vitrinite | | Pseudovitrinte ] Inertod, lnert>+Vrtr ^ Fusinite Vrtr>lnert Semifusinte 30 F i g u r e 8.2.21 F l o a t a b i l i t y of the p a r t i c l e s from the < 1.3 d e n s i t y f r a c t i o n i n methanol s o l u t i o n s . P e t r o g r a p h i c composition of the f l o a t s . 161 Volume % 100 80 — Id • 11! E 'HI Ii luinililHI i.J.,: IE. composite 2 5 10 20 Methanol concentration, vol. % [HI Free vitrinite ] lnertod..lnert>vitr Pseudovitrinte | Vitr>lnert Fusinite VA Semifusinte 30 F i g u r e 8.2.22 F l o a t a b i l i t y of p a r t i c l e s from the 1.30 - 1.35 d e n s i t y f r a c t i o n i n methanol s o l u t i o n s . P e t r o g r a p h i c composition of the f l o a t s . 162 examined d e n s i t y f r a c t i o n s , may be i n d i c a t i v e of s p e c i f i c c r i t i c a l s u r f a c e t e n s i o n f o r these p a r t i c l e s . The low f l o a t a b i l i t y of i n e r t i n i t e p a r t i c l e s , as compared t o v i t r i n i t e i n medium or low v o l a t i l e bituminous c o a l s was c o n s i d e r e d by many (Horsley, 1954; K l a s s e n , 1966; Sarkar, 1984; Bujnowska, 1985) and was found t o be r e l a t e d t o the s t r u c t u r e of t h i s maceral. 8.3.3 S u r f a c e p r o p e r t i e s of c o a l p a r t i c l e s S u r f a c e p r o p e r t i e s of each c o a l p a r t i c l e are the r e s u l t o f t h e heterogeneous nature of c o a l . The f i r s t o r d e r of heterogene-i t y i n terms of the s u r f a c e p r o p e r t i e s i s the presence of h i g h l y h y d r o p h i l i c m i n e r a l matter. The second f a c t o r c o n t r i b u t i n g t o the h y d r o p h i l i c i t y i s the degree of o x i d a t i o n of c o a l p a r t i c l e . Both a r e u s u a l l y expressed as bulk parameters. The degree of o x i d a t i o n i s commonly determined by chemical t i t r a t i o n , FSI index, t r a n s m i t -tance measurements, elemental and IR a n a l y s e s or o t h e r t e c h n i q u e s . A l l of t h e s e methods d e s c r i b e bulk parameters f o r a g i v e n assembly of c o a l p a r t i c l e s , and most of them are s t r o n g l y dependent on and i n f l u e n c e d by l i m i t i n g f a c t o r s such as ash content or p e t r o g r a p h i c c o m p o s i t i o n (e.g. FSI, t r a n s m i t t a n c e , e t c ) . F r e q u e n t l y those bulk parameters are not s e n s i t i v e enough t o d e t e c t changes i n the s u r f a c e p r o p e r t i e s (e.g. F S I ) . The m i n e r a l matter, commonly measured as the ash content, g i v e s t h e same bulk dimension of t h i s important parameter. The amount of ash i n the sample does not n e c e s s a r i l y i n f l u e n c e the 163 a c t u a l s u r f a c e p r o p e r t i e s o f s i n g l e p a r t i c l e s , u n l e s s i t i s intergrown w i t h t h e p a r t i c l e . A c c o r d i n g t o some authors (e.g. Bustamante and Warren, 1983) o n l y when the ash exceeds about h a l f the weight of the g r a i n does i t have an e f f e c t on s u r f a c e proper-t i e s . The next important component c o n t r i b u t i n g t o the s u r f a c e p r o p e r t y o f c o a l i s i t s rank. A change i n rank b r i n g s about a change i n t h e s u r f a c e p r o p e r t i e s of a l l c o a l p a r t i c l e s . For low-rank c o a l s , r e l a t i v e l y s m a l l amounts of h y d r o p h i l i c m i n e r a l matter i n t he composite p a r t i c l e decrease i t s h y d r o p h o b i c i t y , whereas f o r h i g h e r rank, r e l a t i v e l y l a r g e p r o p o r t i o n s of m i n e r a l matter have l i t t l e e f f e c t on i t s s u r f a c e p r o p e r t i e s (Bustamante and Warren, 1983). The degree of h y d r o p h o b i c i t y may change i f t h e c o a l p a r t i c l e s a re o x i d i z e d . Low temperature induced o x i d a t i o n may a c t u a l l y enhance h y d r o p h o b i c i t y of some c o a l p a r t i c l e s as d i s c u s s e d by Fuerstenau (1988b) and Ramesh (Raraesh and Somasundaran, 1991). F i g u r e 8.3.1 i l l u s t r a t e s the e f f e c t o f o x i d a t i o n on a composite sample a t v a r i o u s o x i d a t i o n temperatures. O x i d a t i o n may be r e s t r i c t e d t o c e r t a i n p a r t i c l e s , or even be p r e f e r e n t i a l f o r c e r t a i n macerals (Mazeluaar, 1987; M i l l e r and Ye, 1988), and i n e f f e c t l e a d i n g t o the change i n the h y d r o p h o b i c i t y of o n l y c e r t a i n p a r t s o f the p a r t i c l e s u r f a c e . Three d i f f e r e n t t e c h n i q u e s were used t o d e t e c t o x i d a t i o n o f p a r t i c l e s i n the examined c o a l samples. These were: s t a i n t e s t f o r d e t e c t i o n of o x i d i z e d p a r t i c l e s f o l l o w e d by m i c r o s c o p i c o b s e r v a t i o n s , a l k a l i - e x t r a c t i o n t e s t and a d i f f u s e 164 Surface tension dyne/cm F i g u r e 8.3.1 The e f f e c t o f o x i d a t i o n on the f l o a t a b i l i t y of the composite sample a t v a r i o u s o x i d a t i o n temperatures, (a) non-o x i d i z e d ; (b) o x i d i z e d a t 120 C; (c) o x i d i z e d a t 200 C 165 r e f l e c t a n c e FTIR technique. A c c o r d i n g t o these t e s t s , c o a l p a r t i c l e s i n the s t u d i e d samples appeared t o have u n o x i d i z e d s u r f a c e w i t h the e x c e p t i o n of o x i d i z e d a t 200° C composite sample. A summary of d e t e c t i n g c o a l o x i d a t i o n and d i s c u s s i o n o f the r e s u l t s are g i v e n i n Appendix C. A c o n s t a n t s e a r c h f o r the e x p l a n a t i o n o f s u r f a c e h e t e r o g e n e i t y i n p a r t i c u l a t e c o a l p o p u l a t i o n has l e d some r e s e a r c h -e r s (Ramesh and Somasundaran, 1991) t o the c o n c l u s i o n t h a t the p o p u l a t i o n of c o a l p a r t i c l e s are mixtures of i n d i v i d u a l p a r t i c l e s o f heterogeneous s u r f a c e s . I t has been e s t a b l i s h e d w i t h the use of f i l m f l o t a t i o n technique, t h a t observed h e t e r o g e n e i t y of an assembly of c o a l p a r t i c l e s r e f l e c t s the h e t e r o g e n e i t y o f each s i n g l e p a r t i c l e . In oth e r words, each c o a l p a r t i c l e possesses v a r i o u s s u r f a c e s i t e s which v a r y c o n s i d e r a b l y i n s u r f a c e proper-t i e s . These s i t e s may r e p r e s e n t d i f f e r e n t degrees of h y d r o p h o b i c i t y f o r each p a r t i c l e . A c c o r d i n g t o K e l l e r (1987) the s u r f a c e of c o a l p a r t i c l e appears as a patchwork assembly of areas r a n g i n g from e x c e e d i n g l y hydrophobic i d e n t i f i e d as p a r a f f i n i c , t o areas e x c e e d i n g l y h y d r o p h i l i c r e p r e s e n t e d by m i n e r a l matter and pores f i l l e d w i t h water. In t h i s model, the o r g a n i c matter i s not, however, u n i f o r m l y hydrophobic, but composed of ve r y hydrophobic p a r a f f i n i c areas, l e s s hydrophobic aromatic areas and s t r o n g l y h y d r o p h i l i c spots w i t h h i g h content o f oxygen f u n c t i o n a l groups. Assuming 6 = 110° f o r p a r a f f i n s , 6 = 88° f o r aromatics, 8 = 0 f o r oxygen s i t e s , 0 = 0 f o r m i n e r a l components and 6 = 0 f o r pores, K e l l e r was a b l e t o 166 c a l c u l a t e r e a s o n a b l e w e t t i n g of c o a l s o f d i f f e r e n t ranks u s i n g C a s s i e - B a x t e r (1944). Macerals as d i s c u s s e d i n c h a p t e r s 3 and 4, d i f f e r i n che m i c a l composition, and they may be i d e n t i f i e d as the elements b u i l d i n g t h e patchwork assembly model of c o a l s u r f a c e , as proposed by K e l l e r (1987). The macerals a r e a l s o known t o have d i f f e r e n t s u r f a c e p r o p e r t i e s (Klassen, 1966; Hower, 1986; Sarkar, 1984; Bujnowska, 1985; A r n o l d and Apian, 1989) l e a d i n g t o t h e i r d i f f e r e n t response t o f l o t a t i o n . When the samples are chosen c a r e f u l l y t o r e p r e s e n t c o a l p a r t i c l e s w i t h the minimum of o x i d a t i o n and p o s s i b l y w i t h low m i n e r a l matter content, presumably, the o n l y h y d r o p h i l i c s i t e s on the c o a l would be those which are the r e s u l t o f heteroge-neous p e t r o g r a p h i c c o a l s t r u c t u r e . For the s t u d i e d d e n s i t y samples, the h e t e r o g e n e i t y of c o a l p a r t i c l e s , as observed under the microscope, i s e v i d e n t as the v a r i a t i o n i n p e t r o g r a p h i c composition. The g r e a t e s t p e t r o g r a p h i c v a r i a t i o n among c o a l p a r t i c l e s i s observed i n the two lowest d e n s i t y f r a c t i o n s ( F i g u r e 6.3.2). In these f r a c t i o n s c o a l p a r t i c l e s a re t h e l e a s t contaminated w i t h the m i n e r a l matter, and t h e i r p e t r o g r a p h i c composition i s s i g n i f i c a n t l y d i f f e r e n t . The < 1.30 s p e c i f i c g r a v i t y f r a c t i o n , i s mainly composed of l i b e r a t e d macerals, f r e e v i t r i n i t e and p s e u d o v i t r i n i t e , are the most abundant, w h i l e i n the second lowest d e n s i t y f r a c t i o n p a r t i c l e s of composite nature (V+I; I+V) are i n c r e a s e d i n numbers. D i s t r i b u t i o n of p a r t i c l e s from the lowest d e n s i t y f r a c t i o n ( F i g u r e 8.2.21), a c c o r d i n g t o t h e i r c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y , 167 appears t o be more pronounced w i t h more apparent s e g r e g a t i o n of p a r t i c l e s i n t o f r a c t i o n s of s u r f a c e t e n s i o n . The d i s t r i b u t i o n of p a r t i c l e s from the 1.30 - 1.35 d e n s i t y , i n t o f r a c t i o n s o f d i f f e r e n t s u r f a c e t e n s i o n s , i s l e s s e v i d e n t . The p e t r o g r a p h i c composition of the f r a c t i o n s f l o a t i n g a t v a r i o u s s u r f a c e t e n s i o n s , up t o 30 % methanol c o n c e n t r a t i o n , does not change d r a s t i c a l l y . T h i s may i n d i c a t e t h a t p a r t i c l e s composed mainly of two type of macerals, r e p r e s e n t i n g d i f f e r e n t s u r f a c e p r o p e r t i e s , have l e s s chance t o be se p a r a t e d a c c o r d i n g t o t h e i r r e s p e c t i v e s u r f a c e t e n s i o n s , as they are not l i b e r a t e d from each o t h e r . 8.3.4 M i n e r a l matter c h a r a c t e r i s t i c s The amount of m i n e r a l matter becomes an important f a c t o r when parameters such as y i e l d o f c l e a n c o a l and y i e l d o f r e j e c t s a r e c o n s i d e r e d . The more m i n e r a l matter p r e s e n t i n the c o a l sample, the l e s s t h e y i e l d of c l e a n c o a l . However, i f the m i n e r a l matter i s l i b e r a t e d , t h a t i s , not a s s o c i a t e d w i t h the c o a l p a r t i c l e s , i t does not c o n t r i b u t e t o the d i f f i c u l t y o f c l e a n i n g the c o a l . The q u a l i t y of c l e a n c o a l remains the same as long as the amount of m i n e r a l matter does not h i n d e r the pro c e s s o f s e p a r a t i o n . The comparison of the cumulative ash ver s u s cumulative y i e l d of f l o a t s curves f o r the two composite samples w i t h c o n s i d e r -a b l y d i f f e r e n t ash contents ( F i g u r e s 8.2.10 and 8.2.11), shows almost no d i f f e r e n c e s i n the q u a l i t y of f l o t a t i o n p roducts, a t y i e l d s o f c l e a n c o a l from 30 t o 80 % f o r the low-ash sample, and 168 from 30 t o 70 % f o r the high-ash sample. The ash content of the c l e a n c o a l o b t a i n e d from the low-ash composite sample i n t h i s range i s 12.5 %, and f o r the high-ash sample ranges from 12.5 t o 13 %, even though the y i e l d of c l e a n c o a l i n c r e a s e f o r both samples. The q u a l i t y o f c l e a n c o a l o b t a i n e d by f l o t a t i o n of the low-ash sample improves as the y i e l d of product decreases, whereas f o r the h i g h -ash composite sample, the ash content of the c l e a n c o a l f r a c t i o n s a t low y i e l d s i s much hi g h e r , which, as d i s c u s s e d b e f o r e , i n d i c a t e s t h e e f f e c t of c l a y p e p t i z a t i o n a t h i g h methanol c o n c e n t r a t i o n s . In t h e low-ash composite sample a t h i g h y i e l d s of f l o a t s , ash tends t o i n c r e a s e , even though the y i e l d s t a y s constant, which suggests t h a t the more p a r t i c l e s are f l o a t i n g , the g r e a t e r the chance of m i n e r a l matter p a r t i c l e s b e i n g trapped w i t h i n the hydrophobic f i l m . The d e n s i t y d i s t r i b u t i o n of the high-ash composite sample (Table G . l i n Appendix G) shows an abundance of the h i g h d e n s i t y m i n e r a l matter f r a c t i o n , which c o n t r i b u t e s t o h i g h ash i n the sample. Most of which i s i n l i b e r a t e d form, s i n c e i t was r e l a t i v e l y easy t o remove i t i n a simple g r a v i t y s e p a r a t i o n p r o c e s s without major change i n h y d r o p h o b i c i t y d i s t r i b u t i o n , and reduce i t s ash from 28.34% t o 16.03% i n the composite sample. M i c r o s c o p i c examination of the composite sample confirms the presence of h i g h amounts of c l a y s as s e p a r a t e bands. In some cases, c l a y s f i l l c l e a t s and c a v i t i e s i n macerals, w i t h fewer p a r t i c l e s i n t i m a t e l y i ntergrown w i t h m i n e r a l matter. The cumulative a s h - y i e l d r e l a t i o n s h i p s f o r the two d e n s i t y f r a c t i o n s (<1.30, and 1.30-1.35), shows t h a t the q u a l i t y of 169 p r o d u c t s does not change when the y i e l d i n c r e a s e s . I t can be concluded t h a t f o r these samples f l o a t a b i l i t y does not depend on the ash con t e n t (mineral m a t t e r ) . The ash content f o r these samples was 3.01% and 7.87% r e s p e c t i v e l y . For the 1.35-1.40 f r a c t i o n , the l o w - y i e l d f l o a t a b i l i t y i s a t t r i b u t e d t o the h i g h e r ash content. As observed from p e t r o g r a p h i c a n a l y s i s , t h i s sample i s v e r y h i g h i n cont e n t o f m i n e r a l matter c o n f i n e d t o the c o a l p a r t i c l e s . From g r a i n a n a l y s i s ( F i g u r e 6.3.2), over 60 % of v i t r i n i t e p a r t i c l e s were contaminated w i t h m i n e r a l matter; t h e r e f o r e , the y i e l d of f l o a t i n g f r a c t i o n s i n maximum f l o a t a b i l i t y r e g i o n was much lower than f o r the two lower d e n s i t y f r a c t i o n s . The low f l o a t a b i l i t y of t h i s and remaining d e n s i t y f r a c t i o n s may a l s o be a t t r i b u t e d t o the f a c t t h a t the m i n e r a l matter i n these f r a c t i o n s was u n l i b e r a t e d . I t may a l s o be concluded, t h a t f o r t h i s c o a l , the maximum a c c e p t a b l e m i n e r a l matter content a t which the s u r f a c e p r o p e r t i e s are s t i l l determined by c o a l o r g a n i c matter (macerals) and not by m i n e r a l matter, i s 14.89 % (ash content of 1.35 - 1.40 f r a c t i o n ) . At h i g h e r ash c o n t e n t s , s u r f a c e p r o p e r t i e s of t h i s c o a l sample are predomi-n a n t l y determined by the m i n e r a l matter content. 8.3.5 P e t r o g r a p h i c composition P e t r o g r a p h i c a n a l y s i s of the d e n s i t y f r a c t i o n s ( F i g u r e 6.3.1) shows t h a t the l i g h t e s t f r a c t i o n i s overwhelmingly e n r i c h e d i n v i t r i n i t e , w h i l e the subsequent d e n s i t y f r a c t i o n s have shown t o have g r e a t e r abundance of i n e r t i n i t e macerals. L i p t i n i t e content i n 170 examined c o a l i s n e g l i g i b l e , as d i s c u s s e d e a r l i e r . G r a i n - t y p e a n a l y s i s ( F i g u r e 6.3.2) r e v e a l s more d e t a i l s about the c h a r a c t e r of c o a l p a r t i c l e s w i t h i n each d e n s i t y f r a c t i o n . On the b a s i s of t h i s examination, the two l i g h t e s t d e n s i t y f r a c t i o n s , <1.30 and 1.30-1.35, r e p r e s e n t the h i g h e s t v a r i a t i o n i n the p r o p o r t i o n of v i t r i n i t e and i n e r t i n i t e c ontent. The 1.35-1.40 f r a c t i o n , has more i n e r t i n i t e , however, most of i t i s i n a s s o c i a t i o n w i t h v i t r i n i t e , and almost 70 % of a l l v i t r i n i t e i s contaminated w i t h m i n e r a l matter. An i n c r e a s e i n d e n s i t y above 1.35 s p e c i f i c g r a v i t y appears t o be caused mainly by the i n c r e a s i n g p r o p o r t i o n s of m i n e r a l matter i n the composite g r a i n s , r a t h e r than v a r i a t i o n s i n r e l a t i v e p r o p o r t i o n s of i n e r t i n i t e and v i t r i n i t e . The w e t t a b i l i t y and f l o a t a b i l i t y d i s t r i b u t i o n s of these two d e n s i t y f r a c t i o n s are d i f f e r e n t . As d i s c u s s e d i n s e c t i o n s 8.1.2 and 8.2.2.2, the 1.30 s p e c i f i c g r a v i t y f r a c t i o n has a much wider spectrum of s u r f a c e t e n s i o n s among c o a l p a r t i c l e s . The 5 % methanol c o n c e n t r a t i o n r e g i o n shows i n c r e a s e d f l o a t a b i l i t y of p a r t i c l e s composed mainly of i n e r t i n i t e w i t h v i t r i n i t e (I > V) and v i t r i n i t e w i t h i n e r t i n i t e (V > I) , ( F i g u r e 8.2.21). The p a r t i c l e s f l o a t i n g a t 10 % methanol c o n c e n t r a t i o n are the most abundant i n t h i s d e n s i t y f r a c t i o n . T h i s c o i n c i d e s w i t h the maximum f l o a t a b i l i t y f o r f r e e v i t r i n i t e g r a i n s as found from m i c r o s c o p i c a n a l y s i s . C o a l g r a i n s f l o a t i n g a t 20 % methanol c o n c e n t r a t i o n are found t o be e n r i c h e d i n f r e e v i t r i n i t e and p s e u d o v i t r i n i t e , which may i n d i c a t e t h a t t h i s s u r f a c e t e n s i o n was the c r i t i c a l s u r f a c e t e n s i o n f o r those p a r t i c l e s . T h i s range i s a h i g h f l o a t a b i l i t y r e g i o n , and the most 171 hydrophobic p a r t i c l e s would o n l y be f l o a t a b l e a t t h i s s u r f a c e t e n s i o n . T h i s i m p l i e s t h a t p s e u d o v i t r i n i t e has h i g h e r h y d r o p h o b i c i -t y than o t h e r macerals, which i s i n agreement w i t h the l a r g e s t c o n t a c t angle measured f o r t h i s maceral (Arnold and Apian, 1989). The 1.30-1.35 f r a c t i o n has the m a j o r i t y of p a r t i c l e s f l o a t i n g a t 5 % methanol c o n c e n t r a t i o n . From the m i c r o s c o p i c a n a l y s i s i t was observed t h a t , p a r t i c l e s f l o a t i n g a t t h i s s u r f a c e t e n s i o n are v i t r i n i t e w i t h i n e r t i n i t e (V > I and I > V) w i t h fewer f r e e v i t r i n i t e g r a i n s ( F i g u r e 8.2.22). There i s some i n c r e a s e d amount of f r e e v i t r i n i t e f l o a t i n g a t 10 % methanol c o n c e n t r a t i o n . For t h i s d e n s i t y f r a c t i o n i t i s more d i f f i c u l t t o observe pro-nounced t r e n d s i n maceral f l o a t a b i l i t y , as the m a j o r i t y of p a r t i c l e s a re of a more complex nature. The c r i t i c a l s u r f a c e t e n s i o n f o r the m a j o r i t y of p a r t i c l e s i n t h i s d e n s i t y l i e s a t 5 % methanol c o n c e n t r a t i o n , c o r r e s p o n d i n g t o 62 dyne/cm. For both d e n s i t y f r a c t i o n s , the y i e l d of f l o a t i n g p a r t i c l e s i s independent of ash content, and t h e r e f o r e i t i s p o s s i b l e t o assume t h a t r e s u l t i n g f l o a t a b i l i t y and w e t t a b i l i t y d i s t r i b u t i o n s a re caused by v a r i a t i o n s i n the p e t r o g r a p h i c c o m p o s i t i o n o f c o a l g r a i n s . From w e t t a b i l i t y d i s t r i b u t i o n s of l i t h o t y p e s one can n o t i c e t h a t , l i t h o t y p e s w i t h i n c r e a s e d i n e r t i n i t e c ontent (banded d u l l and banded c o a l ) have the r e g i o n f o r the f l o a t a b i l i t y ( f i l m f l o t a t i o n ) o f m a j o r i t y of p a r t i c l e s s h i f t e d towards lower methanol c o n c e n t r a t i o n . The m i n e r a l matter content does not appear t o have an i n f l u e n c e on the f l o a t a b i l i t y of the p a r t i c l e s . The ash content 172 of f l o a t i n g f r a c t i o n s a t d i f f e r e n t s u r f a c e t e n s i o n s i s almost c o n s t a n t over the s t u d i e d range ( F i g u r e 8.1.3 a,b). Banded b r i g h t and b r i g h t l i t h o t y p e s have t h e i r m a j o r i t y o f p a r t i c l e s f l o a t i n g a t 10 and 20 % methanol c o n c e n t r a t i o n , whereas banded d u l l and banded c o a l l i t h o t y p e p a r t i c l e s are f l o a t i n g a t 5 and 10 % methanol c o n c e n t r a t i o n s . In g e n e r a l , f o r the examined c o a l s , v i t r i n i t e e n r i c h e d samples have maximum p a r t i c l e s f l o a t i n g a t 10 % methanol c o n c e n t r a -t i o n (55 dyne/cm). The maximum f l o a t a b i l i t y r e g i o n f o r pseudo-v i t r i n i t e i s a t 20 % methanol c o n c e n t r a t i o n (45 dyne/cm), and f o r composite v i t r i n i t e and i n e r t i n i t e p a r t i c l e s i t i s a t lower methanol c o n c e n t r a t i o n (2 t o 5 methanol c o n c e n t r a t i o n s t h a t i s a t 62-68 dyne/cm). 8.4 Comparison of the w e t t a b i l i t y and f l o a t a b i l i t y d i s t r i b u t i o n s W e t t a b i l i t y d i s t r i b u t i o n s of c o a l p a r t i c l e s f o r two composite samples, d e n s i t y and s i z e f r a c t i o n s , were examined and compared t o the f l o a t a b i l i t y d i s t r i b u t i o n s . S i n c e w e t t a b i l i t y and f l o a t a b i l i t y a re not n e c e s s a r i l y synonymous, f l o a t a b i l i t y e s t a b -l i s h e d under dynamic c o n d i t i o n s , does not have t o be i d e n t i c a l t o the w e t t a b i l i t y , d e r i v e d from the s t a t i c t e s t such as f i l m f l o t a t i o n . F i l m f l o t a t i o n , as implemented by Fuerstenau e t a l . , -(1985; 1987; 1987a; 1988a,b), p r o v i d e s the means t o determine the 173 average v a l u e o f c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y f o r an assembly of hydrophobic p a r t i c l e s . For heterogeneous p a r t i c l e s the minimum and maximum s u r f a c e t e n s i o n are the v a l u e s r e p r e s e n t i n g the range of the c r i t i c a l s u r f a c e t e n s i o n s f o r a g i v e n assembly of p a r t i c l e s . A band of w e t t a b i l i t y l i n e s on the adhesion t e n s i o n diagram w i l l be produced i n s t e a d of one w e t t a b i l i t y l i n e (Hornsby, 1981; Hornsby and L e j a , 1983; see F i g u r e 8.4.1 a,b). In some cases t h e band may be extended t o 0 = 0. Only f o r v e r y homogeneous s o l i d s , one w e t t a b i l i t y l i n e c h a r a c t e r i z e s the c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y . In f i l m f l o t a t i o n , p a r t i c l e s are p l a c e d on the s u r f a c e of the s o l u t i o n and p a r t i c l e s a re imbibed a t a g i v e n s u r f a c e t e n s i o n when t h e i r c o n t a c t angle j u s t reached zero. Due t o g r a v i t a t i o n a l e f f e c t s , s i n k i n g u s u a l l y occurs a t c o n t a c t angles s l i g h t l y g r e a t e r than zero (Fuerstenau, 1988b). The v a l u e of 6C W i s always h i g h e r than z e r o . The boundary of w e t t a b i l i t y f o r an assembly of p a r t i c l e s can be found from the i n t e r c e p t o f the adhesion t e n s i o n l i n e w i t h 8C W, the c r i t i c a l c o n t a c t angle of w e t t a b i l i t y . The t h e o r e t i c a l example i l l u s t r a t i n g t he Y Cmin a n d Y c m a x o f w e t t a b i l i t y , f o r the examined c o a l samples, i s d e p i c t e d i n F i g u r e 8.4.1, a,b. The v a l u e s of Y Cmin a n d Y Cmax a r e t a k e n from the estimated w e t t a b i l i t y ranges f o r t he < 1.30 and 1.30-1.35 d e n s i t y f r a c t i o n s (see s e c t i o n 8.3.1). In s m a l l - s c a l e f l o t a t i o n under a c t u a l f l o t a t i o n c o n d i -t i o n s , a p a r t i c l e i s f l o a t a b l e o n l y i f i t s u c c e s s f u l l y a t t a c h e s t o a i r bubble and i s l i f t e d w i t h i t out of the f l o t a t i o n s l u r r y . For t h i s t o occur, not o n l y does p a r t i a l dewetting of the p a r t i c l e 174 F i g u r e 8.4.1 The t h e o r e t i c a l adhesion t e n s i o n diagram f o r the examined c o a l . L i m i t s f o r w e t t a b i l i t y and f l o a t a b i l i t y f o r : (a) the <1.30 d e n s i t y f r a c t i o n ; (b) the 1.30-1.35 d e n s i t y f r a c t i o n . 175 s u r f a c e have t o be hydrodynamically p o s s i b l e , but s e v e r a l other c r i t e r i a have t o be s a t i s f i e d (Laskowski, 1974; Trahar and Warren, 1976). The p a r t i c l e must c o l l i d e w i t h a bubble, the adhesion must occur w i t h i n time of c o n t a c t , and the p a r t i c l e - b u b b l e aggregate must be s t a b l e enough t o a l l o w f o r the s e p a r a t i o n from the f l o t a t i o n s l u r r y , as d i s c u s s e d i n s e c t i o n 2.1.3. Under these c o n d i t i o n s , s i z e and d e n s i t y may become l i m i t i n g parameters i n f l o a t a b i l i t y . S i n c e , i n both s m a l l - s c a l e and f i l m f l o t a t i o n t e s t s , o n l y narrow s i z e and d e n s i t y f r a c t i o n s were used, such a comparison i s more c r e d i b l e . The c o n t a c t angle, 6 C f , c o r r e s p o n d i n g t o Y C f m i n and Ycfmax (estimated from f l o a t a b i l i t y d i s t r i b u t i o n s , s e c t i o n 8.3.1), f o r the examined samples i s much g r e a t e r than the one c o r r e s p o n d i n g t o Y Cwmin a n d YCwmax ( c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y ) . T h i s would i n d i c a t e t h a t the minimum c o n t a c t angle of f l o a t a b i l i t y , 6 C f / i s h i g h e r than minimum c o n t a c t angle of w e t t a b i l i t y © c w , f o r the examined c o a l samples ( F i g u r e 8.4.1 a,b). A comparison of the w e t t a b i l i t y and f l o a t a b i l i t y d i s t r i b u t i o n s of the low-ash composite sample ( F i g u r e 8.1.1,b and 8.2.4,b) i n d i c a t e s v e r y s i m i l a r d i s t r i b u t i o n s of c o a l p a r t i c l e s v e r s u s s u r f a c e t e n s i o n s . The y i e l d of f l o a t i n g p a r t i c l e s , a t any g i v e n methanol c o n c e n t r a t i o n i n the w e t t a b i l i t y d i s t r i b u t i o n ( f i l m f l o t a t i o n ) , i s much lower than f o r the same p a r t i c l e s i n the f l o a t a b i l i t y d i s t r i b u t i o n ( s m a l l - s c a l e f l o t a t i o n ) . The ash content of the f l o t a t i o n p roducts from f i l m f l o t a t i o n decreases as the methanol c o n c e n t r a t i o n i n c r e a s e s (Table F . l . l ) . The same t r e n d i s n o t i c e d f o r the f l o a t s o b t a i n e d from s m a l l - s c a l e f l o t a t i o n (Table 176 E . l . l ) . The ash c ontent of the f l o a t i n g p r o d u c t s o b t a i n e d from both types of f l o t a t i o n appears t o be v e r y s i m i l a r . The s m a l l - s c a l e f l o t a t i o n shows more s e l e c t i v i t y ; f o r the same ash content the y i e l d s of f l o a t i n g p a r t i c l e s are h i g h e r i n s m a l l - s c a l e f l o t a t i o n than th e y i e l d s of f l o a t i n g f r a c t i o n s i n f i l m f l o t a t i o n experiment. Lower s e l e c t i v i t y of f i l m f l o t a t i o n i s b e l i e v e d t o be due t o the entrapment of s m a l l p a r t i c l e s w i t h i n the hydrophobic f i l m . The w e t t a b i l i t y and f l o a t a b i l i t y d i s t r i b u t i o n s of d e n s i t y f r a c t i o n s can be compared (see F i g u r e s 8.1.2 and 8.2.7). Trends i n the w e t t a b i l i t y and f l o a t a b i l i t y d i s t r i b u t i o n s f o r the d e n s i t y f r a c t i o n s are v e r y s i m i l a r . F i l m f l o t a t i o n i s a g a i n l e s s s e l e c t i v e than s m a l l - s c a l e f l o t a t i o n , over the s t u d i e d range of methanol c o n c e n t r a t i o n s . For the dynamic f l o t a t i o n c o n d i t i o n s ( s m a l l - s c a l e f l o t a t i o n ) i n h i g h methanol c o n c e n t r a t i o n s the s m a l l - l i g h t hydrophobic p a r t i c l e s are more s e l e c t i v e l y s e p a r a t e d than i n the f i l m f l o t a t i o n . To d e l i n e a t e the dependance of both methods on the s i z e of f l o a t i n g p a r t i c l e s , the s m a l l - s c a l e and f i l m f l o t a t i o n s were c a r r i e d out w i t h f o u r d i f f e r e n t s i z e f r a c t i o n s as d e s c r i b e d i n s e c t i o n s 8.1 and 8.2. D i f f e r e n t s i z e f r a c t i o n s were o b t a i n e d from the v i t r a i n l i t h o t y p e ( n a t u r a l c o n c e n t r a t e of v i t r i n i t e ) t o a v o i d the i n f l u e n c e of p e t r o g r a p h i c composition on w e t t a b i l i t y and f l o a t a b i l i t y d i s t r i b u t i o n s ( F i g u r e 8.1.4 and 8.2.3). I t i s e v i d e n t t h a t s m a l l - s c a l e f l o t a t i o n i s more dependant on the s i z e of the f l o a t i n g p a r t i c l e s than f i l m f l o t a t i o n . 177 CHAPTER 9 CONCLUSIONS The aim of the study was t o show an i n f l u e n c e of p e t r o g r a p h i c composition on the s u r f a c e p r o p e r t i e s of c o a l p a r t i c l e s . Concepts of c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y and c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y have been used t o i n v e s t i g a t e the f l o a t a b i l i t y and w e t t a b i l i t y of c o a l samples wi t h v a r y i n g p e t r o g r a p h i c composition. 9.1 General The h e t e r o g e n e i t y of a c o a l p a r t i c l e s u r f a c e was examined m i c r o s c o p i c a l l y . I t was shown t h a t s u r f a c e h e t e r o g e n e i t y of c o a l i s s t r o n g l y i n f l u e n c e d by the amount of u n l i b e r a t e d m i n e r a l matter, degree of o x i d a t i o n and p e t r o g r a p h i c composition. The p e t r o g r a p h i c c o n t r i b u t i o n t o the s u r f a c e heterogene-i t y , as determined from w e t t a b i l i t y and f l o a t a b i l i t y t e s t s , becomes dominant o n l y when the e f f e c t of other f a c t o r s such as m i n e r a l matter content, degree of o x i d a t i o n and s i z e of c o a l p a r t i c l e s are n e g l i g i b l e . The p e t r o g r a p h i c components r e p r e s e n t o n l y d i f f e r e n t degrees of the h y d r o p h o b i c i t y , whereas parameters such as m i n e r a l matter and o x i d a t i o n r e p r e s e n t s t r o n g l y h y d r o p h i l i c s i t e s on the s u r f a c e of c o a l p a r t i c l e . Under c e r t a i n c o n d i t i o n s , w e t t a b i l i t y and f l o a t a b i l i t y 178 d i s t r i b u t i o n s of p a r t i c l e s a c c o r d i n g t o t h e i r c r i t i c a l s u r f a c e t e n s i o n are shown t o be s e n s i t i v e t o v a r i a t i o n i n p e t r o g r a p h i c c o m p o s i t i o n of c o a l g r a i n s . Once p e t r o g r a p h i c composition becomes a s i g n i f i c a n t f a c t o r i n h y d r o p h o b i c i t y , the y i e l d - a s h r e l a t i o n s h i p i s independent of the m i n e r a l matter content. P e t r o g r a p h i c h e t e r o g e n e i t y of c o a l might not n e c e s s a r i l y match i t s s u r f a c e h e t e r o g e n e i t y , i t c e r t a i n l y c o n t r i b u t e s towards i t s c o m p l e x i t y . 9.2 W e t t a b i l i t y d i s t r i b u t i o n of v a r i o u s c o a l p a r t i c l e s W e t t a b i l i t y d i s t r i b u t i o n s were o b t a i n e d from f i l m f l o t a t i o n f o r a number of c o a l samples v a r y i n g i n p e t r o g r a p h i c c o m p o s i t i o n . The l i t h o t y p e s and the two lowest d e n s i t y f r a c t i o n s were used i n the t e s t s , s i n c e they d i s p l a y e d the most pronounced change i n p e t r o g r a p h i c composition of c o a l g r a i n s . A l l these samples have low ash content t o a v o i d the c o n t r i b u t i o n of h y d r o p h i l i c m i n e r a l s t o the s u r f a c e p r o p e r t i e s of the c o a l p a r t i c l e s . In w e t t a b i l i t y t e s t s , p a r t i c l e s were sep a r a t e d a c c o r d i n g t o t h e i r c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y . The mean va l u e of t h e c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y , Y"c/ w a s estimated from th e w e t t a b i l i t y d i s t r i b u t i o n s f o r each of the samples. For samples e n r i c h e d i n v i t r i n i t e , the average v a l u e of Y Cw' •"•s a l w a Y s lower than t h a t f o r samples h i g h i n i n e r t i n i t e . S i n c e , each of the samples s t i l l r e p r e s e n t s an assembly of p a r t i c l e s of v a r y i n g 179 s u r f a c e t e n s i o n s , t h e minimum, Y Cmin' a n ( * m a x i m u m / Y Cmax' v a l u e s o f the c r i t i c a l s u r f a c e t e n s i o n o f w e t t a b i l i t y a re observed. These v a l u e s a r e the same f o r the two lowest d e n s i t y f r a c t i o n s , and f o r a l l t h e l i t h o t y p e s and they may i n d i c a t e the range of w e t t a b i l i t y f o r t h e s e p a r t i c l e s . W e t t a b i l i t y d i s t r i b u t i o n i s almost independent of the s i z e of f l o a t i n g p a r t i c l e s . F i l m f l o t a t i o n t e s t i s found t o be l e s s s e l e c t i v e than the s m a l l - s c a l e f l o t a t i o n t e s t , due t o d i f f e r e n t hydrodynamic c o n d i t i o n s . 9.3 F l o a t a b i l i t y d i s t r i b u t i o n s of v a r i o u s c o a l p a r t i c l e s In the f l o a t a b i l i t y t e s t s , which were c a r r i e d out as s m a l l - s c a l e f l o t a t i o n t e s t s (P/S c e l l ) , p a r t i c l e s were separated a c c o r d i n g t o t h e i r c r i t i c a l s u r f a c e t e n s i o n o f f l o a t a b i l i t y , Y C f The f l o a t a b i l i t y and n o n - f l o a t a b i l i t y ranges were a g a i n c h a r a c t e r -i z e d by the v a l u e s of Ycf™ 1 1" 1' a n c * Y c f m a X * These ranges, however, are d i f f e r e n t f o r each sample and much narrower, than the ranges i n c r i t i c a l s u r f a c e t e n s i o n of w e t t a b i l i t y , e s p e c i a l l y f o r samples of v a r y i n g p e t r o g r a p h i c composition. F l o a t a b i l i t y d i s t r i b u t i o n s a re found t o be independent of the l i b e r a t e d m i n e r a l matter content. Only when t h e m i n e r a l matter o c c u r r e d as u n l i b e r a t e d from the composite c o a l g r a i n s i t e f f e c t e d the f l o a t a b i l i t y d i s t r i b u t i o n s . The y i e l d - a s h r e l a t i o n s h i p s of f l o t a t i o n p roducts are independent of m i n e r a l matter content f o r the two l i g h t e s t d e n s i t y 180 f r a c t i o n s . For the composite samples the y i e l d - a s h r e l a t i o n s h i p s are o n l y independent o f the m i n e r a l matter i n the range between maximum and minimum of f l o a t a b i l i t y . F l o a t a b i l i t y d i s t r i b u t i o n s of the p a r t i c l e s from d i f f e r e n t d e n s i t y f r a c t i o n s are found t o d i f f e r s i g n i f i c a n t l y i n shape. T h i s i n d i c a t e s t h a t these f r a c t i o n s c o n t a i n e d p a r t i c l e s of d i f f e r e n t s u r f a c e p r o p e r t i e s . M i c r o s c o p i c a n a l y s e s confirmed v a r i a t i o n i n p e t r o g r a p h i c composition o f c o a l g r a i n s i n the s t u d i e d d e n s i t y f r a c t i o n s . In g e n e r a l , as observed under the microscope, samples e n r i c h e d i n f r e e v i t r i n i t e have t h e i r maximum f l o a t a b i l i t y a t 10 % methanol c o n c e n t r a t i o n (54 dyne/cm). T h i s v a l u e i s i n good agreement w i t h the y c v a l u e s f o r v i t r a i n samples r e p o r t e d elsewhere ( E i s s l e r , 1962). Samples, where c o a l p a r t i c l e s a re of more composite nature ( v i t r i n i t e w i t h i n e r t i n i t e ) , have the maximum f l o a t a b i l i t y s h i f t e d towards l o w - f l o a t a b i l i t y r e g i o n s (low-methanol c o n c e n t r a t i o n ) . The p s e u d o v i t r i n i t e g r a i n s are found t o have t h e i r maximum f l o a t a b i l i t y a t 20 % methanol c o n c e n t r a t i o n (45 dyne/cm) t h a t i s a t h i g h - f l o a t a b i l i t y r e g i o n s i n d i c a t i n g t he h i g h e s t h y d r o p h o b i c i t y . T h i s i s found t o be i n an agreement wi t h the g r e a t e r v a l u e s of c o n t a c t angle measured on t h i s maceral, as r e p o r t e d i n the l i t e r a t u r e (Arnold and Apian, 1989). A comparison of the w e t t a b i l i t y and f l o a t a b i l i t y d i s t r i b u t i o n s c o n f i r m s , t h a t f l o t a t i o n response of p a r t i c l e s cannot be f u l l y p r e d i c t e d from w e t t a b i l i t y c h a r a c t e r i s t i c s . S m a l l - s c a l e f l o t a t i o n i s shown t o be more s e l e c t i v e i n s e p a r a t i n g p a r t i c l e s 181 i n t o f r a c t i o n s of equal c r i t i c a l s u r f a c e t e n s i o n s . The f l o a t a b i l i t y d i s t r i b u t i o n s as o b t a i n e d from the s m a l l - s c a l e f l o t a t i o n are more dependant on the s i z e of f l o a t i n g p a r t i c l e s . 182 CHAPTER 10 RECOMMENDATIONS The p r e s e n t study i s b e l i e v e d t o be the f i r s t one t o d e r i v e c r i t i c a l s u r f a c e t e n s i o n v a l u e s o f macerals by techn i q u e s d i f f e r e n t than c o n t a c t angle. N a t u r a l c o n c e n t r a t e s o f macerals were used t o as s e s s the r e l a t i o n s h i p between w e t t a b i l i t y and p e t r o g r a p h i c composition of c o a l . Due t o i n s u f f i c i e n t q u a n t i t i e s o f the l i t h o t y p e s ( n a t u r a l maceral c o n c e n t r a t e s ) , d e t a i l e d s t u d i e s of f l o a t a b i l i t y o f these samples were l i m i t e d . T h e r e f o r e the f o l l o w i n g recomendations are proposed: - l a r g e r q u a n t i t i e s of l i t h o t y p e s w i l l be r q u i r e d t o study t h e i r response t o the s m a l l - s c a l e f l o t a t i o n i n methanol s o l u t i o n s ; - more comprehensive m i c r o s c o p i c a n a l y s i s o f f l o t a t i o n p r o d u c t s s h o u l d be a p p l i e d t o assess q u a n t i t e v e l y r e c o v e r y of v a r i o u s c o a l g r a i n s i n f l o t a t i o n i n methanol s o l u t i o n s ; - the s e l e c t i v e f l o t a t i o n o f macerals should be s t u d i e d u s i n g t h e i r e s t i m a t e d v a l u e s of c r i t i c a l s u r f a c e t e n s i o n of f l o a t a b i l i t y ; - t he c l a y p e p t i z i n g e f f e c t i n h i g h methanol c o n c e n t r a t i o n s s h o u l d be i n v e s t i g a t e d i n g r e a t e r d e t a i l . 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Yarar, B., 1985, Gamma f l o t a t i o n : a new approach t o f l o t a t i o n , u s i n g l i q u i d - v a p o r s u r f a c e t e n s i o n c o n t r o l ; F r o t h F l o t a t i o n . Proc.  of the 2nd L a t i n - m e r i c a n Congress on F r o t h F l o t a t i o n . Conception, C h i l e , 19-23 August 1985, pp.41-63. Ye, Y., and M i l l e r , J.D., 1988, B u b b l e / p a r t i c l e c o n t a c t time i n the a n a l y s i s of c o a l f l o t a t i o n ; Coal P r e p a r a t i o n . 5. pp.147-166. Yoon, R.H., and L u t t r e l l , N.G.H., 1989, The e f f e c t o f bubble s i z e on the f i n e p a r t i c l e f l o t a t i o n ; F r o t h i n g i n F l o t a t i o n . J.S. Laskowski, ed., Gordon and Breach, N.Y., pp.101-121. Young, Th., 1805, An essay on the cohesion of f l u i d s ; Trans. Roy.  Soc.. 95. pp.65-87. Zisman W.A. 1964, R e l a t i o n of the e q u i l i b r i u m c o n t a c t angle t o l i q u i d and s o l i d c o n s t i t u t i o n ; American Chemical S o c i e t y . Contact Angle, W e t t a b i l i t y and Adhesion, Washington, D.C, vo l . 4 3 , pp.1 -51. 197 APPENDIX A PETROGRAPHIC DATA A . l P e t r o g r a p h i c a n a l y s e s Maceral a n a l y s e s of f i v e l i t h o t y p e samples, as d e s c r i b e d i n s e c t i o n 7.3.1, are g i v e n i n T a b l e A . l The v i t r i n i t e group was s u b d i v i d e d i n t o t e l o c o l l i n i t e , p s e u d o v i t r i n i t e , d e s m o c o l l i n i t e and v i t r o d e t r i n i t e . The i n e r t i n i t e group c o n s i s t e d of s e m i f u s i n i t e , f u s i n i t e and o t h e r i n e r t s . The r e f l e c t a n c e v a l u e s were i n c l u d e d f o r a l l l i t h o t y p e s except f o r f u s a i n ( f i b r o u s ) . The f u s a i n sample was mainly composed of f u s i n i t e p a r t i c l e s w i t h v e r y few v i t r i n i t e s u i t a b l e f o r t a k i n g r e l i a b l e r e f l e c t a n c e measurements. Maceral composition of the d e n s i t y f r a c t i o n s are shown i n T a b l e A.2. In these a n a l y s e s a t o t a l of 300 p o i n t s was counted f o r each p e l l e t r e p r e s e n t i n g c o a l sample. R e s u l t s are r e p o r t e d on a m i n e r a l - m a t t e r - f r e e b a s i s . In these a n a l y s e s v i t r i n i t e and pseudo-v i t r i n i t e r e p r e s e n t v i t r i n i t e group macerals, i n e r t i n i t e group i s d i v i d e d i n t o s e m i f u s i n i t e , f u s i n i t e and i n e r t o d e t r i n i t e macerals. I n e r t o d e t r i n i t e i n c l u d e s a l l o t h e r i n e r t s found i n the sample. In g r a i n type a n a l y s i s (Table A. 3) g r a i n s were counted a c c o r d i n g t o the set-up c a t e g o r i e s (see s e c t i o n 7.3.1). T a b l e s A.4 and A. 5 i n c l u d e g r a i n - t y p e a n a l y s i s of f l o a t s and r e j e c t s from f l o t a t i o n of d e n s i t y f r a c t i o n s d e r i v e d from s m a l l - s c a l e f l o t a t i o n . 198 Bright Banded Bright Banded Dull Banded Coal Fibrous volume % volume % volume % volume % volume % Telocollinite 32.00 24.0 16.00 23.00 27.0 Pseudovitrinite 10.00 7.0 9.00 0.00 5.0 Desmocollinite 28.00 35.0 30.00 30.00 12.0 Vitrodetrinite 0.00 0.0 1.00 1.00 0.0 Total Vitrinite 70.00 66.0 56.00 54.00 44.0 Semifusinite 11.00 10.0 22.00 21.00 29.0 Fusinite 10.00 16.0 11.00 11.00 21.0 Other Inerts 7.00 5.0 10.00 11.00 6.0 Total Inertinite 28.00 31.0 43.00 43.00 56.0 Total Liptinite 2.00 2.0 0.00 3.00 1.0 Inerts/Vitrinite 0.40 0.5 0.77 0.80 1.3 Ro mean 1.06 1.0 0.88 1.04 T a b l e A . l Maceral a n a l y s e s of f i v e l i t h o t y p e samples, (from p o i n t -c o u n t i n g technique) Density fraction <1.30 Density fraction 1.30-1.35 Density fraction 1.35-1.40 Density fraction 1.40-1.45 Density fraction 1.45-1.50 Density fraction >1.50 Vrtrinit© 95 80 70 69 70 80 Semifusinite 3 10 15 15 10 5 Fusinite 1 4 6 8 16 10 Inertodetrinite 1 6 9 8 4 5 Total Inertinite 5 20 30 31 30 20 T a b l e A.2 Maceral composition of d e n s i t y f r a c t i o n s (from p o i n t -c o u n t i n g t e c h n i q u e ) . Density fraction <1.30 Density fraction 1.30-1.35 Density fraction 1.35-1.40 Density fraction 1.40-1.45 Density fraction 1.45-1.50 Density fraction >1.50 Free vitrinite 60 46 29 26 25 49 Pseudovitrinite 23 6 2 2 1 0 Vitr> Inert 13 28 39 41 44 31 Total vitrinite 96 80 70 69 70 80 Inertod, lnert>Vitr 1 6 9 8 4 5 Fusinite 0 4 6 8 16 10 Semifusinite 3 10 15 15 10 5 Total inetrinite 4 20 30 31 30 20 *Oxidized vitrinite 3 4 3 3 4 3 *Vrtrinite+MM 4 24 64 100 100 100 * on the basis of total vitrinite T a b l e A.3 D i s t r i b u t i o n of g r a i n s i n d e n s i t y f r a c t i o n s . D e s c r i p t i o n i n terms of a s s o c i a t i o n with m i n e r a l matter and v i s i b l e o x i d a t i o n . Concentrate 5% meth cone Rejects 5% meth cane. Concentrate 10% meth cone Rejects 10% meth cone Concentrate 20% meth cone. Rejects 20% meth cone Concentrate 30% meth cone. Rejects 30% meth cone Free vitrinite 59 53 81 71 69 71 77 29 Pseudovitrinite 13 19 8 12 16 9 9 1 Vitr>lnert 19 4 8 12 12 12 11 47 Total vitrinite 91 76 97 95 97 92 97 77 Inertod, Inert >V1tr 8 1 1 0 2 5 0 3 Fusinite 0 1 1 0 1 0 0 3 Semifusinite 1 2 1 3 0 3 3 17 Total inetrinite 8 4 3 3 3 8 3 23 "Oxidized vitrinite 3 2 7 2 10 •Vitrinite+MM 6 18 3 0 3 1 54 * on the basisof total vitrinite T able A. 4 G r a i n - t y p e a n a l y s i s of the f l o a t s and r e j e c t s f o r 1.30 s p e c i f i c g r a v i t y , a t d i f f e r e n t methanol c o n c e n t r a t i o n s . Concert! ate 5% meth cone Rejects 5% meth cone Concentrate 10% meth core Rejects 10% meth cone Concentrate 20% meth cone Rejects 20% meth cane Concentrate 30% meth cone. Rejects 30% meth cane Free vitrinite 32 32 35 23 30 47 66 29 Pseudovitrinite 1 1 0 2 2 1 4 1 V1tr> Inert 45 42 45 50 39 15 4 47 Total vitrinite 78 75 80 75 71 63 74 77 Inertod, Inert >Vitr 5 1 3 4 5 5 4 3 Fusinite 2 2 2 4 3 2 2 3 Semifusinite 15 22 15 17 21 30 20 17 Total inetrinite 22 25 20 25 29 37 26 23 'Oxidized vitrinite 3 10 1 12 3 15 4 10 *Vitrinite+MM 31 59 23 66 32 90 49 54 * on the basis of total vitrinite T a b l e A.5 G r a i n - t y p e a n a l y s i s of the f l o a t s and r e j e c t s f o r 1.30-1.35 s p e c i f i c g r a v i t y , a t d i f f e r e n t methanol c o n c e n t r a t i o n s . APPENDIX B SURFACE TENSION MEASUREMENT B . l Du Nouy r i n g method The s t a t i c s u r f a c e t e n s i o n of the methanol s o l u t i o n s was measured by the Du Nouy r i n g method (Adamson, 1967) . In t h i s method a p l a t i n u m wire r i n g i s immersed i n the l i q u i d s o l u t i o n and the f o r c e n e c e s s a r y t o l i f t and detach a f i l m o f the l i q u i d i s measured. The f o r c e o f detachment W i s d e s c r i b e d as: W = 2*R y + 2n(R + 2r) y + (* (R + 2 r ) 2 - irR 2)2y and Y = W/2TI (R + r) (1 + 2r) The dimensions a t the plane o f breakage, R and r , are r e l a t e d t o the dimensions o f the r i n g , and the mass of the l i q u i d l i f t e d d u r i n g t h e detachment ( F i g u r e B . l ) . The maximum weight W cau s i n g r i n g t o se p a r a t e i s r e l a t e d t o the s u r f a c e t e n s i o n through a c o r r e c t i o n f a c t o r F. The c o r r e c t i o n f a c t o r i s c a l c u l a t e d from the equ a t i o n g i v e n below: (F - a ) 2 = (4b/n-2 * 1/R2) * y' / d w + C where a = 0.7250 b = 0.00090705 C = 0.04534 - 1.679 (r/R) cLy - d e n s i t y o f water Y - apparent s u r f a c e t e n s i o n 204 a b F i g u r e B . l . l D i s t e n t i o n of s u r f a c e f i l m d u r i n g s u r f a c e t e n s i o n measurement ( a ) ; c o n d i t i o n of s u r f a c e f i l m a t b r e a k i n g p o i n t (b). 205 Y = Y ' * F P r i o r t o the s u r f a c e t e n s i o n measurement, the c a l i b r a -t i o n o f the tensiometer was performed u s i n g known weights. The weights were p l a c e d on the r i n g and the d i a l r o t a t e d t o keep the index l e v e l . The r e s u l t s were graphed as the d i a l v a l u e s versus apparent s u r f a c e t e n s i o n y' by u s i n g the r e l a t i o n s h i p y' = Mg/2L M i s weight p l a c e d on r i n g , i n grams g i s the g r a v i t y v a l u e cm/sec 2 L mean c i r c u m f e r e n c e of the r i n g y' apparent s u r f a c e t e n s i o n , dyne/cm, d i a l r e a d i n g For each measurement, 50 ml of prepared methanol s o l u t i o n i s poured i n a c l e a n sample c o n t a i n e r and p l a c e d c a r e f u l l y on the l e v e l e d p l a t f o r m of the tensiometer. The p l a t f o r m i s r a i s e d u n t i l the r i n g i s immersed i n the s o l u t i o n t o a depth not exceeding 6 mm. Then the p l a t f o r m i s lowered s l o w l y , i n c r e a s i n g the torque of the r i n g by keeping the p o i n t e r on the zero mark. Proceeding s l o w l y w i t h the adjustment, the d i a l r e a d i n g a t which the r u p t u r e of the s o l u t i o n f i l m took p l a c e i s recorded. From the c a l i b r a t i o n the apparent v a l u e o f the s u r f a c e t e n s i o n i s read, and u s i n g the 206 Concentration Tensiometer (F-A)~2 Correction Actual value % Methanol Reading (dyne/cm) Factor (dyne/cm) 0 74.1 0.0440 0.935 69.3 10 58.9 0.0378 0.920 54.2 20 49.6 0.0341 0.910 45.1 30 43.1 0.0314 0.902 38.9 50 36.1 0.0286 0.894 32.3 70 30.8 0.0265 0.888 27.3 100 24.5 0.0239 0.880 21.6 Surface Tension Measurements for methanol/water T a b l e B . l The s u r f a c e t e n s i o n v a l u e s f o r methanol s o l u t i o n s used i n experiments. The v a l u e s of s u r f a c e t e n s i o n f o r the methanol s o l u t i o n s used the experiments are g i v e n i n T a b l e B . l . 208 APPENDIX C OXIDATION DETECTION - PROCEDURES C . l S t a i n t e s t f o r d e t e c t i o n o f o x i d i z e d p a r t i c l e s To d e t e c t o x i d i z e d c o a l p a r t i c l e s a s t a i n i n g procedure was used. T h i s t echnique was developed by Gray (Gray e t a l . , 1976) f o r bituminous c o a l s and s u c c e s s f u l l y used by o t h e r s M a r c h i o n i (1983). M a r c h i o n i , i n h i s study of the d e t e c t i o n o f weathering i n Western Canadian c o a l s , concluded t h a t s t a i n i n g w i t h s a f r i n i n i s the most s e n s i t i v e parameter f o r d e t e c t i n g o x i d i z e d c o a l , even more s e n s i t i v e than r h e o l o g i c a l t e s t s . T h i s t echnique i n v o l v e s immersing the p o l i s h e d c o a l p e l l e t i n a s p e c i a l l y prepared s t a i n i n g s o l u t i o n . The s o l u t i o n f o r the t e s t i s prepared by mixing 2 grams of KOH i n 50 ml of water and 1 gram of s a f r i n i n O (a r e d s t a i n ) . The c o a l p e l l e t s a re soaked f o r approximately 20 minutes, and then r i n s e d and blown d r y w i t h a i r f o r m i c r o s c o p i c examination. Unweathered c o a l g r a i n s a re u n a f f e c t e d by the e t c h s t a i n , whereas o x i d i z e d areas are accentuated by p r e f e r e n t i a l s t a i n i n g . S l i g h t l y o x i d i z e d , moderately o x i d i z e d , and h i g h l y o x i d i z e d c o a l p a r t i c l e s become l i g h t green, y e l l o w green and o l i v e - g r e e n r e s p e c t i v e l y . The number of o x i d i z e d g r a i n s was p o i n t - c o u n t e d and i n c l u d e d i n the g r a i n - t y p e a n a l y s i s of samples used i n the f l o t a t i o n t e s t s , as d e p i c t e d i n F i g u r e s 6.3.2.b, and Ta b l e s A.3, A.4 and A.5. 209 C.2 A l k a l i - e x t r a c t i o n t e s t f o r o x i d i z e d c o a l p a r t i c l e s In t h i s t e s t a s m a l l amount of r e p r e s e n t a t i v e c o a l sample i s immersed i n 100 ml of one normal NaOH s o l u t i o n and brought t o a b o i l . When the c o a l i s o x i d i z e d the humic a c i d s are produced, and as r e s u l t d i s c o l o r a t i o n of the s o l u t i o n o c c u r s . The d i s c o l o r a t i o n u s u a l l y i n c r e a s e s w i t h the i n c r e a s e i n o x i d a t i o n . A f t e r the s o l u t i o n i s f i l t e r e d , t he t r a n s m i s s i o n a t 520 nm r e l a t i v e t o a stan d a r d of one normal NaOH, r e p r e s e n t i n g 100 % l i g h t t r a n s m i s -s i o n , i s measured. A c o a l w i t h t r a n s m i t t a n c e v a l u e l e s s than 80 pe r c e n t i s c o n s i d e r e d t o be o x i d i z e d . The d e t a i l e d t e s t procedure a c c o r d i n g t o Gray (Lowenhaupt and Gray, 1980) i s g i v e n below: 1. Weigh out 1.0 gram of c o a l (+/- 0.001) of - 60 mesh c o a l . 2. T r a n s f e r the c o a l t o a 400 ml beaker c o n t a i n i n g b o i l i n g c h i p s or g l a s s beads. 3. Add 100 ml of NaOH s o l u t i o n and one drop t e r g i t o l t o the c o a l . 4. B r i n g the s o l u t i o n t o a b o i l f o r 2 t o 3 minutes, s t i r r i n g with a g l a s s rod, then remove the beaker and a l l o w the contents t o c o o l t o room temperature. 5. F i l t e r t he s l u r r y on No. 40-42 f i l t e r paper i n t o an Erlenmeyer f l a s k . T r a n s f e r the f i l t r a t e i n t o a graduated c y l i n d e r . There sh o u l d be approximately 80 per c e n t r e c o v e r y . I f not, the f i l t r a t e volume should be brought up t o 80 ml u s i n g d i s t i l l e d water. 6. Set spectrophotometer t o a wavelength of 520 nm. 210 7. A d j u s t the spectrophotometer t o read zero p e r c e n t t r a n s m i t -tance, then f i l l c u v e t t e w i t h a blank s o l u t i o n and a d j u s t r e a d i n g t o 100 p e r c e n t t r a n s m i t t a n c e . 8. U s i n g t h e same c u v e t t e as f o r the blank, t e s t the t r a n s m i t -tance o f the c o a l a l k a l i e x t r a c t and r e p o r t p e r c e n t t r a n s m i t -tance. The two p e r c e n t r e p e a t a b i l i t y s hould be allowed f o r the same o p e r a t o r i n the same l a b o r a t o r y . T a b l e C.6 The t r a n s m i t t a n c e v a l u e s f o r composite sample and d e n s i t y f r a c t i o n s (%T, p e r c e n t l i g h t t r a n s m i t t e d ) . Sample Transmittance % D e s c r i p t i o n Composite 86.1 (low-ash) < 1.30 92.0 1.30 - 1.35 95.2 1.35 - 1.40 92.6 1.40 - 1.45 90.3 1.45 - 1.50 89.5 > 1.50 84.8 T h i s procedure was f o l l o w e d when examining the degree of o x i d a t i o n o f composite and d e n s i t y f r a c t i o n samples used i n w e t t a b i l i t y - f l o a t a b i l i t y study. The t r a n s m i t t a n c e v a l u e s f o r these samples are i n c l u d e d i n Tab l e C.6. The t r a n s m i t t a n c e v a l u e f o r the 1.3 0-1.35 s p e c i f i c g r a v i t y f r a c t i o n appears t o be g r e a t e r than the one f o r the lowest d e n s i t y . A l l of the examined samples had t r a n s m i t t a n c e v a l u e s h i g h e r than 80 p e r c e n t i n d i c a t i n g an un-211 o x i d i z e d s u r f a c e . C.3 A d i f f u s e r e f l e c t a n c e FTIR te c h n i q u e . A F o u r i e r Transform I n f r a Red (FTIR) technique i s f r e q u e n t l y used t o d e t e c t o x i d a t i o n i n c o a l samples. An i n t e r e s t i n g i n f r a r e d study on n a t u r a l l y weathered c o a l was r e p o r t e d by G r i f f i t h s (1982). In a t y p i c a l i n f r a r e d s p e c t r a of c o a l t h e r e are t h r e e r e g i o n s of major i n t e r e s t . The area between 2800 t o 3200 wave numbers (cm - 1) r e p r e s e n t s the C-H aromatic and the a l i p h a t i c s t r e t c h i n g mode, the 3200 t o 3500 c m - 1 corresponds t o -OH s t r e t c h i n g frequency, and 1700 cm" 1 t o the -CO s t r e t c h i n g frequency. In a d d i t i o n , important i n f o r m a t i o n may be gathered from the o b s e r v a t i o n of ot h e r f r e q u e n c i e s , such as the r e g i o n of 1100 t o 1300 cm - 1, where p h e n o l i c and a l c o h o l i c -CO s t r e t c h i n g i s d e t e c t e d . The FTIR s p e c t r a a n a l y s i s of the c l e a n e d (low-ash) composite, lowest d e n s i t y f r a c t i o n (1.30 s.g.) and o x i d i z e d composite sample were obt a i n e d . The a n a l y s e s were performed i n the Department of M e t a l l u r g i c a l E n g i n e e r i n g , of U n i v e r s i t y of Utah, thanks t o p r o f e s s o r Jan D. M i l l e r . For the composite sample and 1.30 s p e c i f i c g r a v i t y f r a c t i o n no s i g n i f i c a n t d i f f e r e n c e ( i n c l u d i n g both peak p o s i t i o n and i n t e n s i t y ) between s p e c t r a were d e t e c t e d . The s p e c t r a f o r these samples are e n c l o s e d i n F i g u r e C l . On the othe r hand, the s p e c t r a of the samples l a b e l e d B u l l A u n o x i d i z e d (low-ash composite) and B u l l A o x i d i z e d (composite o x i d i z e d a t 212 4000 3500 3000 2500 2000 1500 1000 500 Uavenumbers BULL-UNOXID DIFFUSE REFLECTANCE FTIR SPECTRUM OF BULL'A' CLEANED UNOXIDIZED COAL 4000 3500 3000 2500 2000 1500 1000 500 Uavenumbers FEED DIFFUSE REFLECTANCE FTIR SPECTRUM OF FEED SAMPLE (BULL'A' < 1.3 G/CC) F i g u r e C l The FTIR s p e c t r a f o r two samples; composite and 1.30 s p e c i f i c g r a v i t y f r a c t i o n . 213 1.4 F i g u r e C.2 The FTIR s p e c t r a of the samples l a b e l e d B u l l A u n o x i d i z e d (low-ash composite) and B u l l A o x i d i z e d (at 200°C). 214 200°C) d i f f e r s i g n i f i c a n t l y ( F i g u r e C.2). The important p o i n t s t o note f o r the o x i d i z e d sample a r e : 1. A s i g n i f i c a n t i n c r e a s e i n the -OH s t r e t c h i n g frequency a t 3200 t o 3500 cm - 1. 2. A s i g n i f i c a n t i n c r e a s e i n the -CO s t r e t c h i n g frequency a t 1700 cm - 1. 3. A decrease i n aromatic hydrogen (out of phase v i b r a t i o n ) a t 780 t o 900 cm - 1. 4. An i n c r e a s e i n o t h e r oxygen f u n c t i o n a l i t y i n the frequency r e g i o n 1100 t o 1300 cm" 1. The s p e c t r a l data were c o l l e c t e d under the f o l l o w i n g c o n d i t i o n s : Spectrometer: Bio-Rad FTS-40 Temperature: 25°C Sampling Technique: DRIFT S p e c t r a l C o n d i t i o n s : 256 scans, 4 c m - 1 r e s o l u t i o n . The samples examined were c o n s i d e r e d t o have f r e s h u n o x i d i z e d s u r f a c e s w i t h the e x c e p t i o n of the sample l a b e l e d as o x i d i z e d . 215 APPENDIX D STATISTICAL ANALYSIS The ash c o n t e n t s of the f l o a t s and r e j e c t s w i t h the c o r r e s p o n d i n g y i e l d (wt%), from each s m a l l - s c a l e f l o t a t i o n t e s t , were used t o b a c k - c a l c u l a t e the ash content of the f e e d c o a l sample. These data are g i v e n i n Appendix E. The mean c a l c u l a t e d ash c o n t e n t s are compared w i t h the measured f e e d ash (from the proximate a n a l y s i s ) . The c a l c u l a t e d ash c o n t e n t s of the f e e d data a r e assumed t o be a normally d i s t r i b u t e d , t h e r e f o r e the c o n f i d e n c e i n t e r v a l s are c a l c u l a t e d f o r the two composite samples and t h r e e d e n s i t y f r a c t i o n s (Table D.l) 216 T a b l e D . l Comparison of the c a l c u l a t e d feed ash v a l u e s w i t h the measured ash v a l u e s . T e s t i n g the c o n f i d e n c e i n t e r v a l f o r fe e d ash co n t e n t data. Sample H i - a s h Lo-ash <1.30 1.30-1.35 1.35-1.40 Measured ash . . . 28.34 . 16.03 . . 3.01 . . 7.87 . . . . 14.89 Mean c a l c . ash . . . 28.53 . 16.06 . • 2*82 • . 7.94 . . . . 14.90 n^ . s i ' ' . 0.636 . . 0.496 . . 0.144 . . 0.183 . . . . 0.049 , ] 95% c o n f i -dence i n t e r v a l +0.36 . +0.57 . +0.20 +0.19 . . +0.051 where n^ - number of ash v a l u e s S^- st a n d a r d d e v i a t i o n 217 APPENDIX E SMALL-SCALE FLOTATION TESTS The f o l l o w i n g t a b l e s (Table E . l , E.2, E.3 and E.4) l i s t the f l o t a t i o n t e s t r e s u l t s as d e r i v e d from s m a l l - s c a l e t e s t s (P/S). The cumulative y i e l d and cumulative ash content of f l o a t s and r e j e c t s from each f l o t a t i o n run are r e c o r d e d a c c o r d i n g t o the t e s t c o n d i t i o n s . The mean cumulative y i e l d s were c a l c u l a t e d whenever r e p l i c a t e data was a v a i l a b l e . From the ash content of f l o a t s and r e j e c t s the ash content of the f e e d sample was b a c k - c a l c u l a t e d . A l l t e s t s were c a r r i e d out w i t h the+149-212 nm s i z e f r a c t i o n . 218 T a b l e E . l S m a l l - s c a l e f l o t a t i o n r e s u l t s (from t e s t s w i t h P/S c e l l ) . The y i e l d vs f l o t a t i o n time and y i e l d vs c o n d i t i o n i n g time, f o r the high-ash composite sample. Bullmoose A (-212+149um), high-ash Yield vs fl o t a t i o n time Methanol Time Yield Ash % Ash % Feed ash cone. min cone. cone. rejects c a l c M Run 1 Run 2 2 0.5 73.53 67.5 18.45 58 .02 28 .92 2. 1 78.87 77.6 19.01 61.46 27.97 2 2 81.18 79.21 20.22 61.69 28 . 02 2 3 81.44 82.04 20.89 62.66 28 . 64 2 4 84 .06 83 .18 22.91 61.4 29.05 Bullmoose A (-212+149um), high-ash Yield vs conditioning time Methanol Condit Yield Yield Yield Ash % Ash % Feed ash cone. time cone. cone. cone. cone. rejects calc'd Run 1 Run 2 Run 3 2 0 85. 8 84 . 6 83. 9 21.82 63.47 27.73 2 3 86.61 85.8 86. 3 22.36 66.54 28.28 2 5 86.76 86.8 86. 8 22.43 63 . 56 27 .88 2 10 87.09 87.51 87. 9 22.88 63.85 28.17 219 Table E.2 Smal l - sca le f l o t a t i o n r e s u l t s (from t e s t s with p / s c e l l ) . The y i e l d vs surface t ens ion , for h igh and low-ash composite sample. Bullmoose A (-212+149um), high-ash Yields vs surface tension Methanol Yield cone. cone. 2 5 10 20 30 40 Run 1 80.4 81.2 67.5 31.82 23.75 23.37 Yield cone. Run 2 81.2 78.3 66.9 31.98 22.83 21.56 Ash % Ash % Feed ash Inc.yld inc.ash cone. rejects c a l c v d 19.08 18.67 14.32 12. 66 15.27 34.21 71.37 70.09 56.41 35.88 33.62 29.33 28.34 27.99 28.49 29.26 29.92 1. 05 12.55 35.3 8.61 23.29 24.03 0.93 0.32 0.7 15.27 Bullmoose A (-212+149um), low-ash Yields vs surface tension Methanol Yield cone. cone. Ash % Ash % Feed ash Incr.yld cone. rejects calcvd 2 5 10 20 30 40 Run 1 Run 2 93.23 95.12 92.74 81.69 30.96 30.01 29.81 93.41 80.12 29.91 29.09 29.06 14.55 13 .2 12.44 12.25 10.9 11. 03 35.28 46. 64 36.99 18.17 17.86 17.76 15.95 15.63 16.94 16.34 15.77 15.75 1.1 12.17 50.47 30.44 Icr.ash 10.95 0.81 0.17 12.25 220 T a b l e E.3 S m a l l - s c a l e f l o t a t i o n r e s u l t s (from t e s t s w i t h P/S c e l l ) . The y i e l d vs s u r f a c e t e n s i o n f o r the d e n s i t y f r a c t i o n s . Bullmouse A (-212+149uin) , <1.3 s.g. P/S s m a l l s c a l e f l o t a t i o n . Y i e l d s vs s u r f a c e t e n s i o n Methanol Y i e l d Ash % Ash % Feed ash I n c r . y l d I n c r . a s h cone. cone. cone. r e j . c a l c 2 96.83 2.43 2.25 1.24 5 94.58 2.41 10. 54 2.85 21.27 0.07 10 73 .31 2.82 3.07 2.89 32.45 0.021 20 40.86 2.55 2.6 2.58 11.27 0.11 30 29.59 2.68 2.86 2.81 29.59 2.68 40 32. 67 2.62 3.12 2.96 Bullmouse A (-212+149um), 1.3-1 .35 s. g-P/S s m a l l s c a l e f l o t a t i o n . Y i e l d s vs s u r f a c e t e n s i o n Methanol Y i e l d Ash % Ash % Feed ash I n c r . y l d I n c r . a s h cone. cone. cone. r e j . c a l c 2 93.32 7.69 11.28 7.93 7.87 0.72 5 85.45 7.76 9.32 7.99 51.14 0.1 10 34 .31 7.71 8 .33 8.11 6.46 0.7 20 27.85 7.54 7.97 7.85 27.85 7.54 30 27.45 7.62 7 . 97 7.87 40 25.4 7.69 7.98 7.91 221 T a b l e E.4 S m a l l - s c a l e f l o t a t i o n r e s u l t s (from t e s t s w i t h P/S c e l l ) . The y i e l d vs s u r f a c e t e n s i o n f o r the d e n s i t y f r a c t i o n s ( c o n t i n u a t i o n ) . Bullmouse A (-212+149um), 1.35-1.40 s.g. P/S small scale f l o t a t i o n Y i e l d vs surface tension cone. )1 Y i e l d cone. Ash % cone. Ash % r e j . Feed ash% c a l c x d I n c r . y i e l d Incr.ash 2 58. 52 14. 64 15. 35 14.93 14.09 0.75 5 44. 43 14. 77 14.86 14.82 9.3 0.46 10 35. 13 15. 33 14.78 14.94 6.05 0.38 20 29. 08 15. 14 14 . 8 14.92 4.91 0. 23 30 24 . 17 18. 57 13.69 14.87 24.17 18.57 40 22. 95 18. 46 13.89 14.94 Bullmoose seam A (-212+l49um), density f r a c t i o n s P/S small-scale f l o t a t i o n Y i e l d vs surface tension 1.4-1.45 1.45-1.5 >1.50 Methanol Y i e l d Y i e l d Y i e l d cone. cone. cone. cone. 2 27.13 24.67 12.61 5 25.25 23.03 11.02 10 20.05 23.09 10.96 20 20.04 ' 23 10.43 30 20.88 22.9 9.89 222 APPENDIX F FILM FLOTATION TESTS T a b l e s F . l , E.2, and E.3 l i s t f i l m f l o t a t i o n t e s t r e s u l t s . The cumulative y i e l d and cumulative ash co n t e n t of f l o a t s and r e j e c t s from the f l o t a t i o n runs are g i v e n . The mean cumulative y i e l d s were c a l c u l a t e d whenever r e p l i c a t e data was a v a i l a b l e . A l l t e s t s were c a r r i e d out w i t h the 149-212 nm s i z e f r a c t i o n and f o l l o w i n g the f i l m f l o t a t i o n procedure as d e s c r i b e d i n s e c t i o n 7.1. 223 T a b l e F . l F i l m f l o t a t i o n r e s u l t s of the two composite samples and the d e n s i t y f r a c t i o n s . Bullmoose A (-212+l49um), composite samples F i l m f l o t a t i o n Low-ash High-ash Methanol Y i e l d Ash % Ash % Feed ash Y i e l d cone. cone. cone. r e j e c t s c a l c x d cone. 2 73.58 14.47 21.97 16.07 58.48 5 71.66 14.29 22.27 16.55 53.31 10 45.5 14.71 20.6 17.92 31.68 15 28.81 13.11 18.71 17.09 16.21 20 14.43 10.92 17.25 16.33 11.23 30 8.42 10.67 17.15 16.69 7.49 F i l m F l o t a t i o n of d e n s i t y f r a c t i o n s <1.30 1.30-1.35 1.35-1.40 1.40-1.45 >1.50 Methanol Y i e l d Y i e l d Y i e l d Y i e l d Y i e l d cone. cone. cone. cone. cone. cone. 2 69.7 55.01 19.31 10.1 6.27 5 64.54 49.51 11.95 9.66 3.87 10 43.66 15.05 10 8.29 2.84 15 22.22 12.31 8.33 5 1.69 20 10.65 8.04 4.83 3.35 30 5.74 2.56 2.87 224 T a b l e F.2 F i l m f l o t a t i o n r e s u l t s o f l i t h o t y p e s samples. B r i g h t - V i t r a i n Banded C o a l Methanol Y i e l d Y i e l d Ash % Y i e l d Ash % cone. cone. cone. cone. cone. cone. Run 1 Run 2 2 98.62 94.76 3.65 86.94 7.03 5 95.19 93.74 3.74 85.17 7.25 10 92.71 93.43 3.5 51.44 6.78 15 45.12 43.11 3.49 34.5 6.46 20 42.78 41.72 4.01 18.19 6.54 30 29.51 29.62 3.86 7.59 3.15 F i l m F l o t a t i o n F i l m F l o t a t i o n Banded B r i g h t F i b r o u s - F u s a i n Methanol Y i e l d Ash % Y i e l d Ash % cone. cone. cone. cone. cone. 2 95.47 4.56 18.71 3.56 5 92.35 4.12 16.32 3.87 10 87.52 3.94 4.29 4.01 20 35.18 3.58 1.99 3.45 30 20.54 3.57 225 T a b l e F.3 F i l m f l o t a t i o n r e s u l t s of l i t h o t y p e s samples ( c o n t i n u a -t i o n ) . F i l m F l o t a t i o n Banded D u l l Methanol Y i e l d Y i e l d Ash % cone. cone. cone. cone. Run 1 Run 2 2 92.04 91.84 5.54 5 91.56 89.31 5.06 10 42.71 41.34 5.19 20 23.75 24.37 5.12 30 15.31 16.76 3.19 226 APPENDIX G GENERAL The f o l l o w i n g T a b l e G . l c o n t a i n s w a s h a b i l i t y data on the -212 + 149 Jim s i z e f r a c t i o n of the Bulmoose seam A composite c o a l sample, as o b t a i n e d form s i n k - a n d - f l o a t a n a l y s i s . 227 T a b l e G . l W a s h a b i l i t y data of composite ( - 212 + 149 nm) Bullmoose seam A. Wt% floats Ash % floats Cum. wt %, floats Cum. ash %, floats Cum. wt %, rejects Cum. ash %, rejects +1.30 32.71 aoi 3271 aoi 100.00 2a 72 1.30-1.35 14.08 7.87 46.79 4.47 67.29 41.21 1.35-1.40 7.32 14.89 54.11 5.88 sa 21 50.03 1.40-1.45 5.15 20.89 59.26 7.19 45.89 55.64 1.45-1.50 294 25.24 6220 ao4 40.74 60.03 +1.50 37.80 6274 100.00 2a 72 37.80 6274 228 

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