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Effect of particle size on the kinetics of microbiological leaching of chalcopyrite Blancarte-Zurita, Martha Alicia 1983

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EFFECT OF PARTICLE SIZE ON THE KINETICS OF MICROBIOLOGICAL LEACHING OF CHALCOPYRITE By MARTHA ALICIA BLANCARTE-ZURITA IBQ I n s t i t u t o Pol i tecnico Nacional, Mexico 1981 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 Chemical Engineering) We accept t h i s thesis as conforming to^ th^ required standard THE UNIVERSITY OF BRITISH COLUMBIA December 1983 Martha A l i c i a B l a n c a r t e - Z u r i t a , 1983 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements fo r an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e for reference and study. I further agree that permission for extensive copying of t h i s thesis f o r scholarly purposes may be granted by the head of my department or by h i s or her representatives. I t i s understood that copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Chemical E n g i n e e r i n g The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date 'DecesnhisT 1 Qft ^  - i i -ABSTRACT An experimental investigation was undertaken to study the microbiological leaching of chalcopyrite by Thiobacillus  ferrooxidans. Leach tests were conducted on a small scale using shake flasks. Tests were done which showed that the optimal time for transfer of inocula was between 6 and 8 days. Attempts were made to c la r i fy the complex media-mineral-bacteria interactions that occur in the bioleaching process relating bacterial growth with the changes in media composition as a result of the act iv i t ie s of the bacteria at the mineral surface. In so doing i t was observed that a significant amount of copper was leached during the stationary phase of bacterial growth. A sedimentation technique was used to separate the chalcopyrite into various size fractions which were then used to determine bacterial leaching rates in separate experiments. The particle size ranges had average diameters of 1.07, 1.78, 2.52, 3.56, 5.48 and 7.41 ym. The method used to measure particle size was based on the direct comparison of the particles with the scale of an eyepiece micrometer using a microscope. - i i i -Measurements of particle size distribution made during the course of leaching showed that as the leach proceeded, particle size decreased and the particle size distribution moved in the direction of more particles in the smaller size ranges. An attempt was made to apply Levenspiel's shrinking core model to the data obtained for leaching of the various sized particles. Agreement was reasonable but not perfect between the predicted and measured values of % copper extraction. Better agreement was observed at lower leaching times. Electron micrographs are presented which i l lus t ra te the attack of the chalcopyrite particles by the organisms. They also show the effects of jarosite precipitation. - iv -TABLE OF CONTENTS Page Abstract i i Table of Contents iv Lis t of Tables v i i Li st of Figures vi i i Acknowledgements x l CHAPTER 1 2 1.1 Introduction 2 1.1.1 Objective 3 CHAPTER II THE BACTERIA THIOBACILLUS FERROOXIDANS 4 2.1 MORPHOLOGY AND CHEMICAL COMPOSITION 5 CHAPTER III SUBSTRATE 6 3.1 DESCRIPTION 6 3.2 MINERAL-MICROBE INTERACTIONS 8 3.2.1 Mechanism of Oxidation of Ferrous Iron 9 3.2.2 Mechanism of Oxidation of Sulphides 11 3.3 MINERAL-MEDIA INTERACTIONS 13 Chapter IV FACTORS AFFECTING BIOLOGICAL LEACHING 15 4.1 PARTICLE SIZE AND SURFACE AREA 15 4.2 NUTRIENTS. 15 4.2.1 Carbon Source 15 4.2.2 Nitrogen Source 16 4.3 TEMPERATURE 16 4.4 pH 17 4.5 DISSOLVED OXYGEN 17 4.6 AGE OF CELLS 18 Chapter V MODELLING BIOLOGICAL SYSTEMS 19 5.1 BACTERIAL KINETICS AND MODELLING 19 5.2 MODELLING BIOLOGICAL LEACHING 20 5.3 THE SHRINKING CORE MODEL 22 - V -TABLE OF CONTENTS (Continued) Page CHAPTER VI MATERIALS AND METHODS 25 6.1 BIOLOGICAL LEACHING TECHNIQUES 25 6.1.1 Sampling Techniques . . . 27 6.2 ANALYSIS 27 6.2.1 Metal Leach Rates 27 6.2.2 Hydrogen Ion A c t i v i t y 28 6.2.3 Oxidation-Reduction P o t e n t i a l 28 6.2.4 B a c t e r i a l Growth 28 6.3 FRACTIONATION OF CONCENTRATE 30 6.3.1 D e f l o c c u l a n t S e l e c t i o n Tests 36 6.4 PARTICLE SIZE MEASUREMENT 40 6.4.1 Preparation o f Concentrate f o r Size Measurement 41 6.4.2 Scanning E l e c t r o n Microscope Techniques 43 CHAPTER VII EXPERIMENTAL RESULTS AND DISCUSSION 45 7.1 SELECTION OF THE INOCULUM AGE 45 7.2 BACTERIAL GROWTH KINETICS 46 7.2.1 Copper E x t r a c t i o n 46 7.2.2 Surface Area U t i l i z a t i o n 50 7.2.3 S t e r i l e Run 55 7.2.4 Leaching i n the Absence o f B a c t e r i a 57 7.3 EFFECTS OF PARTICLE SIZE ON THE LEACHING OF COPPER. 60 7.3.1 Changes i n the P a r t i c l e S i z e D i s t r i b u t i o n d u ring Leaching 65 7.4 APPLICATION OF THE SHRINKING CORE MODEL OF LEVENSPIEL 66 7.5 POST LEACHING OBSERVATIONS 73 CHAPTER VIII SUMMARY AND CONCLUSIONS 79 8.1 RECOMMENDATIONS FOR FUTURE STUDIES 81 - v i -TABLE OF CONTENTS (Continued) Page CHAPTER IX REFERENCES 82 Appendix 1 89 Appendix II 99 - v i i -LIST OF TABLES Page Table 1 Culture Media Composition 25 Table 2 Elemental A n a l y s i s o f the Copper Concentrate. . . 26 Table 3 F r a c t i o n s of B a l I m i l i e d Concentrate: T h e o r e t i c a l S i z e Ranges, Free F a l l i n g V e l o c i t i e s and S e t t l i n g Times 35 Table 4 F r a c t i o n s o f B a l l m i l l e d Concentrate: Weight Percentages C o l l e c t e d 35 Table 5 Average P a r t i c l e S i z e i n F r a c t i o n a t e d Concentrate 43 - v i i i -LIST OF FIGURES Page Figure 1 Space L a t t i c e o f C h a l c o p y r i t e 7 2 Ping Pong bi bi Mechanism of Fe +Jt Cytochrome C Reductase o f T h i o b a c i l l u s ferrooxidans. . . . 12 3 Standard Curve f o r Nitrogen Determination . . . . 31 4 E f f e c t o f Aerosol i n the Growth o f J_. ferrooxidans 37 5 Martin's Diameter 41 6 E f f e c t of the Inoculum Age on Copper E x t r a c t i o n . 47 7 B a c t e r i a l Growth o f T h i o b a c i l l u s f e r r o o x i d a n s i n Copper Concentrate 49 8 B i o l e a c h i n g Data Averages f o r Three Experiments . .51 9 Average Values o f Copper/Iron Ratios f o r Three Leaches 54 10 B a c t e r i a l Coverage of the Mineral Surface . . . . 56 11 Chemical Leaching of C h a l c o p y r i t e 59 12 E f f e c t of P a r t i c l e S i z e on the Copper E x t r a c t i o n . 61 13 Copper E x t r a c t i o n Rates as a Function o f the P a r t i c l e Diameter 63 14 E x t r a c t i o n Rate as a Function o f the Surface Area 64 15 Changes i n the P a r t i c l e S i z e D i s t r i b u t i o n f o r the 1.78 nm Leach 67 16 Changes i n the P a r t i c l e S i z e D i s t r i b u t i o n f o r the 2.52 urn Leach 68 17 Changes i n the P a r t i c l e S i z e D i s t r i b u t i o n f o r the 5.48 pm Leach 69 18 Average P a r t i c l e S i z e f o r Three D i f f e r e n t Leaches vs. Time 70 - i x -LIST OF FIGURES (Continued) Page 19 Experimental and T h e o r e t i c a l Copper E x t r a c t i o n Values f o r the Leaching o f C h a l c o p y r i t e . . . . 72 20 C h a l c o p y r i t e P a r t i c l e s before Handling 74 21 C h a l c o p y r i t e P a r t i c l e s a f t e r 200 h o f Leaching. . 75 22 C h a l c o p y r i t e P a r t i c l e s a f t e r 300 h o f Leaching. . 77 23 Second Pass Leaching o f C h a l c o p y r i t e 78 - X -APPENDIX I Page 1.1 B a c t e r i a l Growth Data 90 1.2 Average Results f o r Three B i o l o g i c a l Leaching Experiments 91 1.3 C h a l c o p y r i t e Concentrate Surface Area 92 1.4 B a c t e r i a l Coverage of the Surface Area 92 1.5 S t e r i l e Run Data 93 1.6 Leach Using Monosized Mate r i a l of 1.07 urn 94 1.7 Leach Using Monosized M a t e r i a l o f 1.78 nm 95 1.8 Leach Using Monosized M a t e r i a l o f 2.52 pm 96 1.9 Leach Using Monosized M a t e r i a l o f 3.56 um 97 1.10 Leach Using Monosized Material o f 5.48 ym 98 1.11 Leach Using Monosized M a t e r i a l o f 7.41 ym 98 APPENDIX II 1.1 K i n e t i c Data f o r the S h r i n k i n g Core Model 102 1.2 C a l c u l a t e d Percentage E x t r a c t i o n A f t e r 50 h o f Leaching 103 1.3 Copper Concentration and Percentage Copper E x t r a c t i o n f o r C h a l c o p y r i t e Leaches 104 - xi -ACKNOWLEDGEMENTS F i n a n c i a l support f o r t h i s research program was provided by the U n i v e r s i t y o f B r i t i s h Columbia, B.C. Research and El Consejo Nacional de C i e n c i a y Tecnologia (Conacyt) Mexico. - 1 -CHAPTER 1 - 2 -CHAPTER I 1.1 INTRODUCTION B i o l o g i c a l l e a c h i n g i s a process i n which metals are ex t r a c t e d from ores and minerals by enzymic transformations. The le a c h i n g o f metals using T h i o b a c i l l u s f e r r o o x i d a n s i s c u r r e n t l y a p p l i e d t o the le a c h i n g o f low grade, and waste sulphide ores by dump and heap l e a c h i n g techniques f o r the recovery of copper and uranium. Studies conducted on a v a r i e t y o f sulphide minerals have demonstrated t h a t b a c t e r i a l o x i d a t i o n can a l s o be used f o r the recovery o f l e a d , c o b a l t , n i c k e l , z i n c and other base metals. The p o s s i b i l i t y of using T h i o b a c i l l u s ferrooxidans f o r the l e a c h i n g o f metals from ore concentrate i s c u r r e n t l y being considered. This type o f l e a c h i n g would take place i n a batch or a continuous flow chemical r e a c t o r i n which a c o n t r o l l e d process could be e s t a b l i s h e d . The advantages of b i o l o g i c a l l e a c h i n g over conventional p y r o m e t a l l u r g i c a l and hydrometal1urgical processes are claimed t o be lower c o s t s , the e l i m i n a t i o n o f the a i r p o l l u t i o n problems a s s o c i a t e d with smelting operations, and s u i t a b i l i t y f o r a smaller s c a l e o f op e r a t i o n . - 3 -Studies have been p r e v i o u s l y c a r r i e d out with the purpose o f o p t i m i z i n g the parameters t h a t a f f e c t the b i o l o g i c a l process such as temperature, pH, type and concentration o f n u t r i e n t s , a e r a t i o n , e t c . , and t o o b t a i n increased metal y i e l d s . It i s only r e c e n t l y t h a t attempts to descr i b e the b i o l o g i c a l l e a c h i n g process using mathematical models have been made. Given t h a t the b i o l o g i c a l l e a c h i n g process i n v o l v e s complex, i n t e r a c t i o n s between the m i n e r a l , the b a c t e r i a and the aqueous phase, attempts a t modelling m u l t i p a r t i c l e l e a c h i n g systems have only been p a r t i a l l y s u c c e s s f u l . Mathematical models are based on hypotheses about the mechanisms t h a t c o n t r o l the process and when the r e s u l t s o f such models are compared with experimental r e s u l t s , a greater understanding of the process i s generated. Mathematical models are a l s o used t o p r e d i c t the r e s u l t s o f changes i n the operating c o n d i t i o n s thereby e l i m i n a t i n g lengthy and c o s t l y experiments. 1.1.1 O b j e c t i v e The o b j e c t i v e s o f t h i s work were to o b t a i n i n f o r m a t i o n about the mechanisms of l e a c h i n g o f c h a l c o p y r i t e (copper-iron sulphide) by T h i o b a c i l l u s f e r r o o x i d a n s using monosize p a r t i c l e s i n batch r e a c t o r s , to t r y to qu a n t i f y the r e a c t i o n k i n e t i c s and v e r i f y the a p p l i c a b i l i t y o f the s h r i n k i n g core model t o the b i o l o g i c a l l e a c h i n g o f copper. - 4 -CHAPTER II THE BACTERIA THIOBACILLUS FERROOXIDANS During the f i r s t h a l f o f the twentieth century l a r g e amounts of copper were recovered from c h a l c o p y r i t e - p y r i t e heaps a t the Rio T i n t o o p e r a t i o n i n south-western Spain ( T r u s s e l l , 1964), but i t wasn't u n t i l 1947 t h a t b a c t e r i a were recognized as an i n t e g r a l p a r t o f t h i s process. Colmer and Hinkle (1947) showed t h a t f e r r o u s i r o n o x i d a t i o n o c c u r r i n g i n a c i d mine water was b i o l o g i c a l i n o r i g i n ; the i s o l a t i o n o f the organism r e s p o n s i b l e was made by Colmer, Temple and Hinkle i n 1949. Further s t u d i e s were conducted by Temple and Colmer (1951) t o e s t a b l i s h t h a t the bacterium was an autot r o p h i c i r o n o x i d i z e r ; they named i t T h i o b a c i l l u s f e r r o o x i d a n s . Autotrophic b a c t e r i a can be d i v i d e d i n t o two groups on the b a s i s o f t h e i r source of energy: the f i r s t group i s named photosynthetic and de r i v e s i t s energy from l i g h t ; the second group i s c a l l e d chemosynthetic and der i v e s i t s energy from the o x i d a t i o n o f i n o r g a n i c compounds. T h i o b a c i l l u s f e r r o x i d a n s belongs to t h i s second group o f b a c t e r i a which a l s o uses carbon dioxide as a carbon source f o r the sy n t h e s i s o f i t s organic compounds. I t has been f u r t h e r considered as an o b l i g a t e chemoautotroph given i t s i n a b i l i t y to use a l t e r n a t e carbon sources (more complex than carbon d i o x i d e ) . - 5 -2.1 MORPHOLOGY AND CHEMICAL COMPOSITION T h i o b a c i l l u s ferrooxidans i s a m o t i l e , non-spore forming, gram negative, rod-shaped organism which occurs s i n g l y or o c c a s i o n a l l y i n p a i r s . I t s s i z e i s 0.6-1.0 u.m width by 1.0-1.6 ym i n length and l i k e any other microorganism i t s b a s i c elemental composition i s C, H, 0, N, S, P. A l l of these elements are then r e q u i r e d f o r i t s growth and have t o be su p p l i e d i n forms u t i l i z a b l e by the b a c t e r i a . In a d d i t i o n an energy source i s r e q u i r e d f o r t r a n s p o r t o f n u t r i e n t s , s y n t h e s i s , locomotion, e t c . T h i o b a c i l l u s ferrooxidans can o b t a i n energy from the o x i d a t i o n o f sulphide minerals such as: copper-iron s u l p h i d e s , l e a d s u l p h i d e , n i c k e l s u l p h i d e , z i n c s u l p h i d e , e t c . - 6 -CHAPTER III SUBSTRATE 3.1 DESCRIPTION C h a l c o p y r i t e i s p a r t of a s e r i e s o f complex copper-iron sulphides that occur as minerals. I t i s a widely disseminated mineral t h a t occurrs i n m e t a l l i c veins and pockets f r e q u e n t l y a s s o c i a t e d with i r o n p y r i t e s , p y r r h o t i t e , s i d e r i t e , b o r n i t e and o t h e r minerals ( M e l l o r , 1947). The mineral sometimes contains gold and s i l ver. 1 Burdick and E l l i s (1917) found t h a t the s p a c e - l a t t i c e of c h a l c o p y r i t e i s tetragonal with the a x i a l r a t i o s a:b:c = 1 :1 :0.985. The i r o n and copper atoms are l o c a t e d so th a t they together form a face-centred tetragonal l a t t i c e , the planes p e r p e n d i c u l a r t o the tetragonal a x i s being made up a l t e r n a t e l y of copper atoms alone and i r o n atoms alone. The sulphur atoms are l o c a t e d on a s i m i l a r face centred l a t t i c e with the planes of the sulphur atoms l y i n g midway i n a l l three of the a x i a l d i r e c t i o n s between the planes of the i r o n and copper atoms (see Figure 1). The composition o f the mineral can be represented by the formula CuFeS 2, although i t has been suggested t h a t the atoms have no + +++ f i x e d valences, but f l u c t u a t e between Cu Fe S 2 and C u + + F e + + Sg ( P a u l i n g , 1932). - 7 -Fig. 1 Space - Lattice of Chalcopyrite - 8 -3.2 MINERAL AND MICROBE INTERACTIONS Chemical l e a c h i n g o f m e t a l l i c sulphides i s c a r r i e d out using f e r r i c - s u l p h a t e s o l u t i o n s i n s u l p h u r i c a c i d media. The main r e a c t i o n can be expressed as: MS + 2 F e 3 + M2"*" + S° + 2 F e + + (3.1) where MS represents a m e t a l l i c sulphide. The f e r r i c i r o n i s reduced to f e r r o u s i r o n and has to be su p p l i e d c o n s t a n t l y . F e r r i c sulphate a l s o hydrolyses a t low pH to f e r r i c hydroxide according t o : F e 3 + + 3H 20 F e ( 0 H ) 3 + 3H + (3.2) It was f i r s t suggested (Silverman, 1961, 1963, Duncan, 1973, Lau, 1970) t h a t the r o l e o f b a c t e r i a i n the l e a c h i n g o f sulphide minerals was to o x i d i z e the fe r r o u s i r o n produced i n r e a c t i o n 3.1 as f o l l o w s : 2 F e + + + l / 2 0 2 + 2H + 2 F e 3 + + H 20 (3.3) This r e a c t i o n would r e p l e n i s h the f e r r i c i r o n (consumed i n r e a c t i o n 3.1 and 3.2). The b a c t e r i a would a l s o produce s u l p h u r i c a c i d from the o x i d a t i o n of sulphur i n a d d i t i o n t o the - 9 -a c i d generated by the h y d r o l y s i s of f e r r i c i r o n according to the f o l l o w i n g r e a c t i o n : S° + 3/2 0 2 + H 20 bacteria?- H 2S0 4 (3.4) Subsequently Duncan (1973) provided evidence of the d i r e c t a t t a c k of T h i o b a c i l l u s ferrooxidans on the mineral surfaces of c h a l c o p y r i t e and p y r i t e . The o x i d a t i o n of i n s o l u b l e f e r r o u s i r o n and sulphide occurs simultaneously (Landesman, 1966) and independently (Duncan, 1967) but the r e l a t i v e r a t e s depend on how the c e l l s are grown. I t has been demonstrated t h a t the a b i l i t y of T h i o b a c i l l u s  ferrooxidans to grow on i r o n i s c o n s t i t u t i v e , while the use of sulphide minerals seems to be subject to s p e c i f i c adaptation mechanisms (Touvinen, 1972). A n a l y s i s of the base r a t i o of DNA obtained from c e l l s growing on d i f f e r e n t substrates conducted by Guay (1976) l e d him to suggest t h a t s u b c u l t u r i n g would cause the production of high metal c o n c e n t r a t i o n r e s i s t a n t s t r a i n s or new s p e c i e s by s e l e c t i o n and mutation mechanisms. 3.2.1 Mechanism of o x i d a t i o n of f e r r o u s i r o n I f T h i o b a c i l l u s f e r r o x i d a n s uses the o x i d a t i o n of ions from the mineral surface of sulphides to obtain energy then the two p o s s i b l e energy t r a n s f e r mechanisms are t h a t e i t h e r the b a c t e r i a - 10 -attach to the surface where the ions can be contacted with enzymes a t the membrane l e v e l o r , the b a c t e r i a use e x t r a c e l l u l a r enzymes to make these ions a v a i l a b l e and subsequently t r a n s p o r t them i n t o the c e l l . Attachment of T h i o b a c i l l u s ferrooxidans t o mineral surfaces has been demonstrated ( R a z z e l l , 1963, McGoran, 1969) and st u d i e s o f the c e l l envelope o f T h i o b a c i l l u s . ferroo x i d a n s (Berry, 1980) have provided evidence f o r both mechanisms. According to Lundgren (1978) the c e l l envelope o f T h i o b a c i l l u s ferrooxidans c o n s i s t s of three zones: 1) A cytoplasmic membrane which c o n s t i t u t e s the inn e r l a y e r of the envelope bordering on the cytoplasm. 2) A c e n t r a l zone comprising a r i g i d l a y e r o f peptidoglycan and a p e r i p l a s m i c space. 3) An outer l a y e r which contains lypopolysaccharide and l i p o p r o t e i n . T h is outer l a y e r might a c t as an i n i t i a l b i n d i n g s i t e f o r f e r r o u s i r o n (Touvinen, 1972). The t r a n s f e r o f e l e c t r o n s i s c a r r i e d out a t the outer membrane or a t the ++ ++ peroplasmic space l e v e l (2Fe ^ 2Fe + 2e ) while the energy a s s o c i a t e d r e a c t i o n (2e~ + 1/2 0^ + 2H + v H.,0) i s probably l o c a t e d w i t h i n the i n n e r r C membrane (Lundgren, 1978). - 11 -An e x t r a c e l l u l a r complex from the c u l t u r e f i l t r a t e o f T h i o b a c i l l u s ferrooxidans has a l s o been i s o l a t e d (Agathe, 1968) and suggested to a c t as a substrate f o r f e r r o u s i r o n o x i d a t i o n (donating e l e c t r o n s f o r e l e c t r o n t r a n s p o r t v i a a cytochrome system w i t h i n the c e l l ) or as a solvent (Touvinen, 1972). The cytochrome system r o l e i n i r o n o x i d a t i o n was f i r s t presented by Duncan (1967) who showed t h a t cytochrome i n h i b i t o r s i n h i b i t e d i r o n o x i d a t i o n ; furthermore cytochromes a and b were i s o l a t e d from T h i o b a c i l l u s ferrooxidans by Din (1967a) who a l s o suggested a ping pong bi bi mechanism f o r i r o n o x i d a t i o n shown i n Figure 2 (Din, 1967b). 3.2.2 Mechanism o f Oxidation of Sulphides Concerning the mechanism of sulphide o x i d a t i o n , Duncan (1967) found t h a t N-ethyl maleimide (NEM), a t h i o l - b i n d i n g i n h i b i t o r acted as an i n h i b i t o r of sulphur o x i d a t i o n , showing that t h i o l groups p a r t i c i p a t e d i n sulphur o x i d a t i o n . A suggested mechanism i s the o x i d a t i o n of sulphur to s u l p h i t e and to sulphate e i t h e r by a sulphite:cytochrome c oxidoreductase or with the intermediate formation of adenylyl sulphate. The mechanism o f c o n t a c t o f T h i o b a c i l l u s f e r r o o x i d a n s with sulphur i s not c l e a r but Agathe (1968) suggested t h a t the e x t r a c e l l u l a r complex might a c t as a wetting agent f o r sulphur granules. Fe i Fe +++ 1 cytochrome c I reduced cytochrome c • E = enzyme r lr +++. r ++ E (Fe ) Fe E (Fe ) Fe E ( F e + + ) E ( F e + + ) cytochrome c E ( F e + + + ) E ( F e + + + ) reduced cytochrome c ++ Fig . 2 Ping Pong bi bi mechanism of Fe -cytochrome c reductase of Thiobaci l lus ferrooxidans (Din, 1967b) - 13 -T r i b u t s c h (1981) suggested t h a t b a c t e r i a l a c t i v i t y on sulphides was based on the chemical r e a c t i o n of protons with the metal sulphide surface which then caused a s h i f t i n the e l e c t r o n i c - S -s t a t e s and produced surface s t a t e s described as -SH groups which were removed by b a c t e r i a l a c t i v i t y . The use of sulphide as a source of energy by T h i o b a c i l l u s  f e r r o o x i d a n s has been considered the r a t e l i m i t i n g step i n the l e a c h i n g process. I t has been f u r t h e r suggested t h a t the high i n i t i a l l e a c h i n g r a t e s are due to o x i d a t i o n o f f e r r o u s i r o n atoms a v a i l a b l e at the surface of the mineral (Duncan, 1967). When these atoms are exhausted, the use o f sulphide c o n t r o l s the r a t e of d i s s o l u t i o n o f the mineral ( T r i b u t s c h , 1981). 3.3 MINERAL-MEDIA INTERACTIONS During the b i o l o g i c a l l e a c h i n g o f sulphide minerals a v a r i e t y o f i n o r g a n i c species i s present i n the media at any time and secondary r e a c t i o n s take place between these s p e c i e s . McGoran (1969) found t h a t most of the f e r r i c sulphate hydrolyzed would p r e c i p i t a t e as a b a s i c f e r r i c sulphate. At pH <3 j a r o s i t e w i l l normally form (Duncan, 1972; Sakaguchi, 1976) according t o the f o l l o w i n g r e a c t i o n : 3 F e 2 ( S 0 4 ) 3 + 14H 20 > 2 ( H 3 0 ) F e 3 ( S 0 4 ) 2 ( 0 H ) 6 + 5H 2S0 4 (3.5) - 14 -The j a r o s i t e s a l t s o f potassium, sodium, ammonium and hydronium are formed when these ions are a v a i l a b l e ( P i c k e r i n g , 1968). The l e a c h i n g o f c h a l c o p y r i t e u s u a l l y y i e l d s 50-60% copper e x t r a c t i o n (Bruynesteyn, 1970). T h i s incomplete s o l u b i l i z a t i o n o f copper has been a t t r i b u t e d t o the formation o f an impermeable l a y e r o f sulphur around the p a r t i a l l y leached c h a l c o p y r i t e ( M i l l e r , 1979; Chakraborti, 1979) and to the accumulation o f gangue and p r e c i p i t a t i o n o f b a s i c f e r r i c sulphates ((Fe(0H)S0 4 and H [Fe ( S 0 4 ) 2 '2Fe(0H) 3]) (Torma, 1973). T h i s l a t t e r e x p l a n a t i o n i s supported by the f a c t t h a t increased y i e l d s can be obtained when the residues o f the l e a c h i n g are subject t o r e - g r i n d i n g and r e - l e a c h i n g (Torma, 1973, 1 977). The o v e r a l l r e a c t i o n s of b i o l o g i c a l l e a c h i n g o f c h a l c o p y r i t e can be expressed as: 2 CuFeS. + 8 1/2 0- + H_S0. b a c t e r i a 2 CuSO. + Fe.fSO.),, + H o0 (3.6) 3 F e 2 ( S 0 4 ) 3 + 14 H 20 > 2 ( H 3 0 ) F e 3 ( S 0 4 ) 2 (0H) g + 5H 2S0 4 (3.7) CuFeS 2 + 2 F e 2 ( S 0 4 ) 3 > CuS0 4 + 5FeS0 4 + 2S° (3.8) 2S° + 3 0 2 + 2H 20 b a c t e r i a } 2H 2S0 4 (3.9) The b i o l o g i c a l l e a c h i n g of c h a l c o p y r i t e can then be considered as a s e r i e s o f events caused by i n t e r a c t i o n s o f b a c t e r i a , the mineral and the aqueous phase. - 15 -CHAPTER IV FACTORS AFFECTING BIOLOGICAL LEACHING 4.1 PARTICLE SIZE AND SURFACE AREA The e x t r a c t i o n r a t e i s a f u n c t i o n o f the surface area and w i l l have i t s maximum value a t the s t a r t of the leach and gradual l y decrease when accumulation of by-products i n c r e a s e s the mass t r a n s f e r r e s i s t a n c e . The surface area a v a i l a b l e depends on the p a r t i c l e s i z e and f o r a f i x e d amount of material increases with the fineness o f the m a t e r i a l . Optimum p a r t i c l e s i z e s f o r b i o l o g i c a l l e a c h i n g have been proposed as: <325 mesh (Duncan, 1964), 42 nm (Torma, 1 977), <44 nm ( R a z z e l l , 1963). In theory, the optimum (minimum) p a r t i c l e s i z e w i l l be reached when the p a r t i c l e i s formed by a s i n g l e c r y s t a l (Touvinen, 1972). 4.2 NUTRIENTS 4.2.1 Carbon Source T h i o b a c i l l u s ferrooxidans being an autotroph uses carbon d i o x i d e as a carbon source. The mechanisms of carbon f i x a t i o n are the C a l v i n r e d u c t i v e pentose phosphate c y c l e and the secondary c a r b o x y l a t i o n o f phosphoenolpyruvate (PEP) derived from the carbon c y c l e (Touvinen, 1972). - 16 -The carbon d i o x i d e can be s u p p l i e d to the l i q u i d media through gas exchange with the atmosphere or sparged. For the f i r s t case Touvinen (1972) showed t h a t the carbon d i o x i d e consumption exceeds the maximum s o l u b l e amount present i n the media at any time. For t h i s reason the use of a carbon dioxide enriched atmosphere i s recommended. 4.2.2 Nitrogen Source The primary source of n i t r o g e n f o r T h i o b a c i l l u s ferrooxidans i s ammonium i o n . Mackintosh and Herbet (Duncan, 1972) b e l i e v e d t h a t the bacterium can f i x n i t r o g e n , but attempts to detect nitrogenase i n T h i o b a c i l l u s sp. f a i l e d (Tsuchiya, 1974). Silverman (1959) found t h a t the media composition o f h i s 9K medium s u p p l i e d ammonia and other n u t r i e n t s (potassium, magnesium, calcium) i n adequate amounts to support the growth o f o up to 5 x 10 c e l l s / m L . 4.3 TEMPERATURE The optimum temperature f o r T h i o b a c i l l u s ferrooxidans growing on c h a l c o p y r i t e was determined to be 35°C (Duncan, 1964; Landesman, 1966, Sakaguchi, 1976). - 17 -4.4 pH The optimum pH has been determined to be 2.0 (Landesman, 1966b) although i t grows well between 2.0-4.5 (Morrison, 1969). 4.5 DISSOLVED OXYGEN The e f f e c t s o f the d i s s o l v e d oxygen co n c e n t r a t i o n on the growth of T h i o b a c i l l u s f e r r o x i d a n s were studied by L i u (1973) who c a l c u l a t e d the s o l u b i l i t y o f oxygen i n 9K medium at 35°C to be 6.42 mg O2/L and found the c r i t i c a l oxygen concentration to be 0.29 mg 0 2/L. The maximum r e s p i r a t i o n r a t e f o r T h i o b a c i l l u s ferrooxidans growing on c h a l c o p y r i t e was reported to be Q0 2(N) = 3200 uL (STP)/mgN-h (Landesman, 1966). During the l e a c h i n g of m e t a l l i c s u l p h i d e s , oxygen concentrations have been found to be as low as 0.2-0.55 ppm (Torma, 1973), which suggest a p o s s i b l e oxygen l i m i t a t i o n when oxygen i s provided only by surface exchange. - 18 -4.6 AGE OF CELLS There i s no agreement on the l i t e r a t u r e as to the best inoculum age. Some of the reported values are: 3 days (Landesman, 1966), 4 days (Landesman, 1966b), l a t e l a g phase (Torma, 1977) and s t a t i o n a r y phase (Sakaguchi, 1976). - 19 -CHAPTER V MODELLING BIOLOGICAL SYSTEMS 5.1 BACTERIAL KINETICS AND MODELLING In order to use mathematical models to desc r i b e m i c r o b i o l o g i c a l processes, i t i s necessary to e s t a b l i s h r e l a t i o n s h i p s between the p h y s i c a l l y important v a r i a b l e s which w i l l best d e s c r i b e the phenomena. M i c r o b i o l o g i c a l processes f o r the most part are described by making use of the r e l a t i o n s h i p s between biomass production, s u b s t r a t e u t i l i z a t i o n and product y i e l d k i n e t i c s . The knowledge o f these r e l a t i o n s h i p s i s then used to s e t the process operating c o n d i t i o n s i n which maximum y i e l d o f the product of i n t e r e s t would be obtained. Most o f the models used f o r b i o l o g i c a l systems have been de r i v e d f o r homogeneous systems i n which a l l the r e a c t i n g m a t e r i a l s are found w i t h i n a l i q u i d phase. In the case of heterogeneous systems, where the r e a c t i n g m a t e r i a l s are found i n more than one phase, k i n e t i c analyses have been made to qua n t i f y r e a c t i o n r a t e s i n m i c r o b i a l f i l m s (Atkinson, B. and Fowler, H.W. 1974), l i q u i d hydrocarbon fermentations (Moo-Young, M. 1975) and f o r immobilized enzymes - 20 -( B a i l e y , J.E. and O l l i s , O.F., 1977). These analyses are based on mathematical models p r e v i o u s l y developed f o r n o n - b i o l o g i c a l r e a c t i o n s . MODELLING BIOLOGICAL LEACHING E a r l i e r k i n e t i c s t u d i e s of b i o l o g i c a l l e a c h i n g processes were conducted t o i n v e s t i g a t e the r e l a t i o n s h i p s between e i t h e r product formation and c e l l growth (Landesman, 1966a, 1966b; McGoran, 1969) or s u b s t r a t e u t i l i z a t i o n and product y i e l d (Torma, 1973; Bruynesteyn, 1974). The r e s u l t s of these i n v e s t i g a t i o n s provided a l i m i t e d understanding of the i n t e r a c t i o n s between the b a c t e r i a , the mineral and the l i q u i d phase i n a b i o l o g i c a l l e a c h i n g process. The importance of those aspects r e l a t i n g to the r o l e of b a c t e r i a on the l e a c h i n g process has been underestimated f o r the most p a r t . It has been proposed ( B a i l e y and O l l i s , 1977) that f o r b a c t e r i a growing a t i n t e r f a c e s , two d i f f e r e n t growth r a t e s would be present depending on the r a t i o between c e l l s i z e and substrate s i z e . One growth r a t e would be evident f o r the case when the c e l l diameter was l e s s than the substrate diameter, and another growth r a t e when the s u b s t r a t e s i z e was l e s s than the c e l l s i z e and the substrate would be absorbed onto the c e l l s u r f a c e . - 21 -Based on surface area the k i n e t i c a n a l y s i s would show two d i f f e r e n t growth stages. The f i r s t a f t e r i n t r o d u c t i o n of the inoculum when the b a c t e r i a would grow at i t s maximum growth r a t e ; and the second stage i n which growth would occur at expense o f substrate present a t the i n t e r f a c e between phases, when the s u r f a c e s were t o t a l l y covered by b a c t e r i a . These two stages combined produce a growth curve which i s l i n e a r a f t e r the s u r f a c e i s saturated. Gormely (1973) found t h a t when the substrate surface was completely covered by b a c t e r i a , the l e a c h i n g r a t e o f z i n c from a z i n c sulphide concentrate was a f u n c t i o n of the substrate area. He t r i e d to model t h i s using the S h r i n k i n g Core Model o f Levenspiel (1972) f o r the case when chemical r e a c t i o n c o n t r o l s . Based on a constant l e a c h i n g r a t e per u n i t surface area, he c a l c u l a t e d the l e a c h i n g r a t e s of p a r t i c l e s of d i f f e r e n t s i z e s . Estimates o f product formation using these values gave percentage e x t r a c t i o n s of z i n c which were low by a f a c t o r of ten compared with the experimental values. He a l s o found t h a t the r a t e of l e a c h i n g reached a maximum soon a f t e r i n i t i a t i o n of the metal r e l e a s e , then the leach curve became l i n e a r u n t i l c l o s e to the completion of the l e a c h , but he d i d not provide an e x p l a n a t i o n f o r t h i s phenomena. Sanmugasunderam (1981) a l s o conducted s t u d i e s on z i n c sulphide l e a c h i n g . He determined experimentally the l e a c h i n g r a t e s f o r d i f f e r e n t p a r t i c l e s i z e s and used them to p r e d i c t e x t r a c t i o n o f - 22 -z i n c using the S h r i n k i n g Core Model. His p r e d i c t i o n s o f percentage e x t r a c t i o n of z i n c were equal or l e s s than the experimental values with a maximum d i f f e r e n c e of 25 percent. The d i f f e r e n c e was a t t r i b u t e d t o the methods used to estimate the surface area of the p a r t i c l e s and i t s s i z e s . THE SHRINKING CORE MODEL For n o n - c a t a l y t i c r e a c t i o n s o f p a r t i c l e s with surrounding f l u i d there are two simple i d e a l i z e d models according to Levenspiel (1972): 1) The p r o g r e s s i v e conversion model i n which the s o l i d reactant i s converted continuously and p r o g r e s s i v e l y through the p a r t i c l e . 2) The unreacted-core model i n which the r e a c t i o n zone moves i n t o the p a r t i c l e and the unreacted core shrinks i n s i z e with time. Given t h a t the b a c t e r i a l a c t i v i t y on s o l i d s u b s t r a t e s i s l i m i t e d to the surface since the b a c t e r i a cannot penetrate the i n t e r i o r o f the p a r t i c l e u n t i l the outer l a y e r i s d i s s o l v e d , the unreacted core model suggests i t s e l f f o r a p p l i c a t i o n to the m o d e l l i n g o f b i o l o g i c a l l e a c h i n g systems. - 23 -There are several conversion-time expressions f o r p a r t i c l e s o f d i f f e r e n t s i z e and shapes, and f o r r e a c t i o n s i n which the rate c o n t r o l l i n g step i s e i t h e r d i f f u s i o n c o n t r o l l e d o r chemical r e a c t i o n c o n t r o l l e d . For the case of s p h e r i c a l p a r t i c l e s when chemical r e a c t i o n c o n t r o l s , the i n t r i n s i c r e a c t i o n k i n e t i c data (or the time needed f o r complete r e a c t i o n o f a p a r t i c l e ) can be obtained f o r monosized p a r t i c l e s . At any time the extent of conversion o f the substrate can be c a l c u l a t e d from the p a r t i c l e s i z e d i s t r i b u t i o n data and the o v e r a l l f r a c t i o n reacted f o r any given s i z e . The s h r i n k i n g core model was used s u c c e s s f u l l y f o r modelling the chemical l e a c h i n g o f c h a l c o p y r i t e (Sepulveda, 1978) where the mechanism was suggested t o be an electrochemica l r e a c t i o n i n which the conduction of e l e c t r o n s through the sulphur l a y e r was the ra t e l i m i t i n g step. Levenspiel's s h r i n k i n g core model p r e d i c t s that with mixed flow of s i n g l e s i z e s o l i d s , the f r a c t i o n o f the s o l i d t h a t i s converted t o product i n a c e r t a i n time i s given by: f T e " t / £ Z = l - \ ( 1 - X a ) - dt Xa <1 (1) where: Z i s the average f r a c t i o n a l conversion o f the s o l i d , T the time required f o r complete conversion o f a s i n g l e p a r t i c l e , Xa the f r a c t i o n a l conversion f o r p a r t i c l e s i n time t + dt, t the mean residence time o f p a r t i c l e s i n the r e a c t o r and t time. i - 24 -If chemical r e a c t i o n i s the rate c o n t r o l l i n g step, then: j = ( 1 - X a ) 1 / 3 (2) S u b s t i t u t i n g and i n t e g r a t i n g we get: • Z = 3 ( j ) - 6 ( ^ ) 2 '+ 6 ( ^ ) 3 [l - exp ( - T / t ) ] (3) where T f o r m i c r o b i o l o g i c a l l e a c h i n g i s given by: T (4) * V s where: p i s the d e n s i t y o f the concentrate, do i s the diameter o f the feed s o l i d p a r t i c l e s , and rzfs i s the metal e x t r a c t i o n per u n i t s o l i d surface area. Thus, i f the metal e x t r a c t i o n r a t e f o r p a r t i c l e s i n each step i s known and the p a r t i c l e s i z e d i s t r i b u t i o n o f the concentrate i s a l s o known, Equation 3 can be used t o c a l c u l a t e the o v e r a l l e x t r a c t i o n at any given time. - 25 -CHAPTER VI MATERIALS AND METHODS BIOLOGICAL LEACHING TECHNIQUES The b a c t e r i a used f o r the experiments was a s t r a i n o f T h i o b a c i l l u s ferrooxidans o r i g i n a l l y i s o l a t e d from the B r i t a n n i a Mine near Vancouver (Ra z z e l l and T r u s s e l l , 1963), and r o u t i n e l y maintained on copper concentrate a t B.C. Research. The l i q u i d medium used was the medium 9K described by Silverman (1959) i n which the copper concentrate replaced FeS0 4 as the energy source. The medium had the f o l l o w i n g composition (Table 1 ). Table 1 Culture Media Composition Component Concentration (g/L) ( N H 4 ) 2 S 0 4 KC1 K2HPO4 3.0 0.1 0.5 0.5 0.01 MgSOA • 7H?0 Ca ( N 0 3 ) 2 The c h a l c o p y r i t e concentrate used i n t h i s study was a commercial f l o t a t i o n concentrate s u p p l i e d by Newmont Mines L i m i t e d , Similkameen D i v i s i o n , P r i nceton, B.C. - 26 -A l l l e a c h i n g experiments were c a r r i e d out on concentrate from a 2 kg grab sample drawn from a b a r r e l c o n t a i n i n g approximately 120 kg of thoroughly mixed concentrate which had p r e v i o u s l y been b a l l m i l l e d a t 55 percent s o l i d s f o r 1 h to 91.8 percent -400 T y l e r mesh, f i l t e r e d and d r i e d a t 60°C. The a n a l y s i s of the concentrate i s t a b u l a t e d i n Table 2. Table 2 Elemental A n a l y s i s of the Copper Concentrate (B.C. Research Data) Element Percentage by Weight Copper 27.8 Iron 28.0 Sulphur 31.1 In s o l . 5.5 T h i s study was c a r r i e d out using the shake f l a s k l e a c h technique where 7.5 g of concentrate were placed i n bottom-baffled, 250 mL, Erlenmeyer f l a s k s ; 70 mL of i r o n - f r e e 9K medium s o l u t i o n were added and the pH of the suspension was adjusted to 2.0. The f l a s k s were l o o s e l y stoppered with a c o t t o n plug, and incubated on a gyratory shaker (Model 591-70, New Brunswick S c i e n t i f i c , N.J.). The shaker was l o c a t e d i n a dark room with a carbon d i o x i d e enriched atmosphere provided by bubbling carbon d i o x i d e through water i n a c o n t a i n e r open to the atmosphere (dry carbon d i o x i d e , Canadian L i q u i d A i r L t d . ) . - 27 -The temperature o f the room was c o n t r o l l e d a t 35°C by means o f a temperature c o n t r o l l e r (Honeywell type RP 908). Before i n o c u l a t i o n the f l a s k s were incubated f o r 24 h to allow f o r a c i d consumption caused by a l k a l i n e gangue present i n the concentrate; a f t e r t h i s p e r i o d the pH was adjusted back t o 2.0 using s u l p h u r i c a c i d and the f l a s k s were stored i n a r e f r i g e r a t o r a t 4°C u n t i l they were used. 6.1.1 Sampling Techniques D i f f e r e n t sampling techniques were used depending on the type of a n a l y s i s to be c a r r i e d out. The s o l u b l e metal content was determined i n l mL of supernatant drawn from the f l a s k a f t e r 10-15 min s e t t l i n g time. For the a n a l y s i s o f c e l l s and p a r t i c l e s i z e , a sample o f s l u r r y was used; the sample was obtained using a p i p e t t e t o draw the r e q u i r e d amount of s l u r r y from the f l a s k , a f t e r i t s contents were thoroughly mixed by shaking. 6.2 Analyses 6.2.1 Metal Leach Rates The copper and i r o n contents o f the medium were determined by atomic absorption spectrophotometry (Atomic Absorption Spectrophotometer, Perkin Elmer 306). - 28 -1 mL samples, a f t e r the necessary d i l u t i o n s , were analysed f o l l o w i n g the standard p r a c t i c e s recommended i n Perkin-Elmer's manual (1973). The copper e x t r a c t i o n rate was c a l c u l a t e d as the slope o f the l i n e a r p o r t i o n of the copper concentration vs. time curve using a l e a s t squares curve f i t t i n g method. 6.2.2 Hydrogen Ion A c t i v i t y Measurements o f hydrogen i o n a c t i v i t y (pH) were made by in t r o d u c i n g a pH e l e c t r o d e i n t o the s l u r r y . T h i s was connected t o a pH meter ( F i s h e r Accumet model 61 OA). 6.2.3 Oxidation-Reduction P o t e n t i a l Measurements o f the Eh p o t e n t i a l were made d i r e c t l y i n the f l a s k using a platinum e l e c t r o d e connected to a pH meter (model 28 Radiometer, Copenhagen). 6.2.4 B a c t e r i a l Growth In order to ob t a i n i n f o r m a t i o n on the r o l e o f T h i o b a c i l l u s ferrooxidans i n the l e a c h i n g of m e t a l l i c sulphides and of the r e l a t i o n s h i p between b a c t e r i a l growth and substrate u t i l i z a t i o n , a method of est i m a t i o n o f c e l l numbers o r biomass i s necessary. A l i t e r a t u r e search showed t h a t measurements o f l e a c h i n g - 29 -k i n e t i c s r e l a t e d to b a c t e r i a l growth have been n e i t h e r c o n s i s t e n t nor systematic. T h i s a r i s e s from the f a c t t h a t no s i n g l e proven method of e s t i m a t i n g b a c t e r i a l numbers has been e s t a b l i s h e d . When T h i o b a c i l l u s f e r r o o x i d a n s i s c u l t u r e d on s o l i d s u b s t r a t e s , i t attaches to the s o l i d surface (Gormely and Duncan, 1974). Because o f t h i s attachment the conventional methods o f e s t i m a t i n g c e l l numbers or c e l l mass ( t u r b i d i t y , dry weight, d i r e c t count) cannot be used. 14 Measurements o f C0 2 f i x a t i o n , oxygen u t i l i z a t i o n , ATP and DNA l e v e l s have been used as estimators o f biomass, but r e q u i r e the use o f complex instruments and techniques. A simple and widely used method f o r e s t i m a t i n g biomass i s the measurement of organic nitrogen or p r o t e i n content; t h i s l a t t e r method u s u a l l y i n v o l v e s a c o l o r i m e t r i c determination and cannot be used when c o l o r e d substances are present. Organic nitrogen i s normally measured usi n g the t o t a l K j eldahl n i t r o g e n a n a l y s i s (AOAC, 1965), but Gormely and Duncan (1974) found t h a t the ammoniojarosite p r e c i p i t a t e , produced during the l e a c h i n g o f m e t a l l i c s u l p h i d e s , would be included as b a c t e r i a l n i t r o g e n . They suggested t h a t a method based on the d i f f e r e n c e between the organic and i n o r g a n i c n i t r o g e n contents o f the media would e l i m i n a t e t h i s problem. - 30 -B a c t e r i a l n i t r o g e n i s then c a l c u l a t e d as the d i f f e r e n c e between Kjeldahl nitrogen (organic and i n o r g a n i c nitrogen) and the d i s t i l l able ammonium i o n co n c e n t r a t i o n ( i n o r g a n i c n i t r o g e n ) . Samples of 1 mL o f s l u r r y were used to measure the Kjeldahl n i t r o g e n (Micro-Kjeldahl technique (AOAC, 1965)) and the d i s t i l l able ammonium i o n con c e n t r a t i o n was measured by the a c i d i m e t r i c method using a p r e l i m i n a r y d i s t i l l a t i o n step (APHA, 1973). Using L-Alanine (15.69%N) a standard curve f o r the t e s t was obtained. Samples c o n t a i n i n g 0.6, 0.8, 1.0, 1.2, 1.4, 1.6 and 1.8 mL of a s o l u t i o n o f L-Alanine (1 mgN/mL) were analysed f o r n i t r o g e n content. The standard curve i s shown i n Figure 3. Twenty i d e n t i c a l samples of s l u r r y were used to measure the accuracy of the t e s t . The probable e r r o r s were c a l c u l a t e d t o be 2.0U f o r the Kjeldahl t e s t and 3.98% f o r the d i s t i l l a b l e ammonia t e s t . FRACTIONATION OF CONCENTRATE Methods f o r sepa r a t i o n by s i z e o f p a r t i c l e s i n the subsieve range are based on d i f f e r e n c e s i n the terminal s e t t l i n g v e l o c i t i e s o f the p a r t i c l e s . C e n t r i f u g a t i o n , e l u t r i a t i o n and sedimentation methods are a l l based on the p r i n c i p l e of g r a v i t y sedimentation. Fig. 3 Standard curve for nitrogen determination. - 32 -E l u t r i a t i o n grades p a r t i c l e s by means of an upward c u r r e n t o f f l u i d , u s u a l l y water or a i r . The process i s the reverse o f g r a v i t y sedimentation ( A l l e n , 1968). C e n t r i f u g a l methods speed up the g r a v i t a t i o n a l s e t t l i n g and are useful f o r s i z e s <5pm where the s e t t l i n g times are long. A number o f apparatus f o r p a r t i c l e s i z e separation has been designed based on these p r i n c i p l e s such as the C y c l o s i z e r ( h y d r a u l i c cyclone e l u t r i a t o r ) , and the Bahco m i c r o p a r t i c l e c l a s s i f i e r ( a i r e l u t r i a t o r combined with a c e n t r i f u g e ) . These apparatus are normally used f o r determination" 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 i n f i n e l y d i v i d e d m a t e r i a l s and are not s u i t a b l e f o r the recovery o f l a r g e amounts of m a t e r i a l . Beaker decantation (Pryor, 1965) i s a simple sedimentation method which does not r e q u i r e any s p e c i a l equipment. The parameter by which p a r t i c l e s are c l a s s i f i e d i s t h e i r f a l l i n g speed which i s not uniquely r e l a t e d to t h e i r s i z e ( A l l e n , 1968), but beaker decantation can be used t o o b t a i n the f r a c t i o n s and subsequently t h e i r s i z e could be measured by some other means. The beaker decantation method i s based on the d i f f e r e n c e i n the f r e e terminal v e l o c i t i e s of s p h e r i c a l p a r t i c l e s o f d i f f e r e n t s i z e s f a l l i n g through a f l u i d a t such r a t e s t h a t the Reynolds' number i s l e s s than 0.2. - 33 -T h e o r e t i c a l s i z e ranges were i n i t i a l l y a r b i t r a r i l y d e f i ned and the f r e e f a l l i n g v e l o c i t i e s (V) o f the s m a l l e s t d e f i n e d p a r t i c l e s i n each f r a c t i o n were c a l c u l a t e d on the b a s i s of the o v e r a l l d e n s i t y of the concentrate according t o Stokes' Law: _ d 2 g (g-P) v rEr"— where: V = f r e e f a l l i n g v e l o c i t y cm/sec 3 a = density o f the p a r t i c l e g/cm P = density of the f l u i d g/cnr 2 g = g r a v i t a t i o n a l a c c e l e r a t i o n cm/sec n = absolute v i s c o s i t y g/cm'sec d = Stokes diameter o f the p a r t i c l e cm T h e o r e t i c a l s e t t l i n g times f o r 6 f r a c t i o n s of diameters <40um were then c a l c u l a t e d f o r a l i q u i d height o f 13.5 cm employed i n the beaker decantation method. Using a mechanical s t i r r e r 100 g o f the concentrate were dis p e r s e d i n a l i t r e o f water with the a i d of a d e f l o c c u l a n t . When the suspension was uniform the o u t s i d e o f the beaker was sharply tapped with a g l a s s rod covered with rubber t u b i n g , and the suspended p a r t i c l e s allowed t o s e t t l e f o r the c a l c u l a t e d time, a f t e r which the supernatant pulp was poured q u i c k l y i n t o a second beaker. The s e t t l e d p a r t i c l e s remained as a compact cake - 34 -which was again d i s p e r s e d i n water and the procedure repeated f i v e more times to e l i m i n a t e the material of smaller s i z e s t h a t was entrapped during s e t t l i n g . The recovered material was then d r i e d and weighed. The c a l c u l a t e d v e l o c i t i e s and t h e o r e t i c a l s e t t l i n g times f o r the d i f f e r e n t f r a c t i o n s obtained are shown i n Table 3. The p a r t i c l e s i z e d i s t r i b u t i o n f o r the b a l l m i l l e d concentrate was obtained from the weight of the d i f f e r e n t f r a c t i o n s and i s shown i n Table 4. The weight percentage of f r a c t i o n seven was c a l c u l a t e d by d i f f e r e n c e since t h i s , the f i n e s t f r a c t i o n , forms a very s t a b l e suspension. The beaker decantation method r e q u i r e s the use o f a d e f l o c c u l a n t i n order to ob t a i n a uniform suspension. A v a r i e t y of d i s p e r s i n g agents are suggested i n the l i t e r a t u r e : Aerosol O.T., sodium l i n o l e a t e , sodium a r s e n i t e , sodium pyrophosphate, sodium s i l i c a t e , potassium c i t r a t e , sodium oxalate (Skinner e t a l , 1965), aerosol N.Y. (Pryor, 1965) and sodium hexametaphosphate (Pinches, 1972). The c r i t e r i a used to s e l e c t the d e f l o c c u l a n t were as f o l l o w s : 1) S o l u b i l i t y o f the d i s p e r s a n t i n water. 2) Amount of f i n e s obtained during the f r a c t i o n a t i o n (the amount o f f i n e s i n d i c a t e s the e f f e c t i v e n e s s of the d i s p e r s a n t ) . - 35 -Table 3 F r a c t i o n s of B a l l m i l l e d Concentrate: T h e o r e t i c a l S i z e Ranges, Free F a l l i n g V e l o c i t i e s and S e t t l i n g Times F r a c t i o n Stokes Diameter f o r C a l c u l a t e d T h e o r e t i c a l S e t t l i n g No. Assumed P a r t i c l e V e l o c i t y Time (sec) For Density (4.3 g/cm3) L i q u i d Height=13.5 cm (nm) (cm/sec) 1 >40 0.992 13.60 2 >32 <40 0.635 21.26 3 >24 <32 0.357 37.81 4 >16 <24 0.159 84.90 5 >8 <16 0.0396 340.90 6 >4 <8 0.009 1500 7 . .<4 Table 4 F r a c t i o n s of B a l l m i l l e d Concentrate: Weight Percentages C o l l e c t e d F r a c t i o n Weight No. Percentage 1 11.55 2 2.33 3 3.86 4 11.95 5 - 32.62 6 18.33 7 19.36 - 36 -3) P o s s i b l e e f f e c t s of r e s i d u a l d i s p e r s a n t on the growth of the 1eaching b a c t e r i a . Based on these c r i t e r i a , sodium a r s e n i t e was r u l e d out f o r p o s s i b l e t o x i c i t y . T r i v a l e n t a r s e n i c ( a r s e n i t e s ) are reported t o be t o x i c f o r b a c t e r i a ( P o r t e r , 1946). R a z z e l l ' s (1963) and Landesman's (1966) s t u d i e s have shown t h a t c a r b o x y l i c a c i d s and f a t t y a c i d s are i n h i b i t o r s of i r o n o x i d a t i o n by T h i o b a c i l l u s f e r r o o x i d a n s ; based on these s t u d i e s sodium l i n o l e a t e , potassium c i t r a t e and sodium oxal a t e were a l s o r u l e d out. The use of sodium s i l i c a t e was not considered due t o the d i f f i c u l t y o f i t s removal by simple washing a f t e r the f r a c t i o n a t i o n . 6.3.1 D e f l o c c u l a n t S e l e c t i o n Tests The f i r s t d i s p e r s i n g agent used was aerosol G.P.G. (sodium d i o c t y l s u l f o s u c c i n a t e i n ethanol and water. Cyanamid Canada Inc.). A 0.1% s o l u t i o n o f t h i s d i s p e r s a n t was prepared and added to a leach t e s t to detect any e f f e c t s on the a b i l i t y of the b a c t e r i a t o e x t r a c t copper from c h a l c o p y r i t e . The r e s u l t of t h i s t e s t i s shown i n Figure 4 compared with a s i m i l a r t e s t i n which no d i s p e r s a n t was added. - 37 -ispersant i r- r 2 4 6 TIME (DAYS) ispersant ispersant 2 4 6 TIME (DAYS) . 4 Effect of aerosol in the growth of T._ ferrooxidans - 38 -The r e s u l t s i n d i c a t e t h a t the copper e x t r a c t i o n over a s i x day pe r i o d was only 20% of the e x t r a c t i o n i n the blank; t h i s d i f f e r e n c e was a t t r i b u t e d t o the presence o f the d i s p e r s a n t aerosol G.P.G. Considering t h a t the a e r o s o l ' s chemical s t r u c t u r e has two l a r g e hydrocarbon chains with hydrophobic p r o p e r t i e s , the molecule then has an a f f i n i t y f o r organic s o l v e n t s . Acetone, chloroform and isopropanol were used t o remove the residues of the aerosol from the f r a c t i o n a t e d concentrate. 10 g o f concentrate were placed i n a separatory funnel and 50 mL of the solvent added. The funnel was v i g o r o u s l y shaken f o r 10 minutes, and the phases allowed t o separate; then a small p o r t i o n of concentrate was withdrawn and t e s t e d f o r MBAS (Methylene Blue A c t i v e Substances) (APHA, 1973). The MBAS t e s t i n d i c a t e d that the f o l l o w i n g amounts of di s p e r s a n t had been e x t r a c t e d by the va r i o u s solvents used: acetone-96%, chloroform-95% and isopropanol-98%. Isopropanol was the most e f f e c t i v e . Concentrate t r e a t e d with isopropanol was then washed with d i s t i l l e d water and d r i e d a t 50°C f o r 24 h, then the b i o l o g i c a l l e a ch t e s t was repeated. This time the copper e x t r a c t i o n was 33% o f t h a t o f the blank, showing t h a t the aerosol maintained i t s i n h i b i t o r y e f f e c t even at very low con c e n t r a t i o n s . - 39 -At t h i s p o i n t two other d i s p e r s i n g agents were considered; sodium hexametaphosphate and Tween 40 (polyoxyethylene (20) s o r b i t a n monopalmitate) both from J.T. Baker Chemical Co., N.J. B i o l o g i c a l l e a c h i n g i n h i b i t i o n t e s t s using 0.1% v/v media of dis p e r s a n t showed no e f f e c t s on the copper e x t r a c t i o n rate by Tween 40; hence t h i s d i s p e r s i n g agent was used i n the f r a c t i o n a t i o n procedures. Subsequent t e s t s with f r a c t i o n s o f concentrate obtained by f r a c t i o n a t i o n showed an unexpected r e t a r d a t i o n i n the copper e x t r a c t i o n r a t e , suggesting t h a t b i n d i n g o f the d i s p e r s i n g agent t o the surface of the mineral during f r a c t i o n a t i o n had taken place and a f f e c t e d i t s l e a c h i n g p r o p e r t i e s . T h i s apparently d i d not occur during the e a r l i e r i n h i b i t i o n t e s t . A more d r a s t i c treatment t o remove r e s i d u a l Tween 40 was then implemented based on the 0ECD method (1976). This method i s used f o r the e x t r a c t i o n o f s u r f a c t a n t s from detergents, and i n v o l v e s a binary e x t r a c t i o n with isopropanol i n the presence of K 2C0 3. Using t h i s method, 99% e x t r a c t i o n s o f the d i s p e r s a n t were obtained. To remove I^CO^, a s e r i e s o f washing steps followed by c e n t r i f u g a t i o n were used u n t i l the l i q u i d medium showed no signs of carbonates; no i n h i b i t i o n occurred when the ma t e r i a l obtained by t h i s procedure was subjected t o l e a c h i n g . - 40 -6.4 PARTICLE SIZE MEASUREMENT The measurement o f p a r t i c l e s i z e i n the subsieve range has been analyzed e x t e n s i v e l y i n the l i t e r a t u r e (Schweyer and Work, 1941; Loveland, 1958; Chamot and Mason, 1938; A l l e n , 1968). The most widely used methods are based on measurements of p h y s i c a l p r o p e r t i e s o f the material p r e v i o u s l y c o r r e l a t e d with the s i z e , such as: l i g h t s c a t t e r i n g , absorption of l i g h t , f i l t r a t i o n by media o f known pore s i z e , sedimentation, c e n t r i f u g i n g , e t c . The s i z e that i s measured w i l l then depend on the method employed. The use of the microscope i s the only method i n which the i n d i v i d u a l p a r t i c l e s are measured and i t i s oft e n used as a standard f o r comparison with other methods. D i r e c t observation and measurement can be made down to l e s s than one micron (Pryor, 1965). The measured p a r t i c l e s i z e depends on the p a r t i c l e shape. The diameter o f an equidimensional p a r t i c l e (sphere or cube) has a s i n g l e value but f o r i r r e g u l a r p a r t i c l e s the s i z e may be expressed by any one of several dimensions (Pryor, 1965) such as the length o f the c i r c u m s c r i b i n g r e c t a n g l e , when the p a r t i c l e i s i n i t s most s t a b l e p o s i t i o n ; by the diameter of a sphere having the same terminal v e l o c i t y ; by the diameter of a sphere having the same volume; and so f o r t h . - 41 -Mar t in 's diameter i s the simplest expression of the diameter o f i r r e g u l a r pa r t i c les and i s s u f f i c i e n t l y accurate when averaged f o r a large number of measurements. I t i s the horizontal dimension b isect ing the projected area of the p a r t i c l e as shown i n Figure 5 (Welcher, 1963). Experimental comparison of various proposed diameters are reported (Chamot and Mason, (1938) to have shown sat is fac tory agreement between Mart in 's diameter and the three actual dimensions of the ind iv idual pa r t i c les ( length, breadth and th ickness). Fig. 5 MARTIN'S DIAMETER d d d d In t h i s study, a microscope eyepiece micrometer ca l ibra ted fo r the object ive i n use against a stage micrometer (Ann Arbor, U .S .A . ) , was used to measure Mar t in 's diameter i n a Leitz-Wetzlar microscope (HM-Lux, Germany). . 1 Preparation of Concentrate fo r Size Measurement A small sample of concentrate was placed on a microscope s l ide and a few drops of water were added. The powder was worked in to the f l u i d using a small glass rod and a cover s l i p was put - 42 -c a r e f u l l y i n place so as to exclude a i r bubbles. Two s l i d e s were prepared f o r each sample and observed under the microscope. The number of p a r t i c l e s counted was 100 c o n s i d e r i n g the standard p r a c t i c e o f a model c l a s s c o n t a i n i n g at l e a s t 25 p a r t i c l e s . For the narrow range of s i z e s examined the count w i l l give a standard e r r o r 10 i n the mean s i z e ( A l l e n , 1968; ASTM, 1974). The average p a r t i c l e diameter was then c a l c u l a t e d by the Sauter mean (mean diameter based on surface) using the f o l l o w i n g expression (Coulson and Richardson, 1976). z z 3 ds = z S z where: n = number o f p a r t i c l e s d = measured Martin's diameter S = t o t a l surface of u n i t mass material The computed p a r t i c l e s s i z e s f o r the d i f f e r e n t f r a c t i o n s o f concentrate are shown i n Table 5. - 43 -Table 5 Average P a r t i c l e S i z e i n F r a c t i o n a t e d Concentrate S i z e C l a s s L i m i t s Based on Stokes diameter P a r t i c l e S i z e vim >32 <40 7.41 >24 <32 5.48 >16 <24 3.56 >8 <16 2.52 >4 <8 1.78 <4 1.07 The values o f p a r t i c l e s i z e s were a l s o used to c a l c u l a t e the s p e c i f i c s u r f a c e area o f the p a r t i c l e s with the f o l l o w i n g expression assuming s p h e r i c a l p a r t i c l e s : 6 6.4.2 Scanning E l e c t r o n Microscope Techniques For p r e - l e a c h i n g observations samples of c h a l c o p y r i t e were obtained from several f r a c t i o n s of the dry-concentrate. Samples f o r p o s t - l e a c h i n g observations were obtained as f o l l o w s : At the end of the leach the contents o f the f l a s k s were f i l t e r e d through Whatman f i l t e r paper #1 and d r i e d i n a i r i n a covered c o n t a i n e r f o r 48 h at 35°C. The specimens to be examined i n the scanning e l e c t r o n microscope were drawn from the surface o f the f i l t e r using a m e t a l l i c s p a t u l a . - 44 -A l l specimens were then mounted on aluminium stubs (14 mm x 14 mm) over a t h i n l a y e r of g r a p h i t e i n ethanol (20% g r a p h i t e (Dag 154) Acheson C o l l o i d s Canada Limited) and coated with gold using a Hummer gold s p o t t e r coater f o r 4 minutes at 170 m i l l i t o r r vacuum and 9 m i l l i a m p e r s D.C. The mounted specimens were examined i n a scanning e l e c t r o n microscope (Autoscan number 26, Etec Corporation) operated a t 20 kV i n the secondary e l e c t r o n emission mode. - 45 -CHAPTER VII EXPERIMENTAL RESULTS AND DISCUSSION SELECTION OF THE INOCULUM AGE When f r e s h medium i n a clos e d system i s i n o c u l a t e d with c e l l s a number o f changes take p l a c e . A f t e r a l a g phase where no increa s e i n c e l l numbers occurs, the c u l t u r e enters a phase o f exponential growth u n t i l some n u t r i e n t i s exhausted o r some by-products reach t o x i c l e v e l s . At t h i s p o i n t the r a t e s o f death and growth are i n e q u i l i b r i u m and the c u l t u r e i s i n the s t a t i o n a r y phase. What f o l l o w s i s a d e c l i n e phase when the death r a t e exceeds the growth r a t e . The length o f the l a g phase i s r e l a t e d t o the age and s i z e o f the inoculum. What i s meant by age i s the time between the s t a r t of growth of the parent c u l t u r e and the t r a n s f e r o f the inoculum t o the subculture (Dean and Hinshelwood, 1966). B a i l e y and O l l i s (1977) found t h a t when young c e l l s are t r a n s f e r r e d , s h o r t l a g phases are obtained and when o l d e r populations are t r a n s f e r r e d long l a g phases r e s u l t , because o l d e r populations have a slower growth r a t e due to n u t r i e n t d e p l e t i o n i n the media and/or the accumulation o f t o x i c products. I t i s c l e a r then, t h a t the i n t r o d u c t i o n o f an a c t i v e c u l t u r e growing i n the exponential phase w i l l reduce the l a g phase. For t h i s study the s e l e c t i o n o f the inoculum age was based on the - 46 -r e s u l t s o f a s e r i e s o f batch leaches c a r r i e d out usi n g i n o c u l a o f v a r i o u s ages between 1-10 days. The copper c o n c e n t r a t i o n was monitored during the leaches and the r e s u l t s used as a measure of inoculum performance. The r e s u l t s are shown i n Figure 6a, b. Figure 6a shows the time elapsed between i n o c u l a t i o n and the maximum copper c o n c e n t r a t i o n found i n s o l u t i o n f o r the d i f f e r e n t inoculum ages. The gradual decrease i n the number of days needed to reach the maximum copper c o n c e n t r a t i o n i n d i c a t e d a shortening o f the l a g phase (assuming a d i r e c t r e l a t i o n s h i p between copper e x t r a c t i o n and c e l l growth), and hence a minimum o f 6 days between t r a n s f e r s would ensure s h o r t l a g times. Figure 6b shows the copper e x t r a c t i o n r a t e as a f u n c t i o n o f the inoculum age. The curve shows t h a t the highest r a t e s were obtained f o r between 6 and 8 day o l d i n o c u l a . Based on these r e s u l t s a s e r i a l s ubculture was s t a r t e d , and r o u t i n e l y performed throughout the experimental study, making t r a n s f e r s every 8 days t o provide i n o c u l a f o r a l l the experiments. 7.2 BACTERIAL GROWTH KINETICS 7.2.1 B a c t e r i a l Growth In t h i s s e c t i o n the r e l a t i o n s h i p between b a c t e r i a l growth and copper e x t r a c t i o n i s explored. I t i s shown t h a t b a c t e r i a l growth was l i m i t e d t o the e a r l y stages o f l e a c h i n g . - 47 -T 1 1 1 1 1 1 1 1 r 1 2 3 4 5 6 7 8 9 10 INOCULUM AGE (DAYS) Fig. 6 Effect of the inoculum age on copper extraction - 48 -An estimate o f the mineral s u r f a c e area c a l c u l a t e d from the mean diameter of the p a r t i c l e s and t h e i r s i z e d i s t r i b u t i o n i n the concentrate was used to c a l c u l a t e the f r a c t i o n of the t o t a l surface area a v a i l a b l e f o r b a c t e r i a l coverage. In order to c a l c u l a t e the number of b a c t e r i a present at any given time during the l e a c h , the n o n - d i s t i l l a b l e n i t r o g e n (n.d.n.) concentration was measured during fermentation i n d u p l i c a t e experiments. The n.d.n. measurements were c o r r e l a t e d to b a c t e r i a l numbers using the values derived by Gormely and Duncan (1974). These 10 workers c a l c u l a t e d that 10 c e l l s are e q u i v a l e n t to 0.191 mg c e l l n i t r o g e n . T h i s gives a lower estimate of b a c t e r i a l numbers compared to those c a l c u l a t e d using Beck's y i e l d (Touvinen, 1972) who reported a nitrogen content of only 0.033 mgN/10^ c e l l s . A t y p i c a l growth curve f o r T h i o b a c i l l u s ferrooxidans growing on c h a l c o p y r i t e i s shown i n Figure 7 with the data tabulated i n Table I (Appendix I ) . The curve shows a l a g phase of 20 h followed by an exponential i n c r e a s e i n c e l l numbers f o r 30 h and a s t a t i o n a r y phase up to 200 h. o 1400 t-H o x 1200 A 00 1000 A 800 c_> 2 600 400 A 200 A T 1 1 1 1— 1 r 20 40 60 80 100 120 140 160 180 100 TIME (HOURS) IX) F i g . 7 B a c t e r i a l Growth o f J _ L f e r r o j ^ i d _ a n s i n copper c o n c e n t r a t e . • B a c t e r i a l numbers vs ti m e . - 50 -7.2.2 Copper E x t r a c t i o n A s e r i e s o f experiments were conducted to i n v e s t i g a t e the r e l a t i o n s h i p between b a c t e r i a l growth and copper e x t r a c t i o n . C e l l numbers, copper c o n c e n t r a t i o n , i r o n c o n c e n t r a t i o n , Eh, and pH were c a r e f u l l y monitored i n b i o l o g i c a l leaches. Figure 8 shows the average values determined i n t h r e e o f such experiments. The data are presented i n Table II (Appendix I ) . A n a l y s i s o f Figure 8 shows t h a t the exponential growth was again l i m i t e d t o the e a r l y stages o f the l e a c h . During t h i s p e r i o d a c l o s e c o r r e l a t i o n between growth and copper and i r o n e x t r a c t i o n s was found. McGoran (1969) conducted s i m i l a r experiments and found t h a t the l o g a r i t h m i c r a t e s of copper r e l e a s e and c e l l m u l t i p l i c a t i o n were i d e n t i c a l , but he f u r t h e r s t a t e d t h a t copper e x t r a c t i o n c o u l d be used as an i n d i c a t o r of growth r a t e . Figure 8 i n d i c a t e s t h a t the bulk o f the copper e x t r a c t i o n occurs during the l a t e l a g phase and s t a t i o n a r y phase. This d i f f e r e n c e i n the growth patterns o f T h i o b a c i l l u s f e r r o o x i d a n s a r i s e s from the f a c t t h a t McGoran estimated h i s b a c t e r i a l c o n c e n t r a t i o n s using a Kjeldahl a n a l y s i s which probably i n c l u d e d the n i t r o g e n content of j a r o s i t e p r e c i p i t a t e formed during the l e a c h . - 51 -T u 1 1 1 1 l i " • 2 4 6 8 10 12 14 16 18 20 TIME (DAYS) F i g . 8 Bioleaching data average f o r three experiments Soluble copper and iron concentrations Cel l n u m b e r s , pH, Eh - 52 -During the leach the pH g r a d u a l l y decreased, i n d i c a t i n g b a c t e r i a l a c t i v i t y . A c i d production stops (minimum pH i s reached) a t the same time t h a t the maximum copper co n c e n t r a t i o n i s reached. The Eh i n c r e a s e i s a l s o an i n d i c a t o r of b a c t e r i a l a c t i v i t y . I t i s caused by the o x i d a t i o n of f e r r o u s i r o n . This r i s e i n p o t e n t i a l has been p r e v i o u s l y r e l a t e d to l o g a r i t h m i c growth (Touvinen, 1972). The t r a n s i t i o n from the l o g a r i t h m i c growth phase to the s t a t i o n a r y phase shown i n Figures 7 and 8 could be caused by a number o f environmental f a c t o r s . N u t r i e n t exhaustion and accumulation of by-products are known to cause the change from l o g a r i t h m i c growth to s t a t i o n a r y phase i n m i c r o b i a l c u l t u r e s . For the b i o l e a c h i n g of c h a l c o p y r i t e , the by-products are s u l p h u r i c a c i d and j a r o s i t e s . The pH values i n d i c a t e t h a t the production of s u l p h u r i c a c i d had lowered the pH but i t was s t i l l w i t h i n the normal range of growth of T h i o b a c i l l u s ferrooxidans. J a r o s i t e p r e c i p i t a t i o n becomes s i g n i f i c a n t above Eh values o f 500 mv (Torma, 1977), where most of the i r o n present i s i n the f e r r i c form from which hydroxides and j a r o s i t e s are formed. T h i s change of growth phase from l o g a r i t h m i c to s t a t i o n a r y occurred when the Eh values were below 500 mV and so cannot be a t t r i b u t e d to t h i s phenomena. - 53 -It i s assumed then, t h a t n u t r i e n t l i m i t a t i o n s caused the change o f growth phase, i n t h i s case the a v a i l a b i l i t y o f an energy source which f o r the b i o l e a c h i n g o f c h a l c o p y r i t e i s provided by the concentrate s u r f a c e . Above 500 mV of Eh the p r e c i p i t a t i o n o f j a r o s i t e s becomes s i g n i f i c a n t and may e x p l a i n the decrease i n the copper e x t r a c t i o n r a t e between days 4-6 and u l t i m a t e l y the ter m i n a t i o n of copper e x t r a c t i o n . This may be because the ammonium and potassium ions are s t r i p p e d out o f s o l u t i o n when the j a r o s i t e s are formed. The j a r o s i t e t h a t p r e c i p i t a t e s over the mineral s u r f a c e (see photographs of leached p a r t i c l e s , s e c t i o n 7.5), w i l l cause mass t r a n s f e r l i m i t a t i o n s o f carbon d i o x i d e , oxygen and n u t r i e n t s from the bulk o f the s o l u t i o n t o the b a c t e r i a attached to the su r f a c e . An estimate o f the magnitude o f p r e c i p i t a t e s o f b a s i c f e r r i c sulphates and j a r o s i t e can be obtained when the i r o n and copper con c e n t r a t i o n s i n s o l u t i o n are compared. The chemical composition o f the c h a l c o p y r i t e CuFeSg i n d i c a t e s t h a t equal amounts of copper and i r o n are produced when the mineral d i s s o l v e s . F i g u r e 9 shows the copper/iron r a t i o (average values f o r 3 leaches) and i n d i c a t e s t h a t h y d r o l y s i s and p r e c i p i t a t i o n r e a c t i o n s are t a k i n g p l a c e because the r a t i o i s always >1. - 54 -2.4 J — i 1 1 1 — 6 8 10 12 TIME (DAYS) Fig. 9 Average Values of Copper/Iron Ratios for 3 Leaches - 55 -7.2.3 Surface Area U t i l i z a t i o n The t o t a l s u r f a c e area f o r the 7.5 g o f concentrate used i n each of the b i o l o g i c a l leaches was c a l c u l a t e d from the mean diameters o f the p a r t i c l e s and the s i z e d i s t r i b u t i o n o f the concentrate, 2 and has a value of 4.96 m (Table I I I , Appendix I ) . The average dimensions o f one bacterium (length 1.0 urn and breadth 0.6 urn) can be used t o c a l c u l a t e the surfac e area covered by a s i n g l e bacterium, assuming an e l l i p t i c a l form f o r i t s p r o j e c t e d area. Thus, the s u r f a c e area covered by a s i n g l e bacterium 2 would be approximately 0.5 ym . The number of b a c t e r i a times the surface area used by one b a c t e r i a would then give an estimate of the surface covered by b a c t e r i a at any given time. It i s assumed t h a t a l l b a c t e r i a are found a s s o c i a t e d with the mineral and none can be found i n the l i q u i d phase. Pinches (1972) has shown t h i s t o be t r u e up to the end o f the exponential phase. F i g u r e 10 shows the percentage o f the t o t a l s u r f a c e covered by b a c t e r i a a g a i n s t time f o r the average values of c e l l numbers obtained i n thre e leaches. The data are presented i n Table IV (Appendix I ) . The curve i n Figure 10 shows a maximum coverage a f t e r 4 days when 88% of the surface i s covered by b a c t e r i a . The chemical - 56 -Fig. 10 Bacterial coverage of the mineral surface - 57 -a n a l y s i s data of t h i s concentrate showed t h a t 86.9% of the ma t e r i a l i s s u l p h i d e , which suggests t h a t the b a c t e r i a a t t a c h s e l e c t i v e l y t o the sulphide phase over gangue m a t e r i a l s present i n the concentrate. Berry (1978) showed t h a t the attachment of T h i o b a c i l l u s ferrooxidans t o low-grade waste-rock surfaces was s p e c i f i c t o exposed FeS 2 and CuFeS 2 r e g i o n s . Myerson and K l i n e (1983), a r r i v e d a t the same c o n c l u s i o n a f t e r c a l c u l a t i n g a surface 2 u t i l i z a t i o n value o f 122 ym / c e l l f o r coal with a sulphide content o f 1.66% when they compared t h i s value with the sulphide 2 u t i l i z a t i o n value per bacterium (0.5 ym ). Our experiments then i n d i c a t e t h a t most of the a v a i l a b l e surface i s covered by b a c t e r i a 4 days a f t e r i n o c u l a t i o n and f u r t h e r supports the hypothesis o f a change i n growth phase due t o sur f a c e area l i m i t a t i o n s . 7.2.4 Leaching i n the Absence of B a c t e r i a To evaluate the c o n t r i b u t i o n o f chemical l e a c h i n g to the copper e x t r a c t i o n obtained i n the b i o l o g i c a l l e a c h i n g experiments, a s t e r i l e l e a ch was s e t up. - 58 -No b a c t e r i a were introduced and s t e r i l e c o n d i t i o n s were provided by adding phenol which i s a known germicide. Porter (1946) reported t h a t a r a t i o o f 1:70 v/v phenol:media was e f f e c t i v e i n 10 minutes f o r Staphylococcus aureus, the most r e s i s t a n t o f the four species he examined. This same r a t i o was used i n the s t e r i l e c o n t r o l ; microscopic examination f a i l e d t o d e t e c t any microorganism i n the media c o n t a i n i n g phenol. The r e s u l t s f o r the a n a l y s i s o f samples f o r the s t e r i l e run are t a b u l a t e d i n Table V i n Appendix I and shown i n Figure 11. During the s t e r i l e run the Eh values remained constant, an i n d i c a t i o n o f the low l e v e l s o f o x i d a t i o n of fe r r o u s i r o n . Duncan (1972) i n d i c a t e d t h a t there i s seldom any f e r r o u s i r o n present when the b a c t e r i a are a l i v e . The h y d r o l y s i s o f f e r r i c i r o n which generates a c i d was t h e r e f o r e almost n i l and no a c i d was formed. The pH curve i n d i c a t e s consumption o f a c i d , probably due t o a l k a l i n e gangue and to chemical e x t r a c t i o n o f copper and i r o n . Given the low values o f copper e x t r a c t i o n (2.95%) obtained during the s t e r i l e experiment, no account f o r chemical l e a c h i n g was introduced i n the c a l c u l a t i o n s o f copper e x t r a c t i o n i n the b i o l o g i c a l l e a c h i n g experiments. - 59 -Fig. 11 Chemical Leaching of Chalcopyrite - 60 -EFFECTS OF PARTICLE SIZE ON THE LEACHING OF COPPER A s e r i e s of experiments using monosized f r a c t i o n s of copper concentrate was conducted. Results of these experiments are t a b u l a t e d i n Tables VI-XI (Appendix I ) , and the equations f o r copper c o n c e n t r a t i o n as a f u n c t i o n of time, f i t t e d by the method o f l e a s t squares are given. Figure 12 presents the r e s u l t s f o r the l e a c h i n g of copper using c h a l c o p y r i t e concentrates having the f o l l o w i n g mean p a r t i c l e s i z e s : 1.07, 1.78, 2.52, 3.56, 5.48 and 7.41 nm. Experiments u s i n g the 3.56 nm f r a c t i o n were conducted i n t r i p l i c a t e to v e r i f y the accuracy of the measurements, and the r e s u l t s are p l o t t e d together i n Figure 12. The s e r i e s of curves obtained i n d i c a t e s t h a t the amount of copper e x t r a c t e d increased when the p a r t i c l e s i z e decreased from 5.48 nm to 1.07 nm, with the maximum being obtained f o r the 1.07 nm f r a c t i o n . The extent of the copper e x t r a c t i o n was maximum f o r the 1.07 nm f r a c t i o n and could not be reached with any other p a r t i c l e s i z e . This suggests t h a t f o r the case when the ore p a r t i c l e s have s i z e s s maller or equal t o the bacterium s i z e the attachment of p a r t i c l e s to the c e l l surface i n c r e a s e s the l e a c h i n g r a t e . M i c r o s c o p i c examination o f the c u l t u r e showed a tangled mass of b a c t e r i a and p a r t i c l e s i n the fermentation broth which was not found f o r any other p a r t i c l e s i z e . - 61 -- i 1 1 1 1 1 1 1 1 1 1 1 1 20 40. 60 80 100 120 140 160 180 200 220 240 260 TIME (h) Fig. 12 Effect of particle size on the copper extraction - 62 -The e x t r a c t i o n rate was approximately constant during the leach f o r the l a r g e r s i z e s (7.41, 5.48 and 3.56 urn), while a two rate curve was obtained f o r the smaller s i z e s (2.52, 1.78 and 1.07 um). Two rate copper e x t r a c t i o n curves would r e s u l t from the two phases of growth of the b a c t e r i a . The f i r s t rate would occur when the c e l l s are growing l o g a r i t h m i c a l l y and surface i s a v a i l a b l e . The second lower rate would occur f o r the s t a t i o n a r y phase when the surface becomes l i m i t i n g . For the p a r t i c l e s i n the l a r g e r s i z e s (>3.56 ym) the surface was r a p i d l y covered with b a c t e r i a during the f i r s t few hours of the leach and surface l i m i t a t i o n occurred e a r l i e r i n the le a c h ; consequently the curves showed a trend towards a s i n g l e copper e x t r a c t i o n r a t e . Copper e x t r a c t i o n r a t e s as a f u n c t i o n o f the p a r t i c l e diameter are shown i n Figure 13. The copper e x t r a c t i o n rate i n c r e a s e s as the p a r t i c l e s i z e decreases. The upper p a r t o f Figure 13 shows how the surface i n c r e a s e s with reduction of the p a r t i c l e diameter. If the e x t r a c t i o n rate was a unique f u n c t i o n o f the surface area a v a i l a b l e , then the e x t r a c t i o n rate would increase i n a s i m i l a r f a s h i o n . A p l o t o f copper e x t r a c t i o n versus s p e c i f i c surface would produce a s t r a i g h t l i n e . Figure 14 shows such a p l o t f o r the experimental data. - 63 -11 1 i 1 1 1 1 1 1 r 1 2 3 4 5 6 7 8 PARTICLE DIAMETER ( ym) Fig. 13 Copper extraction rates as a function of the particle diameter — i 1 1 1 1 — 1 r~ .2 .4 .6 .8 1.0 1.2 1.4 SPECIFIC SURFACE AREA (m 2 /g) F i g . 14 Extraction rate as a function of the surface area. - 65 -Using f r a c t i o n s o f d i f f e r e n t s i z e s o f z i n c sulphide concentrate i n s i m i l a r experiments Sanmugasunderam (1981) found a p r o p o r t i o n a l i n c r e a s e between z i n c e x t r a c t i o n r a t e and s p e c i f i c 2 s u r f a c e area up t o s p e c i f i c surface area values o f 1.1 m /g and reported t h a t beyond t h i s value i n c r e a s e s i n s p e c i f i c surface area had almost no e f f e c t on z i n c e x t r a c t i o n r a t e . The r e s u l t s o f t h i s study show t h a t the maximum in c r e a s e i n the copper e x t r a c t i o n r a t e of c h a l c o p y r i t e occurred when the 2 s p e c i f i c surface area increased from 0.78 to 1.3 m /g. 7.3.1 Changes i n the P a r t i c l e S i z e D i s t r i b u t i o n During Leaching The p a r t i c l e s i z e used to c h a r a c t e r i z e each f r a c t i o n of the concentrate, was i n f a c t the average s i z e o f a group o f p a r t i c l e s w i t h i n a small range of s i z e s . The d i s t r i b u t i o n o f s i z e s i s l i k e l y to change as the leach progresses when i n c r e a s i n g amounts of material are d i s s o l v e d and o x i d i z e d . In order to determine these changes a s e r i e s o f measurements o f 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 i n d i f f e r e n t leaches was made. Samples o f concentrate were withdrawn from the f l a s k s using a Pasteur p i p e t t e and t h e i r s i z e d i s t r i b u t i o n was determined using the technique described i n m a t e r i a l s and methods. - 66 -F i g u r e s 15, 16 and 17 show the p a r t i c l e s i z e d i s t r i b u t i o n f o r the 1.78, 2.52 and 5.48 nm leaches. A gradual s h i f t towards the s m a l l e r s i z e s i s e vident (see Figure 18). I t was not p o s s i b l e to q u a n t i f y the amount o f p a r t i c l e s of s i z e below 0.5 pm which appear to in c r e a s e r a p i d l y during the fermentation, Ps a r e s u l t the average p a r t i c l e diameter c a l c u l a t e d from the s i z e d i s t r i b u t i o n d i d not appear to change very much during the l e a c h (see Figure 18). The changes i n s i z e could only be e x a c t l y q u a n t i f i e d i f the t o t a l contents of the f l a s k were analyzed, or a mass-based d i s t r i b u t i o n determined and some c o r r e c t i o n f a c t o r introduced to account f o r the i n c r e a s e i n mass due to the o x i d a t i o n and j a r o s i t e p r e c i p i t a t i o n processes. APPLICATION OF THE SHRINKING CORE MODEL OF LEVENSPIEL The r e s u l t s o f the t e s t s to determine the copper e x t r a c t i o n rate obtained i n leaches of s i x monosize f r a c t i o n s presented i n s e c t i o n 7.3, and the p a r t i c l e diameter and surface area data f o r the same leaches were used to c a l c u l a t e the o v e r a l l e x t r a c t i o n a g a i n s t time curve f o r the b i o l o g i c a l l e a c h i n g of a copper concentrate of known p a r t i c l e s i z e d i s t r i b u t i o n by using the Levenspiel model. Data f o r t h i s c a l c u l a t i o n are presented i n Table II.1 (Appendix I I ) . • DAY 1 3.225 urn 5 30 Q. 20 15 10 5 DAY 10 2.051 v im DAY 3 2.9506 y m DAY 7 2.5427 DAY 12 1.9789 p m DAY 14 1.7815 F i g . 15 Changes in the par t i c le s ize d i s t r i b u t i o n for the 1.78 ym Leach (Percentage vs par t i c l e s ize) DAY 1 3.2768 ym 35 . 30 £ 25 20 . 15 . 10 -5 DAY 3 3.024 ym DAY 7 2.517 ym DAY 10 3.031 ym DAY 12 2.04 ym DAY 14 1.3494 ym CO J Z L ym F i g . 16 Changes in the par t i c le s ize d i s t r ibu t ion for the 2.52 ym leach. (Percentage v s :par t i c l e size) 35 . 30 . 25 . 20 . 15 • 10 • 5 • 40 35 • 30-25 • 20-15 • 10. 5 • 40 • 35 . 30-25 ' 20-15-10' 5-DAY 0 6.1284 ym ~1—I DAY 1 5.3763 ym tL DAY 3 6.1514 ym DAY 5 6.1515 ym ZL DAY 7 4.7941 ym DAY 10 6.1641 ym DAY 14 6.1136 ym l O M CO >t O l O CM PO lO KO 00 O f-t CO T—< 1 I t I ym DAY 17 6.2368 ym F i g . 17 Changes in the par t i c le size d i s t r i b u t i o n for the 5.48 ym leach. (Percentage vs pa r t i c l e s ize) - 70 -1 1 • 2.52 ym leach o 5.48 ym leach A 1.78 ym leach 10 -9 -1= 3 8-e> jcvj Q. Q-c ! c 7 -LU M 1 2 4 6 8 10 12 14 16 18 TIME (DAYS) F i g . 18 Average p a r t i c l e s ize for 3 d i f ferent leaches vs time. - 71 -A sample c a l c u l a t i o n of the copper e x t r a c t i o n a f t e r 48 h o f b i o l o g i c a l l e a c h i n g p r e d i c t e d by the s h r i n k i n g core model i s shown i n Appendix I I . The p r e d i c t e d values of copper e x t r a c t i o n versus time are shown i n Figure 19. Experimental r e s u l t s from a s e r i e s o f leaches u s i n g copper concentrate of known p a r t i c l e s i z e d i s t r i b u t i o n are a l s o shown i n Figure 19 f o r comparison purposes with data shown i n Table 11.3 (Appendix I I ) . Previous attempts t o use the s h r i n k i n g core model can be summarized as f o l l o w s : 1) Gormely (1973) working with z i n c sulphide concentrates, p r e d i c t e d values of z i n c e x t r a c t i o n using the s h r i n k i n g core model t h a t were below the experimental e x t r a c t i o n s by a f a c t o r of ten. He estimated the l e a c h i n g r a t e s f o r d i f f e r e n t p a r t i c l e s i z e s based on a constant l e a c h i n g r a t e per u n i t surface area. This study has shown t h a t the l e a c h i n g r a t e s need t o be determined experimentally. 2) Samugasunderam (1981) obtained z i n c e x t r a c t i o n s w i t h i n 10% o f the p r e d i c t e d values (with a maximum d i f f e r e n c e o f 25%). He a t t r i b u t e d t h i s d i f f e r e n c e to the method he used t o estimate s u r f a c e area and p a r t i c l e diameter. Although the method used f o r surface area and p a r t i c l e diameter determination i n t h i s - 72 -• Experimental Value • Predicted values using the shrinking core model 50 -o cn UA CL. ex. CD 40 -30 -I CJ3 o cm 20 -10 • — i 1 1 — 100 200 300 LEACHING TIME (h) Fig. 19 Experimental and theoretical copper extraction values for the leaching of chalcopyrite. - 73 -study was d i f f e r e n t , the model p r e d i c t i o n s f e l l i n the same range, which suggests the e x i s t e n c e o f a f a c t o r r e l a t e d to m i c r o b i a l physiology t h a t has not been incorporated i n the model and causes these d e v i a t i o n s . POST LEACHING OBSERVATIONS A s e r i e s o f scanning e l e c t r o n photographs were taken o f several f r a c t i o n s of the concentrate p r i o r t o and a f t e r l e a c h i n g . The o b j e c t i v e was t o o b t a i n i n f o r m a t i o n on the nature of the attack by T h i o b a c i l l u s f e r r o o x i d a n s on the surface of the m i n e r a l . Figure 20 shows p a r t i c l e s of c h a l c o p y r i t e before l e a c h i n g . In g e n e r a l , the faces of the p a r t i c l e s are smooth s u r f a c e s , while the edges are h i g h l y i r r e g u l a r . Figure 21 shows c h a l c o p y r i t e p a r t i c l e s a f t e r 200 h of l e a c h i n g . A c a v i t y with dimensions s i m i l a r t o the dimensions o f one bacterium i s present i n the centre of the p a r t i c l e shown i n F i g u r e 21a. A s e r i e s o f c a v i t i e s c o v e r i n g s u r f a c e areas approximately equal to the areas covered by one bacterium are present i n Figure 21b. The b a c t e r i a seem t o at t a c h only t o the c e n t r a l p o r t i o n o f the p a r t i c l e s f a r from the edges. T h i s same phenomena was p r e v i o u s l y a t t r i b u t e d to s u r f a c e t e n s i o n e f f e c t s (Berry, 1978). I t i s c l e a r t h a t the edges of the p a r t i c l e s w i l l F i g . 20 C h a l c o p y r i t e p a r t i c l e s before leaching - 75 -10 ym 10 ym j 1 F i g . 21 C h a l c o p y r i t e p a r t i c l e s a f t e r 200 h of leaching - 76 -be subject t o f r i c t i o n a g a i n s t other p a r t i c l e s when the suspension o f p a r t i c l e s i s a g i t a t e d . The shear f o r c e s generated during a g i t a t i o n w i l l make i t d i f f i c u l t f o r the b a c t e r i a t o at t a c h t o the edges of the p a r t i c l e s . Small d e p o s i t s of hexagonal c r y s t a l s s i m i l a r t o j a r o s i t e c r y s t a l s appear as small granules a t the sur f a c e s o f the p a r t i c l e s . The amount of these d e p o s i t s increases with time. P a r t i c l e s o f c h a l c o p y r i t e a f t e r 300 h of l e a c h i n g are almost covered by these d e p o s i t s (Figure 22). The presence o f j a r o s i t e d e p o s i t s on top o f the c h a l c o p y r i t e p a r t i c l e s prevents the contact between the b a c t e r i a and the n u t r i e n t s found i n the l i q u i d phase, when material subjected t o 300 h of le a c h i n g was recovered and n u t r i e n t s o l u t i o n and inoculum added, no f u r t h e r e x t r a c t i o n could be obtained. See r e s u l t s i n Figure 23. If j a r o s i t e p r e c i p i t a t i o n was avoided or the p r e c i p i t a t e removed by r e - g r i n d i n g the m a t e r i a l , then the copper y i e l d of the process would i n c r e a s e . F i g . 22 C h a l c o p y r i t e p a r t i c l e s a f t e r 300 h of l e a c h i n g - 78 -Fig 23 Second - Pass Leaching of Chalcopyrite - 79 -CHAPTER VIII SUMMARY AND CONCLUSIONS 1. An experimental i n v e s t i g a t i o n was undertaken to study the a p p l i c a t i o n o f the s h r i n k i n g core model of Levenspiel to the modelling o f copper e x t r a c t i o n from c h a l c o p y r i t e by T h i o b a c i l l u s  f e r r o o x i d a n s . 2. M i c r o s c o p i c a l examination o f the p a r t i c l e s subject to l e a c h i n g supported the idea of a s h r i n k i n g core type of r e a c t i o n . 3. The p r e d i c t e d e x t r a c t i o n s using the s h r i n k i n g core model f i t the experimental r e s u l t s and are useful t o p r e d i c t the copper e x t r a c t i o n up t o 30-35% e x t r a c t i o n l e v e l s . Since no account f o r the p h y s i o l o g i c a l s t a t e o f the bacterium i s in c l u d e d i n the model, i t tends t o overestimate the copper e x t r a c t i o n which l e v e l s o f f a f t e r 120 h of l e a c h i n g . The d e p o s i t o f a s o l i d l a y e r o f o x i d a t i o n products which l i m i t e d the r a t e o f d i f f u s i o n o f n u t r i e n t s and metabolic products to and from the c e l l s a t the r e a c t i n g s u r f a c e , was found t o be re s p o n s i b l e f o r the incomplete e x t r a c t i o n . 4. Using e l e c t r o n microphotographs the s o l i d r e a c t i o n product d e p o s i t s were i d e n t i f i e d as j a r o s i t e s and t h e i r appearance on the mineral surface was found t o be d i r e c t l y r e l a t e d t o the end of the copper e x t r a c t i o n . - 80 -5. In order t o determine the e f f e c t s o f the p a r t i c l e s i z e on the l e a c h i n g o f copper, the <400 mesh concentrate was f r a c t i o n a t e d i n t o 7 p a r t i c l e s i z e s and each f r a c t i o n was leached s e p a r a t e l y . The mineral p a r t i c l e s of various s i z e s were o x i d i z e d simultaneously and independently with v a r y i n g l e a c h i n g r a t e s dependent on t h e i r surface area. The highest r a t e was obtained f o r p a r t i c l e s o f 1 urn s i z e and had a value o f 28.3 mg Cu/l.h. These r e s u l t s i n d i c a t e t h a t the optimum p a r t i c l e s i z e was reached when the p a r t i c l e s of c h a l c o p y r i t e had a s i z e comparable t o the b a c t e r i a l s i z e and t h a t the extent o f the e x t r a c t i o n obtained a t t h i s s i z e (97%) could not be reached with any other p a r t i c l e s i z e . 6. To understand the r o l e o f the b a c t e r i a i n the l e a c h i n g process, the growth patterns o f T h i o b a c i l l u s ferrooxidans were determined. Using organic and i n o r g a n i c n i t r o g e n determinations to measure b a c t e r i a l growth, the l a g time was shortened t o <1 day when inoculum from a 6-8 days o l d c u l t u r e was used t o seed the new f l a s k s . T h is study provided evidence t h a t the bulk o f the copper e x t r a c t i o n (62% of the t o t a l e x t r a c t i o n ) occurred once the c u l t u r e had entered the s t a t i o n a r y phase and t h a t no d i r e c t r e l a t i o n s h i p e x i s t e d between metal e x t r a c t i o n r a t e s and b a c t e r i a l growth. - 81 -RECOMMENDATIONS FOR FUTURE STUDIES Studying the k i n e t i c properties; o f i n d i v i d u a l mineral p a r t i c l e s provides an i n s i g h t to the l e v e l of m i n e r a l - b a c t e r i a i n t e r a c t i o n s , which i n turn serves t o c l a r i f y the mechanism of le a c h i n g . In a d d i t i o n to what was done i n t h i s work, f u r t h e r s t u d i e s are required regarding the e f f e c t s o f the changes i n pH and redox p o t e n t i a l produced by the b a c t e r i a l metabolism and the leached products because the d i r e c t i o n and i n t e n s i t y o f b a c t e r i a l s y n t h e s i s i s known to depend on these parameters. The d i s s o l v e d oxygen co n c e n t r a t i o n should a l s o be studied since i t plays a very important r o l e given the o x i d a t i v e c h a r a c t e r i s t i c s o f t h i s process. High oxygen demands would l i k e l y r e s u l t i n oxygen d e p l e t i o n given the l i m i t e d oxygen s o l u b i l i t y o f the medium. Studies are a l s o r e q u i r e d to i n v e s t i g a t e the chemical r e a c t i o n s r e s u l t i n g i n the p r e c i p i t a t i o n of j a r o s i t e type m a t e r i a l s and i t s e f f e c t s on b a c t e r i a l metabolism. The use of a continuous c u l t u r e c o u l d prove valuable i n studying the e f f e c t s of these and other parameters and i n so doing would increase the co n t r o l over the process and s e l e c t the optimum operating c o n d i t i o n s f o r the l e a c h i n g o f copper from c h a l c o p y r i t e . - 82 -CHAPTER IX REFERENCES Agathe, A.D., Korczynski, M.S., and Lundgren, D.G. E x t r a c e l l u l a r Complex from the Culture F i l t r a t e of F e r r o b a c i l l u s f e r r o o x i d a n s . Canadian Journal of M i c r o b i o l o g y . , l b , ZbD ( i y b 8 ) . A i b a , S., Humphrey, A.E., and Mil l i s , N.F. Biochemical Engineering, U n i v e r s i t y o f Tokyo Press, Tokyo (1973). A l l e n , T. P a r t i c l e S i z e Measurement i n Powder Technology S e r i e s , ed. by J.C. Williams, Chapman and Hall L t d . , London (1968). AOAC. O f f i c i a l Methods of A n a l y s i s o f the A s s o c i a t i o n o f O f f i c i a l A g r i c u l t u r a l Chemists. 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Van Nostrand Company Inc. 6th E d i t i o n 351 (1963). - 89 -TABLE 1.1 BACTERIAL GROWTH DATA Time (hours) Ammonia Nitrogen (ppm) Kjeldahl Nitrogen (ppm) C e l l Nitrogen (ppm) C e l l Numbers x l O " 1 0 (1) (2) (1) (2) (1) (2) (1) (2) 21 1886.26 1862.56 1886.26 1886 .26 0 23.7 0 151 27 1672.89 1672.89 1815.14 1767 .72 142.25 94.83 906 604 44.5 1578/05 1554.34 1767.72 1744 .01 189.67 189.67 1208 1208 50.5 1554.34 1530.64 1791.43 1767 .72 237.09 237.09 1208 1510 71.0 1435.80 1412.09 1625.47 1649 .18 189.67 213.38 1208 1359 97.0 1269.84 1317.26 1471.36 1542 .49 201.52 225.23 1283 1434 121.0 1103.88 1222.42 1317.26 1459 .51 213.88 237.09 1510 145.0 1151.3 1198.72 - 1412 .09 - 213.37 - 1359 193.5 1103.88 1103.88 1317.26 1317 .26 213.88 213.88 1359 1359 - 91 -TABLE 1.2 AVERAGE RESULTS FOR THREE BIOLOGICAL LEACHING EXPERIMENTS Time pH Eh Cu Fe Time C e l l (days) (ppm) (ppm) (days) x 10" 2 1.96 386 4033 2533 1 360 4 1.91 460 6750 4150 2 730 6 1.69 567 7875 3537 4 880 9 1.52 665 8000 4350 6 790 11 1.50 676 7933 4375 8 760 13 1.52 676 7833 4366 10 760 15 1.48 680 6750 4158 14 790 17 1 .50 683 5766 3550 16 630 - 92 -TABLE 1.3 CHALCOPYRITE CONCENTRATE SURFACE AREA F r a c t i o n Surface F r a c t i o n Area No. Area (m 2) Percentage 1 9.78045 0.1936 1.8934 2 5.87925 0.1833 1.07766 3 4.15275 0.3262 0.35124 4 2.93925 0.1195 0.35124 5 1.90950 0.0742 0.14168 6 1.37475 0.1032 0.14187 Total area i n 7.5 g of concentrate = 4.96047 m 2 TABLE 1.4 BACTERIAL COVERAGE OF THE SURFACE AREA DATA Time Area Occupied Percentage of Total C e l l (days) By B a c t e r i a Surface Covered Numbei x 1 0 " I U ynr By B a c t e r i a x 10" 1 180 36.29 360 2 365 73.58 730 4 440 88.70 880 6 395 79.63 790 8 380 76.61 760 10 380 76.61 760 - 93 -TABLE 1.5 STERILE RUN DATA Time pH Eh Copper Iron (h) Cone. Cone. (ppm) (ppm) 0 2.0 355 0 0 44.5 2.17 355 795 532 97.5 2.17 355 820 525 143.75 2.25 355 880 550 215.25 2.26 355 880 520 J - 94 -TABLE 1.6 LEACH DATA USING MONOSIZED MATERIAL OF 1.07 Pm Time pH Eh Cu Fe (h) (ppm) (ppm) 28 2.03 385 2125 540 69.5 1.81 415 3825 1650 115 1.63 575 7000 3850 158.5 1.49 610 8300 5550 208 1.49 650 8750 6350 256.5 1.58 660 9700 6500 305 1.46 660 10000 6450 1.57 660 [Cu] = 0.02833 t + 2.4834 TABLE 1.7 LEACH DATA USING MONOSIZED MATERIAL OF 1.78 um Time (h) pH Eh Cu (ppm) Fe (ppm) C e l l s x 10-10 24 2.06 345 1357 785 178 72.25 1.89 540 3532 1750 446 168 1.52 560 4157 3900 446 i 240.5 1.47 560 4357 4225 535 286 1.53 550 4507 4225 446 c n 337 1.52 570 4807 4325 535 i [Cu] = 0.00894 + 2.1053 TABLE 1.8 LEACH DATA USING MONOSIZED MATERIAL OF 2.52 w Time pH . Eh Cu Fe C e l l s (h) (ppm) (ppm) x l O - 1 0 22 2.19 355 1057 785 446 70.25 1.93 530 2407 1650 713 166 1.49 560 3107 3325 446 238.5 1.47 545 3408 3500 535 i 284 1.52 550 3508 3500 535 <£> 335 1.47 575 3807 3550 535 CTi I [Cu] = .00766 t + 1.4576 - 97 -TABLE 1.9 LEACH DATA USING MONOSIZED MATERIAL OF 3.56 um Time pH Eh Cu Fe (h) (ppm) (ppm) 28 2.05 505 1450 830 69.5 1.74 560 1950 1950 115 1.51 620 2250 2450 158.5 1.43 625 2400 2350 208 1.39 640 2700 2900 256.5 1.47 640 2800 2875 305 1.40 660 2900 3050 [Cu] = 0.004971 t + 1 .5399 - 98 -TABLE 1.10 LEACH DATA USING MONOSIZED MATERIAL OF 5.48 um Time pH Eh Cu Fe (h) (ppm) (ppm) 18 1.98 525 572 532 73 1.83 565 922 1025 124.4 1.73 565 1172 1900 171.65 1.60 560 1321 1900 241.9 1.56 560 1421 2000 337.65 1.46 555 1771 2300 409.15 1.42 550 1872 2350 [Cu] = .00315 t + 0.6730 -TABLE 1.11 LEACH DATA USING MONOSIZED MATERIAL OF 7.41 um Time pH Eh Cu Fe (h) (ppm) (ppm) 24 1.95 395 782 717 72.25 1.88 535 1307 1050 160 1.57 550 1807 1300 240.5 1.47 545 2108 1400 [Cu] = .00315 t + 0.6730 - 99 -APPENDIX II - 100 -APPENDIX II Sample C a l c u l a t i o n f o r The Copper E x t r a c t i o n Using The S h r i n k i n g Core Model o f Levenspiel C a l c u l a t i o n s f o r the percentage copper e x t r a c t i o n are done f o r 50 h o f l e a c h i n g time. The s i z e d i s t r i b u t i o n o f the concentrate i s given i n Table 4. Percentage Copper E x t r a c t i o n For the f i r s t f r a c t i o n with mean diameter 1.07 vm 2 ssa = s p e c i f i c surface area of the p a r t i c l e s = 1.30 m /g r z = copper e x t r a c t i o n r a t e = 28.33 mg/l.h. w = weight f r a c t i o n = 0.1936. then S surface area c o n c e n t r a t i o n of the p a r t i c l e s S feed pulp d e n s i t y x weight f r a c t i o n x ssa r S z/s Z i L a x 1 ™ 0 J ! x 0 i 1 9 3 6 x ! .30406 m 2 = 27.049 m2/L 70 mL L ^ g copper e x t r a c t i o n rate per u n i t s o l i d surface area r z/s .001047 g/h.m - 101 -with the density of the c h a l c o p y r i t e concentrate being 4.3 x 1 0 6 g/m3. The time f o r complete r e a c t i o n o f one p a r t i c l e i s given by: T = = 2196.47 h The f r a c t i o n a l e x t r a c t i o n w i l l then be c a l c u l a t e d using equation 3, page 24: 2 T 3 z = 3 (|)- 6 (^) + 6 (|) £l - exp (-T/t)J z = 3 ( 5 0 ) - 6 ( 5 0 V + 6 ( 5 0 ) 3 f l - exp ( - 2 1 9 6 - 4 7 2196.47 21 96.47 21 96.47 L 50 z = '0.065 The f r a c t i o n a l e x t r a c t i o n o f the r e s t o f the 6 f r a c t i o n s o f the copper concentrate are s i m i l a r l y c a l c u l a t e d and tabulated i n Table II.2. The t o t a l copper e x t r a c t i o n a f t e r 50 h o f le a c h i n g i s found to be 16.15%. - 102 -TABLE II.1 KINETIC DATA FOR THE SHRINKING CORE MODEL P a r t i c l e S p e c i f i c Surface Area Release S i z e Surface Area Concentration Rate of Copper (nm) (m2/g) (m 2/L) (mg/Lh) 1.07 1.30406 27.049 28.33 1.78 0.7839 15.395 8.94 2.52 0.5537 19.352 7.66 3.56 0.3919 5.0176 4.31 5.48 0.2546 2.024 3.15 7.41 0.1883 2.026 5.89 TABLE II.2 CALCULATED PERCENTAGE EXTRACTION AFTER 50 h OF LEACHING F r a c t i o n Diameter ssa r z / s Weight F r a c t i o n T C o n t r i b u t i o n nm m2/g mg/h.m2 (h) 1 1.07 1.3040 1.047 0.1936 2196.47 0.06525 2 1.78 0.7839 0.580 0.1833 6590.23 0.02241 3 2.52 0.5537 0.645 0.3262 8387.9 0.01767 4 3.56 0.3919 0.859 0.1195 8900.28 0.01666 5 5.48 0.2546 1.550 0.0742 7570.4 0.01954 6 7.41 0.1883 2.907 0.1032 5480.0 0.02686 Calc u l a t e d Total E x t r a c t i o n = 16.15% - 104 -TABLE 11.3 COPPER CONCENTRATION DATA FOR BIOLOGICAL LEACHING OF CHALCOPYRITE ppm of copper Time (h) 24 3199 3059 3259 3079 47.8 5120 4460 5040 4860 69.25 6921 5460 6661 5981 116.8 9581 7179 8780 9781 144 9781 9981 8780 9781 183 9581 10781 9581 10181 214.5 10181 11182 9380 11182 239.25 9581 9380 9581 10181 284.8 9781 11582 9781 10381 PERCENTAGES OF COPPER EXTRACTION FOR BIOLOGICAL LEACHING OF CHALCOPYRITE ppm of copper Time (h) 24 10.74 10.27 10.94 10.33 47.8 17.18 14.97 16.92 16.31 69.25 23.23 18.33 22.36 20.08 116.8 32.16 24.10 29.47 26.79 144 32.83 33.50 29.47 32.83 183 32.16 36.19 32.16 34.18 214.5 34.18 37.54 31.49 37.54 239.25 32.16 31.49 32.16 34.18 284.8 32.83 38.88 32.83 34.85 

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