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The chemical stability of heavy metal xanthates Sheikh, Naseeruddin 1972

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THE CHEMICAL STABILITY OF HEAVY METAL XANTHATES b y Naseeruddi n Shei kh B.Sc. (Hons.) M.Sc. A Thesis Submitted in Partial .Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY in the Department of MINERAL ENGINEERING We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA January, 197-2 I n p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree a t t h e U n i v e r s i t y o f B r i t i s h C olumbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . ( N . Sheikh ) Department o f M i n e r a l Eng ineer ing The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada March T , 1972 ( i ) ABSTRACT The p r e c i p i t a t i o n o f l e a d , copper and i r o n xanthates was s t u d i e d as a f u n c t i o n of metal and xanthate ion c o n c e n t r a t i o n . These p r e c i p i t a t e s were suspended i n aqueous s o l u t i o n s of pH 3.5 to 11.5 and 25° to 60°C. The concen-t r a t i o n s of xanthate and metal ions obta ined upon d i s s o l u t i o n of the metal xanthates were measured to e s t a b l i s h t h e i r s o l u b i l i t i e s as f u n c t i o n s of pH and temperature . The concurrent h y d r o l y s i s and decomposi t ion of these ions l e d to the f o r m a t i o n o f i n s o l u b l e products such as metal s u l p h i d e s , hydrated oxides and carbonates . These became d e p o s i t e d on the u n d i s s o l v e d f r a c t i o n o f . t h e metal xanthate p r e -c i p i t a t e . The u l t r a v i o l e t and i n f r a r e d s p e c t r o s c o p i c methods and X - r a y d i f f r a c -t i o n , d i f f e r e n t i a l thermal a n a l y s i s and vapour phase chromatography were used t o c h a r a c t e r i s e the products of d e c o m p o s i t i o n . The s t a t e of o x i d a t i o n of copper and i r o n i n the corresponding metal xanthate was i n v e s t i g a t e d w i t h the a i d of. EPR, ESCA and s t u d i e s of the Mossbauer e f f e c t . Cuprous and f e r r i c e t h y l x a n t h a t e s were found to be the s t a b l e forms. Ferrous ions d i d not r e a c t w i t h xanthate i o n s . A hydroxyxanthate o f i r o n was detec ted at pH 5 to 6 by Mossbauer s t u d y . The optimum pH f o r the f o r m a t i o n 3+ of dixanthogen i n Fe / ( E t X ) system was found to be i n the range o f 2 .5 to 3 . 7 . ( i i ) TABLE OF CONTENTS CHAPTER 1. INTRODUCTION 1 1.1 The Use o f Xanthates as S u r f a c t a n t s 1 1.2 The Mechanism of A d s o r p t i o n o f Xanthate on S u l p h i d e M i n e r a l s 2 1.3 The Role o f Oxygen i n S u l p h i d e M i n e r a l F l o t a t i o n 3 1.4 The Nature o f Chemical Species Adsorbed on S u l p h i d e M i n e r a l s 5 1.5 The Chemical and P h y s i c a l P r o p e r t i e s of Heavy Metal Xanthates 6 1.5.1 Lead E t h y l x a n t h a t e (PbX 2 ) 7 1.5.2 I r o n E t h y l x a n t h a t e ( F e X 3 ) 7 1.5.3 Cuprous E t h y l x a n t h a t e ( C u 2 X 2 ) 8 1.6 The E f f e c t o f Temperature and pH on the S t a b i l i t y o f Heavy Metal 9 1.6.1 The E f f e c t o f Temperature 9 1.6.2 The E f f e c t of pH 10 1.7 O b j e c t i v e of Research Undertaken 11 CHAPTER 2. THE PREPARATION AND CHARACTERIZATION OF MATERIALS 14 2.1 Potass ium E t h y l x a n t h a t e (KEtX) 14 2.2 Dixanthogen ( X 2 ) 14 2.2.1 The Use o f Vapour Phase Chromato-graphy (UPC) to Determine the P u r i t y o f Dixanthogen 17 2.3 Lead E t h y l x a n t h a t e 18 2.4 Ferrous E t h y l x a n t h a t e 20 2.5 F e r r i c E t h y l x a n t h a t e 20 2.6 Cuprous E t h y l x a n t h a t e 21 ( i i i ) Page CHAPTER 3 . EXPERIMENTAL TECHNIQUES AND PROCEDURES . . . 24 3 .1 The Use o f X - r a y P h o t o e l e c t r o n Spectroscopy to Measure the O x i d a t i o n S t a t e of Copper i n Copper E t h y l x a n t h a t e 24 3 . 1 . 1 Theory and A p p l i c a t i o n s 24 3 . 1 . 2 The Exper imenta l D e t e r m i n a t i o n 27 3 .2 The A p p l i c a t i o n o f Mossbauer Spectroscopy to the C h a r a c t e r i z a t i o n of I r o n E t h y l x a n t h a t e 27 3 . 2 . 1 Chemical o r I s o m e r ' S h i f t (s) 28 3 . 2 . 2 Quadrupole S p l i t t i n g ( A E Q or A) 29 3 . 2 . 3 Exper imental Procedures 31. 3 .3 The Use o f the D i f f e r e n t i a l Thermal A n a l y s i s 32 3 . 3 . 1 Technique to Study F e r r i c E t h y l X a n t h a t e : T h e o r e t i c a l I n t r o d u c t i o n . 32 3 . 3 . 2 Exper imenta l Procedure 3 3 3.4 The Exper imenta l Procedure Employed to Study the E f f e c t o f pH and Temperature on Heavy Metal Xanthate 33; " 3 , 5 The A p p l i c a t i o n o f U l t r a - V i o l e t Spectroscopy to the A n a l y s i s o f the Xanthate S o l u t i o n . . . 34 3 . 5 . 1 The E l e c t r o n i c T r a n s i t i o n i n Xanthates 2 5 3 . 5 . 2 The D e t e r m i n a t i o n o f Xanthate Ion C o n c e n t r a t i o n by UV Spectrometer _35 3.6 The A p p l i c a t i o n o f E l e c t r o n Paramagnetic Resonance to a Study of the O x i d a t i o n S t a t e o f Copper i n Copper E t h y l x a n t h a t e . 36 3 . 6 . 1 T h e o r e t i c a l Aspects o f EPR i a t f 3 . 6 . 2 Exper imenta l Technique 38 3.7 IR Study of Heavy Meta lxanthates 38a CHAPTER 4 . THE STABILITY OF SUSPENSION OF LEAD ETHYLXANTHATE IN AQUEOUS SOLUTIONS . . . . . . . 39 4 . 1 The P r e c i p i t a t i o n o f Lead E t h y l x a n t h a t e 39 4 . 1 . 1 Exper imenta l Procedure 40 4 . 1 . 2 R e s u l t s and D i s c u s s i o n 41 ( i v ) Page 4.2 The E f f e c t o f A c i d i c S o l u t i o n s on Lead E t h y l x a n t h a t e 46 4.3 The E f f e c t o f A l k a l i n e S o l u t i o n s on Lead E t h y l x a n t h a t e 49 4.4 The Formation o f Dixanthogen i n the Course o f D i s s o l u t i o n o f Lead E t h y l x a n t h a t e 54 4.5 The I n f r a r e d S p e c t r o s c o p i c Study o f Lead E t h y l x a n t h a t e and I t s D e r i v a t i v e s 54 4.6 The A p p l i c a t i o n of Thin Layer Chromatography to the I d e n t i f i c a t i o n o f Dixanthogen 57 4.7 I d e n t i f i c a t i o n o f Lead E t h y l x a n t h a t e Decomposit ion Products by X - r a y D i f f r a c t i o n 60 CHAPTER 5. THE STABILITY OF CUPROUS ETHYLXANTHATE IN AQUEOUS SOLUTIONS -63 5.1 The P r e c i p i t a t i o n Study o f Cuprous E t h y l x a n t h a t e 63 5.2 The E f f e c t o f pH and Temperature on Cuprous _ E t h y l x a n t h a t e ..6.5 5.2.1 The E f f e c t o f A c i d i c S o l u t i o n s on Copper E t h y l x a n t h a t e 65 5.2.2 The E f f e c t o f A l k a l i n e S o l u t i o n s on Copper E t h y l x a n t h a t e 66 5.3 The K i n e t i c s o f D i s s o l u t i o n and Decomposit ion o f Copper E t h y l x a n t h a t e i n A c i d i c and A l k a l i n e So 1 u t i o n s _6.9j 5.4 E l e c t r o n Paramagnetic Resonance Study o f Copper E t h y l x a n t h a t e ;74 5.5 The X - r a y P h o t o e l e c t r o n S p e c t r o s c o p i c Study o f Copper E t h y l x a n t h a t e and I t s D e r i v a t i v e s 77 5.6 V i s i b l e E f f e c t s Due to Atmosphere on C u 2 ( E t X ) 2 83 5.7 IR S p e c t r a o f Decomposit ion Products o f C u 2 ( E t X ) 2 86 (v) Page 5.8 The X - r a y D i f f r a c t i o n Study of the Decomposit ion Products o f C u 2 ( E t X ) 2 94 CHAPTER 6. THE STABILITY OF SUSPENSION OF FERRIC ETHYLXANTHATE 95 6 .1 The P r e c i p i t a t i o n Study o f F e r r i c E t h y l x a n t h a t e 95 6 .2 The E f f e c t s o f A c i d i c and B a s i c S o l u t i o n s o f F e r r i c E t h y l x a n t h a t e 97 6 .3 The K i n e t i c s o f D i s s o l u t i o n and Decomposit ion o f F e ( E t X ) 3 i n A c i d i c and B a s i c S o l u t i o n s . 100 6.4 S t a b i l i t y o f F e r r i c E t h y l x a n t h a t e i n Organic S o l v e n t s 105 6 .5 P h y s i c a l Appearance o f F e r r i c E t h y l x a n t h a t e Prepared a t Var ious pH Values 107 6.6 V i s i b l e E f f e c t s of A c i d i c and B a s i c S o l u t i o n s on F e ( E t X ) 3 108 6 .7 A Study o f F e r r i c E t h y l x a n t h a t e by Means o f Mossbauer E f f e c t 110 6 .8 IR Spec t ra o f F e ( E t X ) 3 and I t s Decomposit ion Products 120 6.9 The DTA and X - r a y D i f f r a c t i o n S t u d i e s o f the Decomposit ion Products o f F e ( E t X ) 3 127 CHAPTER 7. GENERAL DISCUSSION 129 7.1 P r e c i p i t a t i o n o f Heavy Metal Xanthates 130 7.2 The S t a b i l i t y o f Heavy Metal Xanthates i n Aqueous S o l u t i o n s 131 7 .2 .1 The E f f e c t o f pH 132 7 . 2 . 2 The E f f e c t o f Temperature 133 7.3 Xanthate Ion C o n c e n t r a t i o n 136 7.4 Metal Ion C o n c e n t r a t i o n 136 7.5 Formation o f Metal Complexes w i t h Xanthate Ions 136 7.6 S o l i d S t a t e React ions i n Heavy Metal Xanthates 137 7.7 The Chemical Nature o f Copper E t h y l x a n t h a t e 137 ( v i ) Page 7.8 The Chemical Nature of I ron E t h y l x a n t h a t e 139 7.9 The Formation o f F e r r i c E t h y l x a n t h a t e and Dixanthogen 140 SUMMARY AND CONCLUSIONS 142 REFERENCES 144 APPENDIX A 150 APPENDIX B 153 ( v i i ) LIST OF FIGURES F i g u r e Page 1 Schemetic Diagram of X - r a y P h o t o e l e c t r o n Spectrometer (ESCA) 26 2 Mossbauer Parameters 30 3 P r e c i p i t a t i o n Regions o f P b ( E t X ) 2 Obtained on M i x i n g KEtX and Pb(N0 3 )2 of V a r y i n g C o n c e n t r a t i o n s 42 4 R e l a t i v e T u r b i d i t y a g a i n s t Time Curve f o r P r e c i p i t a t i o n o f P b ( E t X ) 2 43 5 S t a b i l i t y o f P b ( E t X ) ? a t Var ious pH Values and a t 25°C 47 6 S t a b i l i t y o f P b ( E t X ) 2 a t Var ious pH Values and a t 45°C 48 7 Lead Ion C o n c e n t r a t i o n as a F u n c t i o n o f Time i n T r e a t i n g P b ( E t X ) 2 a t Var ious pH values and a t 45 and 25°C 50 8 Absorbed E l e c t r o n Images o f P b ( E t X ) 2 (510X) 51 9 Photographs showing the Changes i n the Appearance o f P b ( E t X ) 2 Due to PbS Formation 53 10 I n f r a r e d S p e c t r a of P b ( E t X ) 2 and I t s Decomposit ion Products 56 11 P r e c i p i t a t i o n Regions o f Cuprous E t h y l x a n t h a t e . . . 64 12 UV Spec t ra of the Aqueous S o l u t i o n s o f C u 2 ( E t X ) 2 . 67 13 Changes i n the I n i t i a l pH Values Due to the Decomposit ion and H y d r o l y s i s o f the Compounds o f C u 2 ( E t X ) 2 71 14 Copper Ion C o n c e n t r a t i o n as a F u n c t i o n o f Time i n C u 2 ( E t X ) 2 a t Var ious pH Values and Temperatures . . 73 15 EPR Spec t ra of Copper E t h y l x a n t h a t e 74a 16 X - r a y P h o t o e l e c t r o n Spec t ra of the Reference Compounds o f Copper 80 17 X - r a y P h o t o e l e c t r o n Spec t ra of Copper E t h y l x a n t h a t e and I t s Decomposit ion Products • 82 18 Appearance o f Cuprous E t h y l x a n t h a t e A f t e r Treatment a t Var ious pH Values and Temperatures . . 84 19 ' IR S p e c t r a o f E ther Treated C u J E t X ) 9 87 ( v i i i ) F i g u r e Page 20 E s t i m a t i o n o f C u 2 ( E t X ) 2 by IR 89 21 Some D e t a i l s o f IR Spec t ra o f the Decomposit ion Products o f Cuprous E t h y l x a n t h a t e and Reference Compounds 91,92 22 P r e c i p i t a t i o n Regions of F e r r i c E t h y l x a n t h a t e . . . 96 23 UV Spec t ra o f the S o l u t i o n s From Suspension o f F e ( E t X ) 3 99 24 The V a r i a t i o n s i n pH, F e r r i c and Xanthate Ion 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 a t 25 C 103 25 The V a r i a t i o n s i n pH, F e r r i c and Xanthate Ion 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 a t 45°C 104 26 The V a r i a t i o n s o f pH, F e r r i c and Xanthate Ion C o n c e n t r a t i o n as a F u n c t i o n o f Time a t 60°C 106 27 V i s i b l e E f f e c t s o f A c i d i c and B a s i c S o l u t i o n s on F e ( E t X ) 3 109 28 Mossbauer Spec t ra of F e ( E t X ) 3 112 29 Mossbauer Spectrum of F e ( E t X ) 3 115 30 Mossbauer Spec t ra F e ( E t X ) 3 119 31 IR Spec t ra of F e ( E t X ) 3 121 32 IR Spec t ra of I ron Compounds 124 33 IR Spec t ra o f Fe(X)3 Suspension a t pH 9 .5 and 45°C A f t e r Var ious Time I n t e r v a l s 126 ( i x ) LIST OF TABLES Table Page 1 S o l u b i l i t y Product (Ksp) o f Heavy Metal Xanthates 6 2 The P r o p e r t i e s o f Dixanthogen ( X 2 ) as A f f e c t e d by the Use o f D i f f e r e n t O x i d i z i n g Agents 19 3 Chemical A n a l y s i s o f L e a d , Copper and Iron E t h y l xanthates 23 4 I d e n t i f i c a t i o n o f Dixanthogen i n Hexane E x t r a c t s o f P b ( E t X ) 2 Suspension by Chromatography 58 5 I n t e r p l a n a r Spacings and R e l a t i v e R e f l e c t i o n s f o r P b ( 0 H ) 9 , P b C O v PbS, P b ( E t X ) 9 and I t s Decomposit ion Products f 62 6 Xanthate Ion C o n c e n t r a t i o n A f t e r 4 Hours o f S o l u t i o n Treatment i n Case o f Ether Treated and Untreated Cuprous E t h y l x a n t h a t e 72 7 The E l e c t r o n B i n d i n g Energies o f Copper E t h y l x a n t h a t e and Re la ted Compounds 79 8 Sample P r e p a r a t i o n o f F e ( E t X ) - and Rela ted Compounds I l l 9 Mossbauer Parameters f o r F e ( E t X ) , and Re la ted Compounds a t 78°C 7 116 (x) L i s t o f Symbols KEtX E t X " x 2 P b ( E t X ) 2 C u 2 ( E t X ) 2 F e ( E t X ) 3 C u ( E t X ) 2 FeCE'tX) 2 = Potass ium E t h y l x a n t h a t e CCH 3 -CH 2-0 -C-SV") S II _ = E t h y l x a n t h a t e i o n ( C H 3 - C H 2-0 - C - S ] • S S = Dixanthogen ( C ^ - O - C - S - S - C - O - C ^ ) S S = Lead E t h y l x a n t h a t e ( C 2 H 5-0 - C - S - P b - S - C-0 - C 2 H 5 ) S = Cuprous E t h y l x a n t h a t e { ( C 2 H 5-0 - C - S ) 2 Cu 2> F e r r i c E t h y l x a n t h a t e {(Fe ( C 2 H 5-0 - C - S ) 3 > S H C u p r i c E t h y l x a n t h a t e {(Cu ( C 2 H 5-0 - C - S ) 2 ) Ferrous E t h y l x a n t h a t e {(Fe (C 2 Hg-0 -C-S) 2 } 9 ( x i ) Acknowledgement I w i s h to express my s i n c e r e thanks to D r . J . L e j a for h i s a d v i c e and guidance throughout the course o f t h i s s t u d y . My thanks are a l s o due to D r . G.W. P o l i n g f o r h i s u s e f u l sugges t ions and to P r o f e s s o r J . B . Evans f o r h i s h e l p and encouragement. I would l i k e to thank D r . A . R . Lane f o r h i s he lp i n spending many hours i n d i s c u s s i o n . I am g r a t e f u l to D r . J . R . Sams and M r . J . C . S . S c o t t o f the Department o f Chemistry f o r t h e i r h e l p w i t h the Mossbauer S t u d y . The he lp g i v e n by D r . A . I s h i t a n i i n ESCA Study i s g r a t e f u l l y acknowledged. I am a l s o g r a t e f u l to D r . Z . Dogan "and D r . R . S . Pa thania f o r t h e i r h e l p i n p r e p a r i n g t h i s t h e s i s . My thanks are a l s o due to Miss C l a r e L e j a f o r her a s s i s t a n c e i n t y p i n g t h i s t h e s i s . The f i n a n c i a l s u p p o r t g i v e n by CIDA under the Colombo P l a n i s g r a t e f u l l y acknowledged. CHAPTER I INTRODUCTION The s a l t s of d i t h i o c a r b o n i c a c i d , g e n e r a l l y known as x a n t h a t e s , have been o f c o n s i d e r a b l e research i n t e r e s t s i n c e 1922. T h e i r r o l e i n impor tant i n d u s t r i a l processes such as those o f c e l l u l o s e s y n t h e s i s , rubber p o l y m e r i z a t i o n and the manufacture o f p e s t i c i d e s was f u l l y e s t a b l i s h e d a t the b e g i n n i n g o f t h i s c e n t u r y . C. H . K e l l e r i n t r o d u c e d xanthates to the minera l i n d u s t r y i n 1924. He c la imed i n h i s patent tha t these compounds were the most e f f e c t i v e c o l l e c t i n g agents f o r s u l p h i d e m i n e r a l s . S ince then they have been w i d e l y used i n t h i s c a p a c i t y . T h e i r u t i l i t y as c o l l e c t o r s was thought to be due to the d i s s o c i a t i o n o f the molecule i n water to g i v e xanthate ions which adsorbed a t the s o l i d / l i q u i d i n t e r f a c e o f the minera l p a r t i c l e s . 1.1 The Use o f Xanthates as S u r f a c t a n t s S Only the a l k a l i metal x a n t h a t e s , R - 0 - C - S _ K + ( N a , e t c . ) , are used as c o l l e c t o r s i n f l o t a t i o n p r a c t i c e . The n o n - p o l a r group R i n these cases r e p r e -sents a s h o r t c h a i n hydrocarbon r a d i c a l - C g H ^ ) . Potassium e t h y l x a n t h a t e denoted by KEtx i s the most important compound o f t h i s c l a s s , and consequent ly has been the most w i d e l y s t u d i e d . I t was the f i r s t xanthate i n v e s t i g a t e d i n which the bond between the s u l p h u r and the metal atom was proved to be l a r g e l y i o n i c i n c h a r a c t e r . The c r y s t a l l o g r a p h i c s tudy (1) based on the l a t t i c e p a r a -meters l e d to the b e l i e f t h a t the molecule c o u l d be represented as a h y b r i d o f the f o l l o w i n g three r e s o n a t i n g m o l e c u l a r s t r u c t u r e s . S s" s" I! - « /• C 5 H , - 0 - C - S t CoH,0-C = S ± C J - L - O - C V (2) Potassium e t h y l x a n t h a t e i s prepared by d i s s o l v i n g potass ium hydroxide i n e t h y l a l c o h o l and the a l c o h o l ate thus formed i s a l l o w e d t o r e a c t s l o w l y w i t h carbon d i s u l p h i d e : KOH + C 2 H 5 0 H C 2 H 5 0 K + H 2 0 1.1 C 2 H 5 0 K + C S 2 - C 2 H 5 0CSSK 1.2 The commerc ia l ly a v a i l a b l e product c o n t a i n s i m p u r i t i e s l i k e free a l k a l i , t h i o s u l p h a t e , t r i t h i o c a r b o n a t e , s u l p h i d e and p o l y s u l p h i d e s . These i m -p u r i t i e s and p a r t i c u l a r l y t h e i r products o f o x i d a t i o n may a f f e c t the f l o t a t i o n performance and hence the f r e s h l y prepared xanthate i s p r e f e r r e d f o r f l o t a t i o n . The c o n c e n t r a t i o n of the compound n o r m a l l y used i n f l o t a t i o n pulp before ab--5 s t r a c t i o n i s about 15-35x10 m o l e / 1 . The r e s i d u a l c o n c e n t r a t i o n s i n f l o t a t i o n c e l l s g e n e r a l l y found i s lower by one or two orders of magnitude. 1.2 The Mechanism of A d s o r p t i o n o f Xanthate on S u l p h i d e M i n e r a l s . The f i r s t a d s o r p t i o n theory was put forward by Taggart and h i s c o l -l a b o r a t o r s ( 2 , 3 ) . I t was based on the hypothes i s t h a t s imple d i sp lacement r e a c t i o n s occur between xanthates and s u l p h i d e m i n e r a l s which r e s u l t e d i n the f o r m a t i o n o f i n s o l u b l e , compounds. Taggart suggested t h a t these compounds were r e s p o n s i b l e f o r the f l o t a t i o n . T h i s t h e o r y , however, f a i l e d to e x p l a i n the l a c k of r e a c t i o n of xanthate ions w i t h u n o x i d i z e d s u l p h i d e m i n e r a l s . S u t h e r l a n d and Wark (4) suggested t h a t the a d s o r p t i o n occurred by an i o n exchange mechanism. The xanthate ions were c o n s i d e r e d to exchange w i t h ' 2 - 2 -s u l f o x y l a t e ions (S0^ , S 2 0 3 . ) at the m i n e r a l s u r f a c e . I t was l a t e r po in ted out by Cook and co-workers (5 ,6) t h a t the e x i s t -ence o f the negat ive p o t e n t i a l • ( - 100 - 300 mV) on the s u l p h i d e minera l (3) would not a l l o w the xanthate ions to penetra te the e l e c t r i c a l double l a y e r . In order to ensure the e l e c t r i c a l n e u t r a l i t y o f the f l o a t e d minera l a counter i o n ( i . e . H + ) must adsorb w i t h each i o n . The n e u t r a l m o l e c u l e , x a n t h i c a c i d , was cons idered to be the adsorb ing s p e c i e s . The weakness o f t h i s theory was t h a t i t f a i l e d to e x p l a i n the f l o t a t i o n a t b a s i c pH values where x a n t h i c a c i d was not a v a i l a b l e . ' L e j a (7) suggested t h a t the d i x a n t h o g e n , formed on o x i d a t i o n o f xanthate i n the f l o t a t i o n sys tem, was able to pass through the charged e l e c t r i c a l double l a y e r a t the s u r f a c e and then d i s s o c i a t e d , and chemisorbed on the minera l s u r f a c e . The t h e o r i e s which i n v o l v e d the attachment o f xantha.te ions to the minera l s u r f a c e by i n s o l u b l e compound f o r m a t i o n or by i o n exchange c o u l d not e x p l a i n many o f the exper imental f i n d i n g s on h igh s e l e c t i v i t y of s u l p h i d e s f l o t a t i o n . With the use o f the modern methods o f i n v e s t i g a t i o n i t was found t h a t the r e a c t i o n o f xanthate w i t h s u l p h i d e m i n e r a l s was o f a more complex nature than was f o r m e r l y r e a l i z e d . The presence o f oxygen i n the s o l u t i o n was found to a f f e c t the mode o f a d s o r p t i o n o f xanthate and to l e a d to the presence o f oxygenated spec ies a t the minera l s u r f a c e . 1.3 The Role o f Oxygen i n S u l p h i d e M i n e r a l F l o t a t i o n Most o f the r e s e a r c h , i n t h i s a r e a , has been concerned w i t h galena and the f o l l o w i n g three mechanisms o f s u r f a c e r e a c t i o n s have been proposed : (1) I f galena s u r f a c e s are o x i d i z e d , numerous o x i d a t i o n products are formed. The spec ies t h a t predominates depends on the exper imental c o n d i t i o n s mainta ined i n the p a r t i c u l a r p r o c e s s . Severa l i n v e s t i g a t o r s (4) employed i n f r a r e d spectroscopy (8 ,9) and e l e c t r o c h e m i c a l measurements (10 , 11) to show tha t double decomposi t ion takes p l a c e between xanthate and t h i o s u l p h a t e ions i n a r e a c t i o n which leads to the f o r m a t i o n of l e a d e t h y l x a n -t h a t e . 2PbS + 2 0 2 + H 2 0 P b S 2 0 3 + P b ( 0 H ) 2 1.3 P b S 2 0 3 + 2C 2 H 5 0CSSK + P b ( C 2 H 5 0 C S S ) 2 f K 2 S 2 0 3 1.4 The l e a d e t h y l x a n t h a t e helps to make the s u r f a c e o f galena h y d r o p h o b i c . (2) The oxygen r a i s e d the e l e c t r o c h e m i c a l p o t e n t i a l o f the galena s u r f a c e to a p o i n t where o x i d a t i o n o f xanthate to dixanthogen o c c u r r e d . 2C 2 H 5 0CSS" -v ( C 2 H 5 0 C S S ) 2 + 2e" 1.5 This mechanism was based on e l e c t r o c h e m i c a l o x i d a t i o n o f xanthate a t mercury e l e c t r o d e s and was i n v e s t i g a t e d i n i t i a l l y by Salamy and Nixon ( 1 2 , 13, 14 ) . S t rong bubble adhesion was observed by Tolun and K i t c h e n e r (15) on the galena s u r f a c e a t the p o t e n t i a l corresponding to the xantha te -d ixanthogeh redox poten-t i a l . The mechanism was a l s o i n v e s t i g a t e d by s e v e r a l o t h e r workers (16 , 17) who used m e t a l - s u l p h i d e e l e c t r o d e s . (3) Oxygen was cons idered to e x t r a c t f r e e e l e c t r o n s from the c o n d u c t i o n bands o f galena to change i t from an n- type to a p- type semiconductor w i t h the r e s u l t t h a t the p o t e n t i a l o f anodic areas was r a i s e d to a va lue which a l l o w e d xanthate to be chemisorbed. P l a k s i n e t a l (18 , 19) used autoradiography to show the extreme h e t e r o g e n i t y of xanthate d i s t r i b u t i o n on s u l p h i d e m i n e r a l s , thus p r o v i n g h i s h y p o t h e s i s . (5) 1.4 The Nature o f the Chemical Species Adsorbed on S u l p h i d e M i n e r a l s Dewey ( 2 0 ) , Schuhman (21) and Gaudin [22) i n d i c a t e d two forms o f adsorbed spec ies on c h a l c o c i t e . Both were q u i t e d i s t i n c t i n t h e i r chemical c h a r a c t e r i s -t i c s . E l e c t r o n d i f f r a c t i o n s t u d i e s by Sato (23) and Hagihara (24) o f xanthate a d s o r p t i o n on galena i n . v a r i o u s s t a t e s o f o x i d a t i o n a l s o r e v e a l e d the e x i s t e n c e of two s p e c i e s . The i n f r a r e d s p e c t r o s c o p i c s tudy of adsorbed xanthate on galena under atmospheric c o n d i t i o n s by Greenler ( 8 ) , and the a d s o r p t i o n of xanthate and on vacuum d e p o s i t e d s u l p h i d e f i l m s by P o l i n g L e j a (25) i n d i c a t e d two d i s t i n c t s p e c i e s . These two spec ies were i d e n t i f i e d as a chemisorbed s u r f a c e xanthate (PbX) and a p h y s i c a l l y coadsorbed bulk xanthate ( P b X 2 ) . S p e c i e s , , l i k e those observed i n case of g a l e n a , were found by Yamasaki and Usui (26) on s p h a l e r i t e . S i m i l a r s p e c i e s were observed on p y r i t e s u r f a c e (27) which u n l i k e b u l k i r o n xanthate was i n s o l u b l e i n water and benzene. R e c e n t l y Prasad and Rao (28) i n d i c a t e d the f o r m a t i o n o f dixanthogen ( X 2 ) on g a l e n a , s p h a l e r i t e and molybdenite s u r f a c e s . They f u r t h e r r e p o r t e d l e a d xanthate ( P b X 2 ) and dixanthogen i n a molar r a t i o o f 3:1 on g a l e n a . On the b a s i s of these f i n d i n g s they proposed a c o n f i g u r a t i o n o f xanthate dixanthogen m u l t i l a y e r s . Wood (29) found the m u l t i l a y e r s o f d ixanthogen p h y s i c a l l y adsorbed on p l a t i n u m , g o l d , copper and galena e l e c t r o d e s d u r i n g the e l e c t r o x i d a t i o n of potass ium e t h y l x a n t h a t e . A smal l q u a n t i t y o f dixanthogen (< 1%) was de tec ted by A l i s o n ( 3 0 ) i n the course o f the a n a l y s i s o f r e a c t i o n products ob ta ined from the i n t e r a c t i o n of ga lena w i t h aqueous xanthate s o l u t i o n . I t was g e n e r a l l y accepted t h a t under atmospheric c o n d i t i o n s , the adsorp-t i o n of xanthate on to s u l p h i d e m i n e r a l s r e s u l t e d i n the f o r m a t i o n of two o r (5A) p o s s i b l y three p r o d u c t s . The f i r s t product c o n s i s t e d o f a 1:1 c o o r d i n a t i o n compound (MX i . e . PbX) which i s chemisorbed. T h i s f o l l o w e d a p h y s i c a l l y coadsorbed 1:2 c o o r d i n a t i o n compound (MX 9 i . e . PbX„). (6) In many cases the molecule ( M ^ ) was coadsorbed w i t h dixanthogen to form m u l t i l a y e r s which were h e l d on the m i n e r a l s u r f a c e by Van der Waals ' bonds. The a d s o r p t i o n o f xanthates on t o s u l p h i d e m i n e r a l s as s p e c i f i c s u r f a c e compounds i s c o n s i d e r e d by most Russ ian workers to be the l a t e s t s tage of the theory of a d s o r p t i o n . 1.5 The Chemical and P h y s i c a l P r o p e r t i e s o f Heavy Metal Xanthates The f o r m a t i o n of heavy metal xanthates at metal s u l p h i d e - s o l u t i o n i n t e r f a c e i s an important f a c t o r i n the f l o t a t i o n o f s u l p h i d e m i n e r a l s . Heavy metals l i k e l e a d , copper , i r o n e t c . r e a d i l y form x a n t h a t e s . These compounds are s p a r i n g l y s o l u b l e i n water and have d i f f e r e n t s o l u b i l i t i e s i n o r g a n i c s o l -v e n t s . . The low s o l u b i l i t y o f these compounds i s due to a c o v a l e n t bond between . metal and s u l p h u r atoms. The f o l l o w i n g t a b l e of s o l u b i l i t y product values i s compiled from the l i t e r a t u r e (31 ,32 ,33) and shows t h a t the s o l u b i l i t y of the heavy metal xanthates i n c r e a s e s as the c o v a l e n t c h a r a c t e r o f the bonding decreases . Table 1 S o l u b i l i t y Products (Ksp) o f Heavy Metal Xanthates Metal KS£ Metal Ksp B i 3 + 1 . 2 x l 0 " 2 9 S n 2 + l . O x l O " 1 5 A u + 6 . 0 x l 0 " 2 8 C d 2 + 2 . 6 x l 0 " 1 4 S b 3 + l . O x l O " 2 4 C o 2 + l . O x l O " 1 3 C u + 5 . 2 x l 0 " 2 0 N i 2 + 1 . 4 x l 0 " 1 2 A g + 2 . 5 x 1 0 " 1 9 Z n 2 + 4 . 9 x l 0 " 9 P b 2 + 1 . 7 x l 0 " 1 7 T l 2 + 7 . 9 x l 0 " 8 In f l o t a t i o n research the metal xanthates o f l e a d , i r o n and copper have (7) r e c e i v e d a great deal o f a t t e n t i o n . A b r i e f l i t e r a t u r e review o f the p r o p e r t i e s o f x a n t h a t e s , which form the b a s i s of the present s t u d y , i s g iven i n the f o l l o w i n g paragraphs . 1.5.-1" Lead E t h y l x a n t h a t e ( P b X j Most work r e p o r t e d i n the l i t e r a t u r e has concerned the s tudy of l ead e t h y l x a n t h a t e . In the process of l ead ore f l o t a t i o n , t h i s compound i s thought to e x i s t i n the form of l o o s e l y s c a t t e r e d m u l t i l a y e r s on the galena s u r f a c e . The c r y s t a l s t r u c t u r e has been d e s c r i b e d w i t h p a r t i c u l a r re fe rence to f l o t a t i o n p r o p e r t i e s o f galena by Hagihara and co-workers ( 3 4 , 3 5 ) . The compound i s formed by the s i m p l e s t o i c h i o m e t r i c r e a c t i o n shown below andMs q u i t e s t a b l e a t room temperature : P b 2 + + 2C 2 H 5 0CSS" + P b ( C 2 H 5 0 C S S ) 2 1.6 1 . 5 .2 I ron E t h y l x a n t h a t e ( F e X j The f l o t a t i o n of i r o n s u l p h i d e s i s c o n s i d e r e d to be main ly due to the presence o f dixanthogen a t the minera l s u r f a c e but the c o e x i s t e n c e o f i r o n xanthate cannot be r u l e d o u t . The f o r m a t i o n o f f e r r i c xanthate was f i r s t r e -por ted by Gaudin e t . a l . ( 3 6 ) but no f u r t h e r work was c a r r i e d out to c h a r a c t e r i z e t h i s compound. I t s s t a b i l i t y i n the f l o t a t i o n system has been the s u b j e c t o f a c o n t r o v e r s y concerning i t s decomposi t ion i n t o f e r r o u s xanthate and d i x a n t h o g e n . F e 3 + + 3C 2 H 5 0CSS" + F e ( C 2 H 5 0 C S S ) 3 . 1 .7 2 F e ( C 2 H 5 0 C S S ) 3 -> 2Fe(C 2 H 5 0CSS) 2 + ( C 2 H 5 0 C S S ) 2 1 .8 In an o t h e r mechanism (37) the f o r m a t i o n o f dixanthogen was c o n s i d e r e d (8) to be due to the c a t a l y t i c e f f e c t o f f e r r i c i o n s . ~ 2 F e 3 + + 6 ( C 2 H 5 0 C S S " ) +2Fe(C 2 H 5 0CSS) 3 1.9 Z T e ( C 2 H 5 O C S S ) 3 + 3H 2 0 + 3 / 2 0 2 + 6 C 0 2 -> 3 ( C 2 H 5 0 C S S ) 2 + 2 F e + 3 + 6HC0~ 1 . The f e r r i c ions r e l e a s e d i n r e a c t i o n 1.10 r e a c t w i t h xanthate to form f e r r i c xanthate and the whole c y c l e i s r e p e a t e d . However, the s t u d i e s based on magnetic moment measurements ( 3 8 ) , Mossbauer spectroscopy (39) and X - r a y d i f f r a c t i o n s t u d i e s (40) have i n d i c a t e d tha t the compound was q u i t e s t a b l e w i t h i r o n be ing i n f e r r i c s t a t e . 1 .5 .3 Cuprous E t h y l x a n t h a t e (Cu 2X_ 2) The f o l l o w i n g sequence o f r e a c t i o n s which leads to the f o r m a t i o n of s t a b l e cuprous xanthate i s w e l l known i n F l o t a t i o n C h e m i s t r y . • C u 2 + + 2 (C 2 H 5 0CSS" ) C u ( C 2 H 5 0 C S S ) 2 1.11 2 C u ( C 2 H 5 0 C S S ) 2 -»• Ciu ;C 2 H 5 0CSS) 2 + ( C 2 H 5 0 C S S ) 2 1.12 Monovalent cuprous xanthate i s cons idered to be very s t a b l e a t room temperature . Y e l l o w or orange forms are g e n e r a l l y o b s e r v e d , d u r i n g i t s p r e p a r a t i o n , depending on the c o l l o i d a l s i z e of the p r e c i p i t a t e . No i n f o r m a t i o n i s c u r r e n t l y a v a i l a b l e on the c r y s t a l s t r u c t u r e o f cuprous x a n t h a t e . The e l e c t r i c moment work of M a l a t e s t a (41) and a r e c e n t e l e c t r o n paramagnetic resonance (EPR) s tudy (42) suggest t h a t the d i v a l e n t copper i s the s t a b l e form o f copper x a n t h a t e . (9) C 0 H C OC 'Cu , C O C , H K The f o r m a t i o n of a d i v a l e n t copper xanthate i s a c o n t r a d i c t i o n o f the previous theory which suggested cuprous xanthate to be p r i n c i p a l l y i n v o l v e d i n copper s u l p h i d e f l o t a t i o n . 1.6 The E f f e c t o f Temperature and pH on the S t a b i l i t y o f Heavy Metal Xanthates The heavy metal xanthates are s e n s i t i v e to changes i n pH and temperature of the p u l p . These changes have a pronounced i n f l u e n c e on the hydrophobic c h a r a c t e r of the p r o d u c t s . Not many data are a v a i l a b l e i n the l i t e r a t u r e on these important a s p e c t s . 1.6.1 The E f f e c t o f Temperature Only a few workers have obta ined data which concern the f l o t a t i o n performance of s u l p h i d e minera l s a t e l e v a t e d temperatures . Pomianowski and L i s z k a (43) observed a decreas ing y i e l d i n mercury s u l p h i d e f l o t a t i o n w i t h i n c r e a s e o f temperature . The most i n t e r e s t i n g r e s u l t s on the s e l e c t i v e d e s t r u c t i o n o f c o l l e c t o r f i l m s by thermal a c t i o n have been shown by Glembotski ( 4 4 ) . He c la imed tha t the treatment a t 100°C f o r two minutes des t royed 99.5% o f the adsorbed l a y e r s on c h a l c o p y r i t e , 30% on p y r i t e and 10% o f them on the s p h a l e r i t e s u r f a c e . He b e l i e v e d t h a t the f u t u r e development o f the s e l e c t i v e f l o t a t i o n of complex s u l p h i d e ores would depend on the c o n t r o l o f the thermal (10) s t a b i l i t y of the c o l l e c t o r f i l m s . 1 . 6 .2 . The E f f e c t of pH I f the maximum s e l e c t i v i t y i n f l o t a t i o n i s t o be a c h i e v e d , the pH of the pulp must be ad jus ted to the optimum v a l u e f o r the p a r t i c u l a r p r o c e s s . In general f l o t a t i o n p r a c t i c e , these values are approx imate ly 8.5 to 9.5 f o r c h a l c o p y r i t e , 3.5 to 4 .5 f o r p y r i t e and 9.5 to 10.5 f o r g a l e n a . In e a r l y s t u d i e s (45) i t was observed t h a t heavy metal xanthates decompose i n a l k a l i n e s o l u t i o n s and t h i s ra te of decomposi t ion i s a f u n c t i o n of pH. Fleming (46) i n h i s s t u d i e s on the e f f e c t of a l k a l i n i t y on the f l o t a t i o n of l ead m i n e r a l s , r e a l i z e d t h a t the d e p r e s s i o n might be due to the decomposi t ion o f xanthate c o a t i n g s by a l k a l i n e s o l u t i o n s . A recent s tudy (47) conf irmed t h a t the f i x a t i o n of the adsorbed s p e c i e s on s u l p h i d e m i n e r a l s was dependent on the pH of the medium. Only at a c e r t a i n d e f i n i t e p H , the maximum f l o t a t i o n y i e l d was a c h i e v e d . The f o r e g o i n g l i t e r a t u r e review i n d i c a t e s t h a t heavy metal xanthates have not been s t u d i e d s p e c i f i c a l l y f o r t h e i r behaviour under d i f f e r e n t c o n d i t i o n s p r e v a i l i n g i n f l o t a t i o n systems. The reason f o r t h i s l a c k of i n t e r e s t was probably the b e l i e f t h a t heavy metal xanthates once formed are s t a b l e a n d , , a l s o t h a t the bulk phase xanthates d i d not have the same p r o p e r t i e s as the corresponding compounds present as c o a t i n g s on s u l p h i d e m i n e r a l s . A grea t d i f f i c u l t y was encountered i n the i s o l a t i o n of heavy metal xanthate f r e e of contaminat ion from the minera l p a r t i c l e s . The i n s t r u m e n t a l techniques l i k e X - r a y d i f f r a c t i o n and i n f r a r e d spec t roscopy have conf i rmed t h a t heavy metal (11) xanthates which were removed from minera l " p a r t i c l e s and those prepared c h e m i c a l l y had e x a c t l y the same s t r u c t u r e s . •  -A c c o r d i n g to Kakovsky ( 4 8 ) , under some exper imenta l c o n d i t i o n s , the p r o p e r t i e s o f the s u r f a c e compounds can approach those o f the b u l k chemical compounds. F u r t h e r s t u d i e s on these compounds can p r o v i d e not o n l y a b e t t e r unders tanding o f t h e i r behaviour b u t a l s o an e x p l a n a t i o n of unusual s e l e c t i v i t y ( o r l a c k o f i t ) i n f l o t a t i o n o f s u l p h i d e m i n e r a l s . The pH and the temperature have a pronounced i n f l u e n c e on adsorbed x a n t h a t e s . These f a c t o r s cause pronounced changes on the c o l l e c t o r coated m i n e r a l s and o f the b u l k phase compounds. As a r e s u l t , the f l o t a t i o n pulp c o n t a i n s not on ly xanthates but a l s o the products o f t h e i r d e c o m p o s i t i o n . Some o f these newly formed s p e c i e s , which have d i f f e r e n t f l o t a t i o n p r o p e r t i e s may t r a n s f e r from the s o l u t i o n to the c o l l e c t o r coated m i n e r a l s u r f a c e , and they may change the c o m p o s i t i o n o f the s u r f a c e compounds p r o d u c i n g a . s h a r p change i n the hydrophobic c h a r a c t e r o f the s u r f a c e . " 1.7 O b j e c t i v e s o f the Research Undertaken (1) The aim o f the work undertaken i n t h i s p r o j e c t was to e x p l a i n i n q u a l i t a t i v e and q u a n t i t a t i v e terms the e f f e c t o f temperature and pH changes on the s t a b i l i t y o f metal xanthates o f l e a d , copper and i r o n . I t was b e l i e v e d e a r l i e r (46,47) t h a t the v a r i a t i o n s i n f l o t a t i o n performance were due to the chemical changes i n the bulk p r o p e r t i e s o f these compounds. The changes were b e l i e v e d to occur because metal xanthates were s e n s i t i v e to pH and temperature v a r i a t i o n s . However, no data were a v a i l a b l e on the changes i n the (12) b u l k p r o p e r t i e s of these compounds as a f u n c t i o n o f pH and temperature . S t u d i e s of these compounds over a wide range o f pH (3 to 11) and temperature ( 2 5 ° to 60°C) were undertaken to a s c e r t a i n the chemical changes produced i n the s o l i d s . A f t e r such treatments the s o l i d s and t h e i r s o l u t i o n s were analyzed f o r t h e i r chemical composi t ions by the use of v a r i o u s techniques such as i n f r a r e d and u l t r a v i o l e t - s p e c t r o s c o p y . The changes i n p h y s i c a l appearance and chemical c o m p o s i t i o n o f the compounds were observed under atmospheric c o n d i t i o n s over a p e r i o d of 24 weeks. (2) The second o b j e c t i v e o f t h i s s tudy was to i n v e s t i g a t e the s t a t e of the systems ( d i s p e r s e d versus coagulated) d u r i n g the process o f p r e c i p i t a t i o n of heavy metal xanthates by the use o f v a r i o u s combinations o f c o n c e n t r a t i o n 'Of xanthate and metal i o n s . The data ob ta ined from t h i s s tudy were used to i n t e r p r e t the r o l e of c o n c e n t r a t i o n of xanthate ions i n the f l o t a t i o n o f l e a d , copper and i r o n s u l p h i d e s . (3) The e a r l i e r s t u d i e s i n the f l o t a t i o n research were based on the i n d i c a t i o n s t h a t xanthates of copper and i r o n changed from h i g h e r to lower va lence s t a t e s forming more s t a b l e compounds and d i x a n t h o g e n . L a t e r on some.: i n v e s t i g a t o r s (40,42) repor ted t h a t the metal ions i n these compounds mainta ined t h e i r h i g h e r o x i d a t i o n s t a t e s and s t i l l remained s t a b l e . A more d e t a i l e d study o f t h i s phenomenon w i t h p a r t i c u l a r r e f e r e n c e to f l o t a t i o n was undertaken to e v a l u a t e the changes i n o x i d a t i o n s t a t e . (4) The f l o t a t i o n o f p y r i t e i n a c i d i c pH was a t t r i b u t e d to the f o r m a t i o n o f dixanthogen (49,50,51) and the d e p r e s s i o n of p y r i t e i n s o l u t i o n o f b a s i c pH s (13) was a t t r i b u t e d t o the n o n - a v a i l a b i l i t y of the dixanthogen s p e c i e s . The p o s s i b l e r o l e of f e r r i c xanthate was comple te ly ignored i n t h i s f l o t a t i o n system, d e s p i t e the p r o b a b i l i t y t h a t t h i s compound might make a d e f i n i t e c o n t r i b u t i o n to the p y r i t e f l o t a t i o n . Under atmospheric c o n d i t i o n s , i r o n ions r e s u l t i n the f o r m a t i o n of hydrated ox ides of i r o n i n f l o t a t i o n c i r c u i t s . Some hydroxy compounds are a l s o formed i f pH exceeds 5.0. The f e r r i c e t h y l x a n t h a t e and dixanthogen c o a t i n g s p h y s i c a l l y adsorbed on m i n e r a l p a r t i c l e s are contaminated w i t h the i n s o l u b l e products o f a e r i a l o x i d a t i o n . The h y d r o p h i l l i c c h a r a c t e r o f such o x i d a t i o n products e v e n t u a l l y cause a low r e c o v e r y i n the f l o t a t i o n of i r o n s u l p h i d e s . T h e r e f o r e , w i t h the a s s i s t a n c e o f Mossbauer s p e c t r o s c o p y , the s tudy was undertaken to e v a l u a t e the s t u c t u r a l d i f f e r e n c e s between i r o n xanthates formed a t v a r i o u s pH v a l u e s , w i t h i n the range of p y r i t e f l o t a t i o n p r a c t i c e and o u t s i d e t h i s range. Chapter 2 The P r e p a r a t i o n and C h a r a c t e r i z a t i o n of M a t e r i a l s 2.1 Potassium E t h y l x a n t h a t e (KEtX) Potassium e t h y l x a n t h a t e was prepared a c c o r d i n g to the s t a n -dard methods d e s c r i b e d i n the l i t e r a t u r e (52 , 53 ) . The potassium h y d r o x i d e was d i s s o l v e d i n e t h y l a l c o h o l and the potassium e thox ide thus formed was cooled i n an i c e bath at approx imate ly 10°C. Carbon di s u l p h i de was added d r o p - w i s e to the s o l u t i o n w i t h constant a g i t a t i o n . The p r e c i p i t a t e d potassium e t h y l x a n t h a t e was f i l t e r e d o f f and d r i e d . J h i s crude product was d i s s o l v e d i n acetone and r e p r e c i p i t a t e d by the a d d i t i o n o f an excess o f d i e t h y l e t h e r . A f t e r three rec rys t a l l i z a t i o n s - u s i n g the above s o l v e n t s a pure grade potassium e t h y l x a n t h a t e was o b t a i n e d . The m a t e r i a l was found to c o n t a i n some traces of a l k a l i , so a f i n a l p r e c i p i t a t i o n was e f f e c t e d by r e d i s s o l v i n g the m a t e r i a l i n e t h y l a l c o h o l and r e p r e c i pi t a t i ng the product w i t h e t h e r . A f t e r f i l t r a t i o n and d r y i n g under vacuum a t room temperature , i t was s t o r e d i n a d e s s i c a t o r . The p u r i t y o f t h i s potassium e t h y l x a n t h a t e was found to be b e t t e r than 99% by s p e c t r o s c o p i c (54) and v o l u m e t r i c (55) methods. 2 .2 Dixanthogen ( X ? ) Dixanthogen was prepared as mentioned i n the l i t e r a t u r e (56,57) by (15) the o x i d a t i o n o f potass ium e t h y l x a n t h a t e e i t h e r w i t h an a l c o h o l i c s o l u t i o n o f i o d i n e o r w i t h an aqueous s o l u t i o n o f i o d i n e i n potass ium i o d i d e . Copper s u l p h a t e (58) o r c h l o r i n e (59) was a l s o used i n the p r o d u c t i o n of d i x a n t h o g e n . To improve the y i e l d and p u r i t y o f the compound, Bulmer and Mann (60) u t i l i z e d new o x i d i z i n g agents such as potassium t e t r a t h i o n a t e and ch loramine T (CH^ • CgH^ • S 0 2 ( N * C l ) K ) . A number o f o t h e r o x i d i z i n g agents such as n i t r o u s a c i d , n i t r o s y l c h l o r i d e , benzene s u l p h o n y l c h l o r i d e and cyanogen bromide were a l s o used by these authors f o r the p r e p a r a t i o n o f d i x a n t h o g e n . The chemical r e a c t i o n s which i n v o l v e the use of these reagents are as f o l l o w s : 2C 2 H 5 0CSSK + K I 3 + ( C 2 H 5 0 C S S ) 2 + 3KI 2.1 2C 2 H 5 0CSSK + K 2 S 4 0 6 ( C 2 H 5 0 C S S ) 2 + 2 K 2 S 2 0 3 2.2 CN • B r + H 2 0 + HCN + HOBr . 2.3 2.4 2C 2 H 5 0CSSK + 2H0N0 + ( C 2 H 5 0 C S S ) 2 + 2N0 + 2H 2 0 2 .5 2C 2 H 5 0CSSK + 2N0C1 -> ( C 2 H 5 0 C S S ) 2 + 2NaCl + 2N0 2.6 2C 2 H 5 0CSSK + C H 3 • C g H 4 S 0 2 ( N C l ) K + 2H 2 0 + ( C 2 H 5 0 C S S ) 2 + C H 3 C g H 4 -* S 0 2 N H 2 + KC1 + 2K0H 2.7 2C 2 H 5 0CSSK + C 6 H 5 S 0 2 C 1 -> ( C 2 H 5 0 C S S ) 2 + C g H ^ K + KC1 2 .8 (16) 2C 2 H 5 0CSSK + K 2 S 2 0 g - ( C 2 H 5 0 C S S ) 2 + 2 K 2 S 0 4 2.9 In the s tudy c a r r i e d out by Cambron and Whitby (61) on the e f f i c i e n c y o f a v a r i e t y o f o x i d i z i n g agents f o r the p r o d u c t i o n o f dixanthogen i t was concluded t h a t cyanogen bromide and sodium t e t r a t h i o n a t e were the bes t o x i d i z i n g agents . The cyanogen bromide was c o n s i d e r e d to be very s p e c i f i c i n i t s o x i d i z i n g a c t i o n on x a n t h a t e . In c o n t r a s t , B u l m e r (10) found t h a t chloramine T gave a purer compound w i t h h i g h e r y i e l d . In the e a r l y s t u d i e s n e i t h e r i n s t r u m e n t a l nor exper imenta l technique was d e s c r i b e d to a s c e r t a i n the p u r i t y o f the compounds which were obta ined from the o x i d a t i o n r e a c t i o n s . The o n l y c r i t e r i a o f p u r i t y t h a t were employed were those o f m e l t i n g p o i n t s and exper imental y i e l d s . In the present s t u d y , dixanthogen was prepared by o x i d i z i n g the potassium e t h y l x a n t h a t e w i t h r e a g e n t s ; i o d i n e , cyanogen bromide , c h l o r a -mine T , sodium t e t r a t h i o n a t e , sodium n i t r i t e ( a c i d i f i e d w i t h H ^ O ^ ) and potassium p e r s u l p h a t e . In each p r e p a r a t i o n more than the r e q u i r e d s t o i c h i o -m e t r i c q u a n t i t y o f o x i d i z i n g agent was reac ted w i t h the aqueous s o l u t i o n o f xanthate at a temperature o f 5° +_ 1°C. The o x i d i z i n g agent was added s l o w l y w i t h constant s t i r r i n g . A s o l i d p r o d u c t , p a l e y e l l o w i n c o l o u r , was o b t a i n e d i n every case . The p r e c i p i t a t e d m a t e r i a l was c o l l e c t e d on a ny lon m i l l i p o r e f i l t e r w i t h pores o f 0 . 25^ diameter and was washed f i v e times w i t h d i s t i l l e d water (100 ml each time) a t 10°C. I t was r e c r y s t a l l i z e d from ethanol by making a s a t u r a t e d s o l u t i o n a t room temperature and c o o l i n g t h i s # r e s u l t a n t s o l u t i o n i n an i c e b a t h . Pale y e l l o w prisms were ob ta ined which were f u r t h e r (17) p u r i f i e d by another r e c r y s t a l l i z a t i o n from e t h y l a l c o h o l under the same c o n d i t i o n s . To determine the exper imental y i e l d of dixanthogen obta ined from d i f f e r e n t r e a c t i o n s , the crude product was e x t r a c t e d i n t o hexane. The hexane l a y e r was then washed three times w i t h c o l d d i s t i l l e d water to remove the s o l u b l e i m p u r i t i e s and then t r a n s f e r r e d to a weighed beaker from which o r g a n i c s o l v e n t was removed by vacuum. The dixanthogen r e m a i n i n g . i n the beaker was weighed and the y i e l d was c a l c u l a t e d on the bas i s o f the amount o f potassium e t h y l x a n t h a t e consumed i n the p r e p a r a t i o n . 2.2.1 The Use of Vapour Phase Chromatography (VPC) to Determine the P u r i t y o f Dixanthogen The r e l a t i v e a b i l i t y of the o x i d i z i n g agents to produce dixanthogen f r e e o f i m p u r i t i e s was i n v e s t i g a t e d by vapour phase chromatography. The t w i c e -r e c r y s t a l l i z e d dixanthogen was d i s s o l v e d i n spec t rograde hexane and the chromatography was c a r r i e d out us ing a V a r i a n Aerograph Model A-90-P3 which was equipped w i t h a thermal c o n d u c t i v i t y d e t e c t o r . A s t a i n l e s s s t e e l column 10 f t . x 0.25 i n . w i t h 20% DC 550 l i q u i d phase on 60/80 chromosorb W was used . Hel ium was used as the c a r r i e r gas a t an i n l e t pressure o f 50 p . s . i . , and the chromatograms were r e g i s t e r e d on a Honeywell E l e c t r o n i c 15 r e c o r d e r . Some o f the i m p u r i t y peaks c o u l d not be r e s o l v e d s e p a r a t e l y so the r a t i o o f the i m p u r i t i e s to the main compound was determined by c u t t i n g out the peaks from the c h a r t and measuring the d i f f e r e n c e i n t h e i r mass. This method was used i n cases where the base l i n e was c u r v e d . McNair and B o n e l l i (62) (18) have r e p o r t e d t h a t t h i s method was p r e c i s e , the r e s u l t s hav ing r e l a t i v e s t a n d -ard d e v i a t i o n (a) o f 1.7%. This d e v i a t i o n agreed c l o s e l y w i t h the method o f i n t e g r a t i o n to o b t a i n the area under the peaks (a = 1.3%). The m e l t i n g p o i n t s o f the products were taken on a Thomas Hoover . C a p i l l a r y m e l t i n g p o i n t apparatus (Thomas Hoover C o . , P h i l a d e l p h i a , U . S . A . ) . The r e s u l t s g i v e n i n Table 2. ; i n d i c a t e t h a t none of the o x i d i z i n g agents produced dixanthogen f r e e o f i m p u r i t i e s . A p p a r e n t l y , s i d e r e a c t i o n s proceed even a t low temperature . The i s o l a t i o n and c h a r a c t e r i z a t i o n o f these i m p u r i t i e s were not attempted i n t h i s s t u d y . The chromatograms, however, i n d i c a t e t h a t a t l e a s t one i m p u r i t y i s common to a l l o f the p r o d u c t s . In a f u r t h e r s tudy the p o s s i -,S ^ b i l i t y o f f o r m a t i o n o f e t h y l xanthogen monosulphide ^ H ^ O C ' - S - ^CC^Hg) might be i n v e s t i g a t e d . I t s f o r m a t i o n has been d e s c r i b e d by Cambron and Whitby (61) i n cases where a l c o h o l i c s o l u t i o n s o f o x i d i z i n g agents r e a c t w i t h x a n t h a t e s . The o x i d i z i n g agents used i n t h i s s tudy are l i s t e d i n Table 2J. i n a d e c r e a s i n g o r d e r o f t h e i r a b i l i t y to produce d i x a n t h o g e n . 2.3 Lead E t h y l x a n t h a t e ( P b X j - 2 A s o l u t i o n o f 10 M l e a d n i t r a t e was added to a s i m i l a r c o n c e n t r a t i o n of potass ium e t h y l x a n t h a t e under a g i t a t i o n a t room temperature and pH 6 . 0 . S o l u b l e l e a d s a l t s , such as l e a d p e r c h l o r a t e and l e a d n i t r a t e , were used to prepare the l e a d e t h y l x a n t h a t e , because these ions had the l e a s t tendency to form c o o r d i n a t i o n complexes ( 6 3 ) . The p r e c i p i t a t e was f i l t e r e d o f f and ' ; ' ' . T a b l e 2 . • The P r o p e r t i e s ' o f Dixanthogen (Xg) as A f f e c t e d by the Use o f  D i f f e r e n t O x i d i z i n g Agents O x i d i z i n g Agent ~T~. Cynogen Bromide 2 . P o t a s s i u m P e r s u l p h a t e 3 . P o t a s s i u m T e t r a t h i o n a t e . .4.' . Chloramine T.. 5 . I o d i n e 6 . ^ P o t a s s i u m N i t r i t e ( a c i d i f i e d w i t h H 2 S 0 4 ) % y i e l d o f c r u d e - X 2 (as f i rs t . product ) No. o f im p u r i t i e s i n once c r y s t a l -l i z e d product . No. o f im-p u r i t i e s i n t w i c e c r y s t a l -1 i zed-product M e l t i n g p o i n t o f . t w i c e crys^ t a l l i zed p r o d u c t (°c) . % i m p u r i t y % .pur i ty '• i n t w i c e . o f X„ c r y s t a l l i z - i ' ed a ^ t e r s e c " z a t i o n 98 .8 98 .5 97 .5 9 2 . 3 89.6 46 .0 1 3 " 3 31.9 31 .8 30 .7 • 30 .3 29 .5 31 .7 571 11 .3 13 .7 18 .8 24.0 10 .6 94 .8 ' 88.6 86 .2 8 1 . 2 7 6 . 0 . 89 .3 * A l t h o u g h the. a c i d i f i e d potass ium n i t r i t e produces a p u r e r form o f d ixanthogen than i o d i n e , i t s y i e l d i s very low due to. the a c i d d e c o m p o s i t i o n o f potass ium e t h y l x a n t h a t e . ' ' .• (20) washed w i t h d i s t i l l e d water u n t i l f r e e o f n i t r a t e then d r i e d i n vacuum. I t was f i n a l l y washed w i t h hexane to remove dixanthogen and s t o r e d i n a vacuum d e s s i c a t o r . 2.4 Ferrous E t h y l x a n t h a t e ( F e X j An attempt was made to prepare f e r r o u s e t h y l x a n t h a t e by m i x i n g a 10 M s o l u t i o n of potassium e t h y l x a n t h a t e w i t h f e r r o u s ammonium s u l p h a t e . Ferrous ions are more s t a b l e i n the l a t t e r compound. However, no p r e c i p i t a t i o n was observed a f t e r the reac tants had been mixed f o r 4-6 h o u r s , e i t h e r under an i n e r t atmosphere o f n i t r o g e n o r under a r e d u c i n g atmosphere of hydrogen. A s i m i l a r treatment a t 3 .5 and 5.5 pH and 25°C under atmospheric c o n d i t i o n s showed some t u r b i d i t y . These p r e p a r a t i o n s o f f e r r o u s e t h y l x a n t h a t e were deemed u n s u c c e s s f u l . 2 .5 F e r r i c E t h y l x a n t h a t e ( F e X j The f o r m a t i o n of f e r r i c e t h y l x a n t h a t e was c a r r i e d out by m i x i n g the s t o i c h i o m e t r i c q u a n t i t i e s o f potassium e t h y l x a n t h a t e and f e r r i c ammonium s u l p h a t e . The p r e c i p i t a t i o n was e f f e c t e d ' b y the use o f a s o l u t i o n of l e s s _ o than 10 M f e r r i c ions i n an i n e r t atmosphere ( N 2 ) or under normal atmospheric c o n d i t i o n s . The r e a c t i o n s were c a r r i e d out a t a c i d i c ( 2 . 5 to 6.5) and b a s i c (7.5 o r h i g h e r ) pH values a t room temperature . The f e r r i c e t h y l x a n t h a t e prepared a t a c i d i c pH values (2.5<pH<7.0) ( 2 1 ) was found to c o n t a i n more dixanthogen than tha t prepared a t b a s i c pH values ( 7 . 0 < p H < l l . 0 ) . Organic s o l v e n t s such as e t h e r , ace tone , hexane, benzene and carbon t e t r a c h l o r i d e were t r i e d i n an attempt to remove dixanthogen from the f e r r i c e t h y l x a n t h a t e . These o r g a n i c s o l v e n t s p a r t i a l l y d i s s o l v e d the p r e -c i p i t a t e d s a l t as w e l l . Hexane was found to be the most e f f e c t i v e s o l v e n t i n the s e p a r a t i o n o f dixanthogen w i t h the minimum d i s s o l u t i o n of the s a l t . Dark brown hexagonal prisms of f e r r i c e t h y l x a n t h a t e were o b t a i n e d a f t e r washing w i t h the s o l v e n t . The f e r r i c e t h y l x a n t h a t e used i n the subsequent work was prepared by us ing s o l u t i o n s o f 10 M o f both f e r r i c (pH 2.7) and e t h y l x a n t h a t e ions a t 25°C. 2.6 Cuprous E t h y l x a n t h a t e (CUQXQ) The cuprous e t h y l x a n t h a t e was prepared by t r e a t i n g potassium e t h y l x a n t h a t e w i t h copper s u l p h a t e s o l u t i o n under s l i g h t l y a c i d i c c o n d i t i o n s (pH 6.2) at room temperature . In t h i s mix ture the product was ob ta ined i n a good y i e l d even i f the i n i t i a l c o n c e n t r a t i o n o f the reac tants was lower than _ 2 10 M. The p r e c i p i t a t e was f i l t e r e d o f f and washed w i t h d i s t i l l e d water u n t i l i t was f r e e o f s u l p h a t e i o n s . I t was d r i e d i n vacuum and then e x t r a c t e d w i t h hexane to remove d ixanthogen . Very f i n e c r y s t a l s o f a y e l l o w c o l o u r were obta ined which were s t o r e d i n a vacuum d e s s i c a t o r . In an another experiment an attempt was made to determine the a b i l i t y o f cuprous i o n to r e a c t w i t h x a n t h a t e . Cuprous e t h y l x a n t h a t e was, t h e r e f o r e prepared by r e a c t i n g the potassium e t h y l x a n t h a t e w i t h cuprous c y a n i d e . Cuprous cyanide was f r e s h l y prepared by t r e a t i n g cuprous c h l o r i d e w i t h potassium (22) c y a n i d e . The cuprous e t h y l x a n t h a t e p r e c i p i t a t e d r e a d i l y even a t low concen-t r a t i o n s (10"^M) o f the r e a c t a n t s . The compound so formed was washed thoroughly w i t h spec t rograde hexane, but the washings d i d not show the presence o f dixanthogen as determined by U . V. s p e c t r o s c o p y . The compound resembled c l o s e l y i n p h y s i c a l and chemical p r o p e r t i e s to d i x a n t h o g e n - f r e e cuprous e t h y l x a n t h a t e formed w i t h copper s u l p h a t e . The elemental a n a l y s i s o f the metal xanthates g i v e n i n Table .2 i n d i c a t e s tha t t h e i r p u r i t y was reasonably good. An attempt was made to determine the m e l t i n g p o i n t s of the metal xanthates but these compounds d i d not show sharp m e l t i n g p o i n t s . Some decomposi t ion was observed be fore they had melted c o m p l e t e l y . The f i n a l p r o -ducts of t h i s thermal decomposi t ion were found by X - r a y d i f f r a c t i o n to be the metal s u l p h i d e s . The approximate values o f the m e l t i n g p o i n t s are i n c l u d e d i n Table 3._ Table 3 Chemical A n a l y s i s o f L e a d , Copper and  I r o n E th y lx an th a tes • Metal % • Sulphur % Carbon %.. Mel t i n g .• Xanthates P o i n t s C a l c u -1 a ted Found C a l c u -l a t e d Found , ' C a l c u -l a t e d i • • Found > • • °c Lead E t h y l x a n t h a t e .. 46.08 45.80 28.52.: 28.22 16.02 15.95 . 210 . Cuprous E t h y l x a n t h a t e * 34.39 33.95 34.71 31.60 19.50 17.50 .202 .; :.'•;:"•• F e r r i c E t h y l x a n t h a t e " 13.31 13.10 •." 45.86 ' 45.66 25.77 24.80 n o Cuprous E thy lxanthate+ '34.39 33.89 34.71 33.50 . 19.50 18.85 : 200 . . • • • .i * Prepared w i t h copper, s u l p h a t e and washed w i t h hexane : + Prepared w i t h , cuprous cyanide and washed w i t h hexane Chapter 3 Exper imental Techniques and Procedures This chapter d i s c u s s e s the b a s i c p r i n c i p l e s o f the techniques which were employed i n the d e t e r m i n a t i o n of some o f the s t r u c t u r a l p a r a -meters of copper and i r o n e t h y l x a n t h a t e s . The methods o f v e r i f i c a t i o n o f the o x i d a t i o n s t a t e s o f metal atoms i n these xanthates are a l s o i n c l u d e d i n t h i s c h a p t e r . The s e c t i o n i s concluded by a review o f the methods which were used f o r the chemical a n a l y s i s of the metal xanthates and t h e i r decomposi t ion p r o d u c t s . 3.1 The Use o f X - r a y P h o t o e l e c t r o n Spectroscopy to Measure the O x i d a t i o n S t a t e o f Copper i n Copper E t h y l x a n t h a t e 3 .1.1 Theory and A p p l i c a t i o n s E l e c t r o n spec t roscopy f o r chemical a n a l y s i s ( 6 4 , 6 5 ) E S C A , o f t e n r e f e r r e d as X-ray p h o t o e l e c t r o n spec t roscopy i n v o l v e s a s tudy o f the energy d i s t r i b u t i o n of the e l e c t r o n s emi t ted from a sample which has been p r e v i o u s l y i r r a d i a t e d by X - r a y s . The measurable q u a n t i t y i n t h i s technique i s the k i n e t i c energy ( E ^ ) possessed by an e l e c t r o n i n a p a r t i c u l a r energy l e v e l . The energies i n v o l v e d i n the process are r e l a t e d by the f o l l o w i n g e q u a t i o n : (25) E h v = E K E + E B ( i ) 3.1 where E h v i s the energy o f the X - r a y s , and E g ^ j represents the photoel e c t r o n k i n e t i c energy o f the i th l e v e l o f the e l e c t r o n s ( i = K , L , M - e t c . ) . The k i n e t i c energy va lues o f the d i s c r e t e energy l e v e l s are scanned by an e l e c t r o n energy a n a l y z e r and the b i n d i n g energies are o b t a i n e d from the above equa-t i o n (3 . 1 ) . T h i s assumes t h a t the energy of the X-rays i s known. The b i n d i n g energy o f an e l e c t r o n has d i f f e r e n t values f o r d i f f e r e n t e l e c t r o n s h e l l s , and i s a f f e c t e d by the o x i d a t i o n s t a t e , o r the e f f e c t i v e charge on the atom. Therefore the energy o f the e x p e l l e d e l e c t r o n s i s s h i f t e d as the chemical environment i s changed. As a r e s u l t o f e x t e n s i v e s t u d i e s of b i n d i n g energy s h i f t s t h i s technique i s a p p l i e d w i d e l y i n s u r f a c e c h e m i s t r y and s o l i d s t a t e p h y s i c s . The i m p o r t a n t components o f the i n s t r u m e n t " a r e shown i n F i g . 1. These c o n s i s t o f an X - r a y tube w i t h an aluminum anode which generates A£-K r e X - r a y s (1486.6 e V ) , an e l e c t r i c f i e l d s p h e r i c a l a n a l y z e r and an automat ic data r e c o r d i n g sys tem. The i n s t r u m e n t was used i n i t i a l l y to f i n d a r e l a t i o n s h i p between the s p e c t r a l p o s i t i o n of the p h o t o e l e c t r o n l i n e and the o x i d a t i o n s t a t e o f the same element i n d i f f e r e n t chemical compounds. The s p e c t r a l p o s i t i o n s o f chemica l s h i f t s f o r Cu( I ) and C u ( I I ) have been d e s c r i b e d i n the l i t e r a -ture ( 6 6 , 6 7 ) . Very r e c e n t l y a s i m i l a r s tudy (68) o f chemical s h i f t s i n f i f t y copper (I & I I ) compounds (68)has been c a r r i e d o u t . C o n s e q u e n t l y , i f r e f e r -ence i s made t o these d a t a , the o x i d a t i o n s t a t e o f copper i n a p a r t i c u l a r (26) X - r a y P h o t o e l e c t r o n Spectroscopy (ESCA) X - r a y Source X - r a y Spectrometer E l e c t r o n Spectrometer Two s p e c t r o s c o p i c methods f o r the s tudy of atoms and m o l e c u l e s . One i s the c l a s s i c a l method of x - r a y emiss ion s p e c t r o s c o p y . The o ther i s the method of e l e c t r o n spectroscopy (ESCA). The e l e c t r o n s obta ined from an i r r a d i a t e d specimen are analysed i n e l e c t r o n spec t rometer . X - r a y Tube R e s o l u t i o n B a f f l e r—-Electron Detec tor The p lan view of the exper imental arrangement i n the x - r a y p h o t o e l e c t r o n spec t rometer . ( O r i g i n a l mode l , w i t h magnetic f i e l d s p h e r i c a l a n a l y z e r ) . FIGURE 1 (27) compound can be determined w i t h a f a i r degree o f a c c u r a c y . 3 . 1 . 2 The Exper imenta l D e t e r m i n a t i o n The f r e s h l y prepared samples o f copper e t h y l x a n t h a t e were d r i e d under vacuum to remove any t r a c e o f w a t e r . The measurements were made w i t h samples which were ground or p r e c i p i t a t e d (unground s t a t e ) . A l s o , the p r e c i p i t a t e s e i t h e r t r e a t e d w i t h hexane o r those u n t r e a t e d w i t h any s o l v e n t were s u b j e c t e d to the a n a l y s i s . The samples were spread t h i n l y on adhes ive tape (3m) and a t tached to the copper s l u g of the sample probe . A l l the measurements were made a t a pressure of 10~^mm of Hg and a t low temperature ( -100°C) to a v o i d X - r a y photo r e d u c t i o n w i t h i n the s p e c t r o m e t e r . Some samples of p r e c i p i t a t e d copper e t h y l x a n t h a t e , (prepared as p r e v i o u s l y d e s c r i b e d ) , were t r e a t e d w i t h s o l u t i o n s o-f d i f f e r e n t pH a t temper-atures o f 2 5 ° , 3 5 ° , and 45°C. They were then s t u d i e d by ESCA i n an at tempt to determine the o x i d a t i o n s t a t e of copper w h i c h ' p r e v a i l e d under each s e t o f c o n d i t i o n s . In a d d i t i o n , the s t a b i l i t y of the o x i d a t i o n s t a t e o f copper was i n v e s t i g a t e d i n a sample o f copper e t h y l x a n t h a t e which had been s t o r e d under atmospheric c o n d i t i o n s f o r about f o u r months. 3 .2 The A p p l i c a t i o n o f Ho'ssbauer Spectroscopy to the C h a r a c t e r i z a t i o n o f I r o n E t h y l x a n t h a t e Mossbauer Spectroscopy(69 ' ,70 ) i s one o f the most modern techniques a v a i l a b l e to s tudy the s t r u c t u r e o f chemical compounds and to determine the (28) o x i d a t i o n s t a t e o f t h e i r e lements . In t h i s n u c l e a r process V-rays produced by a source are absorbed b y . t h e sample . A f u r t h e r emiss ion and resonant r e a b s o r p t f o n o f Y-rays then occurs due to the e x i t e d n u c l e a r s t a t e o f the sample . To compensate f o r the smal l energy d i f f e r e n c e s i n the Y - r a y s from the source ( 5 ^Co) and the absorber ( s a m p l e ) , the energy i s modulated e i t h e r by moving the source o f - r a y s towards the absorber o r moving the absorber towards the source a t an i n c r e a s i n g r a t e of approx imate ly 1 mm/sec. A t a c e r t a i n v e l o c i t y the resonant a b s o r p t i o n occurs and a f a l l i s observed i n the i n i t i a l count r a t e o f the Y - rays from the source and t h i s i s measured on a s c i n t i l l a t i o n c o u n t e r . The spectrum i s ob ta ined as a p l o t o f Y - r a y s counts a g a i n s t the r e l a t i v e v e l o c i t y o f the s o u r c e . T h i s technique depends, upon e f f e c t s w i t h i n the atom which o c c u r due to the i n t e r a c t i o n o f the n u c l e a r l e v e l s w i t h e x t r a n u c l e a r e l e c t r o n s . These e f f e c t s (71) are ( i ) chemical o r isomer s h i f t (5 ) , ( i i ) quadrupole s p l i t t i n g (AE o r A) and ( i i i ) magnetic h y p e r f i n e s p l i t t i n g . 3 .2 .1 ... • Chemical o r Isomer S h i f t ( 8 •).. The energy d i f f e r e n c e between the ground s t a t e and the e x i t e d n u c l e a r s t a t e of the absorber when compared w i t h t h a t o f the source i s denoted as the chemical s h i f t and i s . measured on the v e l o s i t y a x i s i n mm / s e c . The r a d i u s of the nucleus ( r ) i n the e x i t e d s t a t e d i f f e r s from t h a t i n the ground s t a t e i n both c a s e s . The isomer s h i f t , can be represented (29) Mo)/2 } 3 . 2 source i s the d i f f e r e n c e 3 .3 6 / > s ( o ) / 2 i s the change i n s e l e c t r o n d e n s i t y a t the n u c l e u s . The isomer s h i f t has been used to determine the o x i d a t i o n s t a t e and bond c h a r a c t e r of i r o n compounds. In these compounds the s e l e c t r o n d e n s i t y i s a f f e c t e d by the change i n d e l e c -t rons ( i . e . Fe (3d ) Fe (3d ) ) ; as a r e s u l t an isomer s h i f t i s o b s e r v e d . 3 . 2 . 2 Quadrupole S p l i t t i n g (&EQ o r A) The s p l i t t i n g o f a b s o r p t i o n l i n e s i s caused by the i n t e r a c t i o n o f a non-uni form e l e c t r o n c l o u d w i t h the n u c l e a r c h a r g e . The quadrupole moment, Q, o f the n u c l e a r s t a t e , when s p i n l>h, a l i g n s w i t h the e l e c t r i c f i e l d g r a d i e n t ( q ) . The degeneracy o f the n u c l e a r s u b s t a t e s i s l i f t e d and the a l l o w e d energy i s g i v e n b y : 2 V f r f f i - i ) { 3 m 2 " o+"2/3)% > 3.4 I f , as i n most cases I = 3 / 2 , the above equat ion s i m p l i f i e s to : A E 0 = c o n s t a n t . Q.q . _ _ as f o l l o w s : • • » . - % Ze 2r 2' SL , „ l 0 ) / t . absorber o r 6 = cons tant — 6/^s ( o ) / where 6r = r - r and e x c i ted ground (30) - X . V, 0 V, q = 0 ±± q > 0 T A Nuclear energy level diagram showing the effect of quadrupole interactions ELECTRON-NUCLEAR HYTERHNE INTERACTIONS* Type Manifestation £0 (electric monopolc) E2 (electric quadrupole) M l (magnetic dipole) Chemical shift, S Quadrupole splitting, A Hypcrfinc Zeeman splitting • Higher multipole interactions can normally be neglected. F i g u r e 2. Mossbauer Parameters ( A f t e r Greenwood (71) ) (31) The e l e c t r i c f i e l d g r a d i e n t (q) i s , t h e r e f o r e r e s p o n s i b l e f o r a s p l i t t i n g o f the energy l e v e l o f the e x c i t e d n u c l e u s . The quadrupole s p l i t t i n g g ives i n f o r m a t i o n about the symmetry of s i t e s i n c r y s t a l s and about the s u b s t i t u t i o n o f d i f f e r e n t groups around the c e n t r a l atom. v Other parameters l i k e the n u c l e a r Zeeman e f f e c t and the w i d t h and i n t e n s i t y of a b s o r p t i o n l i n e s a l s o p r o v i d e u s e f u l i n f o r m a t i o n about the o x i d a t i o n s t a t e o f i r o n i n i t s compounds. 3 . 2 . 3 Experimental Procedure The Mossbauer technique was u t i l i z e d i n a s tudy o f i r o n xanthates i n an attempt to o b t a i n the f o l l o w i n g i n f o r m a t i o n : ( i ) The chemical nature o f the i r o n xanthates prepared a t pH values ranging from 2.5 to 1 1 . 0 . ( i i ) The c h a r a c t e r o f the metal l i g a n d bond i n i r o n e t h y l x a n t h a t e . ( i i i ) The degree of s t a b i l i t y of the normal o x i d a t i o n s t a t e of i r o n i n i r o n e t h y l x a n t h a t e . ( i v ) The symmetry o f the i r o n e t h y l x a n t h a t e molecules which were prepared under d i f f e r e n t pH c o n d i t i o n s and the c o o r d i n a t i o n number o f the i r o n i n these compounds. (v) The l i g a n d s u b s t i t u t i o n i n i r o n e t h y l x a n t h a t e ; i . e . the form-a t i o n of hydroxy i r o n e t h y l x a n t h a t e . 57 The Fe Mossbauer e f f e c t s were s t u d i e d on a T e c h n i c a l Measurements C o r p o r a t i o n Model 306 ins t rument ( k i n d l y made a v a i l a b l e by D r . J . Sams, Dept. o f C h e m i s t r y ) . A t ransducer moved the y - r a d i a t i o n source a t a constant , r a t e (32) of . a c c e l e r a t i o n , and the r a d i a t i o n came from a 5 7 C o source (14.4 Kev) which was d i f f u s e d i n t o p a l l a d i u m . The t r a n s m i t t e d y - r a d i a t i o n was d e t e c t e d by a X e n o n - N i t r o g e n p r o p o r t i o n a l c o u n t e r . A 400 channel a n a l y z e r was employ-ed which o p e r a t e d i n time s c a l e mode. The source and d r i v e were c a l i b r a t e d a g a i n s t a s i n g l e c r y s t a l o f sodium n i t r o p r u s s i d e . This was a s t a n d a r d r e f e r e n c e m a t e r i a l No. 725 ( N . B . S . ) . The data were f i t t e d by computer to a L o r e n t z i a n shaped a b s o r p t i o n peak by a n o n l i n e a r l e a s t squares t e c h n i q u e . The quadrupole s p l i t t i n g (A) f o r the r e f e r e n c e m a t e r i a l was taken to be 1.726 ± 0.002 mm/sec. Isomer s h i f t s were r e p o r t e d r e l a t i v e to the c e n t r e of the spectrum o f the s t a n d a r d . The powdered samples , approx imate ly 1mm t h i c k , were c o n t a i n e d i n a c e l l w i t h M y l a r Windows, which c o u l d be coo led to l i q u i d n i t r o g e n temperature ( 7 7 ° K ) . 3.3 The Use o f the D i f f e r e n t i a l Thermal A n a l y s i s 3.3.1 T h e o r e t i c a l I n t r o d u c t i o n . : _ - l~~lzs:': .•" " ~ t l - v " The DTA technique i s used to measure the chemical and s t r u c t u r a l changes i n a sample by comparison w i t h a r e f e r e n c e m a t e r i a l , when r e f e r e n c e and sample under s tudy are p l a c e d toge ther i n an environment which passes through a thermal g r a d i e n t . In the absence o f p h y s i c a l and chemical change, the temperature d i f f e r e n t i a l (AT) i s zero and i t v a r i e s o n l y when an e x o t h e r -mic o r endothermic change takes p l a c e i n the sample . The thermal character !*s (33) t i c s o f the sample can be obta ined from a graph o f AT as a f u n c t i o n o f temp-e r a t u r e . Any a l t e r a t i o n s i n the sample due to thermal changes appear i n the form o f peaks , each a t a w e l l d e f i n e d temperature . The technique has been used e x t e n s i v e l y to i n v e s t i g a t e the chemical composi t ions of many i n o r g a n i c and o r g a n i c compounds, but l i t t l e i n f o r m a t i o n i s a v a i l a b l e about the thermal decomposi t ion o f metal x a n t h a t e s . Only Tyden(72) has s t u d i e d the decomposi t ion products o f a l a k l i metal xanthates by t h i s t e c h n i q u e . 3 . 3 . 2 Experimental Procedure The behaviour of f r e s h l y prepared f e r r i c e t h y l x a n t h a t e i n the temperature range o f 25° to 1100°C was s t u d i e d u s i n g DTA. The samples o f products obta ined on t r e a t i n g f e r r i c e t h y l x a n t h a t e s a t v a r i o u s pH values and temperatures were a l s o s t u d i e d through the above range o f temperature . Each t e s t sample and the re fe rence m a t e r i a l (Al2^3) w e r e conta ined i n an alumina c r u c i b l e and p laced i n a tube furnace equipped w i t h a P t , Pt -Rh thermocouple . A DuPont 900 DTA apparatus was used f o r these a n a l y s e s . 3.4 The Experimental Procedure Employed to Study the E f f e c t of pH and Temperature on Heavy Meta lxanthate A q u a n t i t y o f 500 mg. o f xanthate was added to 500 m l . o f water w i t h a s p e c i f i c pH va lue a t a cons tant temperature . The double d i s t i l l e d (34) water used was i n i t i a l l y b o i l e d and oxygen f r e e n i t r o g e n gas was passed through i t to expel the d i s s o l v e d atmospheric gases . I n o r g a n i c ac ids were used to a d j u s t the pH values and were chosen so as to avo id the f o r m a t i o n o f i n s o l u b l e s a l t s when the xanthate was added.. N i t r i c s u l p h u r i c and h y d r o c h l o r i c ac ids were used f o r the xanthates o f l e a d , copper and i r o n r e s p e c t i v e l y . The b a s i c pH values were always prepared w i t h potassium h y d r o x i d e . The treatment o f metal xanthates i n v a r i o u s s o l u t i o n s was c a r r i e d out a t cons tant temperatures , under atmosphere, w i t h magnetic s t i r r i n g . A l i q u o t s o f about 5 ml were removed from the s o l u t i o n by a p i p e t t e w i t h a porous p lug a f f i x e d to the t i p . Samples taken a t d i f f e r e n t i n t e r v a l s o f time were immediate ly f i l t e r e d through a mi H i pore f i l t e r and were ana lyzed f o r metal ions by a Techtron Model 430 Atomic A b s o r p t i o n S p e c t r o -meter . The xanthate ions were determined by UV on a P e r k i n Elmer Model 450, UV s p e c t r o m e t e r . Small f r a c t i o n s of u n d i s s o l v e d metal xanthate were a l s o removed from the bulk s o l u t i o n a t s h o r t time i n t e r v a l s i n order to s tudy the change i n t h e i r chemical c o m p o s i t i o n . The contents o f the bulk s o l u t i o n were f i l t e r e d a f t e r each s e t o f experiments and the r e s i d u e was d r i e d and p laced i n a vacuum d e s s i c a t o r to awai t f u r t h e r a n a l y s i s . 3 .5 The A p p l i c a t i o n o f U l t r a - V i o l e t Spectroscopy to the A n a l y s i s of the Xanthate S o l u t i o n In the f i e l d of f l o t a t i o n research the a p p l i c a t i o n of UV spec-t roscopy i s w e l l known. The d i s s o c i a t i v e . d e c o m p o s i t i o n and o x i d a t i o n o f (35) xanthates i n aqueous s o l u t i o n s have been e x t e n s i v e l y stucfied (73-77). . . 3 .5 .1 The E l e c t r o n i c T r a n s i t i o n s i n Xanthates Xanthates absorb u l t r a - v i o l e t r a d i a t i o n s t r o n g l y i n the wavelength r e g i o n o f 200-400 my, i n common w i t h o t h e r o r g a n i c molecules which have a chromophore such as t h i o c a r b o n y l g r o u p , - | - . A band o f very h i g h i n t e n s i t y a t 301 my a r i s e s due to the t r a n s i t i o n s from bonding IT o r b i t a l s to a n t i b o n d i n g -n o r b i t a l s . A second band of a medium i n t e n s i t y •k appears a t 226 my and i s a t t r i b u t e d to n->-<5 t r a n s i t i o n s (78);-. I t i s caused by the e x c i t a t i o n o f a non-bonding n o r b i t a l , which i s l o c a l i z e d . o n a s u l p h u r atom, to an a n t i b o n d i n g 6 o r b i t a l . The t h i o c a r b o n y l group e x h i b i t s a t h i r d a b s o r p t i o n band (79V o f a very low i n t e n s i t y which appears a t a h i g h e r wave-* l e n g t h (>400 mu) due to r\->-n t r a n s i t i o n s . I t occurs because o f the i n t e r a c t i o n o f s u l p h u r l o n e - p a i r w i t h the u e l e c t r o n s o f the t h i o c a r b o n y l group . As the * n-Hr t r a n s i t i o n s are f o r b i d d e n , the i n t e n s i t y o f t h i s band i s very low when compared to t h a t o f TT-^TT and n+6 t r a n s i t i o n s . 3 . 5 . 2 : The D e t e r m i n a t i o n o f Xanthate Ion C o n c e n t r a t i o n by UV Spectrometer The a b s o r p t i o n peak o f 301 my i n the UV spectrum of xanthate s o l u t i o n s was used f o r the q u a n t i t a t i v e d e t e r m i n a t i o n o f xanthate i o n s . A c a l i b r a t i o n a t 301 my i n d i c a t e d t h a t B e e r ' s law was obeyed over a c o n c e n t r a t i o n (36) range o f 10~ t o 10" M x a n t h a t e . The molar e x t i n c t i o n c o e f f i c i e n t was found t o be 1750 l i t e r m o l e " 1 cm" 1 a t 301 my and was used i n the d e t e r m i n a t i o n f o r m u l a : A = abc Where A i s absorbance, a. represents molar e x t i n c t i o n c o e f f i c i e n t and £ stands f o r c o n c e n t r a t i o n i n moles per l i t e r . The dixanthogen formed i n aqueous s o l u t i o n was e x t r a c t e d i n t o hexane. The UV s p e c t r o m e t r i c a n a l y s i s of t h i s o r g a n i c l a y e r was c a r r i e d out u s i n g pure hexane as the re fe rence s o l v e n t (80 ) . The measurements were made at 283 my, f o r t h i s w a v e l e n g t h , the B e e r ' s law was obeyed up t o a c o n c e n t r a t i o n -4 o f 10 M dixanthogen i n hexane. The molar e x t i n c t i o n c o e f f i c i e n t , 8600 l i t e r mole 1 c m " 1 , was used f o r the d e t e r m i n a t i o n o f d i x a n t h o g e n . 3.6 The A p p l i c a t i o n of E l e c t r o n Paramagnetic Resonance t o a Study o f the  O x i d a t i o n S ta te of Copper i n Copper E t h y l x a n t h a t e The technique has been used by Russ ian workers (81) t o s tudy problems r e l a t e d to m i n e r a l f l o t a t i o n ; i . e . the e f f e c t of paramagnetic i m p u r i t i e s 2+ 3+ such as Mn and Fe i n galena and s p h a l e r i t e . A study o f the o x i d a t i o n s t a t e o f copper i n x a n t h a t e , d i t h i o p h o s p h a t e and d i t h i o c a r b a m a t e by t h i s method has a l s o been r e p o r t e d (82) . .3 .6 .1 T h e o r e t i c a l Aspects o f EPR (83) E l e c t r o n Paramagnetic Resonance i s based on the p r i n c i p l e t h a t any p a i r of e l e c t r o n s i n atomic or m o l e c u l a r o r b i t a l s has no r e s u l t a n t (37) magnetic component, s i n c e the sp ins are o p p o s i t e and the f i e l d s cancel o u t ; however, molecules or atoms which have one o r more unpaired e l e c t r o n s g i v e r i s e to paramagnetic resonance. A f i x e d magnetic f i e l d i s a p p l i e d to the sample and t h i s r e s u l t s i n a s p l i t t i n g o f the e l e c t r o n energy l e v e l s , thus removing the degeneracy o f the s t a t e . A r a d i o frequency ( r . f . ) f i e l d i s then a p p l i e d p e r p e n d i c u l a r to the magnetic f i e l d ( H ) . I f the r . f . f i e l d i s kept cons tant and the mag-n e t i c f i e l d i s v a r i e d , t r a n s i t i o n s occur between the s p l i t s t a t e s o f e l e c t r o n . Resonance i s t h e r e f o r e observed a t a p a r t i c u l a r va lue o f the magnetic f i e l d . The s p i n angular momentum of an e l e c t r o n , under these c o n d i t i o n s , produces a magnetic moment (p) which can be w r i t t e n a s : v = - g B e s . . 3.6 I t s energy (E) i n terms of the s p i n H a m i l t o n i a n opera tor (K) c a K b e w r i t t e n a s : 3t = - P H 3 .7 where 3 g = ~ - = 0.927120 x 1 0 " 2 0 e r g / o e r s t e d i s c a l l e d Bohr Magneton, "j", = ^ and g ( c o n s t a n t f a c t o r ) = 2.0023 f o r a f r e e e l e c t r o n . The s p i n a n g u l a r momentum (s) can have two values (±%) i n the d i r e c t i o n o f the magnetic f i e l d . Thus an e l e c t r o n i n a magnetic f i e l d has two energies which depend upon i t s s p i n quantum number. The frequency of the e l e c t r o m a g n e t i c r a d i a t i o n needed to induce a t r a n s i t i o n between these two energy l e v e l s can be w r i t t e n a s : v = (ge e /h)H = 1.39969 x 10 6 g'H s e c " 1 3 .8 (38) The unpaired d e l e c t r o n s i n t r a n s i t i o n metal ions such as Cu possess an o r b i t a l angular momentum (J ) i n a d d i t i o n to the s p i n momen-tum. The n u c l e a r magnetic i n t e r a c t i o n o f these ions can be expressed by equat ions 3.6 and 3.7 i f s i s r e p l a c e d by J and g ' by g ; i . e . „ 3J(J+1) + s ( s + l ) - L(L+1) 3.9 9 = 2J ( j + i ) ; . where s and L i n the above equat ion are r e s p e c t i v e l y the s p i n quantum number and the o r b i t a l quantum number o f the atom o r i o n . I f t r a n s i t i o n metal ions are p r e s e n t i n the s o l i d or l i q u i d s t a t e , the l a r g e n u c l e a r o r e l e c t r i c f i e l d s c r e a t e d by the n e i g h b o r i n g l i g a n d s o r Ions g e n e r a l l y quench the o r b i t a l motion o f the e l e c t r o n s l e a v i n g o n l y the s p i n momentum s to i n t e r a c t w i t h the magnetic f i e l d . Thus f o r t r a n s i t i o n metal compounds, equat ions 3 . 6 , 3 .7 and 3.8 can aga in be a p p l i e d , except f o r the f a c t t h a t g i s not e x a c t l y 2 .0023, because o f the s p i n o r b i t i n t e r -a c t i o n s . This r e s u l t s i n a second o r d e r c o n t r i b u t i o n to g due to the o r b i t a l motion o f the e l e c t r o n s . This s p i n o r b i t c o n t r i b u t i o n makes the g v a l u e a c h a r a c t e r i s t i c p r o p e r t y o f the i o n ; i . e . i t i s r e l a t e d to the o x i d a t i o n s t a t e . 3 . 6 . 2 Exper imenta l Procedure The EPR s p e c t r a were recorded a t 22°C u s i n g a 9G Hz ( 1 0 9 c y c l e s s e c " 1 ) spec t rometer w i t h 100 K H z m o d u l a t i o n o f the magnetic f i e l d . The magnetic f i e l d was s e t up from V a r i a n " F i e l d i a l " power s u p p l y . The c a l c u l a t i o n s o f g v a l u e from exper imenta l data have been shown i n Appendix B . 3.7 (38a) The Study of Heavy Meta1xanthat.es by I n f r a r e d Spec t roscopy L i t t l e (84) has reviewed the e a r l y work on the use o f i n f r a -r e d techniques t o c h a r a c t e r i z e b u l k xanthates and those adsorbed on m i n e r a l s s u r f a c e s . S e v e r a l workers (85-87) have used t h i s t echnique t o s tudy the s t r u c t u r e and the v i b r a t i o n a l f r e q u e n c i e s o f d i f f e r e n t groups i n heavy metal x a n t h a t e s . 3 . 7 . 1 A n a l y t i c a l Procedure The potass ium bromide d i s c t echnique (88-90) was used t o . o b t a i n the t r a n s m i s s i o n s p e c t r a o f the x a n t h a t e s . The d i e , P e r k i n Elmer . Model 186-00251 was f i l l e d w i t h a m i x t u r e o f 0 .3 to 0 .5 . g . potass ium bromide and 0 .2 t o 3.0 mg. o f the sample. The d i e f i l l e d w i t h the sample was evacuated f o r f i v e minutes and then s u b j e c t e d to a l o a d o f 5000 p s i ' f o r one m i n u t e . The d i s c was removed from the d i e and p l a c e d i n the i n f r a -r e d beam. The s p e c t r a were recorded on a P e r k i n Elmer Model 521 G r a t i n g I n f r a r e d Spectrophotometer . The s u r f a c e area o f the p a l l e t be ing a f f e c t e d by the i n f r a r e d 2 beam was 2.258 Cm. Chapter 4 The Stabi l i ty of Suspension of Lead Ethylxanthate  in Aqueous Solutions L i t t l e work has been reported in the li terature on the chemical s tab i l i ty of lead ethylxanthate. An investigation of the mode of formation of lead ethylxanthate together with a study of the s tab i l i ty of this compound and its derivatives may therefore result in further under-standing of the process of galena flotation. In this chapter the behaviour of freshly precipitated lead ethylxanthate in aqueous solutions of various pH values and temperatures is discussed. The characterization of the decomposition products of this com-pound in aqueous solutions is also included. F ina l ly , there is a short discussion of the results at the end of each section. 4.1 The Precipitation Study of Lead Ethylxanthate The formation of heavy metal xanthates is an important aspect of the process of sulphide mineral f lotat ion. However, no detailed study has been carried out to investigate the factors which affect the metal (40) xanthate p r e p a r a t i o n . A l s o , no data are a v a i l a b l e w i t h r e s p e c t to the c o n c e n t r a t i o n s of xanthate and metal ions which are needed to p r e c i p i t a t e the heavy metal x a n t h a t e s . Tezak (91) d e s c r i b e d a q u i c k exper imental technique i n which two s o l u t i o n s were mixed together and the e x t e n t o f the r e s u l t a n t t u r b i d i t y ( i n d i c a t i n g p r e c i p i t a t i o n ) was measured. M a t i j e v i c and co-workers (92) a p p l i e d t h i s technique s u c c e s s f u l l y to the c a l c i u m o l e a t e system. A s i m i l a r procedure , as d e s c r i b e d be low, has been adopted to study the f o r m a t i o n o f l e a d e t h y l x a n t h a t e . 4 .1 .1 Experimental Procedure A s e r i e s o f aqueous s o l u t i o n s o f lead n i t r a t e and potassium e t h y l x a n t h a t e o f v a r i o u s known c o n c e n t r a t i o n s was p r e p a r e d . Volumes of 5.0 ml of each of these s o l u t i o n s were mixed r a p i d l y i n t e s t tubes . Each t e s t tube was shaken f o r one minute and then l e f t i n a cons tant temperature bath a t 25°C f o r f i v e minutes . The c o n c e n t r a t i o n o f one o f the r e a c t a n t s was v a r i e d i n each p r e p a r a t i o n w h i l e t h a t o f the o ther was kept c o n s t a n t . Changes i n the e x t e n t of p r e c i p i t a t i o n were f o l l o w e d by T y n d a l l o m e t r i c o b s e r v a t i o n s . The s o l u t i o n s which d i d not become t u r b i d immediately a f t e r m i x i n g were placed i n a constant temperature bath a t 25°C and the t u r b i d i t y was measured a t d i f f e r e n t time i n t e r v a l s . Some o f the mixtures were l e f t over n i g h t and then t e s t e d f o r t u r b i d i t y . T ' i e m i x t u r e s which e x h i b i t e d a low (41) t u r b i d i t y , o r which appeared t r a n s p a r e n t by o t h e r o p t i c a l methods, were s t u d i e d by the l i g h t s c a t t e r i n g t e c h n i q u e . The t u r b i d i t y measurements were made w i t h a B r i c e Phoenix Model 2000 L i g h t S c a t t e r i n g Photometer . The t e s t tubes which c o n t a i n e d the s o l u t i o n mixtures were p laced i n a 3 cm c y l i n d r i c a l c e l l which c o n t a i n e d d u s t - f r e e w a t e r . The r a t i o o f the l i g h t s c a t t e r e d by a s o l u t i o n a t 90°C to the l i g h t t r a n s m i t t e d a t 0°C was determined by the r a t i o o f the d e f l e c -t i o n s i n a ga lvanometer . This s c a t t e r i n g r a t i o was p r o p o r t i o n a l to the a b s o l u t e t u r b i d i t y (T) as shown by the f o l l o w i n g genera l e q u a t i o n : where j j r ^ i s the s c a t t e r i n g r a t i o o r average observed r a t i o o f the g a l v a n o -meter d e f l e c t i o n f o r the l i g h t (436 mu) s c a t t e r e d from the s o l u t i o n a t 9 0 ° (no n e u t r a l f i l t e r i n pr imary beam) to t h a t f o r - t h e t r a n s m i t t e d l i g h t a t 0 ° - p o s i t i o n ( w i t h work ing s tandard plus n e u t r a l f i l t e r ) ; where K i s a c o n s t a n t which depends upon the o p t i c a l geometry o f the i n s t r u m e n t , r e f r a c t i v e index o f s o l u t i o n (which f o r d i l u t e s o l u t i o n can be r e p l a c e d by the r e f r a c t i v e index o f the s o l v e n t ) , c e l l s i z e and the r e f l e c t i v e e f f e c t s , e t c . These c o n d i t i o n s were kept c o n s t a n t throughout the t u r b i d i t y measure-ments. A Corning Model 10 pH meter was used to o b t a i n the pH values o f the s o l u t i o n . 4 . 1 . 2 R e s u l t s and D i s c u s s i o n The r e s u l t s o f the p r e c i p i t a t i o n s tudy are p l o t t e d i n F i g u r e 3 and 4 . F i g u r e 3 i n d i c a t e s t h a t there are three d i s t i n c t reg ions i n the growth (42) -8 LOG MOLAR CONC. OF P b ( N 0 3 ) 2 -FIGURE 3 . P r e c i p i t a t i o n regions o f l e a d e t h y l x a n t h a t e ob ta ined on mix ing KEtX and P b ( N 0 3 ) 2 o f v a r y i n g c o n c e n t r a t i o n s ( 1 ) High t u r b i d i t y r e g i o n (2) Low t u r b i d i t y r e g i o n (3) Zero t u r b i d i t y r e g i o n . The dashed l i n e i n d i c a t e s the s o l u b i l i t y limit f o r the s o l u b i l i t y product of l e a d e t h y l x a n t h a t e . K ( P b ( E t X ) 2 ) = 1 . 5 6 x l 0 ~ 1 6 a t 6 .5 pH and 23.5* C . (43) 100 >-co U J o . co co co 30 60 40 -20 10 15 20 TIME (min) . F i g u r e 4 . A b s o l u t e r T u r b i d i t y a g a i n s t t ime curve f o r the p r e c i p i t a t i o n of P b ( E t X ) 2 The c o n c e n t r a t i o n combinat ions o f the r e a c t a n t ions are as f o l l o w s : - (EtX)"H P b 2 + M ' (E tX)"M P b 2 + M 1. 5 x 1 0 " 5 1 x 1 0 " 5 5 . 1 x 1 0 " 5 1 x 1 0 " 3 2. 1 x I O " 2 1 x 1 0 ' 4 6. 1 x 1 0 " 5 1 x 1 0 " 4 3 . 1 x 1 0 ~ 5 5 x 1 0 " 3 7. 1 x 1 0 " 3 1 x 1 0 " 4 4. 1 x 1 0 " 5 5 x 1 0 " 5 8. 1 x 1 0 " 4 5 x 1 0 " 4 (44) o f l ead e t h y l x a n t h a t e c r y s t a l s . T h e o r e t i c a l l y , uni form p r e c i p i t a t i o n should occur throughout the area above the s o l u b i l i t y product l i n e , K . However, coarse p r e c i p i t a t e , y e l l o w to l i g h t orange i n c o l o u r , appeared immediate ly upon mixing the s o l u t i o n s i n r e g i o n 1. The coarse p r e c i p i t a t e s sedimented r e a d i l y . The p r e c i p i t a t e s formed i n the second r e g i o n were c o l l o i d a l i n s i z e and pa le y e l l o w i n c o l o u r . A very low t u r b i d i t y was a l s o noted around the outer boundary of t h i s r e g i o n 2 to 3 minutes a f t e r m i x i n g of the s o l u t i o n s . In the t h i r d r e g i o n , p r e c i p i t a t i o n was not observed even a f t e r 3 to 4 h o u r s . No p r e c i p i t a t e was obta ined from s o l u t i o n i n the area to the l e f t and the r i g h t o f p r e c i p i t a t i o n regions 1 and 2 , where the c o n c e n t r a t i o n s of l e a d and xanthate ions d i f f e r e d g r e a t l y i n t h e i r o r d e r of magnitude. I t i s supposed t h a t the n u c l e i o f l ead e t h y l x a n t h a t e i n these areas of r e g i o n 3 are surrounded 2+ by an excess of one o f the spec ies ( i . e . e i t h e r Pb or (Etx ) ) which i n h i b i t the growth o f a p r e c i p i t a t e . b y keeping the c o l l o i d i n a d i s p e r s e d s t a t e a t a s i z e l e ss than the wavelength o f the i n c i d e n t l i g h t . A t concen-_ 5 t r a t i o n of xanthate i o n s , l e ss than 10 M, no p r e c i p i t a t e i s formed upon a d d i t i o n o f any c o n c e n t r a t i o n of l e a d i o n s . In the second r e g i o n , p r e c i p i t a --4 -5 t r o n i s e f f e c t e d by v a r y i n g the c o n c e n t r a t i o n of xanthate from 10 to 3x10 M and l e a d ions from 10~ 3 t o 1 0 ~ 4 M . Beyond these c o n c e n t r a t i o n values the p h y s i c a l c h a r a c t e r o f the p r e c i p i t a t e i s found to change. The i n f r a r e d s p e c t r o s c o p i c s tudy i n d i c a t e s t h a t the p r e c i p i t a t e s formed i n the d i f f e r e n t regions are of the same chemical c o m p o s i t i o n but d i f f e r - i n t h e i r p h y s i c a l c h a r a c t e r i s t i c s . ( 4 5 ) Three s i m i l a r d i s t i n c t reg ions o f p r e c i p i t a t i o n have been observed i n o t h e r i n o r g a n i c systems ( 9 3 ) . K o l t h o f f and Vant R e i t (94) have mentioned such regions i n a s tudy o f the p r e c i p i t a t i o n o f l e a d s u l p h a t e . They (94) f u r t h e r p o s t u l a t e d t h a t such mechanisms are a p p l i c a b l e to the p r e c i p i t a t i o n o f o r g a n i c s a l t s such as metal c a r b o x y l a t e s . S o l u t i o n s o f l e a d n i t r a t e and potass ium e t h y l x a n t h a t e a t a pH o f 6 .5 were used f o r the p r e c i p i t a t i o n s t u d y . No s i g n i f i c a n t change i n t h i s pH v a l u e was observed when the s o l u t i o n s were mixed f o r the p r e c i p i t a t i o n . An excess amount o f l e a d e t h y l x a n t h a t e was s u b j e c t e d to the aqueous s o l u t i o n s o f pH 6 . 5 , 7.5 and 8.5 a t a temperature o f 23 .5°C f o r the d e t e r m i n a t i o n o f i t s s o l u b i l i t y p r o d u c t . The xanthate and l e a d ions were determined by UV and atomic a b s o r p t i o n s p e c t r o m e t r i c techniques a t equal , i n t e r v a l s o f t ime u n t i l e q u i l i b r i u m c o n d i t i o n s were a c h i e v e d . I t was observed t h a t the s o l u b i l i t y o f l e a d e t h y l x a n t h a t e i n c r e a s e d as the pH i n c r e a s e d . The s o l u b i l i t y product l i n e determined a t a pH of 6 .5 i s s h i f t e d upward by a p p r o x i m a t e l y one o r d e r o f magnitude on both axes of F i g u r e 3 i f the pH i s ' i n c r e a s e d by one u n i t . The neck between p r e c i p i t a t i o n r e g i o n 3 and t h i s l i n e i s t h e r e f o r e reduced by t h i s i n c r e a s e i n pH. The main reg ions o f p r e c i p i t a t i o n remained a lmost u n a l t e r e d a t a l k a l i n e pH values between 8 .5 and 1 0 . 5 . The p r e c i p i t a t i o n curves may be u s e f u l i n a s s e s s i n g the c o n c e n t r a t i o n o f potass ium e t h y l x a n t h a t e i n galena f l o t a t i o n i n o r d e r to a v o i d the s t a r v a t i o n and overdose o f the c o l l e c t o r . F i g u r e 4 i n d i c a t e s f u r t h e r s t u d i e s c a r r i e d o u t w i t h l i g h t (46) s c a t t e r i n g photometer to i n v e s t i g a t e the e x t e n t of p r e c i p i t a t i o n a long e i t h e r s i d e of the boundary o f the r e g i o n 2. I t was found t h a t immediate ly o u t s i d e of r e g i o n 2, the maximum t u r b i d i t y d i d not exceed 15% as compared to the t u r b i d i t y i n s i d e r e g i o n 2 where the values v a r i e d from 85 to 100%. The t u r b i d i t y o f each system was measured a t 5 minute i n t e r v a l s a f t e r m i x i n g . This t u r b i d i t y was t h e r e f o r e s h a r p l y d e f i n e d . Zero t u r b i d i t y values were observed w i t h c o n c e n t r a t i o n combina-2+ t i o n s o f Pb and (EtX) ions c o r r e s p o n d i n g to c o o r d i n a t e s w e l l w i t h i n r e g i o n 3, and above the s o l u b i l i t y product l i n e shown i n F i g u r e 3. 4.2 The E f f e c t o f A c i d i c S o l u t i o n s on Lead E t h y l x a n t h a t e The d i s s o l u t i o n rates o f l e a d e t h y l x a n t h a t e a t pH values o f 4.5 and 10.5 were s t u d i e d a t temperatures o f 25°, 35°, 45° and 60°C. The r e s u l t s o f two o f the exper imental s e r i e s , one a t 25°C and the o t h e r a t 45°C are shown i n F i g u r e s 5 and 6. They were chosen to form the b a s i s f o r a d i s -c u s s i o n o f the phenomena o f d i s s o l u t i o n and decompos i t ion of t h i s compound. o o The r e s u l t s o f the s t u d i e s a t 35 and 60 C were found to be very - s i m i l a r • o . to those a t 45 C. They are t h e r e f o r e not i n c l u d e d i n t h i s d i s c u s s i o n . The d i s s o l u t i o n study and the s p e c t r o s c o p i c a n a l y s i s o f the aqueous s o l u t i o n s o f l e a d e t h y l x a n t h a t e a t pH 4.5 i n d i c a t e t h a t xanthate i o n s decompose i n a s i m i l a r way to the a l k a l i metal xanthates i n a c i d s o l u t i o n s . E x t e n s i v e work (95,96, and 97) has been c a r r i e d out to e l u c i d a t e the mechanism of a c i d decomposi t ion of xanthate i o n s . The cont inuous i n c r e a s e i n the l e a d (47) 1 1 1 1 r 0 4 0 80 120 160 2 0 0 TIME (min.) FIGURE 5. S t a b i l i t y o f p b ( E t X ) 0 at v a r i o u s pH values and at 25°C (a) changes i n the i n i t i a l pH values (marked on each l i n e ) due to the decomposi t ion and the h y d r o l y s i s of the com-ponents of the system as the process of d i s s o l u t i o n proceeds , (b) Xanthate i o n c o n c e n t r a t i o n as a f u n c t i o n of t ime at 9 .5 and 10.5 pH values (c) Xanthate i o n c o n c e n t r a t i o n as a f u n c -t i o n of t ime at 4 . 5 , 6 .5 and 8.5 pH v a l u e s . (48) TIME (min.) FIGURE 6. Stability of Pb(EtX) 2 at various pH values at 45°C (a) Changes in the i n i t i a l pH values (marked on each line) due to the decomposition and the hydrolysis of the components of the system as the process of dissolution proceeds (b) Xanthate ion concentration as a function of time at pH values as marked on each line. (49) i o n c o n c e n t r a t i o n ( F i g u r e 7 ) and the i n c r e a s e i n the i n i t i a l a c i d i c pH values ( F i g u r e s 5a and 6a) conf irmed the f o l l o w i n g r e a c t i o n s : P b ( C 2 H 5 0 C S S ) 2 + P b 2 + + 2 ( C 2 H 5 0 C S S ) " 4 . 2 C 0 H C OCSS" + HOH -> C 9 H , 0 H ' + C S 0 + OH" 4 .3 2 5 2 5 2 4 . 3 The E f f e c t o f A l k a l i n e S o l u t i o n s on Lead E t h y l x a n t h a t e A marked i n c r e a s e i n xanthate i o n c o n c e n t r a t i o n i s observed above n e u t r a l pH values a t 25°C. The c o n c e n t r a t i o n of xanthate ions i s found to be much h i g h e r a t pH 9.5 than the va lue a t 8 .5 and s t i l l h i g h e r than tha t at pH 1 0 . 5 . I f the experiments a t pH values o f 7.5 and 8.5 are c o n s i d e r e d , i t i s found t h a t as the process o f d i s s o l u t i o n proceeds , the l e a d ions become h y d r o l y z e d . The l e a d h y d r o x i d e t h a t i s formed begins to cover the s u r f a c e o f the l e a d e t h y l x a n t h a t e . Hence, the ra te o f d i s s o l u t i o n d e c l i n e s . Even-t u a l l y , t h i s c o a t i n g i n h i b i t s f u r t h e r d i s s o l u t i o n o f l e a d h y d r o x i d e . In t h i s pH r e g i o n , a t room temperature , l ead h y d r o x i d e forms a s t a b l e p r e c i p i t a t e - ?D w i t h a . s o l u b i l i t y product o f 1.1x10 . The e l e c t r o n micrographs shown i n F i g u r e 8 i n d i c a t e a contamina-t i o n o f the l e a d e t h y l x a n t h a t e suspens ion w i t h f i n e p a r t i c l e s o f l e a d h y d r o x i d e a t pH values o f 7.5 and 8 . 5 . In F i g u r e 6 , i t i s shown t h a t the c o n c e n t r a t i o n o f l ead ions a t these a l k a l i n e pH values i s much lower than the c o r r e s p o n d i n g c o n c e n t r a t i o n i n a c i d i c s o l u t i o n . As the pH i s i n c r e a s e d above 8 . 5 , l e a d h y d r o x i d e begins to l e a v e (50) 4 0 r T I M E ( m i n ) FIGURE 7. Lead i o n c o n c e n t r a t i o n as a f u n c t i o n of t ime t r e a t i n g P b ( E t X ) 2 at v a r i o u s pH values (marked on each l i n e ) at (a) 45°C\ (b) 25°C. ( 5 1 ) FIGURE 8. Absorbed E l e c t r o n Images of P b ( E t X ) 2 (510 X) (a) F r e s h l y prepared P b ( E t X ) 2 > (b) P b ( E t X ) 2 a f t e r t r e a t i n g at 7.5 pH f o r 10 minutes a t 25°C, (c) P b ( E t X ) 2 a f t e r t r e a t -ing at 8.5 pH f o r 10 minutes at 25°C. (52) the s u r f a c e of l ead e t h y l x a n t h a t e t o form a c o l l o i d a l suspens ion w h i c h , i n t u r n , d i s s o l v e s a t pH values h i g h e r than 10 ( l O O ) . A s o l u b l e plumbate i s formed (98) . As the pH exceeds 8 . 5 , a smal l i n c r e a s e i n the c o n c e n t r a t i o n o f l e a d ions i s observed due t o the d i s s o l u t i o n o f l e a d h y d r o x i d e . The lead i o n c o n c e n t r a t i o n was found to i n c r e a s e w i t h t ime a t 45°C as shown by the l i n e s 2 , 3 , and 4 i n F i g u r e 6a . In a l k a l i n e s o l u t i o n s , decomposi t ion of the xanthate ions occurs to g i v e many u n s t a b l e products (101 , 102 & 103) . These i n t u r n break down t o s t a b l e s p e c i e s such as carbonate and s u l p h i d e . C 2 H 5 0 C S S " + 50H" 2 S 2 " + C O 2 " + C ^ O H + 2H 2 0 4 .4 The chemical r e a c t i o n s a t a l k a l i n e pH values and the temperatures h i g h e r than 25°C r e s u l t e d i n the p r o d u c t i o n o f bulk l ead s u l p h i d e w i t h a -29 s o l u b i l i t y product o f 6.8 x 10 (99 ) . C o l l o i d a l suspension of l e a d s u l p h i d e which appeared i n the system was p r o g r e s s i v e l y t u r n i n g the c o l o u r o f the p r e c i p i t a t e s t o b l a c k . The b l a c k product was shown by X - r a y d i f f r a c t i o n to be l e a d s u l p h i d e (Table 5 ) . . S u c h changes were n o t i c e a b l e a t pH 9.5 but became more pronounced a t 10.5 pH i f the l ead e t h y l x a n t h a t e was l e f t f o r 3 to 4 hours i n aqueous suspension a t 25°C ( F i g u r e 9 ) . T h i s f o r m a t i o n of l e a d s u l p h i d e can be seen at pH 6 or 7 and a f t e r s h o r t e r i n t e r v a l s of t ime i f the temperature i s i n c r e a s e d above 25°C. F i g u r e 9 i n d i c a t e s the gradual development o f b l a c k c o l o u r i n the l ead e t h y l x a n t h a t e suspens ion due t o the f o r m a t i o n o f l e a d s u l p h i d e at v a r i o u s pH va lues and a t d i f f e r e n t temperatures . F i g u r e s 5a and 6a i n d i c a t e the v a r i a t i o n i n pH values observed i n the course o f d i s s o l u t i o n of l e a d e t h y l x a n t h a t e a t 25°C and 45°C. These Temp. 45°C (c) Temp. 60°C FIGURE 9 . Photographs showing the changes i n the appearance of P b ( E t X ) 2 due t o PbS f o r m a t i o n , as observed when P b ( E t X ) 2 was l e f t f o r 3 to 4 hours at var ious pH values (marked under each p i c t u r e ) and at (a) 25°C, (b) 35°C, (c) 45°C, (d) 60°C- . (54) i n i t i a l f l u c t u a t i o n s i n pH values i n d i c a t e t h a t d i f f e r e n t types o f decom-p o s i t i o n r e a c t i o n s may o c c u r i n a l k a l i n e s o l u t i o n s . The mechanism o f the r e a c t i o n s has not been a s c e r t a i n e d but the i m p o r t a n t f i n a l products appear to be l e a d s u l p h i d e , l ead h y d r o x i d e and l e a d c a r b o n a t e , (see Table 5 ) . 4 .4 The Format ion o f Dixanthogen i n the Course o f D i s s o l u t i o n of Lead E t h y l x a n t h a t e A f t e r the c o m p l e t i o n o f each s e t o f e x p e r i m e n t s , _ t h e u n d i s s o l v e d p a r t i c l e s o f l e a d e t h y l x a n t h a t e were e x t r a c t e d w i t h hexane to determine the f o r m a t i o n o f d i x a n t h o g e n . The aqueous f i l t r a t e s o f the s u s p e n s i o n were l i q u i d l i q u i d e x t r a c t e d w i t h hexane. E t h y l d ixanthogen was not de tec ted i n the systems s t u d i e d a t d i f f e r e n t pH values and a t e l e v a t e d temperatures except i n the samples t r e a t e d a t pH 10.5 and 25°C. The IR and UV s p e c t r a of the hexane e x t r a c t s i n d i c a t e d the presence o f d ixanthogen both i n the s o l u t i o n s and i n the suspensions o f l e a d e t h y l x a n t h a t e . 4 . 5 _ The I n f r a r e d S p e c t r o s c o p i c Study o f Lead E t h y l x a n t h a t e and I t s D e r i v a t i v e s A potass ium bromide p e l l e t which c o n t a i n e d f r e s h l y prepared l e a d e t h y l x a n t h a t e gave a c l e a r l y r e s o l v e d spectrum w i t h three d i s t i n c t bands i n the r e g i o n o f 1000 to 1250 c m " 1 . This spectrum of l e a d e t h y l x a n t h a t e (55) which i s shown i n F i g u r e 10a has two s t r o n g bands a t 1210 and 1022 cm" which correspond to the c h a r a c t e r i s t i c f r e q u e n c i e s o f C*-° and C=S groups r e s p e c t i v e l y . Severa l authors (85 , 87) have made o p p o s i t e assignments i n t h e i r s t u d i e s r e l a t e d to heavy metal x a n t h a t e s . A s i m i l a r assignment of peaks has been made i n the spectrum o f dixanthogen which i s shown i n F i g u r e l O e . The c h a r a c t e r i s t i c bands c o r r e s p o n d i n g to C-0 and C=S groups appear as double t s between 1242 and 1262 cm" 1 and 1020 &. 1040 cm" 1 r e s p e c t i v e l y . F i g u r e .lO-d i 11 u s t r a t e s the spectrum o f the hexane e x t r a c t o f the l e a d e t h y l x a n t h a t e which was suspended i n a s o l u t i o n o f pH 10.5 a t 25°C ' f o r f o u r h o u r s . I f t h i s spectrum i s compared w i t h t h a t o f d ixanthogen ( F i g -ure lOe) a l l the bands are found to be i n agreement wi th those c h a r a c t e r i s t i c bands o f d i x a n t h o g e n . In F i g u r e 10b i s shown the spectrum o f a s u s p e n s i o n o f l e a d e t h y l x a n t h a t e t h a t was exposed to a s o l u t i o n of pH 10.5 a t 45°C f o r f o u r h o u r s . The f i l t r a t e from a s i m i l a r experiment a t 25°C was evaporated under vacuum to g i v e s o l i d m a t e r i a l and a spectrum o f t h i s r e s i d u e i s shown i n F i g u r e 10c. Many o f the a b s o r p t i o n bands i n s p e c t r a l 0 band c resemble those o f c a r b o n a t e s . I t has been shown (104) t h a t f o u r bands appear a t 1063, 879, -1 ? 1415 and 680 cm which are r e p r e s e n t a t i v e o f the CO^" i o n . These are r e s p e c t i v e l y due to symmetric s t r e t c h i n g (v-|) out of plane bending ( v ^ ) , asymmetric s t r e t c h i n g ( v 3 ) and p l a n a r bending ( v ^ ) . A d l e r and K e r r (105) r e p o r t e d a number of s p e c t r a of anhydrous normal c a r b o n a t e s . They observed t h a t the bending mode ( v ? ) was s h i f t e d to a l o n g e r wavelength w h i l e the (56) J I I 1 I L I I 1 1 1 1 1 1500 1300 1100 900 - 700 500 300 F igure 10: I n f r a r e d s p e c t r a o f : (a) F r e s h l y p r e c i p i t a t e d Pb(EtX)2 as r e f e r e n c e m a t e r i a l (b) Pb(EtX)2 suspended i n a s o l u t i o n of pH 10.5 f o r f o u r hours at 45°c (c) Residue obta ined upon e v a p o r a t i o n of the f i l t r a t e of suspension of Pb(EtX)2 hours at 25°c (d) The hexane e x t r a c t of Pb(EtX)2 s u s p e n s i o n . (e) E t h y l dixanthogen as re fe rence m a t e r i a l . (57) s t r e t c h i n g mode was moved to a s h o r t e r wave length . No s i g n i f i c a n t d i s -placement was observed i n the v^ mode o f v i b r a t i o n which appeared as a . double t i n many cases . The spectrum g i v e n f o r c e r u s s i t e i n the s tudy o f A d l e r and K e r r i s s i m i l a r to the spectrum i n F i g u r e 10c That i n F i g u r e 10 shows a marked s h i f t i n the f r e q u e n c i e s corresponding t o carbonate i n a l l except the v 4 mode o f v i b r a t i o n . Both s p e c t r a , lOb&lOc , suggest t h a t carbonate f o r m a t i o n occurs i n the b u l k phase by r e a c t i o n 4 . 3 . 4 .6 The A p p l i c a t i o n of T h i n Layer Chromatography t o the I d e n t i f i c a t i o n  o f Dixanthogen Eastman chromatogram sheets No. 6060 coated w i t h a h i g h l y a c t i v e grade o f s i l i c a gel combined w i t h a f l u o r e s c e n t i n d i c a t o r were employed i n the t h i n l a y e r chromatographic s t u d i e s . A number o f 1" x 3" s t r i p s cut from the sheet were d r i e d f o r 15 minutes a t 100°C before use. They were s p o t t e d w i t h an aqueous s o l u t i o n o f x a n t h a t e , l i q u i d dixanthogen and the hexane e x t r a c t s d e s c r i b e d i n s e c t i o n 4 . 5 . The s t r i p s were t h e n . p l a c e d i n the d e v e l o p i n g t a n k . The zones were l o c a t e d a f t e r development by i l l u m i n a t i o n w i t h UV l i g h t o f 254 my wave length . The f l u o r e s c e n t spots were marked and t h e i r r e f e r e n c e c o o r d i n a t e s were determined. These va lues represented the r a t i o o f the d i s t a n c e t r a v e l l e d by the spot from the o r i g i n to t h a t t r a v e l l e d . (58) Table 4 I d e n t i f i c a t i o n o f Dixanthogen i n Hexane E x t r a c t s o f P b ( E t X ) 9 Suspensions by Chromatography Table 4a R f values o f xanthate ( x " ) , Dixanthogen ( x 2 ) and unknown compound i n Hexane e x t r a c t s (Y) R f va lue o f s o l vent X x 2 Y Butanol 0 1 1 Hexane 0 0 .3 0 .3 0.77 values o f x , x 2 and Y (as mentioned i n 4a) by Paper Chromatography s o l v e n t R^ va lue o f x x 0 Y water 0.05 0 ' 0 Butanol 0 1 1 Hexane 0 1 1 0 (59) by the s o l v e n t f r o n t . These d e t e r m i n a t i o n s were repeated w i t h the use of chroma-t o g r a p h i c paper s t r i p s . A f u r t h e r s e t of R^ values i n v a r i o u s s o l v e n t s was r e c o r d e d . The t h i n l a y e r chromatographic s t r i p s on which the spots had been developed were g iven a spray treatment w i t h a molar s o l u t i o n of sodium h y d r o x i d e . This was f o l l o w e d , a f t e r an i n t e r v a l o f ten m i n u t e s , by a spray _2 of a s o l u t i o n o f 10 M copper s u l p h a t e . Ye l low spots were obta ined a t i d e n t i c a l p o s i t i o n s f o r dixanthogen and the unknown. Tables 4a and 4b i n d i c a t e the R^ values of xanthate and the dixanthogen r e f e r e n c e . m a t e r i a l , together w i t h the unknown spec ies which was observed i n the hexane e x t r a c t s . The t a b l e s show t h a t the R f values o f the unknown spec ies determined i n the d e v e l o p i n g media of w a t e r , butanol and hexane correspond to the R^ va lue of d i x a n t h o g e n . The spray t e s t s f u r t h e r c o n f i r m the presence of d i x a n t h o g e n . E v e n t u a l l y the sodium h y d r o x i d e converts dixanthogen to xanthate which i n t u r n reac ts w i t h copper s u l p h a t e to g i v e y e l l o w copper x a n t h a t e . In a d d i t i o n to dixanthogen another unknown spec ies w i t h an R^ va lue o f 0 .7 appeared i n the t h i n l a y e r chromatogram o f the hexane e x t r a c t (Table 4 a ) . The spots which corresponded to t h i s spec ies were w e l l d e f i n e d under UV l i g h t but were not observed by the spray t e s t s . The spec ies i s presumably a b y - p r o d u c t o f the decomposi t ion r e a c t i o n o f dixanthogen i n a l k a l i n e s o l u t i o n . No f u r t h e r i n v e s t i g a t i o n was c a r r i e d out to c h a r a c t e r i z e t h i s spec ies . (60) The f o r m a t i o n o f such b y - p r o d u c t s has been d i s c u s s e d by Kharasch (106). . He s t a t e s t h a t o r g a n i c d i s u l p h i d e s i n a l k a l i n e s o l u t i o n s undergo a s e r i e s o f r e a c t i o n s which r e s u l t i n the f o r m a t i o n o f s u l p h e n i c e s t e r s . A d e t a i l e d study o f such r e a c t i o n s i s r e q u i r e d . The presence o f d ixanthogen i n a suspens ion o f l e a d e t h y l x a n -thate a t a pH o f 10.5 and 25°C cannot be e x p l a i n e d by the argument t h a t l e a d ions a c t as promoters i n the o x i d a t i o n o f x a n t h a t e . A c c o r d i n g to the f o l l o w i n g r e a c t i o n mechanism proposed by Rao (107) , the l e a d ions d e r i v e d by the d i s s o l u t i o n o f l e a d h y d r o x i d e a c t as promoters . P b ( C 2 H 5 0 C S S ) 2 + %0 2 + H 2 0 ( C 2 H 5 0 C S S ) 2 + P b ( 0 H ) 2 4 . 5 The f o r m a t i o n o f dixanthogen was not de tec ted i n the d i s s o l u -t i o n tes t s performed a t pH values below 10 a t a temperature o f 25°C o r a t any pH va lues a t a temperature above 25°C. The i d e n t i f i c a t i o n o f d ixanthogen a t 10 .5 i n d i c a t e s t h a t o x i d a t i o n of xanthate ions i s caused by the complex s p e c i e s such as plumbate-. The o x i d i z i n g nature o f t h i s t e t r a v a l e n t l e a d s p e c i e s has been d i s c u s s e d i n the l i t e r a t u r e ( 9 8 ) . 4.7 I d e n t i f i c a t i o n o f Lead E t h y l x a n t h a t e Decomposi t ion Products by X - r a y D i f f r a c t i o n The X-ray d i f f r a c t i o n p a t t e r n s were taken o f the decompos i t ion products o f l e a d e t h y l x a n t h a t e separated from suspensions t h a t were t r e a t e d i n s o l u t i o n s o f pH values o f 4 . 5 to 10.5 a t temperatures r a n g i n g from 25° (61) to 60°C. For compar ison, s i m i l a r d i f f r a c t i o n pat terns were made o f f r e s h l y prepared lead s a l t s such as carbonate , s u l p h i d e , hydrox ide and e t h y l x a n -t h a t e . The i n t e n s i t i e s o f the d i f f r a c t i o n maxima and the i n t e r p l a n a r spacings ( i . e . d va lues ) of the more i n t e n s e l i n e s i n the pat terns were measured. These d values were compared w i t h the s tandard values of i n o r -ganic r e f e r e n c e compounds. Table 5 g ives the X - r a y d i f f r a c t i o n data o f the r e f e r e n c e m a t e r i a l s w i t h the three samples chosen f o r the d i s c u s s i o n of the r e s u l t s . Samples 1 and 2 r e p r e s e n t l e a d e t h y l x a n t h a t e taken a f t e r f o u r hours from s o l u t i o n s of pH 8.5 and 10.5 a t 25°C r e s p e c t i v e l y . Sample 3 was taken from the s o l u t i o n o f pH 10.5 a t 45°C a f t e r the same l e n g t h o f t i m e . A P h i l l i p s D i f f r a c t r o m e t e r was used to s tudy the i n t e n s i t y o f the r a d i a t i o n which was emit ted from the sample. The k^ i n c i d e n t rays came from a copper t a r g e t . \ I f the r e l a t i v e d values and l i n e i n t e n s i t i e s are compared, i t can be seen t h a t i n Sample 1 the i n t e n s e peaks correspond to l e a d h y d r o x i d e . In Samples 2 and 3 the data correspond to those o f l e a d carbon-ate and s u l p h i d e . As the l e a d e t h y l x a n t h a t e suspensions became b l a c k d u r i n g exposure at the pH and temperature values shown i n F i g u r e 9 s e c t i o n , t h i s c o l o u r change a l s o conf irms the presence o f l e a d s u l p h i d e . I n t e n s i v e peaks w i t h d values o f 2 .82A 0 were found i n a l l three samples and a peak w i t h a d va lue of 1.71 A 0 was observed i n Sample 3 . The compounds which gave r i s e to these peaks cou ld not be i d e n t i f i e d . Many o ther l e s s i n t e n s i v e peaks were a l s o observed which i n d i c a t e d t h a t smal l q u a n t i t i e s o f o t h e r decomposi t ion products were p r e s e n t . An i n v e s t i g a t i o n o f these peaks was not attempted i n t h i s s t u d y . Table 5 I n t e r p l a n a r Spacings and R e l a t i v e R e f l e c t i o n s f o r P b ( 0 H ) 2 , PbCO PbS, Pb(EtX)„ and i t s Decomposit ion Products P b ( 0 H ) ? P b ( C 0 J 7 PbS P b ( E t X ) 9 Sample Sample Sample c ^ 1 2 3 d I/I 0 d l'lo d I/I 0 d l / I o d d : l'lo d 3.23 100 3 .59 100 3.43 84 10.76 100 3 .24 100 3.59 90 3 .42 80 3.05 100 3 .40 43 2.97 100 6.28 30 3 .06 100 "3.48 • 40 3 .09 80 2.76 60 3 .07 24 2.1 57 5.37 50 2 .82 30 3.42 80 2 .95 100 2.70 80 2 .52 20 1.79 35 4.74 40 2 .76 50 3.08 60 2 .83 30 2.36 40 2 .48 ' 32 3.54 . 25 2 .71 70 2.82 2.65 30 40 2 .68 40 2.00 40 2 .08 27 2.67 20 2 .61 10 2.52 20 2 .52 20 1.93 40 1 . .93 19 2.2 25 2 .55 10 2.36 40 2 .10 50 1 , .85 21 2 .45 20 1 .98 40 2 .00 30 2 .37 40 1 .93 30 1 .92 30 2 .35 10 1 .91 20 1 .79 30 2 .13 50 1 .85 20 1 .71 30 1 .92 40 d =". A 0 u n i t s Chapter 5 The S t a b i l i t y of Cuprous E t h y l x a n t h a t e i n  Aqueous S o l u t i o n s This chapter d i s c u s s e s the f a c t o r s which c o n t r o l p r e c i p i t a t i o n o f cuprous e t h y l x a n t h a t e and the e f f e c t s o f a c i d i c and b a s i c aqueous s o l u -t i o n s on t h i s compound. X - r a y p h o t o e l e c t r o n spectroscopy and e l e c t r o n paramagnetic r e s -onance were used to determine the o x i d a t i o n s t a t e s o f copper i n products ob ta ined i n d i f f e r e n t environments . I n f r a r e d spectroscopy and X - r a y d i f f r a c -t i o n techniques were employed i n the a n a l y s i s of the decomposi t ion products o f cuprous e t h y l x a n t h a t e . 5.1 The P r e c i p i t a t i o n Study o f Cuprous E t h y l x a n t h a t e The procedure d e s c r i b e d i n s e c t i o n 4.1 was used to observe the t u r b i d i t y which r e s u l t e d upon m i x i n g o f s o l u t i o n s o f copper s u l p h a t e and potass ium e t h y l x a n t h a t e . A s i m i l a r type o f p r e c i p i t a t i o n phenomenon to tha t of l e a d e t h y l x a n t h a t e was observed . The r e s u l t s are shown i n F i g u r e 11. Regions 1 and 2 i n d i c a t e zones o f h igh and low t u r b i d i t y . In zone 3 , above the s o l u b i l i t y product l i n e , no t u r b i d i t y was observed . In F i g u r e 11 , the t u r b i d i t y regions 1 and 2 do not cover as wide a range o f r e a c t a n t c o n c e n t r a -(64) -7 -6 -5 -4 LOG HOLAR CONC. OF CuSO, F i g u r e 11 . P r e c i p i t a t i o n reg ions o f cuprous e t h y l x a n t h a t e (1) High t u r b i d i t y r e g i o n (2) Low t u r b i d i t y r e g i o n (3) T h e o r e t i c a l l y p o s s i b l e p r e c i p i t a t i o n r e g i o n , where t u r b i d i t y i s n o t . o b s e r v e d . The dashed l i n e i n d i c a t e s the s o l u b i l i t y l i m i t f o r the s o l u b i l i t y p r o d u c t o f cuprous e t h y l x a n t h a t e . K s p ( C u 2 ( E t X ) 2 ) = 5 - 2 X 1 0 ' •23 (32) (65) t i o n as was the case w i t h l e a d e t h y l x a n t h a t e . Region 3 covers a g r e a t e r area than e x p e c t e d . In a d d i t i o n to the s t a b i l i z i n g e f f e c t o f excess copper o r xanthate ions on the cuprous e t h y l x a n t h a t e n u c l e i , i t i s s u s -pected t h a t complex f o r m a t i o n i n t h i s r e g i o n f u r t h e r prevents the d e v e l o p -ment o f t u r b i d i t y . 5 .2 The E f f e c t o f pH and Temperature on Copper E t h y l x a n t h a t e Samples o f f r e s h l y prepared copper e t h y l x a n t h a t e , washed w i t h e t h e r , o r l e f t u n t r e a t e d , were suspended i n aqueous s o l u t i o n s o f pH 3.5 to 10 .5 a t temperatures which ranged from 25° to 60°C. The k i n e t i c s o f decompos i t ion were s t u d i e d by UV s p e c t r o -s c o p i c measurements ( F i g . 12) a t a wavelength o f 301 my. The a b s o r p t i o n s p e c t r a a t t h i s wavelength were not c o n s i s t e n t w i t h those o f x a n t h a t e . I t p o s t u l a t e d .- t h a t the metal ions which are r e l e a s e d upon d i s s o l u t i o n o f the cuprous e t h y l x a n t h a t e form complexes which cause s h i f t o f the xanthate a b s o r p t i o n band. 5 .2 .1 • The E f f e c t of A c i d i c S o l u t i o n s on Copper E t h y l x a n t h a t e The decompos i t ion ra tes o f the e t h e r - t r e a t e d and u n t r e a t e d cuprous e t h y l x a n t h a t e s i n aqueous s o l u t i o n s were s t u d i e d a t pH 3.6 and temperatures o f 25°C to 35°C. A t 25°C; no measurable c o n c e n t r a t i o n o f xanthate ions was (66) detec ted i n s o l u t i o n s o f e i t h e r ether-washed or untrea ted copper e t h y l x a n t h a t e d u r i n g a p e r i o d of two h o u r s . A t 35°C the ether-washed copper xanthate gave a UV a b s o r p t i o n peak a t 282 my which d i d not show a s p e c t r a l s h i f t w i t h t i m e , F i g . 12a. In the case of untrea ted copper x a n t h a t e , under s i m i l a r exper imental c o n d i t i o n s , the peak appeared a t the same p o s i t i o n ; the peak t h e r e f o r e , cannot be a t t r i b u t e d to d ixanthogen . A d e t a i l e d decomposi t ion study o f copper e t h y l x a n t h a t e i n a medium o f high i o n i c s t r e n g t h and high a c i d i t y was c a r r i e d out by Nanjo and Yamasaki (108) . They observed a s i m i l a r peak a t 283 my when a 1.24 x 10~ 1 M s o l u t i o n o f c u p r i c c h l o r a t e was mixed w i t h a 6.55 x 10" M s o l u t i o n of potassium e t h y l x a n t h a t e a t pH 1 .8 . This absorp-t i o n band was thought to be due to the f o r m a t i o n o f an e thylxanthogenate copper complex, C u ( E t X ) + . The mechanism of f o r m a t i o n of t h i s complex was not g iven by these a u t h o r s . The r e s u l t s of the present study i n d i c a t e the p o s s i b i l i t y o f such a complex f o r m a t i o n even a t c o n c e n t r a t i o n i n the range of 10~ 4 to - 5 10 M x a n t h a t e . I t i s suggested tha t cuprous ions formed i n the d i s s o l u t i o n o f cuprous e t h y l x a n t h a t e are o x i d i z e d to the c u p r i c f o r m , which l a t e r become complexed to form spec ies such as C u ( E t X ) + . 5 . 2 . 2 The E f f e c t of A l k a l i n e S o l u t i o n s on Copper E t h y l x a n t h a t e The UV s p e c t r o s c o p i c s t u d i e s o f xanthate i o n c o n c e n t r a t i o n d e r i v e d from s o l u t i o n o f untreated copper e t h y l x a n t h a t e , kept a t pH values . (67) 400 340 300 xanthate . / (Reference) / i . 2. 5 m i n . 15 " 1 / U ) y 3 \ 3. 30 " / / pH 3.6 M 2 v -280 _J L 260 240 230 my 0;8 CO. 6 l'-0.4 o CO CO <c 0.2 (b) pH 10.6 4. (117 mn.) . ( y 5 II ) 2 . ( . 4 5 ; ; 1( 30 (c) pH 10.7 : pH 11.6 280 286 292 298 306 my F i g u r e 12. UV s p e c t r a of the aqueous s o l u t i o n s of Cu2(Etx)2 (a) Ether t r e a t e d , and (b) u n t r e a t e d , .(c) Showing the change i n wavelength of a b s o r p t i o n as a f u n c t i o n of t i m e . (68) of 6 .5 and 9.1 a t 35°C gave no measurable absorbance a t the 301 my w a v e l e n g t h , i n 3-4 h o u r s . This suggests t h a t there i s no d e t e c t a b l e complex f o r m a t i o n i n t h i s pH range. The untrea ted copper e t h y l x a n t h a t e was kept i n aqueous s o l u -t i o n s o f pH 9.5 to 11.5 a t 35° and 45°C. Samples o f these s o l u t i o n s were ana lyzed f o r xanthate a t d i f f e r e n t i n t e r v a l s o f t i m e . The a b s o r p t i o n peaks , however, appeared not a t one s p e c i f i c p o s i t i o n but showed a gradual s p e c t r a l s h i f t w i t h time of d e c o m p o s i t i o n . The r e s u l t s shown i n F i g u r e 12b were recorded f o r the s o l u t i o n s of 10.6 a t 35°C. They i n d i c a t e a peak a t 284 my which appeared s h o r t l y a f t e r the copper e t h y l x a n t h a t e was suspended i n the a l k a l i n e s o l u t i o n . This peak g r a d u a l l y s h i f t e d towards h i g h e r w a v e l e n g t h . A f t e r three hours the peak f i n a l l y appeared a t a wavelength of 301 my, and subsequent measurements i n d i c a t e d no f u r t h e r change. This behaviour was i n t e r p r e t e d as due to a v a r i a t i o n i n the degree o f d i s s o c i a t i o n o f a complex spec ies formed d u r i n g the process o f d e c o m p o s i t i o n . C a l v i n and co-workers (T09) observed s i m i l a r behaviour i n 5 and 6 membered c y c l i c di s u l p h i d e s . They found t h a t the a b s o r p t i o n maximum was d i s p l a c e d towards l o n g e r wavelengths as the s i z e of the r i n g was decreased . The UV s p e c t r a i n F i g . 12b conf i rmed t h a t the f i n a l products of copper xanthate decomposi t ion a t pH 10.6 were xanthate ions which absorbed a t 301 my. The two i s o s b e s t i c p o i n t s , a t 287 and 266 my, i n d i c a t e d t h a t more than two spec ies were present i n the sys tem. The time dependence o f such s p e c t r a l s h i f t s observed f o r (69) decomposi t ion a t pH 10.7 and 11 .6 , and 35 C, i s shown i n F i g u r e 12c. I f the above experiments are repeated w i t h ether-washed copper e t h y l x a n t h a t e , a peak appears a t 282 my tha t does not show a  s p e c t r a l s h i f t , as i n F i g . 12a. The s t u d i e s of unt rea ted copper e t h y l x a n t h a t e (which was not washed w i t h ether) i n d i c a t e t h a t a sequence of r e a c t i o n s i s t a k i n g p l a c e , e . g . a f a i r l y f a s t redox r e a c t i o n i n v o l v i n g the r e d u c t i o n of dixanthogen to xanthate and o x i d a t i o n o f cuprous to c u p r i c i o n , then f o r m a t i o n o f a C u ( X ) + complex and the decomposi t ion o f the complex spec ies to xanthate ions a t s t r o n g l y ' b a s i c - p H . Complex ions w i t h a h a l f l i f e o f s e v e r a l hours are f r e q u e n t l y s t u d i e d by s p e c t r o m e t r i c methods u s i n g the f l o w t e c h n i q u e . A study of the conductance o f the s o l u t i o n may g i v e f u r t h e r i n f o r m a t i o n about the f o r m a t i o n o f such complexes. A comprehensive s tudy of the complex r e a c t i o n s encountered d u r i n g t h i s s tudy was not a t tempted. I t i s noted t h a t the metal ions -5 tend to form complexes a t c o n c e n t r a t i o n s as low as 10 M. The s t r u c t u r e o f the complexes and the mechanism of t h e i r f o r m a t i o n i s beyond the scope of t h i s work . 5 .3 The K i n e t i c s of D i s s o l u t i o n and Decomposit ion of Copper E t h y l x a n t h a t e i n A c i d i c and A l k a l i n e S o l u t i o n s A study o f the d i s s o l u t i o n and decomposi t ion rates o f copper e t h y l x a n t h a t e was c a r r i e d out i n the pH range o f 3.5 to 11.5 a t temperatures (70) o f 2 5 ° , 3 5 ° , 45° and 60°C. The e t h e r - t r e a t e d and untrea ted copper e t h y l x a n t h a t e s were suspended s e p a r a t e l y i n the aqueous s o l u t i o n s . The xanthate i o n c o n c e n t r a t i o n was measured u s i n g absorbance a t 301 mp; s p e c t r a l s h i f t s observed a t low and high pH of aqueous s o l u t i o n s caused d i f f i c u l t y i n the measurements of xanthate c o n c e n t r a t i o n . A f t e r prolonged treatment of unt rea ted copper e t h y l x a n t h a t e ( i . e . 4 hours) a t pH values above 1 0 . 0 , a marked i n c r e a s e i n the c o n c e n t r a -t i o n o f xanthate ions was observed. The appearance o f the suspended p a r t i c l e s of copper e t h y l x a n t h a t e changed from y e l l o w to dark g r e e n . I t was observed t h a t pH o f s o l u t i o n s changed as shown i n F i g . 13, i . e . i t i n c r e a s e d f o r i n i t i a l l y a c i d s o l u t i o n s and decreased f o r i n i t i a l l y b a s i c s o l u t i o n s ( s i m i l a r l y to pH changes i n the previous l e a d e t h y l x a n t h a t e s t u d y ) . The d i s s o l u t i o n and decomposi t ion s t u d i e s at h i g h e r temperatures such as 3 5 ° , 45° and 60°C i n the pH range o f 3.5 to 11.5 i n d i c a t e d t h a t the r e a c t i o n s o c c u r r e d a t f a s t e r ra tes than those a t 25°C. The l e v e l o f c o n c e n t r a t i o n o f xanthate ions cou ld not be a c c u r a t e l y determined (due to the s h i f t s i n wavelengths c l o s e to 301 mp of xanthate a b s o r p t i o n ) d u r i n g the f i r s t three hours of t rea tment . However, a f t e r three hours the c o n c e n t r a t i o n o f xanthate was s u c c e s s f u l l y determined a t a wavelength o f 301 mp; r e l a t i v e xanthate i o n c o n c e n t r a t i o n s f o r v a r i o u s pH values and temperatures are l i s t e d on the next page. I t i s seen t h a t the ether-washed copper xanthate (cuprous xanthate alone) produces an o r d e r o f magnitude lower c o n c e n t r a t i o n of xan-thate ions on decomposi t ion than the untrea ted copper x a n t h a t e , a t c o r r e s -ponding pH values and temperatures . (71) pH 3.4 1 £ A ~ & £ ^ I I I [ I | 0 50 100 150 200 250 300 T I M E ( M i Figure 13. Changes in the i n i t i a l pH values (marked on each line) due to the decomposition and the hydrolysis of the components of Cu~(EtX)9 at'(a) 25°C (b) 35°C (c) 45°C. d - 6 (72) Table 6 Xanthate i o n c o n c e n t r a t i o n a f t e r 4 h r s . o f s o l u t i o n treatment i ni t i a l unt rea ted copper ether-washed copper PH e t h y l xanthate e t h y l x a n t h a t e 35°C •45°C 60°C 45°C 60°C 3 .2 0 . 6 x l ' 0 " 4 3.5 0 . 2 5 x 1 0 " 5 7.5 0.1 x l O " . 5 9 .5 4.0 x l O " 5 l . O x l O " 3 0 . 2 x l 0 " 4 10.5 5.0 x l O * 5 0 . 4 x l 0 " 4 11.1 1 . I x l O " 3 11.5 6 .8 x l O " 5 11 .6 4 . 1 x l O " 3 I t i s a l s o seen tha t a t h i g h e r temperatures such as 60°C the c o n c e n t r a t i o n o f xanthate ions are much h i g h e r . F i g u r e 14 shows the c o n c e n t r a t i o n of copper ions i n the s o l u t i o n as a f u n c t i o n of time a t 3 5 ° , 45° and 60°C. The i n i t i a l pH value a t which the s tudy was c a r r i e d out i s noted on each l i n e . Three d i f f e r e n t trends are observed f o r the three pH v a l u e s . The maximum c o n c e n t r a t i o n o f copper ions i s ob ta ined a t pH 3 . 5 , and t h i s f a l l s o f f g r a d u a l l y w i t h t i m e , presumably due to h y d r o l y s i s . In s o l u t i o n s of pH 6.5 and 8.5 the c o n c e n t r a t i o n o f copper ions decreases i n comparison w i t h t h a t i n the a c i d i c pH v a l u e s . A t pH 10.5 and above the c o n c e n t r a t i o n o f copper ions i n c r e a s e s p r o g r e s s i v e l y w i t h t i m e . (73) pH 8 .5 (a) Temp. 60°C pH 10.5 50 (b) Temp. 45°C pH 11.1 (c) Temp. 35°C 100 150 200 TIME (Min) 250 300 F i g u r e 14. Copper i o n c o n c e n t r a t i o n as a f u n c t i o n o f t ime i n t r e a t i n g copper e t h y l x a n t h a t e at v a r i o u s pH values (marked on each l i n e at (a) 60° (b) 45° (c) 3 5 ° . (74) The behaviour o f copper ions i n the pH range of 3 .5 to 11.5 i s analogous to t h a t observed i n the case o f l ead ions between these pH v a l u e s . 5.4 E l e c t r o n Paramagnetic Resonance Study o f Copper E t h y l x a n t h a t e There i s a d i f f e r e n c e o f o p i n i o n w i t h regard to the numerical va lue o f the o x i d a t i o n s t a t e of copper i n copper xanthate formed from c u p r i c and xanthate i o n s . The EPR study c a r r i e d out by S o l o z h e n k i n (82) i n d i c a t e s that the copper atom i n copper xanthate i s i n the d i v a l e n t s t a t e . He argues t h a t dixanthogen i n s o l u t i o n , because o f i t s high o x i d a t i o n p o t e n t i a l , w i l l not a l l o w c u p r i c xanthate to be reduced to the cuprous form. This work however, c o n t r a d i c t s the previous f i n d i n g s , t h a t dixanthogen and cuprous e t h y l x a n t h a t e are the o n l y products of c u p r i c e t h y l x a n t h a t e p r e c i p i t a t i o n (see equations 1.11 and 1 .12 ) . A b r i e f d i s c u s s i o n o f the exper imental procedure and the r e s u l t s o f S o l o z h e n k i n (82) i s necessary . S o l o z h e n k i n presumed t h a t c u p r i c xanthate was a paramagnetic compound w i t h an e l e c t r o n i c c o n f i g u r a t i o n o f 9 +2 3d (Cu ) . This type o f c o n f i g u r a t i o n i s s u i t a b l e f o r EPR i n v e s t i g a t i o n . S o l o z h e n k i n o b t a i n e d the EPR spectrum o f copper b u t y l x a n t h a t e i n benzene s o l u t i o n , which had been recorded a t l i q u i d n i t r o g e n temperature . The p r e v i o u s h i s t o r y o f t h i s compound i s not known. The spectrum of the copper b u t y l x a n t h a t e c o n s i s t e d o f . f o u r h y p e r f i n e components, due to the n u c l e a r s p i n 1= 3/2 of both the copper i s o t o p e s Cu and Cu . The spec-trum was recorded on samples w i t h o u t p r i o r removal of d i x a n t h o g e n , and (74a) Figure 15:"EPR spectra of copper ethylxanthate (1) Ether treated solid (2) /n benzene (3) In benzene (98%) and pyridine (2%) (4) untreated in benzene (98%) and pyridine (2%). (75) the author mentioned t h a t a f t e r removal o f d ixanthogen from the system the e q u i l i b r i u m o f the redox r e a c t i o n was s h i f t e d towards cuprous b u t y l x a n t h a t e , s i n c e the i n t e n s i t y o f the s i g n a l was g r e a t l y r e d u c e d . In c o n c l u s i o n , the a u t h o r c a t e g o r i c a l l y s t a t e d t h a t c u p r i c xanthate was the most dominant s p e c i e s i n the copper s u l p h i d e - x a n t h a t e f l o t a t i o n sys tem. In view o f t h i s h i g h l y c o n t r a d i c t o r y r e s u l t o b t a i n e d by S o l o z h e n k i n , an EPR s tudy o f copper e t h y l x a n t h a t e was c a r r i e d o u t . The s o l i d samples o f e t h e r - t r e a t e d and u n t r e a t e d copper e t h y l x a n t h a t e d i d not produce s p e c t r a w i t h h y p e r f i n e components. A broad s i g n a l o f medium i n t e n s i t y was ob ta ined from the e t h e r - t r e a t e d sample a t . r o o m temperature as shown by l i n e 1 i n F i g u r e 15. An attempt was made to d i s s o l v e copper e t h y l x a n t h a t e i n benzene. The compound (0.05.g) was mixed w i t h benzene (10 ml) f o r f i v e minutes but no measurable (by UV) q u a n t i t y of copper e t h y l x a n t h a t e i n s o l u t i o n was o b t a i n e d . A f t e r a f u r t h e r 15 minutes o f m i x i n g , t h e r e s u l t a n t s o l u t i o n , when f r o z e n , gave the spectrum shown by l i n e 2 i n F i g u r e 15. Only a very smal l amount o f compound was d i s s o l v e d . Other attempts to d i s s o l v e copper e t h y l x a n t h a t e i n o r g a n i c s o l v e n t s such as benzene, t o l u e n e , carbon t e t r a c h l o r i d e , carbon d i s u l p h i d e and c h l o r o f o r m a l s o r e s u l t e d i n f a i l u r e . F i n a l l y , a q u a n t i t y o f each e t h e r - t r e a t e d and u n t r e a t e d copper e t h y l x a n t h a t e (500 mg) was added to separa te m i x t u r e s " of benzene (10 ml) and p y r i d i n e ( 0 . 2 m l ) . Both compounds d i s s o l v e d i n -t h i s s o l u t i o n and gave w e l l r e s o l v e d s p e c t r a w i t h f i n e h y p e r f i n e s p l i t t i n g s . These s p e c t r a are represented by the l i n e s 3 and 4 i n F i g u r e 15 . The l i n e (76) widths and shapes of the s p e c t r a were s i m i l a r to those of copper b u t y l x a n -thate repor ted by S o l o z h e n k i n ( 8 2 ) . The va lue of g f a c t o r f o r e t h e r - t r e a t e d and u n t r e a t e d copper e t h y l x a n t h a t e was 2.095 i n both cases . This va lue was c a l c u l a t e d from the s p e c t r a l and exper imental parameters . The va lue c a l c u l a t e d by S o l o z h e n k i n f o r copper b u t y l x a n t h a t e was 2 .047. B r i e f comment on the e f f e c t of i m p u r i t i e s on EPR measure-ments i s w o r t h w h i l e . Such e f f e c t s were d i s c u s s e d by S o l o z h e n k i n i n the i n t r o d u c t o r y p a r t of h i s paper ( 8 2 ) . A broadening of the EPR s i g n a l i s observed w i t h d i f f e r e n t degrees of o x i d a t i o n o f - a diamagnet ic s p e c i e s to one w i t h paramagnetic p r o p e r t i e s . Even i f the paramagnetic i m p u r i t y i s present on a m i c r o s c a l e the EPR s i g n a l appears as a broad l i n e . A t s l i g h t l y h i g h e r c o n c e n t r a t i o n s o f the paramagnetic s p e c i e s , i n the range o f one percent or l e s s , the i n t e r a c t i o n o f the unpaired e l e c t r o n s w i t h the nucleus leads to a s p l i t t i n g of the EPR s i g n a l i n t o s e v e r a l h y p e r f i n e s p e c t r a l l i n e s . S o l o z h e n k i n c o n s i d e r e d the e f f e c t s o f i m p u r i t i e s on a micro and macro s c a l e but t o t a l l y i g n o r e d the p o s s i b i l i t y o f f o r m a t i o n of such paramagnetic i m p u r i t i e s i n diamagnet ic cuprous e t h y l x a n t h a t e ( 3 d ^ , Cu + ) d u r i n g p r e p a r a t i o n and d i s s o l u t i o n of copper x a n t h a t e . The present study i n d i c a t e s t h a t the EPR s i g n a l s r e s u l t from a paramagnetic i m p u r i t y i n the cuprous e t h y l x a n t h a t e . The s o l i d samples g i v e broad l i n e s p e c t r a because o f t races o f c u p r i c ions which are c o n s i d e r e d to r e s u l t from atmospheric o x i d a t i o n . The e a r l i e r s t u d i e s (110) f u r t h e r support the present f i n d i n g s tha t xanthates are diamagnet ic i n the s o l i d s t a t e , a l though (77) they show paramagnetic properties in basic solvents such as pyridine. In conclusion i t can be said that the formation of cuprous ethylxanthate and dixanthogen is caused by the decomposition of cupric xanthate. The copper, in both the ether-treated and untreated copper ethylxanthates remains in the monovalent state. The EPR signal in solid samples probably results from cupric impurities which are found in sol id or l iquid phases in the course of preparation and dissolution of cuprous ethylxanthate. 5.5 The X-Ray Photoel ectron Spectroscopic Study of Copper Ethylxanthate and i ts Derivatives The oxidation state of copper in a variety of samples of copper ethylxanthate was further studied by the X-ray photoelectron spectroscopic method known as ESCA. I n i t i a l l y , the ESCA measurements of the reference materials, cuprous and cupric oxides and sulphides were recorded. The spectrum of cuprous chloride was recorded to check the sensi t ivi ty of the instrument and the r e l i a b i l i t y of the technique. This compound (Cu^Cl^) turned yellowish-green on exposure to a'ir and showed a spectrum characteristic of the cupric species. Cuprous oxide and sulphide which were exposed to the air for one hour after very fine grind-ing also indicated the presence of cupric species. This confirmed that the effect of atmospheric oxidation on freshly exposed surfaces of compounds is registered in the spectrum. Generally the I- 1 1* LI 11; MI, Mil and M i l l electron bands of copper are recorded. These bands appear at different positions on the i (78) b i n d i n g energy s c a l e of the cuprous and c u p r i c s p e c i e s . The main d i f f e r e n c e between cuprous and c u p r i c compounds i s t h a t i n t e n s e s a t e l l i t e peaks are found i n the 2S, 2P and 3S bands o f the c u p r i c s p e c i e s . These s a t e l l i t e peaks are h e l p f u l i n the study o f c o o r d i n a t i o n bonds i n copper c o m p l e x e s . . The e x i s t e n c e of i m p u r i t i e s of d i f f e r e n t o x i d a t i o n s t a t e s i n copper can 3/2 cause a chemical s h i f t o f 1-2 eV i n the main peaks of 2 P 2 and 2P . The i n t e n s i t y r a t i o between the s a t e l l i t e and the main peak becomes s m a l l e r and v a r i a b l e i n the case o f a mix ture o f c u p r i c and cuprous s p e c i e s . In t h i s study the L I I and LI 11 bands of copper d e r i v e d from the 2P e l e c t r o n s were s t u d i e d . Only the b i n d i n g energy r e g i o n of 930 to 970 eV was scanned to avoid the c o n f u s i o n w i t h the peaks o f o t h e r elements i n the sample . These i n c l u d e d the carbon of the adhes ive tape which c a r r i e d the sample. F igures 16 and 17 show the s p e c t r a o f the compounds i n v e s t i -gated i n t h i s s t u d y . Table 7 g ives the data r e l a t e d to these compounds. The h i s t o r y of the sample i s d i s c u s s e d under F igures 16 and 17. The b l a c k , decomposed copper e t h y l x a n t h a t e samples were c o n s i d e r e d to be contaminated e i t h e r w i t h copper o x i d e or s u l p h i d e . T h e r e f o r e , the r e f e r e n c e s p e c t r a o f cuprous and c u p r i c ox ide and s u l p h i d e were recorded and t h e i r b i n d i n g energy data are i n c l u d e d i n Table 7. The s p e c t r a o f these compounds are represented by the l i n e s 1 , 2 , 3 and 4 i n F i g u r e 16. The s p e c t r a 7 and 8 i n F i g u r e 17 r e p r e s e n t copper e t h y l x a n t h a t e prepared from cuprous cyanide and copper s u l p h a t e r e s p e c t i v e l y . In the l a t t e r compound dixanthogen was removed by e x t r a c t i o n w i t h e t h e r . The s p e c t r a (79) Table 7 The E l e c t r o n B i n d i n g Energies o f Copper E t h y l x a n t h a t e  and Re la ted Compounds spectrum CuL 11 (2P*5) CUL H I ( 2 P 3 / 2 ) no. s a t e l l i te eV . main peak eV s a t e l l i t e main peak eV eV 1 964 .8 956 .5 942.7 936 .2 2 954.7 934.7 3 964.2 956.0 941 .8 936 .3 4 954 .3 934.6 5 954 .2 - 934 .8 6 954.0 935.0 7 954 .3 934 .5 8 954 .5 934 .5 . 9 953.7 934.0 10 955.0 936 .3 11 965.0 . 956 .8 ' 944.0 936 .8 12 955.0 934 .2 13 955 .2 934.6 1 • (80) 970 960 950 940 eV 930 F i g u r e 16. X-Ray Photoel e c t r o n Spec t ra of (1) CuO (2) CupO (3) CuS (4) Cu 2 S (5) C u 2 ( E t X ) 2 a t 4 . 5 pH & 25°C (6) C u 2 ( E t X ) at 11.0 pH & 60°C (81) of these compounds indicate that copper is present in the monovalent form in both cases. The copper ethylxanthate mixed with dixanthogen is confirmed to be cuprous ethylxanthate from the shape of the spectrum and the electron binding energy values. Spectra 10 and 11 in figure 17 represent the old samples of copper ethylxanthate which were washed with acetone and then left open to the atmosphere for a period of one and sixteen weeks respectively. The small chemical shift in the main peaks of LII and L111 in spectrum 10 indicate surface oxidation of the compound. In spectrum 11 the appearance of strong LII ans LI 11 sa te l l i t e peaks clearly indicates the pronounced conversion of cuprous ethylxanthate to cupric decomposition products. A few samples previously treated with solutions of various pH values at different temperatures were also studied. Spectra 5 and 6 in Figure 1 represent the samples of cuprous ethylxanthate treated with aqueous solutions of pH 4.5 at 25°C and of pH 11.0 at 60°C respectively. The other spectra of this series are denoted in Figure 17 by lines 12 and 13. These represent the samples of cuprous ethylxanthate which were suspended in aqueous solutions of pH 8.5 at 25° and 35°C, for four hours. Of the four samples represented by the spectra, 5 and 12 were yellow, 6 was black and 13 was grey in colour. The shapes of the spectra and the values of the electron binding energies in samples 6 and 13 indicate that the copper remains in a monovalent state in the black coloured decomposition products of cuprous ethylxanthate. Surprisingly, the cuprous ethylxanthate which was expected to be contaminated with cupric species after remaining so long (82) 970 960 950 940 eV 930 F i g u r e 17. X-Ray P h o t o e l e c t r o n Spectra of (7) C u 2 ( E t X ) 2 formed w i t h CuSO^ washed w i t h e ther (9) C u 2 ( E t X ) 2 not washed (10) ONE week o l d C u 0 E t X ) 2 (11) 16 weeks o l d (12) C u 2 ( E t X ) 2 at 8 .5 ' pH a t 25°C (13) C u ? ( E t X ) ? a t 8 .5 pH at 35°C. (83) i n suspens ion d i d not g ive any i n d i c a t i o n o f d i v a l e n t copper . I f the metal ions i n aqueous s o l u t i o n s are o x i d i z e d , they presumably form complex i o n s ; w h i l e the s u r f a c e copper ions i n cuprous e t h y l x a n t h a t e r e a c t w i t h s u l p h i d e ions from the s o l u t i o n a t a l k a l i n e pH to form cuprous s u l p h i d e . This s u l p h i d e remains s t a b l e and does not t rans form to the c u p r i c s t a t e . S i m i l a r l y , i n a c i d i c s o l u t i o n s , the copper i n the s o l i d samples was found to remain i n the monovalent s t a t e . 5.6 The V i s i b l e E f f e c t s of Atmospheric Exposure i n S o l u t i o n s of V a r y i n g pH and Temperature on the P h y s i c a l  S t a t e o f Cuprous E t h y l x a n t h a t e The v i s i b l e e f f e c t s of pH and temperature changes on the suspensions of cuprous e t h y l x a n t h a t e has been shown i n F i g u r e 18. The e f f e c t o f v a r i a t i o n s o f these parameters i n the case o f the e t h e r - t r e a t e d cuprous e t h y l x a n t h a t e i s shown i n F i g u r e 17a. In these experiments the compound was suspended i n aqueous s o l u t i o n f o r f o u r h o u r s . The c o l o u r of the compound was found to change from y e l l o w to dark green and e v e n t u a l l y became b l a c k . This sequence of c o l o u r change depended on t i m e , pH and temperature . A t 25°C the p h y s i c a l appearance o f the compound was not markedly changed w i t h t i m e . However, a c o n s i d e r a b l e d i f f e r e n c e was noted a t temperatures o f 3 5 ° , 45° and 60°C. The samples t r e a t e d a t pH 1 0 . 5 , 11.5 and 12.5 a t 25°C f o r a l o n g e r p e r i o d ( i . e . 8 hours) g r a d u a l l y changed from y e l l o w to dark g r e e n . The a n a l y t i c a l r e s u l t s o f these compounds i n d i c a t e d a 5 to 10% decrease i n the p u r i t y o f the cuprous e t h y l x a n t h a t e . (84) Temp. ? 5 ° c P « 4.5 t # P" 9 - 5 pH 10.5 ^ • • PH 8.5 Temp. 35oc PH 7.5 H .  H , Q 5 Temp. 45°C PH 3.5 PH 7.5 Temp. 60°C PH 3.5 PH 6.5 pH 11.5 Temp. j 5 o c Temp. 35°C Temp. 60°C ft • • m PH 3.5 T*. W^-? p H 7 - 5 PH 9:5 * ^ pH 12.5 PH 4.5 PH 7.5 P H 9.5 pH 10.5 " H 9 - 5 PH 11.5 ^ t • • Fresh . 12 Weeks 2 W ° e k S S Weeks 16 weeks 2** Weeks 16 wetks 2» Weeks Figure 18. (a and b) Cuprous ethylxanthate with and without dixanthogen respectively after treatment with aqueous solutions at various pH values and tempera-tures as indicated. (c) Atmospheric effect on these compounds after the periods indicated. (85) Analogous s t u d i e s at 35° and 45°C i n d i c a t e d s i m i l a r c o l o u r changes at pH values such as 9 .5 and 10.5 a f t e r f o u r hours of t rea tment . At 60°C on the same time s c a l e , the suspension a t pH 10.5 and 11.5 turned b l a c k . The cuprous e t h y l x a n t h a t e suspens ion t r e a t e d a t a c i d i c pH values was not markedly a f f e c t e d by the temperatures of 25° and 35°C, but d e f i n i t e changes were noted a t 4 5 ° and 60°C. F i g u r e 18b shows the r e s u l t s obta ined from some samples o f untrea ted cuprous e t h y l x a n t h a t e which were exposed to c o n d i t i o n s i n d i c a -ted i n the l e g e n d . The changes i n p h y s i c a l appearance of the samples were not as pronounced as those observed i n the case of the ether-washed compounds. The extremely f i n e p a r t i c l e s o f e t h e r - t r e a t e d cuprous e t h y l x a n -thate were more s u s c e p t i b l e to chemical changes than the agglomerated mixed p a r t i c l e s o f cuprous e t h y l x a n t h a t e and d i x a n t h o g e n . This was due to the h i g h e r s u r f a c e area of the f i n e r p a r t i c l e s . - In a d d i t i o n , the o i l y c h a r a c t e r of dixanthogen p r o t e c t e d the cuprous e t h y l x a n t h a t e from the changes i n the aqueous phase. However, such changes were not e n t i r e l y absent from the mixed cuprous e t h y l x a n t h a t e and dixanthogen s u s p e n s i o n s . F i g u r e 17b i n d i c a t e s tha t such changes were apparent i n the samples t r e a t e d a t pH 12.5 a t 25°C and a t pH 9.5 and 10.5 a t 35°C. B l a c k e n i n g of the above samples at pH values such as 8.5 to 11.5 was aga in observed a t 60°C. The r a t e of t h i s change was s lower than tha t of e t h e r - t r e a t e d cuprous e t h y l x a n t h a t e . F i g u r e 18c shows the e f f e c t of exposure to the atmosphere on the p h y s i c a l appearance of e t h e r - t r e a t e d and untrea ted cuprous e t h y l x a n t h a t e . I t was noted p r e v i o u s l y tha t the atmospheric a t tack on e t h e r - t r e a t e d (86) samples were more pronounced than on the untrea ted ones. The former compounds were found to be q u i t e s e n s i t i v e to atmospheric o x i d a t i o n . The e f f e c t s o f p a r t i c l e s i z e , p a r t i c l e s i z e d i s t r i b u t i o n and p o r o s i t y of the ether-washed compound a c c e l e r a t e d the s o l i d s t a t e r e a c t i o n s . A marked f a l l i n o x i d a t i o n i s observed under i n e r t atmos-p h e r i c c o n d i t i o n s or i n vacuum. The ether-washed samples t u r n grey two weeks a f t e r p r e p a r a t i o n i f l e f t open to the atmosphere. Prolonged exposure turns them b lack as i s shown i n F i g u r e 17c. The changes i n the samples o f ether-washed cuprous e t h y l x a n t h a t e appear a f t e r f o u r weeks. The presence o f dixanthogen p a r t i a l l y prevents the atmospheric o x i d a t i o n o f the compound. In the f o l l o w i n g s e c t i o n s a s tudy has been c a r r i e d out to c h a r a c t e r i z e the decomposi t ion products of the cuprous e t h y l x a n t h a t e w i t h the a i d of X-ray d i f f r a c t i o n and i n f r a r e d s p e c t r o s c o p y . A study to i n v e s t i g a t e the mechanism o f s o l i d s t a t e o x i d a t i o n and decomposi t ion has not been a t tempted. 5.7 The I n f r a r e d S p e c t r o s c o p i c S t u d i e s of the Decomposi t ion Products of Cuprous E t h y l x a n t h a t e The chemical nature o f the samples of e t h e r - t r e a t e d and untreated cuprous e t h y l x a n t h a t e prepared w i t h c u p r i c or cuprous ions was examined by IR s p e c t r o s c o p y . The re fe rence s p e c t r a mentioned i n the l i t e r a t u r e (53) were f o l l o w e d to i n v e s t i g a t e the p u r i t y and s t r u c t u r a l v a r i a t i o n s i n the t e s t samples . The suspensions of the compound were (87) 1400 1200 1000 800 c m - 1 0 0.1 0 .2 0 .3 0 .4 0 .5 0 .6 Cu 2 (EtX) 2 (mg. ) F i g u r e 1 9 : a) IR s p e c t r a o f e ther t r e a t e d cuprous e t h y l x a n t h a t e b) This c a l i b r a t i o n curve i n d i c a t e s t h a t B e e r ' s law i s obeyed a t 1198 cm" 1 over the i n d i c a t e d range o f C u 2 (E tX)2 c o n c e n t r a t i o n . (88) removed from the aqueous s o l u t i o n s (o f the pH range of 3 .5 to 1 2 . 5 , a t the temperatures o f 25° to 60°C) a t v a r i o u s time i n t e r v a l s and a n a l y z e d . I t was n o t i c e d t h a t the p o s i t i o n o f the 1198 cm 1 band which i s a t t r i b u t e d to the C - 0 group i n cuprous e t h y l x a n t h a t e remained unchanged. The i n t e n s i t y of the band, however, decreased as decomposi t ion proceeded. A marked decrease i n i n t e n s i t y was observed when grey o r b l a c k samples were a n a l y z e d . A s e m i - q u a n t i t a t i v e technique was developed to determine the amount of decomposi t ion products of cuprous e t h y l x a n t h a t e . The c a l i b r a -t i o n curve shown i n F i g u r e 19a i n d i c a t e d t h a t B e e r ' s law was obeyed a t a frequency o f 1198 c m - * over a c o n c e n t r a t i o n range o f 0 .1 to 0 .5 mg of cuprous e t h y l x a n t h a t e . The average va lue o f the molar e x t i n c t i o n c o e f f i -c i e n t , c a l c u l a t e d from the s e r i e s o f s p e c t r a a t t h i s wavelength was 860 -1 -1 l i t e r mole cm . In each i n f r a r e d spectrum the sample (0 .3 mg) was thoroughly mixed w i t h spec t rograde potassium bromide (300 mg) and compressed i n t o a p e l l e t . The amount of cuprous e t h y l x a n t h a t e i n the sample was determined from the absorbance a t 1198 c m " 1 . The c a l i b r a t i o n curve was used to f i n d the q u a n t i t y of undecomposed cuprous e t h y l x a n t h a t e or the amount o f t o t a l decomposi t ion products by d i f f e r e n c e . I t ' w a s assumed t h a t the decomposi t ion products d i d not g i v e t r a n s m i s s i o n band a t t h i s w a v e l e n g t h . F i g u r e 20 shows the r a t e o f decrease i n the t o t a l c o n c e n t r a t i o n o f cuprous e t h y l x a n t h a t e a f t e r treatment w i t h aqueous s o l u t i o n s a t the i n d i c a t e d pH values and temperatures . F igures 20a, b , and c i l l u s t r a t e the r a t e o f decomposi t ion o f cuprous e t h y l x a n t h a t e a t 2 5 ° , 35° and 60°C. This decomposi t ion r a t e depends upon the pH of the aqueous s o l u t i o n w i t h (89) x CM X +-> CM O X 4-> CM o 100 80 H 60 40 20 J 0 40 -20 _ 0 25°c (a) pH 3 .5 8 .5 10.5 12.5 TIME(min.') F i g u r e 20: The r e s u l t s of IR s p e c t r o s c o p i c e s t i m a t i o n of the percentage of Cu2 (EtX) 2 which was decomposed at the p a r t i c u l a r pH values and temperatures i n d i c a t e d . (90) which the compound i s t r e a t e d . I t can be seen from the curves t h a t the percentage o f the decomposi t ion products which accumulate i n the cuprous e t h y l x a n t h a t e suspens ion i s approximate ly 10, 40 and 80% at a pH o f 1 2 . 5 . Such pronounced changes are not seen a t a c i d i c pH v a l u e s . No s o l i d products are formed i n a c i d i c s o l u t i o n to contaminate the cuprous e t h y l -xanthate s u s p e n s i o n . The decomposi t ion ra tes change as the pH v a r i e s from the a c i d i c to the b a s i c r e g i o n . The l i n e s i n F i g u r e 20, marked w i t h the i n i t i a l pH values o f the aqueous s o l u t i o n s , i n d i c a t e the r e s p e c t i v e decomposi t ion r a t e s . Wel l r e s o l v e d s p e c t r a of the s u r f a c e compounds which were formed on cuprous e t h y l x a n t h a t e a f t e r long exposure to atmosphere were o n l y ob ta ined w i t h g r e a t d i f f i c u l t y . The s p e c t r a o f re fe rence compounds such as the b a s i c copper carbonate , C u C O ^ . C u t O H ^ , cuprous and c u p r i c oxides and s u l p h i d e s were recorded f o r compar ison . The s p e c t r a o f s u r f a c e compounds on the samples i n d i c a t e d very weak c h a r a c t e r ! ' s t i c bands . The s p e c t r a o f the dark green samples t r e a t e d i n aqueous s o l u t i o n s a t a l k a l i n e pH values i n d i c a t e d the format ion o f the b a s i c carbonate o f copper . The i n f r a r e d s p e c t r a o f the b l a c k samples obta ined from the aqueous treatment o f cuprous e t h y l x a n t h a t e i n d i c a t e d the presence o f cuprous s u l p h i d e . The presence of carbonate and c u p r i c ox ide was i n d i c a t e d on the samples which turned b l a c k a f t e r long exposure to the atmosphere. Some s p e c t r a o f the decomposi t ion products of cuprous e t h y l x a n t h a t e together w i t h the r e f e r e n c e compounds are shown i n F i g u r e 21 . The i n f r a r e d s p e c t r a of the decomposi t ion products o f heavy metal xanthates under atmospheric c o n d i t i o n s or i n aqueous s o l u t i o n s ~ h a v e (91) Figure 21Q)Some details of IR spectra of the decomposition products of cuprous ethylxanthate a) sol id sample exposed to the atmosphere at 25°c for 24 hours b) sample kept at pH 11.5 at 60°c for 3 hours c) sample kept at pH 11.5 at 60°c for 6 hours. (92) (CuC03 « Cu(OH)2) Figure 21: (2) Some details of the IR spectra of the reference compounds of copper marked on'each l ine . (Reproduced without the inclusion of scale) (93) not been i n v e s t i g a t e d . No w o r k ^ t h e r e f o r e , i s a v a i l a b l e f o r r e f e r e n c e . U n f o r t u n a t e l y , .most o f the decompos i t ion products o f cuprous e t h y l x a n t h a t e which c o n t a i n s u l p h u r compounds absorb i n the same r e g i o n o f the IR spectrum as the o r i g i n a l compound. This makes i t d i f f i c u l t to dec ide whether the bands are due to a new compound or the undecomposed parent compound. However, a s h i f t i n these bands g ives some i d e a about the presence o f such compounds. I f a comparison i s made between spectrum 21(1)c and the r e f e r e n c e spectrum of c u p r i c o x i d e a medium'band i s noted i n the 500 cm~* r e g i o n . The band i n t h i s r e g i o n i s c o n s i d e r e d to be due to asymmetric Cu-0 v i b r a t i o n (111 , 112) . The t r a n s m i s s i o n band i n t h i s r e g i o n i s a l s o found due to the b a s i c copper s a l t s (113) . The i n f r a r e d bands which a r i s e due to the presence o f the carbonate i o n have been f u l l y d i s c u s s e d i n s e c t i o n 4 . 6 . The bands which appeared i n the r e f e r e n c e spectrum o f copper carbonate were compared w i t h those i n some o f the decomposi t ion products o f cuprous e t h y l x a n t h a t e . Spectrum 21c i n d i c a t e d the presence o f c h a r a c t e r i s t i c bands o f carbonate w i t h s l i g h t changes i n t h e i r p o s i t i o n s . The i n t e r p r e t a t i o n o f the s p e c t r a of the b l a c k compounds obta ined from the aqueous treatment was based on a comparison w i t h the t r a n s m i s s i o n s p e c t r a o f copper s u l p h i d e s . The s p e c t r u m . 2 i ( l ) c i n d i c a t e d the presence o f copper s u l p h i d e i n the b l a c k samples a n a l y z e d . The i d e n t i f i c a t i o n o f o t h e r decompos i t ion products such as s u l p h u r compounds w a s ' n o t attempted i n t h i s s t u d y . (94) 5.8 The X-Ray D i f f r a c t i o n Study o f the Decomposit ion Products o f Cuprous E t h y l x a n t h a t e In the~X-ray d i f f r a c t i o n study of the r e f e r e n c e m a t e r i a l s and the decomposi t ion products_,the same procedure o f i d e n t i f i c a t i o n was adopted as was d i s c u s s e d i n s e c t i o n 4.7. This s tudy supported the f i n d -ings obta ined by i n f r a r e d s p e c t r o s c o p y . The b lack product found i n the samples exposed to the atmosphere was c u p r i c o x i d e . The b lack c o l o r e d decomposi t ion product which was obta ined from the samples t r e a t e d a t a l k a l i n e pH values conta ined cuprous s u l p h i d e . This s tudy a l s o i n d i c a t e d the presence of b a s i c copper carbonate and c u p r i c s u l p h i d e i n s e v e r a l samples . The d s p a c i n g values were compared w i t h those of the r e f e r e n c e compounds run s i m u l t a n e o u s l y . The s tandard r e f e r e n c e cards were a l s o used f o r the comparison o f d v a l u e s . Chapter 6 The S t a b i l i t y of Suspension o f F e r r i c E t h y l x a n t h a t e The f a c t o r s which a f f e c t the p r e c i p i t a t i o n o f f e r r i c e t h y l x a n t h a t e and the e f f e c t s of a c i d i c and b a s i c s o l u t i o n s on t h i s compound are d i s c u s s e d i n t h i s c h a p t e r . A Mossbauer study was c a r r i e d out i n an attempt to d e t e r -mine the o x i d a t i o n s t a t e o f i r o n i n the i r o n x a n t h a t e . In a d d i t i o n , UV and IR s p e c t r o s c o p i c methods, DTA and X - r a y d i f f r a c t i o n were used to ana lyze the decomposi t ion products o f f e r r i c e t h y l x a n t h a t e . . 6.1 The P r e c i p i t a t i o n Study of F e r r i c E t h y l x a n t h a t e S o l u t i o n s of f e r r i c ammonium s u l p h a t e and potassium e t h y l x a n t h a t e were mixed a c c o r d i n g to the procedure d e s c r i b e d i n sec -t i o n 4 . 1 . S i m i l a r p r e c i p i t a t i o n regions to those i n s e c t i o n s 4 . 1 and 5.1 were observed . The r e s u l t s are shown i n F i g u r e 22. The s o l u b i l i t y product va lue f o r f e r r i c e t h y l x a n t h a t e was not a v a i l a b l e , so no a b s o l u t e s o l u b i l i t y boundary can be i n c l u d e d . A va lue o f 8x10" was found i n the l i t e r a t u r e f o r f e r r o u s e t h y l x a n t h a t e ( 3 2 ) . An approximate va lue o f 5x10 has been used to c a l c u l a t e a s o l u b i l i t y product l i n e . This va lue i s based on the c o n c e n t r a t i o n of xanthate ions a t e q u i l i b r i u m when f e r r i c e t h y l x a n t h a t e i s d i s s o l v e d i n an aqueous s o l u t i o n o f pH 7.5 at 25°C. (96) -6 _ (1) (3) K s p LINE -6 -5 -3 Log Molar Concentration of Fe (.NH )^.. (504)9 ' Figure 22: Precipitation regions of ferr ic ethylxanthate (1) High turbidity region (2) low turbidity region, (3) region of zero turbidity. The small shaded c i rc le indicates the precipitation region of ferrous ethylxanthate. (97) An attempt to o b t a i n i r o n e t h y l x a n t h a t e f r e e of suspected dixanthogen ( f o r a determi n a t i o n ~>of s o l u b i l i t y product) was unsuccess fu l as the p r e c i p i t a t e was found to be s o l u b l e i n a l l o r g a n i c s o l v e n t s , such as e t h e r , acetone and hexane, g i v i n g a dark brown s o l u t i o n . This may have r e s u l t e d i n a c o n s i d e r a b l e e r r o r of the c a l c u l a t e d K v a l u e . sp As can be seen i n F i g u r e 22, i t was found t h a t s o l u b i l i t y regions 1 and 2 were broader i n shape and covered a l a r g e r area above the s o l u b i l i t y product l i n e than those o f the lead and copper x a n t h a t e s . This l a r g e w i d t h o f regions 1 and 2 together w i t h the narrow zone of r e g i o n 3 may be due to an easy h y d r o l y s i s of f e r r i c ions which would cause an i n c r e a s e i n the t u r b i d i t y i n a d d i t i o n to t h a t due to the f o r m a t i o n o f f e r r i c e t h y l x a n t h a t e . In an attempt to s tudy the p r e c i p i t a t i o n o f f e r r o u s e t h y l x a n t h a t e the c o n c e n t r a t i o n s represented by the a b s c i s s a i n F i g u r e 22 were r e p l a c e d by s i m i l a r c o n c e n t r a t i o n s o f f e r r o u s ammonium s u l p h a t e . Only one c o n c e n t r a t i o n combinat ion was found which gave any t u r b i d i t y . This p r e c i p i t a t i o n zone i s i n d i c a t e d by a smal l c i r c u l a r area a t the top of r e g i o n i n F i g u r e 22. 6 .2 The E f f e c t s o f A c i d i c and B a s i c S o l u t i o n s on F e r r i c E t h y l x a n t h a t e Samples o f f r e s h l y prepared f e r r i c e t h y l x a n t h a t e , u n t r e a t e d w i t h o r g a n i c s o l v e n t , were suspended i n aqueous s o l u t i o n of pH 3.5 to 11.5 (98) a t temperatures i n the range of 25 to 60 C. The k i n e t i c s o f d i s s o l u t i o n and decomposi t ion o f the f e r r i c e t h y l x a n t h a t e were s t u d i e d by UV absorp-t i o n measurements o f xanthate ions a t a wavelength o f 301 my. The xan-thate ions gave a steady peak a t t h i s wavelength i r r e s p e c t i v e of changes i n t i m e , pH and temperature . The absorbance va lue a t 301 mp t h e r e f o r e , can be used to measure a c c u r a t e l y the c o n c e n t r a t i o n of xanthate ions a t the l e v e l o f 5 x l 0 " 5 to 1 0 " 4 M . The c o n c e n t r a t i o n o f xanthate ions obta ined by the d i s s o l u --4 -2 t i o n o f f e r r i c e t h y l x a n t h a t e i s normal ly i n the range of 10 to 10 M. A t these l e v e l s o f c o n c e n t r a t i o n a peak appears a t 345 mp, the i n t e n s i t y o f which increases w i t h t i m e . I f the s o l u t i o n s are d i l u t e d to b r i n g them i n t o the measureable range of xanthate i o n c o n c e n t r a t i o n the peak becomes very s m a l l . The spec ies r e s p o n s i b l e f o r the a b s o r p t i o n a t 345 mp does not cause any s p e c t r a l s h i f t o f the xanthate a b s o r p t i o n peaks a t 301 mp and 226 mp. B a r ! t r o p and coworkers (114) have shown t h a t both the s p e c t r a of t r i t h i o c a r b o n a t e and xanthate ( F i gure 23a) absorb a t 301 mp and 226 mp, but the former compound shows an a d d i t i o n a l peak a t 345 mp. I t i s t h e r e f o r e cons idered that the peak a t 345 mp i n the f e r r i c e t h y l x a n -thate s o l u t i o n i s due to the presence o f . t r i t h i o c a r b o n a t e i m p u r i t i e s . F i g u r e 23a i n d i c a t e s the s p e c t r a of concentra ted and d i l u t e s o l u t i o n s taken a f t e r d e f i n i t e time i n t e r v a l s a t a pH 11.8 a t 35°C. The three f u l l y scanned s p e c t r a i n F i g u r e 23a were obta ined from s o l u t i o n s a f t e r 5 , 20 and 40 minutes which were d i l u t e d by the f a c t o r i n d i c a t e d . The peak a t 345 mp was detec ted over a pH range o f 4 . 5 to 11.8 and temperatures o f 25° to 60°C. The peak h e i g h t i n i t i a l l y decreased as the pH was r a i s e d , Figure 23 : UV s p e c t r a o f s i x s o l u t i o n s taken from a s u s p e n t i o n of Fe(EtX)2 which was kept at pH 11.5 and 3 5 ° c . The s o l u t i o n s were taken a f t e r the t ime i n t e r v a l s i n d i c a t e d and three of the o r i g i n a l s o l u t i o n s were d i l u t e d by the f a c t o r s shown i n parentheses , (b) Reference UV s p e c t r a of (1) xanthate (2) t r i t h i o c a r b o n a t e ( a f t e r B a r l t r o p e t . a l . ( 1 1 4 ) . (100) from 4 .5 to 8 . 5 , then a gradual i n c r e a s e i n peak h e i g h t was observed as the pH exceeded 8 . 5 . The f o r m a t i o n o f t r i t h i o c a r b o n a t e through h y d r o l y t i c decomposi t ion i n n e u t r a l and a l k a l i n e media has been d i s c u s s e d by Rao ( 3 7 ) . In n e u t r a l or m i l d l y a l k a l i n e s o l u t i o n s , the f o l l o w i n g r e a c t i o n i s cons idered to o c c u r : 6CJ-L0CSS" + 3H„0 + 6 C o H c 0 H + C0 2 "+ 3CS„ + 2CS~~ 6.1 2 5 2 2 5 3 2 3 The p o s s i b i l i t y of the f o r m a t i o n of t r i t h i o c a r b o n a t e through the f o l l o w i n g sequence o f r e a c t i o n s has a l s o been d i s c u s s e d ( 3 7 ) . C o H c 0CSS" + HOH + C o H,0CSSH + OH" 6.2 2 5 2 5 C o H c 0CSSH -»• CJiVOH + C S 0 6 .3 2 5 2 5 2 3CS 2 + 60H" + 2CS 3 " + CO 2 " + 3H 2 0 6.4 Kremev and Zatuchanaya (115) have very r e c e n t l y r e p o r t e d t h a t xanthates decompose i n a l a k a l i n e media to form t r i t h i o c a r b o n a t e and s u l p h i des . 6.3 The K i n e t i c s of D i s s o l u t i o n and Decomposit ion o f F e r r i c E t h y l x a n t h a t e i n A c i d i c and B a s i c S o l u t i o n s A study was c a r r i e d out to i n v e s t i g a t e tne changes i n xanthate and f e r r i c i o n c o n c e n t r a t i o n as a f u n c t i o n o f time i n a c i d i c and b a s i c s o l u t i o n s . A s e r i e s of experiments were c a r r i e d out w i t h f r e s h l y prepared f e r r i c e t h y l x a n t h a t e over the pH range of 4 .5 to 11.8 a t temperatures of (101) 25° to 60°C. Some of the r e s u l t s of these experiments are shown i n F igures 24, 25'and 26 which i n d i c a t e r e s p e c t i v e l y s t u d i e s c a r r i e d out a t 2 5 ° , 45° and 60°C. The r e s u l t s obta ined from a s i m i l a r study a t 35°C have "not been i n c l u d e d because the t rend of the r e s u l t s was the same as tha t observed a t 25°C. I t was noted t h a t an i n c r e a s e i n temperature l e d to an i n c r e a s e i n the r a t e o f d i s s o l u t i o n and d e c o m p o s i t i o n . F igures 24a, b and c i n d i c a t e the changes t h a t appear i n pH and c o n c e n t r a t i o n o f i r o n and xanthate i n s o l u t i o n as a f u n c t i o n o f 0 time a t 25 C. F i g u r e 24a shows t h a t i f f e r r i c e t h y l x a n t h a t e i s mainta ined a t pH 4 .5 f o r approximate ly three hours a one u n i t r i s e i n pH i s o b s e r v e d , which may be due to the decomposi t ion o f xanthate i o n s . However, when the compound i s kept a t pH 10.5 f o r the same length of t i m e , the pH f a l l s from 10.5 to 5 . 2 . This shows t h a t b a s i c s o l u t i o n s are more e f f e c t i v e i n decomposing f e r r i c e t h y l x a n t h a t e . The f a l l i n pH from 10.5 to 6.5 i n the f i r s t 10 to 20 minutes i n d i c a t e s tha t decomposi t ion occurs very r a p i d l y as a r e s u l t o f h i g h consumption of hydroxyl i o n s . The b a s i c s o l u t i o n s o f pH 7.0 and 8.5 decompose f e r r i c e t h y l x a n t h a t e l e ss r e a d i l y . F i g u r e 24b shows t h a t the c o n c e n t r a t i o n of f e r r i c ions i s h i g h e s t f o r pH 4 . 5 . The l e v e l then decreases w i t h the r i s e o f pH and the c o n c e n t r a t i o n i s l e a s t at pH 7 .0 . T h e r e a f t e r , i t s t a r t s to i n c r e a s e a g a i n w i t h h i g h e r pH. The reason f o r t h i s l a t t e r i n c r e a s e i s t h a t (as shown by r e f e r e n c e to F igure 24a) a l l a l k a l i n e s o l u t i o n s i n which f e r r i c e t h y l x a n t h a t e i s suspended become a c i d i c a f t e r 10 to 20 minutes and remain s o . (102) F igures 25a and b show the changes i n pH and d i s s o l v e d xanthate i o n c o n c e n t r a t i o n as a f u n c t i o n o f time a t 45°C. Both s t u d i e s , a t 25° and 45°C, i n d i c a t e t h a t the xanthate i o n c o n c e n t r a t i o n g r a d u a l l y i n c r e a s e s as the pH i s i n c r e a s e d above 7. However, a t 45°C and pH values of 10.5 and above, the xanthate c o n c e n t r a t i o n f i r s t increases then f a l l s o f f s h a r p l y . This i n d i c a t e s tha t o f the two s imultaneous r e a c t i o n s , i . e . d i s s o l u t i o n of f e r r i c e t h y l x a n t h a t e and decomposi t ion o f the xanthate i o n s , the r a t e o f decomposi t ion begins to exceed to t h a t of d i s s o l u t i o n . A more s t a b l e s p e c i e s , e . g . F e ( 0 H ) 3 , i s probably d e p o s i t i n g on the s u r f a c e of the f e r r i c e t h y l x a n t h a t e a t such a r a t e a t the temperature o f 45°C t h a t a f t e r ^120 minutes i t slows i t s f u r t h e r d i s s o l u t i o n . Reference to the pH-time curves i n F i g u r e 25a i n d i c a t e s tha t the very sharp drop i n pH from 10.5 to a 5.2 has occurred i n these 120 minutes and a c i d i c pH i s on ly s l i g h t l y decreased t h e r e a f t e r . A t pH 12.5 the preponderance of 0H~ i n r e l a t i o n to the amount of p r e c i p i t a t i n g F e ( 0 H ) 3 r e s u l t s i n a h a r d l y n o t i c e a b l e pH change w i t h t i m e ; s imultaneous decomposi t ion of xanthate i o n a t h igh pH a l s o appears much s l o w e r . F i g u r e 26 i l l u s t r a t e s the r e s u l t s of a s i m i l a r s tudy c a r r i e d out at 60°C. F i g u r e 26c shows t h a t a gradual decrease i n the r a t e of appearance of xanthate i o n i s f o l l o w e d by a steady i n c r e a s e over the pH range of 6 .3 to 11 .6 . This suggests t h a t an i n c r e a s e i n tempera-t u r e a s s i s t s the d i s s o l u t i o n o f f e r r i c e t h y l x a n t h a t e i n a l k a l i n e s o l u t i o n . In t i m e , however, the h y d r o l y z e d spec ies formed by the metal i o n s , together w i t h the o ther i n s o l u b l e r e a c t i o n p r o d u c t s , check the d i s s o l u -(103) TIME ( M i n . ) F igure 24: The V a r i a t i o n (a) I n i t i a l pH values (b) F e r r i c i o n v, c o n c e n t r a t i o n and (c) Xanthate i o n 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 at the i n i t i a l pH values marked on each l i n e . Temp. 2 5 ° c . (104) FIGURE. The v a r i a t i o n o f (a) i n i t i a l pH values and (b) xanthate ions c o n c e n t r a t i o n as a f u n c t i o n o f time a t the l ' n i t i a l pH values marked on each l i n e . Temperature, 45C (105) t i o n r a t e s . The decomposi t ion of xanthate c o n t i n u e s , but the combined e f f e c t of temperature and pH causes a l e ss d r a s t i c decrease i n the xanthate i o n c o n c e n t r a t i o n w i t h time than a t 45°C and pH 8 .5 to 11 .5 . F i g u r e 26a shows the changes i n i n i t i a l pH values of aqueous suspensions o f f e r r i c e t h y l x a n t h a t e a t 60°C. These changes i n pH are o f the same e x t e n t as those at 45°C. The ra tes of change of f e r r i c i o n c o n c e n t r a t i o n a t 60°C i n the pH range o f 4 .0 to 13.0 are shown i n F i g u r e 26b. The curves f o r pH 4 .0 and 5.5 show a decrease i n the c o n c e n t r a t i o n of f e r r i c ions due to h y d r o l y s i s . The c o n c e n t r a t i o n of f e r r i c ions i n c r e a s e s s h a r p l y a t pH 8 .5 and 9 .5 i n d i c a t i n g very high rates of d i s s o l u t i o n o f f e r r i c e t h y l x a n t h a t e by these b a s i c s o l u t i o n s ; the pH values drop c o r r e s p o n d i n g l y to pH 4 and 5. A t these pH values f e r r i c i o n c o n c e n t r a t i o n cont inues to i n c r e a s e i n the s o l u t i o n w i t h o u t apparent r e - p r e c i p i t a t i o n as F e ( 0 H ) 3 . A t pH 11.6 and 13.0 the d i s s o l u t i o n and decomposi t ion of f e r r i c e t h y l -xanthate do n o t ' l o w e r the pH o f the s o l u t i o n s to a c i d values and an i n c r e a s e i n f e r r i c i o n c o n c e n t r a t i o n i s not as pronounced. The presence of i r o n i n s o l u t i o n under these c o n d i t i o n s can o n l y be due to complex f e r r a t e spec ies which are s t a b l e above pH 10 o r 11. 6.4 S o l u b i l i t y of F e r r i c E t h y l x a n t h a t e i n Organic So lvents An attempt was made to remove the dixanthogen i m p u r i t y from the p r e c i p i t a t e d f e r r i c e t h y l x a n t h a t e by washing w i t h hexane. The xanthate was l e a s t s o l u b l e i n t h i s s o l v e n t . However, the dark brown (106) . TIME ( M i n . ) F igure 26: " The v a r i a t i o n of (a) I n i t i a l pH values (b) F e r r i c i o n c o n c e n t r a t i o n and (c) xanthate ions c o n c e n t r a t i o n as a f u n c t i o n of t ime at i n i t i a l pH values marked on each l i n e . Temp. 6 0 ° c . (107) c r y s t a l s o f the compound which were recovered a f t e r the hexane-wash s t i l l gave IR spectrum s i m i l a r to t h a t o f d i x a n t h o g e n . I t was t h e r e f o r e d i f f i c u l t to e s t i m a t e the,purity o f the f e r r i c e t h y l x a n t h a t e by an IR s p e c t r o s c o p i c method. I f the brown s o l u t i o n was a l l o w e d to s t a n d a day o r two, a l i g h t brown f e r r i c o x i d e s e t t l e d out i n s t e a d o f f e r r i c e t h y l -x a n t h a t e . The presence o f dixanthogen i n the s u p e r n a t a n t s o l u t i o n o n l y was then d e t e c t e d by UV s p e c t r o s c o p i c a n a l y s i s . The exposure o f the dark brown s o l i d samples o f f e r r i c e t h y l x a n t h a t e to the atmosphere f o r a p e r i o d o f 2 to 3 weeks r e s u l t e d i n the f o r m a t i o n o f a l i g h t brown c r u s t on the s u r f a c e . I t i s suspected t h a t the i r o n xanthate had decomposed to dixanthogen and f e r r i c o x i d e . 6 .5 P h y s i c a l Appearance of F e r r i c E t h y l x a n t h a t e Prepared a t V a r i o u s pH Values F i g u r e 27a shows samples o f f e r r i c e t h y l x a n t h a t e prepared a t pH values o f 2.5 to 11.5 a t a temperature o f 25°C. The p r e c i p i t a t e s were f i l t e r e d o f f and d r i e d under vacuum f o r h a l f an h o u r . The c o l o u r o f the p r e c i p i t a t e s changed from dark brown to brown as the pH was changes from a c i d i c to b a s i c . An attempt was made to remove dixanthogen from these samples by washing them q u i c k l y w i t h hexane. Each sample (50 mg) was washed w i t h hexane (50 ml) and the s o l v e n t f r a c t i o n s were l e f t to s tand o v e r n i g h t . U l t r a - v i o l e t s p e c t r o s c o p i c a n a l y s i s i n d i c a t e d t h a t the maximum q u a n t i t y o f d ixanthogen was found i n the samples prepared a t pH 2.5 and 3 . 5 . (108) The amount of dixanthogen decreased i n the samples prepared i n the a c i d i c s o l u t i o n s above pH 3.5 and s t i l l dixanthogen was found i n the samples prepared i n a l k a l i n e s o l u t i o n s . 6.6 V i s i b l e E f f e c t s o f S o l u t i o n s of V a r y i n g pH and Temperature on the P h y s i c a l S t a t e o f F e r r i c E t h y l x a n t h a t e F i g u r e 27b shows samples of f e r r i c e t h y l x a n t h a t e which were kept f o r three hours i n aqueous s o l u t i o n s a t v a r i o u s pH values and temperatures . The c o l o u r o f the samples i n s o l u t i o n s of pH 2.5 to 5.5 a t 25°C d i d not show a marked change, but those kept i n a l k a l i n e s o l u t i o n a t t h i s temperature became brown i n c o l o u r . A t temperatures above 25°C the decomposi t ion of f e r r i c e t h y l x a n t h a t e was a c c e l e r a t e d to g i v e a brown p r e c i p i t a t e (DTA a n a l y s i s i n d i c a t e d t h i s to be a hydrated i r o n o x i d e ) . This s tudy i n d i c a t e d t h a t the f o r m a t i o n o f dixanthogen i n the i r o n - x a n t h a t e system was c o n t r o l l e d by the c o n c e n t r a t i o n o f f e r r i c ions i n s o l u t i o n . The o x i d a t i o n of xanthate c a t a l y z e d by f e r r i c ions l e d to the f o r m a t i o n o f d ixanthogen . Many analogous o x i d a t i o n r e a c t i o n s c a t a l y z e d by metal ions have been s t u d i e d i n o r g a n i c and b i o l o g i c a l systems. The a i r o x i d a t i o n o f t h i o l s to d i s u l p h i d e s . . a process which i s c a t a l y z e d by i r o n , has been s t u d i e d by Bunnett (116) . He i n v e s t i g a t e d the r a t e of o x i d a t i o n a t 37 .5°C and at pH 6 .8 to 7.6 and found i t to be p r o p o r t i o n a l to the i r o n concen-t r a t i o n . About 99% o f the observed o x i d a t i o n was c o n s i d e r e d to be due to the c a t a l y t i c e f f e c t of the i r o n . Beven and H i r s t (117) agreed t h a t the (109) * * • a # # # l 9-5 PH loTTpH --^ 11.-5 pH Temp. Z5°C * • pH 3 .5 PH 7 .5 PH 10.5 Temp. 3 5 ° C • • # pH 6 .5 PH 7 .5 pH 8 . 5 P H 12-5 Temp. 4 5 ° C • m PH 6.5 PH I I . | PH 12.5 6 0 ° C * m A PH 5 . 5 PH 8 . 5 pH 11 .5 F i g u r e 27. (a) F e r r i c e t h y l x a n t h a t e prepared a t pH values i n d i c a t e d (b) f e r r i c e t h y l x a n t h a t e a f t e r keep-ing f o r three hours i n aqueous s o l u t i o n s o f pH values and temp-e r a t u r e s as i n d i c a t e d . (no) r a t e o f o x i d a t i o n was p r o p o r t i o n a l to the f e r r i c i o n c o n c e n t r a t i o n . They f u r t h e r observed t h a t the c a t a l y t i c a c t i o n o f f e r r i c i o n was i n h i b i t e d by cyanide i o n s , and disappeared a l t o g e t h e r i n a l k a l i n e s o l u t i o n s where, h y d r o l y s i s o c c u r r e d . 6.7 A Study of F e r r i c E t h y l x a n t h a t e by Means o f the Mossbauer E f f e c t Mossbauer s p e c t r a o f the samples o f f e r r i c e t h y l x a n t h a t e prepared a t the pH values shown i n Table 8 are i l l u s t r a t e d i n F igures 28, 29 and 30. The c i r c l e s r e p r e s e n t the exper imenta l p o i n t s through which s o l i d l i n e s have been drawn by a l e a s t square f i t computer programme, m o d i f i e d to the L o r e n t z i a n type o f c u r v e . . . The i n d i v i d u a l l y r e s o l v e d peaks are shown above these c u r v e s . The values f o r isomer s h i f t and * quadrupole s p l i t t i n g on the v e l o c i t y s c a l e are g i v e n r e l a t i v e to a r e f e r -ence sample o f sodium n i t r o p r u s s i d e . The Mossbau-er parameters f o r the samples o f f e r r i c e t h y l x a n t h a t e are summarized i n Table 9 Samples 1 to 4 were prepared under the c o n d i t i o n s d e s c r i b e d i n Tab le 8, and they gave s i m i l a r types of Mossbauer s p e c t r a . The c o n s i s -t e n t va lues of the isomer s h i f t shown i n Table 9 i n d i c a t e t h a t one i r o n compound i s common to a l l o f these samples . One spectrum o f t h i s s e r i e s i s shown i n F i g u r e 28a. The values of isomer s h i f t and l i n e w i d t h o b t a i n e d f o r these compounds are i n c l o s e agreement w i t h the values f o r f e r r i c e t h y l x a n t h a t e r e p o r t e d by Valov and coworkers ( 4 0 ) . The values o b t a i n e d f o r isomer s h i f t , magnetic moment (y = 2.19 B.M a t 108°K) and c r y s t a l Table 8 Sample P r e p a r a t i o n ' o f F e r r i c E t h y l x a n t h a t e and Re la ted Compounds Sample Before Mi x i ng pH a f t e r Xanthate I ron . . Exper imental n o * . cone. pH cone. pH mix ing C o n d i t i o n s M/L M/L 1 10 c 8.5 K f 2 F e 3 + 2.5 2.7 m i x i n g i n i s o l a t o r box under 2 - 2 10 c 8.5 1 0 - 2 F e 3 + 2.5 2.7 m i x i n g i n open atmosphere 3 I O " 2 8.5 H f 2 F e 3 + " 2.5 2.7 hexane washed p r e c i p i t a t e 4 I O " 2 2.7 1 0 - 2 F e 3 + 2.5 2.6 m i x i n g i n open atmosphere 5 I O ' 2 7.0 -2 3+ 10 Fe - 5 4.0 6.2 f l o a t e d p a r t o f p r e c i p i t a t e 6 _2 10 c 7.0 1 0 " 2 F e 3 + 4.0 6.2 s i n k p a r t of p r e c i p i t a t e 7 i o " 2 8.5 _2 10 c 2.5 2.75 4 week o l d compound 8 IM 7.5 l M F e 2 + 3.6 6.1 i n open atmosphere 9 IM 7.5 ?+ lMFe 3.6 6 .2 i n p a r t i a l l y c o n t r o l l e d atmosphere 10 IM 7.5 l M F e 2 + . 3.6 6 .3 i n i s o l a t o r box under N 0 (112) T O O H 95 J 90 85 J (a) V e l o c i t y (mm/sec.) F igure 28: Mossbauer s p e c t r a of F e r r i c e t h y l x a n t h a t e . Spec t ra (a) and (b) represent samples.1 and 7 i n Table 8. r e s p e c t i v e l y (113) s t r u c t u r e data (39) are i n e x c e l l e n t agreement and suggest tha t f e r r i c e t h y l x a n t h a t e i s a low s p i n compound w i t h oc tahedra l symmetry. The c e n t r a l i r o n atom i s surrounded by s i x s u l p h u r atoms i n an o c t a h e d r a l c o n f i g u r a -t i o n . The s u l p h u r atoms are s i t u a t e d a t the corners of two p a r a l l e l e q u i l a t e r a l t r i a n g l e s 2 .48A 0 a p a r t . The absence of quadrupole s p l i t t i n g shows t h a t there i s no d i s t o r t i o n o f the oc tahedra l symmetry of the l i g a n d s . 57 The isomer s h i f t o f Fe i s a f u n c t i o n of the 3d and 4s e l e c t r o n charge d e n s i t y . I t i s t h e r e f o r e a s s o c i a t e d w i t h the normal va lence s t a t e s of i r o n . The values of the isomer s h i f t f o r i r o n i n i o n i c and c o v a l e n t compounds are a v a i l a b l e f o r the d i v a l e n t and t r i v a l e n t s t a t e s . The va lue f o r d i v a l e n t i r o n i s l a r g e r than t h a t f o r t r i v a l e n t , ?+ 6 3 + 5 because the loss of the 3d e l e c t r o n i n going from Fe (3d ) to Fe (3d ) r e s u l t s i n an i n c r e a s e of the charge d e n s i t y a t the n u c l e u s . A study o f the samples 1 to 4 i n comparison w i t h the compounds having the i r o n atom i n a s i m i l a r c o o r d i n a t i o n s t a t e c l e a r l y i n d i c a t e s t h a t the i r o n i s i n the t r i v a l e n t s t a t e and i s c o v a l e n t l y bonded to the l i g a n d s . The f i r s t f o u r samples show narrow l i n e s p e c t r a i n d i c a t i v e o f a high degree o f p u r i t y . However, s l i g h t l i n e broadening i s a l s o observed i n samples 2 , 3 and 4 which may be due to some i m p u r i t y . The i m p u r i t y may a r i s e as a r e s u l t o f f e r r i c ions r e a c t i o n w i t h atmospheric gases . This type of r e a c t i o n would cause a broadening of the l i n e s because o f an i n c r e a s e i n the range of neares t neighbour environments which can produce inhomogeneous isomer s h i f t . F i g u r e 28b r presents the spectrum of sample 7 i n Table 8 . (114) This i s a f o u r week o l d sample o f f e r r i c e t h y l x a n t h a t e prepared under the same c o n d i t i o n s as those o f sample 1. The main spectrum represented by sample 7b i n Table 9 has values f o r isomer s h i f t and l i n e w i d t h which correspond to those of f e r r i c e t h y l x a n t h a t e . The Mossbauer parameters of o ther peak i n spectrum 28b are recorded as sample 7a i n Table 9 . This peak gives very high values f o r quadrupole s p l i t t i n g and l i n e w i d t h . These values do not correspond to any of the compounds i n c l u d e d i n t h i s s t u d y . This i n d i c a t e s t h a t there are some s o l i d s t a t e decomposi t ion products of i r o n ( I I I ) which cause changes i n the chemical nature o f f e r r i c e t h y l -x a n t h a t e . In the p r e p a r a t i o n of samples 5 and 6, the f i l t e r e d s o l u t i o n o f i r o n a t pH 4.0 was mixed w i t h a xanthate s o l u t i o n a t pH 7 . 0 . The f i n a l pH va lue of the mix ture was 6 . 2 . I t was observed t h a t a s e p a r a t i o n o c c u r r e d . A smal l amount o f dark brown m a t e r i a l rose to the s u r f a c e , w h i l e the bulk o f the s o l i d formed a brown p r e c i p i t a t e . The f l o a t i n g p a r t , sample 5 , gave s p e c t r a l values which corresponded to f e r r i c e t h y l x a n t h a t e . Sample 6 , the p r e c i p i t a t e , e x h i b i t e d a d i f f e r e n t spectrum which i s shown i n F i g u r e 29. A d i f f e r e n c e i n the va lue o f isomer s h i f t and quadrupole s p l i t t i n g between samples 5 and 6 i s c l e a r l y seen . The d i f f e r e n c e i n isomer s h i f t can be r e l a t e d to e i t h e r a d i f f e r e n c e i n the e l e c t r o n i c c o n f i g u r a t i o n o f the complex or a change i n environment of i t s c e n t r a l atom. The quadrupole s p l i t t i n g i n d i c a t e s a change i n chemical s t r u c t u r e . I t i s s e n s i t i v e to the p o i n t symmetry o f the immediate environment o f the atoms under o b s e r v a t i o n . The spectrum c l e a r l y i n d i c a t e s a s i g n i f i c a n t (115) VELOCITY (mm/sec.) F i g u r e 29: Mossbauer spectrum of f e r r i c e t h y l x a n t h a t e . * The spectrum represents sample 6 i n -table 8. Table 9 Mossbauer Parameters f o r F e r r i c E thy lxanthate and Re la ted Compounds a t 78°K Sample No Quadrupole S p l i t t i n g Isomer S h i f t L i n e Width A (mm/sec) 6 (mm/sec) [- (mm/sec) r ^ (mm/sec) 1 - 0.728 0.321 -2 - 0.725 0.330 -3 - 0.725 0.405 -4 - 0.727 0.378 -5 - 0.725 0.323 -6 0.73 . 0.71 0.720 0.74 7(a) 1.09 0.725 0.625 0.53 7(b) - 0.730 0.430 -8 0.58 0.74 0.34 0.35 9 . 0 .58 0.73 0.37 0.36 10(a) 0.56 0.73 0.31 0.30 10(b) 2.43 0.86 0.36 0.34 (117) d i s t o r t i o n from o c t a h e d r a l symmetry. This study i n d i c a t e s tha t f e r r i c e t h y l x a n t h a t e format ion i s a f f e c t e d by changes i n pH. E v i d e n t l y , the compound i s s u b j e c t to s u b s t i t u t i o n by hydroxyl groups . A t low pH the amount o f s u b s t i t u t i o n may be small but a t h i g h e r values of pH the q u a n t i t y i s more s i gni f i c a n t . The s u b s t i t u t i o n i n the c o o r d i n a t i o n sphere o f the c e n t r a l atom i s one of the f a c t o r s which cause quadrupole s p l i t t i n g . Wertheim (118) has d i s c u s s e d t h i s e f f e c t i n the case of the f e r r o c y a n i d e i o n , K 4 ( C N ) g . 3 ^ 0 , which gives a s l i g h t l y broadened l i n e . The l i n e which i s c h a r a c t e r i s t i c o f the almost oc tahedra l f e r r o c y a n i d e i o n , becomes a w e l l r e s o l v e d d o u b l e t i f one o f the CN groups_is" r e p l a c e d ' b y an'NO group. S i m i l a r l y , the s i n g l e t r e p r e s e n t a t i v e of t e t r a h e d r a l l y c o o r d i n a t e d t e t r a p h e n y l t i n becomes a double t when one phenyl group i s r e p l a c e d by a h a l i d e i o n . The s u b s t i t u t i o n o f a c h e l a t e group by one o r two d i f f e r e n t groups leads to a decrease i n the isomer s h i f t . Sample 6 i s cons idered to be a new compound w i t h f e r r i c e t h y l x a n t h a t e present as an i m p u r i t y . This new substance i s thought to be a hydroxyxantha te , as the f o r m a t i o n of such a compound under the c o n d i -t i o n o f pH which o b t a i n e d i n the p r e p a r a t i o n o f sample 6 i s d i s t i n c t l y p r o b a b l e . The Mossbauer s p e c t r a of the f r o z e n s o l u t i o n s of i r o n ( I I I ) c o n t a i n i n g the h y d r o l y z e d spec ies have been s t u d i e d a t d i f f e r e n t pH v a l u e s . 2+ A t a l k a l i n e pH, quadrupole s p l i t s p e c t r a are ass igned to the Fe(OH) and FetOH)* s p e c i e s . In an attempt to prepare f e r r o u s xanthate IM f e r r o u s ammonium s u l p h a t e was reacted w i t h potassium e t h y l x a n t h a t e o f s i m i l a r (118) c o n c e n t r a t i o n under the c o n d i t i o n s recorded i n Table 8 f o r samples 8 , 9 and 10. I f the pH of the s o l u t i o n was between 2.5 and 3 .5 f e r r i c xanthate was formed when the p r e p a r a t i o n was l e f t open to the atmosphere. However, samples 9 and 10 were prepared under the i n e r t atmospheric c o n d i t i o n s (Table 8 ) . Samples 8 and 9 gave s i m i l a r s p e c t r a , w h i l e t h a t e x h i b i t e d by sample 10 was s l i g h t l y d i f f e r e n t . The narrow l i n e s p e c t r a of samples 8 and 10, shown i n F i g u r e 30a i n d i c a t e tha t the product formed under the c o n d i t i o n s mentioned i n Table 8 i s a pure chemical compound. I f i t were impure or a mixture of c l o s e l y r e l a t e d m a t e r i a l s , the l i n e s would be b r o a d e r . In the case of a mixture o f i r o n xanthate and i r o n h y d r o x i d e , the i r o n xanthate peak would c e r t a i n l y appear . The isomer s h i f t values t h e r e f o r e are i n d i c a t i v e o f f e r r i c x a n t h a t e . There i s no i n d i c a t i o n o f f e r r i c h y d r o x i d e as t h i s compound gives two peaks . I t would g i v e d i f f e r -ent values f o r isomer s h i f t , as i t i s a h i g h - s p i n i r o n compound. The spectrum i n F i g u r e 30b g i v e n by sample 10 shows an a d d i t i o n a l peak w i t h an isomer s h i f t o f 0.86 mm/sec and quadrupole s p l i t t i n g of 2.43 mm/sec. These values suggest t h a t some spec ies of h i g h - s p i n Fe ( I I ) may be present i n the m i x t u r e . The compounds represented by samples 6 , 8 and 9 are of a very s i m i l a r n a t u r e . The study i n d i c a t e s t h a t they are presumably hydroxy-complexes of x a n t h a t e . The f e r r i c and f e r r o u s ions open to the atmosphere, as d e s c r i b e d i n Table 8, are expected to form h y d r o l y z e d 2+ spec ies such as Fe(0H) . This complex i o n can r e a c t w i t h xanthate to form the hydroxy x a n t h a t e , F e ( 0 H ) ( E t X ) C ) . (119) V e l o c i t y (mm/sec.) F igure 30: Mossbauer s p e c t r a of f e r r i c e t h y l x a n t h a t e . S p e c t r a ( a ) and ( b ) . r epresent samples 8 and 1 0 - r e s p e c t i v e l y i n t a b l e 8. ' (120) The chemical nature and s t r u c t u r a l changes i n f e r r i c e h t y l x a n t h a t e can adequately be e x p l a i n e d by the Mossbauer e f f e c t . Al though the technique i s not a q u a n t i t a t i v e a n a l y t i c a l t o o l , i t g ives v a l u a b l e q u a l i t a t i v e i n f o r m a t i o n about the changes which occur i n i r o n xanthates under d i f f e r e n t pH and temperature c o n d i t i o n s . 6.8 I n f r a r e d S p e c t r o s c o p i c Study o f F e r r i c E t h y l x a n t h a t e and I t s Decomposit ion Products An i n f r a r e d t r a n s m i s s i o n study was c a r r i e d out to determine the f requenc ies o f the a b s o r p t i o n bands o f f e r r i c e t h y l x a n t h a t e . F i g u r e 31a shows the spectrum o f a sample prepared a t pH-3 .5 and 25°C. The i n t e n s e a b s o r p t i o n band a t 1005 c m - 1 i s ass igned to the C=S s t r e t c h i n g mode. In most metal xanthates the C=S occurs a t 1020-1050 c m " 1 ; due to hexacoordinated s t r u c t u r e o f f e r r i c e t h y l x a n t h a t e , t h i s band i s -1 1 s h i f t e d to 1005 cm . An extremely i n t e n s e band a t 1255 cm and another o f medium i n t e n s i t y a t 1115 c m " 1 are a t t r i b u t e d to the s t r e t c h i n g v i b r a t i o n s o f the C-0-C l i n k a g e . The C=S and C-0-C s t r e t c h i n g bands show c o n s i d e r a b l e s p l i t t i n g which may be 'due to the i n t e r a c t i o n of o t h e r v i b r a t i o n modes w i t h these s t r e t c h i n g v i b r a t i o n s . For hexacoordi nated f e r r i c e t h y l x a n t h a t e , the band due to the C=S group i n c o v a l e n t l y bonded metal xanthates such as cuprous and lead e t h y l x a n t h a t e s , i s a f f e c t e d by the c o o r d i n a t i o n of the s u l p h u r atoms to the c e n t r a l i r o n atom, and i s s h i f t e d to 1005 c m - 1 . The change i n bond c h a r a c t e r form C=S to C-S causes a s h i f t to a lower frequency o f 1005 c m - 1 . (121) Figure 31: The IR spectra of ferr ic ethylxanthate treated and untreated with hexane compared with the residue which remained upon evaporation of the hexane extracts. The ferr ic ethylxanthate was prepared at pH 3.5 and-25°C as described in section 2.5. (122) F i g u r e 31b shows the spectrum o f f e r r i c e t h y l x a n t h a t e washed three times w i t h hexane. The shape and the p o s i t i o n of the a b s o r p t i o n bands are the same as those o f the compound untrea ted w i t h hexane. The hexane washings o f f e r r i c e t h y l x a n t h a t e a f t e r evapora-t i o n gave a t h i c k brown o i l . F i g u r e 31c represents the spectrum of t h i s m a t e r i a l . The p o s i t i o n o f the a b s o r p t i o n bands which corresponds to the C-O-C l i n k a g e remains u n a l t e r e d . The shape and the p o s i t i o n of the a b s o r p t i o n band which corresponds to the C-S s t r e t c h i n g v i b r a t i o n changes and a very s t r o n g a b s o r p t i o n band a t 1025 c m " 1 , c h a r a c t e r i s t i c o f the s t r e t c h i n g mode of the C=S group appears . A change i n the r e g i o n o f 800 to 870 cm 1 i s a l s o o b s e r v e d . This spectrum i n d i c a t e s tha t the o i l y l i q u i d i s mainly dixanthogen and the bands are p r i m a r i l y due to the s t r e t c h i n g v i b r a t i o n of the C=S group and the asymmetric s t r e t c h i n g mode o f the C - S - S - C cha in i n dixanthogen (119) . The group frequency o f C=S may be cons idered as a b a s i s o f d i f f e r e n t i a t i o n between the s p e c t r a o f dixanthogen and f e r r i c e t h y l x a n t h a t e . However, i f both o f these spec ies are present i n the p r e c i p i t a t e as a m i x t u r e i n n e a r l y equal amounts then t h e i r d i s t i n c t i o n by IR s p e c t r a becomes d i f f i c u l t . A s tudy was c a r r i e d out to i n v e s t i g a t e the nature of the compound formed on mix ing 0.1M f e r r o u s ammonium s u l p h a t e (pH 4.5) and potass ium e±hylxanthate (pH 7.5) under atmospheric c o n d i t i o n s . F i g u r e 32a shows the spectrum o f the compound. The shape and the p o s i t i o n o f the a b s o r p t i o n bands showed t h a t t h i s compound had a d i f f e r e n t s t r u c -ture to that o f f e r r i c e t h y l x a n t h a t e . The c h a r a c t e r i s t i c f requenc ies o f (123) the s t r e t c h i n g v i b r a t i o n a l modes o f C-O-C and C-S are s h i f t e d . This change seems to r e s u l t from changes i n the c o o r d i n a t i o n sphere o f i r o n . The broad band which appears i n the r e g i o n of 3250 to 3050 cm * i s presumably due to the c o o r d i n a t e d and hydrogen bonded OH group. The f o r m a t i o n o f the compound which i s c o n s i d e r e d to be a h y d r o x y - x a n t h a t e has been d i s c u s s e d i n s e c t i o n 6 . 7 . F i g u r e 32b shows the spectrum o f a compound formed by m i x i n g the s o l u t i o n s o f f e r r o u s and xanthate ions i n a g l o v e box under an i n e r t atmosphere o f n i t r o g e n . The procedures o f f i l t r a t i o n , d r y i n g o f the sample, and the p r e p a r a t i o n o f t h e - m i x t u r e w i t h potass ium bromide p r i o r to making a p e l l e t 5 w e r e c a r r i e d out i n the g love b o x . The spectrum o b t a i n e d was s i m i l a r to t h a t f o r a h y d r a t e d i r o n o x i d e . F i g u r e 33 shows s p e c t r a o f the decompos i t ion products o f f e r r i c e t h y l x a n t h a t e . The s o l i d samples were taken a t d i f f e r e n t t ime i n t e r v a l s from the suspens ion of f e r r i c e t h y l x a n t h a t e a t pH 9 . 5 and 45°C. T h e i r s p e c t r a showed t h a t the band a t 1255 c m - 1 remained a lmost unchanged, d e s p i t e the decompos i t ion o f f e r r i c e t h y l x a n t h a t e . When the compound was c o m p l e t e l y decomposed, the samples taken showed the s p e c t r a to have a l l the bands c h a r a c t e r i s t i c o f d i x a n t h o g e n . This i n d i c a t e d t h a t a f t e r the decompos i t ion o f f e r r i c e t h y l x a n t h a t e , d i x a n t h o g e n remained a s s o c i a t e d w i t h the decompos i t ion p r o d u c t s . F i g u r e 33.&shows the spectrum o f a sample o f f e r r i c e t h y l x a n t h a t e which was suspended i n s o l u t i o n a t pH 9 .5 and 45°C f o r a p e r i o d o f f i v e m i n u t e s . A f t e r 15 minutes the spectrum was e n t i r e l y t h a t of d i x a n t h o g e n . A f t e r two h o u r s , the c o n c e n t r a t i o n o f dixanthogen decreased due to decompos i t ion to xanthate i o n s . (124) 100 _ 80 60 40 20. 80 60 40 20 3500 3300 2900 l 1 f 1 1 1 , 1 r 1500 1300 1100 900 500 1 Wave number- (cm" ) F i g u r e 32: IR s p e c t r a of compounds formed by m i x i n g 0.1M s o l u t i o n s of f e r r o u s and xanthate ions a) under atmospheric c o n d i t i o n s at pH 7.5 and 2 5 ° c . b) under iner t -a tmosphere of n i t r o g e n i n g love box. (125) F i g u r e 3 3 -b i n d i c a t e s the spectrum o f the f i n a l p r o d u c t o f d e c o m p o s i t i o n . This product was removed a f t e r a p e r i o d o f three hours from an aqueous suspens ion o f f e r r i c e t h y l x a n t h a t e kept a t pH 9 . 5 and 45°C. The comparat ive s tudy o f d i f f e r e n t p o s s i b l e compounds i n d i c a t e s t h a t the p r o d u c t c o n t a i n s b a s i c i r o n carbonate and a v a r i e t y of hydra ted i r o n o x i d e s . . The g r e a t e r p a r t o f the spectrum i n F i g u r e 33b resembles the spectrum o f l e p i d o c r o c i te ( V FeOOH ) r e p o r t e d by Wickersheim and Korpi ( 1 2 0 ) . The peaks a t 470 cnf^and 882 c m - 1 are g i v e n by l e p i d o c r o c i t e and g o e t h i t e (• c< FeOOH) r e s p e c t i v e l y . The spectrum i n the r e g i o n o f 400 to 800 c m - 1 resembles the r e f e r e n c e spectrum o f F e ( 0 H ) 3 . Many a d d i t i o n a l bands are observed i n the s p e c t r a o f the f i n a l products o b t a i n e d from treatments a t v a r i o u s pH values and t e m p e r a t u r e s , as des-c r i b e d i n s e c t i o n 6 . 3 . S t a b l e i n o r g a n i c r e a c t i o n products such as s u l p h u r -oxygen compounds, carbonates and s u l p h i d e s might be p r e s e n t . The q u a n t i t i e s might be too s m a l l to be d e t e c t a b l e but the p o s s i b i l i t y o f t h e i r occurrence cannot be r u l e d o u t . An attempt was made to determine the q u a n t i t y o f f e r r i c e t h y l x a n t h a t e l e f t undecomposed i n samples which were suspended i n the r aqueous s o l u t i o n s d e s c r i b e d i n s e c t i o n 6-.'3. A c a l i b r a t i o n curve o f absorbance a g a i n s t c o n c e n t r a t i o n o f f e r r i c e t h y l x a n t h a t e was p r e p a r e d . This curve i n d i c a t e d t h a t the band o f f e r r i c e t h y l x a n t h a t e a t 1255 c n T 1 obeyed B e e r ' s law up to the q u a n t i t y o f 0 .5 mg ( i n 500 mg KBr as p e l l e t ) . The molar e x t i n c t i o n c o e f f i c i e n t c a l c u l a t e d a t t h i s wavelength was 2280 l i t e r m o l e " 1 c m " 1 . ( 1 2 6 ) 80 - f : .1500 ~7~725Q 1000 : 750 , Wave number (cm - ) F i g u r e 33a: IR s p e c t r a of f e r r i c e t h y l x a n t h a t e removed from suspens ion at pH 9 .5 and 45°c a f t e r the t ime i n t e r v a l s i n d i c a t e d . (126a) (127) A d i f f i c u l t y i s encountered i n such q u a n t i t a t i v e de termina-t i o n s a t 1255 c m " 1 . Dixanthogen, which i s always a s s o c i a t e d w i t h f e r r i c e t h y l x a n t h a t e , a l s o absorbs a t t h i s f requency . The measurements are t h e r e f o r e s u b j e c t to an e r r o r . However, an approximate e s t i m a t i o n of f e r r i c e t h y l x a n t h a t e and dixanthogen i n the decomposi t ion products can be made. 6.9 The DTA and X - r a y D i f f r a c t i o n S t u d i e s of the Decomposit ion Products of F e r r i c E t h y l x a n t h a t e The decomposi t ion products of f e r r i c e t h y l x a n t h a t e i d e n t i f i e d as hydrated i r o n oxides by IR spectroscopy were s u b j e c t e d to DTA and X-ray d i f f r a c t i o n s t u d i e s . The X-ray d i f f r a c t i o n pat terns and DTA thermograms of r e f e r e n c e m a t e r i a l s such as f e r r i c e t h y l x a n t h a t e , hydrated i r o n ox ide and anhydrous ox ide of i r o n were recorded f o r compar ison . The s l i g h t v a r i a b i l i t y i n the DTA curves suggests t h a t the decomposi t ion products depend on the c o n d i t i o n s of pH and temperature . No DTA data on f e r r i c e t h y l x a n t h a t e or the products of i t s decomposi t ion are a v a i l a b l e to check the v a l i d i t y of the r e s u l t s . The thermal e f f e c t s due to phase t r a n s i t i o n s and decomposi t ion r e a c t i o n s are comparable w i t h the re fe rence hydrated and anhydrous i r o n o x i d e s . The s t u d y , t h e r e f o r e , i n d i c a t e s t h a t the f i n a l products ob ta ined a t a l k a l i n e pH values d e s c r i b e d i n s e c t i o n 6.3 are p r i m a r i l y hydrated i r o n o x i d e s . The X-ray d i f f r a c t i o n p a t t e r n s of the decomposi t ion products show two very i n t e n s e l i n e s o f the d spacings of 2 . 9 A 0 ( i n t e n s i t y 90%) (128) and 9.1A° ( i n t e n s i t y 90%). This conf irms t h a t the predominant hydra ted i r o n o x i d e i s l e p i d o c r o c i t e , ( Y . F e O O H . ) The l e s s i n t e n s e l i n e s which i n d i c a t e the presence o f o t h e r decomposi t ion products have not been a n a l y z e d . Chapter 7 GENERAL DISCUSSION Chapters 4, 5 and 6 include a separate discussion of the data obtained for xanthates of lead, copper and iron respectively. In this general discussion the overall results are compared and a correlati with flotation of the sulphide minerals of lead, copper and iron is attempted. When the sulphide minerals are subjected to wet grinding metal ions pass into the pulp. In addition, the reaction of oxygen with sulphide minerals causes formation of soluble oxidation products which enrich the pulp in-heavy metal.ions. By the time the flotation c i rcu i t is reached by the pulp the concentration of metal ions becomes either comparable with or much greater than the concentration of added flotation reagents^ (121). On the addition of soluble a lkal i metal xanthates, the interaction of metal and xanthate ions results in the formation of heavy metal xanthates. Such ionic reactivity is of great importance in sulphide mineral f lotat ion. At one time i t was considered that the insoluble reaction products formed from xanthate anions and heavy metal cations played (130) a d e c i s i v e r o l e i n the s e l e c t i v i t y of f l o t a t i o n . Then they were thought not to a s s i s t the f l o t a t i o n of s u l p h i d e m i n e r a l s , but t h e i r f o r m a t i o n was cons idered to be u n d e s i r e a b l e because i t l e d to the useless consumption of c o l l e c t o r . L a t e r i t was e s t a b l i s h e d t h a t the heavy metal xanthates d i d p r e c i p i t a t e i n the f o r m a t i o n o f c o l l e c t o r c o a t i n g s . These compounds which are s p a r i n g l y s o l u b l e i n the aqueous phase co-adsorb on s u l p h i d e minera l s to form m u l t i - l a y e r f i l m s h e l d by Van der Waals b o n d i n g . The minera l s are then rendered hydrophobic and on i n t e r a c t i o n w i t h f r o t h e r m o l e c u l e s , may be c a r r i e d to the s u r f a c e , o f the pulp by ai r bubbles . The s u l p h i d e s o f l e a d , copper and i r o n are among the most i m p o r t a n t ones and are concentra ted i n the m i n e r a l i s e d f r o t h . A knowledge o f the f o r m a t i o n o f the corresponding metal xanthates and t h e i r subsequent b e h a v i o r i n the f l o t a t i o n pulp i s o f fundamental impor tance . The experimental f i n d i n g s i n the present study of these heavy metal xanthates may c o n t r i b u t e to the unders tanding o f s e l e c t i v i t y i n f l o t a t i o n , as d i s c u s s e d i n the f o l l o w i n g s e c t i o n s . 7.1 P r e c i p i t a t i o n of Heavy Metal Xanthates I t i s a fundamental p r i n c i p l e t h a t p r e c i p i t a t i o n should occur when the va lue o f the s o l u b i l i t y product i s exceeded. A l a r g e number of de terminat ions o f s o l u b i l i t y products o f heavy metal xanthates have a l r e a d y been made i n an attempt to c o r r e l a t e the s o l u b i l i t y o f heavy metal xanthates w i t h t h e i r hydrophobic c h a r a c t e r . (131) There i s a d e f i n i t e connect ion between the c o l l e c t o r e f f e c t and the s o l u b -i l i t y product of heavy metal x a n t h a t e s . However, the present s tudy i n d i c a t e s t h a t i n homogenous sytems the p r e c i p i t a t i o n may not occur even when the s o l u b i l i t y product i s reached. F igures 3 , 11 , and 22 show the r e s u l t s of the p r e c i p i t a t i o n of xanthates of l e a d , copper and i r o n r e s p e c t i v e l y . The shapes of the curves i n d i c a t e t h a t the mechanism o f p r e c i p i t a t i o n of these heavy metal xanthates i s alnost the same. Three d i s t i n c t reg ions of p r e c i p i -t a t i o n 1 , 2 , and 3 , which i n d i c a t e r e s p e c t i v e l y h i g h , low and zero t u r b i d i t y reg ions are observed. In the r e g i o n one, the m i x i n g of metal and xanthate ions produces a coarse p r e c i p i t a t e which sediments r a p i d l y . T h i s form of the p r e c i p i t a t e i s thought not to be adsorbed on minera l p a r t i c l e s but to c o - e x i s t i n the pulp as separate hydrophobic p a r t i c l e s . In r e g i o n 2 , the c o n c e n t r a t i o n combinat ion of ions produces a c o l l o i d a l p r e c i p i t a t e which i s more l i k e l y t o co-adsorb on the m i n e r a l s i n the form of m u l t i - l a y e r s . The xanthate i o n c o n c e n t r a t i o n normal ly used i n s u l p h i d e m i n e r a l f l o t a t i o n -3 -4 (~ 10 to 10 M) f a l l s i n t h i s r e g i o n . F i n a l l y i n r e g i o n 3 , the zero t u r b i d i t y zone , no p r e c i p i t a t i o n i s observed w i t h i n the r e s i d e n c e t ime o f the m i n e r a l s i n f l o t a t i o n c i r c u i t s . No p r e c i p i t a t i o n i s ob ta ined i n the r e g i o n where the c o n c e n t r a t i o n s of metal and xanthate ions d i f f e r s u b s t a n t i a l l y i n magnitude. Here i t i s supposed t h a t the n u c l e i of the metal xanthate ( i n these areas of r e g i o n 3) have adsorbed on t h e i r s u r f a c e an excess o f one of the spec ies ( i . e . e i t h e r metal or xanthate (132) i o n ) and formed i o n i z e d complexes o r i o n i z e d aggregates . S t a b i l i z a t i o n occurs as a r e s u l t o f e l e c t r o s t a t i c r e p u l s i v e forces between the i o n i z e d spec ies and the growth o f a p r e c i p i t a t e i s i n h i b i t e d . . Some minor d i f f e r e n c e s i n the shapes o f the curves and the w i d t h s o f the t u r b i d i t y regions are observed i n the three examples shown i n F igures 3 , 11'and 22. These d i f f e r e n c e s depend upon the b e h a v i o r o f the metal ions i n s o l u t i o n . For example, i n the case o f f e r r i c e t h y l x a n t h a t e , the c o m p a r a t i v e l y l a r g e area of reg ions 1 and 2 toge ther w i t h the narrow zone o f r e g i o n 3'may a r i s e from the easy h y d r o l y s i s o f the f e r r i c ions to form f e r r i c h y d r o x i d e . This causes an i n c r e a s e i n the t u r b i d i t y i n a d d i t i o n to t h a t due to the f o r m a t i o n o f f e r r i c e t h y l x a n t h a t e . The e f f e c t s observed w i t h these p r e c i p i t a t i o n curves s h o u l d prove u s e f u l i n a s s e s s i n g the c o r r e c t c o n c e n t r a t i o n o f the reagents to a v o i d s t a r v a t i o n or overdose of the. c o l l e c t o r i n the f l o t a t i o n o f l e a d , copper and i r o n s u l p h i d e m i n e r a l s . 7.2 The S t a b i l i t y o f Heavy Metal Xanthates i n Aqueous S o l u t i o n s In the roughing and scavenging c i r c u i t s o f s u l p h i d e minera l f l o t a t i o n , the optimum s e l e c t i v i t y i s r a r e l y p o s s i b l e , p a r t i c u l a r l y in the case of complex o r e s . S e l e c t i v i t y can o n l y be a c h i e v e d i n c l e a n i n g and r e c l e a n i n g c i r c u i t s . But re f inements o f the f l o t a t i o n (133) o p e r a t i o n s r e q u i r e changed c o n d i t i o n s to improve the s e l e c t i v i t y of the mi n e r a l s . The heavy metal xanthates co-adsorb i n the form of m u l t i - l a y e r s which produce a not n e c e s s a r i l y coherent hydrophobic f i l m t h a t a l lows the f l o t a t i o n o f the minera l p a r t i c l e s . The d i f f e r e n t i a l s o l u b i l i t i e s and s t a b i l i t y o f the c o l l e c t o r coa t ings can be used to r e g u l a t e the s e l e c t i v i t y of the s u l p h i d e minera l f l o t a t i o n . A s u i t a b l e pH va lue and temperature c o n t r o l can be u t i l i z e d to achieve t h i s purpose . The rates o f d i s s o l u t i o n o f the metal xanthates o f l e a d , copper and i r o n were e s t a b l i s h e d . These rates are i n f l u e n c e d by pH and temperature . The e f f e c t o f these v a r i a b l e s on the processes o f d i s s o l u t i o n and decomposi t ion are d i s c u s s e d i n the f o l l o w i n g s e c t i o n s . 7 .2 .1 The E f f e c t o f pH The e f f e c t of pH on e t h y l x a n t h a t e s o f l e a d , copper and i r o n has been d i s c u s s e d i n Chapters 4 , 5 a'nd 6. These compounds are found to be very s e n s i t i v e to changes i n i n i t i a l pH. A change i n the i n i t i a l pH va lue occurs due to the processes o f d i s o l u t i o n , . decomposi t ion o f xanthate ions and h y d r o l y s i s o f xanthate and metal i o n s . The products o f decomposi t ion and h y d r o l y s i s , a l though present i n very smal l q u a n t i t i e s , may have a pronounced e f f e c t on the f l o a t a b i l i t y o f the (134) m i n e r a l s . The s e n s i t i v i t y o f metal xanthates to decomposi t ion a t a l k a l i pH i s found to be i n the o r d e r of F e ( E t X ) > C u ^ E t X ) ^ P b ( E t X ) 2 . For a c i d i c pH the f o l l o w i n g s e r i e s represents the case o f d e c o m p o s i t i o n : P b ( E t X ) ^ F e ( E t X ) ^ C u 2 ( E t X ) 2 . This suggests t h a t the r e l a t i v e f l o t a t i o n o f s u l p h i d e m i n e r a l s o f l e a d , copper and i r o n may d i f f e r under a c i d i c and b a s i c c o n d i t i o n s and may be a f f e c t e d by pH i n the same order as shown above. F igures 5a , 6 a , 13, 24a, 25a and 26a p r o v i d e d e t a i l e d i n f o r m a t i o n o f the s u s c e p t i b i l i t y to decompose of the heavy metal xanthate by a c i d i c or b a s i c s o l u t i o n s . 7 . 2 . 2 The E f f e c t of Temperature The decomposi t ion o f metal xanthates i n a c i d i c and a l k a l i media i s a c c e l e r a t e d by the h igher temperature o f the s u s p e n s i o n . The c o n c e n t r a t i o n o f decomposi t ion products i n c r e a s e s p a r t i c u l a r l y i n a l k a l i n e pH v a l u e s . F igures 9 and 18a and b show the r e s u l t s o f i n t e r a c t i o n producing metal s u l p h i d e s PbS and CuS which p r e c i p i t a t e i n s o l u t i o n and d e p o s i t on u n d i s s o l v e d metal x a n t h a t e s . The c o l l e c t o r c o a t i n g co-adsorbed heavy metal xanthates l o s e , t h e r e f o r e , t h e i r hydrophobic c h a r a c t e r as s u l phi d i z a t i o n p r o g r e s s e s . The s u l p h i d e i s formed by c leavage of the weak C-S l i n k a g e i n xanthate i o n . This l i n k a g e i s r e s i s t a n t to a t t a c k by a c i d i c s o l u t i o n s but i s r e a d i l y a t t a c k e d by a l k a l i , e s p e c i a l l y at h igh c o n c e n t r a t i o n and temperature . (135) The presence of t r i t h i o c a r b o n a t e i n aqueous suspens ion o f f e r r i c e t h y l x a n t h a t e a t pH 11.8 and 35°C i s shown i n F i g u r e 23. The c o n c e n t r a t i o n o f t h i s decomposi t ion product increases w i t h time and may a f f e c t the p r o p e r t i e s o f the s u r f a c e l a y e r s on the minera l p a r t i c l e s i n a way d i f f e r e n t from tha t o f f e r r i c h y d r o x i d e . S u l p h i d e and t r i t h i o c a r b o n a t e are formed by the d e -compos i t ion o f xanthate ions i n a l k a l i n e s o l u t i o n s . Both of these ions r e a c t w i t h metal ions i n the aqueous phase to form i n s o l u b l e products which adhere to the xanthate l a y e r s on the m i n e r a l p a r t i c l e s . T h e i r r e a c t i o n w i t h metal ions i s not c o n f i n e d to the aqueous phase. They may change the s u r f a c e c h a r a c t e r of the metal xanthate as a r e s u l t of t h e i r i n t e r a c t i o n w i t h metal ions on s o l i d / l i q u i d i n t e r f a c e . Conse-q u e n t l y a low recovery o f minera l i n f l o t a t i o n at h i g h e r pH i s o b s e r v e d , p a r t i c u l a r l y i f s u f f i c i e n t t ime has e lapsed f o r such a l t e r a t i o n s of s u r f a c e c o a t i n g s to o c c u r . At temperatures h i g h e r than 25°C these depressant s p e c i e s are produced r a t h e r q u i c k l y i n a l k a l i n e s o l u t i o n . T h i s study shows t h a t the metal xanthates s u s c e p t i b l e to t h i s depresant a c t i o n are i n the f o l l o w i n g order -P b ( E t X ) 2 > C u 2 ( E t X ) 2 >Fe(EtX) 3 The e l e v a t e d tempera tures , t h e r e f o r e , may be used to improve the s e l e c t i v i t y by caus ing changes i n the hydrophobic c h a r a c t e r o f once-f l o a t e d m i n e r a l s . (136) 7.3 XANTHATE ION CONCENTRATION The c o n c e n t r a t i o n o f xanthate ions i n s o l u t i o n a t v a r i o u s pH v a l u e s , and temperatures has been recorded i n f i g u r e s 5 , 6 , 2 4 , 2 5 , 2 6 and t a b l e 4 . I t i s noted t h a t the d i s s o l u t i o n o f metal xanthate v a r i e s w i t h the pH and temperature o f the aqueous phase. The r a t e o f d i s s o l u t i o n i s markedly a f f e c t e d by l e s s s o l u b l e s p e c i e s such as metal h y d r o x i d e over the wide range of a l k a l i n e pH va lues s t u d i e d i n t h i s work. The data i n d i c a t e t h a t under these c o n d i t i o n s , the s o l u b i l i t y o f the metal xanthates i n c r e a s e s i n the f o l l o w i n g o r d e r F e ( E t X ) 3 >Pb(EtX) 2 >Ci^(EtX) 2 7.4 METAL ION CONCENTRATION F i g u r e s 7 , 16 , 29 and 26 i n d i c a t e t h a t the heavy metal ions are s t a b l e i n a c i d i c pH v a l u e s . However, i f pH exceeds 7 , i n the case o f l e a d and copper e t h y l x a n t h a t e , and 4 i n f e r r i c e t h y l x a n t h a t e , t h e metal ions are h y d r o l y z e d and i n s o l u b l e metal hydrox ides are produced. A t pH va lues above 10, the s o l u b i l i t y of the metal hydrox ides i n c r e a s e s and complex i o n i c s p e c i e s (oxyanions) are formed. A decreased r e c o v e r y i n s u l p h i d e f l o t a t i o n a t pH va lues i n the r e g i o n of 6 t o 8 may be a t t r i b u t e d t o the f o r m a t i o n o f metal h y d r o x i d e s . The recovery i s i n c r e a s e d by the d i s s o l u t i o n o f the hydrox ides and the f u r t h e r f o r m a t i o n o f complex s p e c i e s such as plumbate and f e r r a t e . These l a t t e r s p e c i e s have o x i d i z i n g p r o p e r t i e s and may a i d the f o r m a t i o n o f dixanthogen which i n c r e a s e s the r e c o v e r y by f l o t a t i o n . 7 .5 FORMATION OF METAL COMPLEXES WITH XANTHATE IONS T r a n s i t i o n metals such as copper and i r o n form complex s p e c i e s w i t h xanthate i o n s . The i o n i c s p e c i e s such as C u ( X ) + , F e ( X ) 2 , F e ( X ) 2 + are (137) produced i n the aqueous phase. In n e u t r a l and a l k a l i n e s o l u t i o n s the i o n i c complex s p e c i e s such as F e ( 0 H ) ^ + and Fe(0H)2 are p r e s e n t . -The f o r m a t i o n o f such complex s p e c i e s t o g e t h e r w i t h metal : hydrox ides appears to have a depressant a c t i o n i n • f l o t a t i o n o f s u l p h i d e m i n e r a l s of copper and i r o n . 7.6 SOLID. STATE REACTIONS IN HEAVY METAL XANTHATES Heavy metal xanthates are s u b j e c t t o aging i f ' s t o r e d at room temperature under atmospher ic c o n d i t i o n s . The xanthate o f copper and i o r n produce a c h a r a c t e i s t i c smel l which p r o b a b l y comes from the f o r m -a t i o n o f v o l a t i l e c y c l i c compounds. Cuprous e t h y l x a n t h a t e o x i d i z e s i n a i r t o cuprous o x i d e which f u r t h e r o x i d i s e s to c u p r i c ox ide i n an u n l i m i t e d s u p p l y o f a i r . I t has been noted t h a t cuprous and f e r r i c e t h y l x a n t h a t e s g r a d u a l l y h y d r o l y z e i n . m o i s t a i r . The r a t e o f h y d r o l y s i s i n c r e a s e s w i t h an i n c r e a s e i n r e l a t i v e h u m i d i t y and temperature . Lead e t h y l x a n t h a t e i s found t o be c o m p a r a t i v e l y s t a b l e i n d r y and mois t a i r . 7.7 > THE CHEMICAL NATURE OF COPPER ETHYLXANTHATE An e l e c t r o n paramagnetic resonance s tudy by S o l o z h e n k i n (82) c la imed to show t h a t c u p r i c e t h y l x a n t h a t e i s a s t a b l e s p e c i e s i n the copper s u l p h i d e - e x a n t h a t e f l o t a t i o n system. A d e t a i l e d EPR s tudy o f e t h e r - t r e a t e d copper e t h y l x a n t h a t e and u n t r e a t e d one was c a r r i e d out both i n s o l i d s t a t e and i n benzene s o l u t i o n . The copper e t h y l x a n t h a t e p r e c i p i t a t e s ( t r e a t e d and u n t r e a t e d ) were found t o be i n i t i a l l y i n s o l u b l e i n b e n z i n e , but a pro longed t reatment produced a very d i l u t e s o l u t i o n . The EPR. spectrum i n d i c a t e d o n l y . t r a c e s of d i v a l e n t copper i n t h i s benzene s o l u t i o n . " (138) I f two per cent of p y r i d i n e was added to the copper xanthate s o l u t i o n i n benzene a complex was formed i n which copper was i n the d i v a l e n t s t a t e t h i s s o l v e n t mixture was used to d i s s o l v e the e t h e r - t r e a t e d and the untrea ted copper e t h y l x a n t h a t e s . Both s o l u t i o n s produced EPR s p e c t r a of a s i m i l a r n a t u r e . The r e s u l t s c a l c u l a t e d from the exper imenta l data were i n agreement w i t h those repor ted by S o l o z h e n k i n (82) . The present s tudy c o n f i r m s , however, t h a t the s t a b l e form o f copper s u l p h i d e m i n e r a l s c o n t a i n s copper i n the monovalent s t a t e . Unpaired e l e c t r o n s are r e s p o n s i b l e f o r g i v i n g an EPR s i g n a l due to paramagnetic s p e c i e s , such as c u p r i c e t h y l x a n t h a t e . T h i s compound w i l l produce an.EPR s i g n a l even i f the c o n c e n t r a t i o n of copper i n the s o l u t i o n i s as low as I O " 4 t o 10" 5 M. Such c o n c e n t r a t i o n s cou ld e a s i l y be obta ined by o x i d a t i o n o f s o l i d s i n a i r on C u + ions by oxygen d i s s o l v e d i n s o l v e n t . I f a m i x t u r e conta ins Cu(I) and Cu( I I ) compounds, or a C u ( I I ) compound i s present as an i m p u r i t y i n a Cu(I) compound, the EPR s i g n a l w i l l o n l y be g i v e n by C u ( I I ) compound. This technique w i l l not i n d i c a t e a Cu(I) compound even i f i t i s the main c o n s i s t u e n t of the m i x t u r e . X - r a y p h o t o e l e c t r o n spec t roscopy (ESCA) was used to analyse the copper e t h y l x a n t h a t e samples and t h e i r decomposi t ion p r o d u c t s . T h i s s tudy conf irmed the f i n d i n g s of the EPR study on copper e t h y l x a n t h a t e , namely tha t copper was present in the monovalent s t a t e . However, some copper was present i n a d i v a l e n t s t a t e i n some of the decomposi t ion p r o d u c t s . (139) 7.8 THE CHEMICAL NATURE OF IRON ETHYLXANTHATE A Mossbauer s tudy was c a r r i e d out i n an attempt t o a s c e r t a i n the va lue o f the v a r i a b l e o x i d a t i o n s t a t e e x h i b i t e d by i r o n i n i r o n e t h y l x a n t h a t e . T h i s s t u d y conf i rmed t h a t c o n t r a r y t o the e x p e c t a t i o n (by analogy w i t h cuprous e t h y l x a n t h a t e ) f e r r o u s e t h y l x a n t h a t e i s not the s t a b l e form o f i r o n x a n t h a t e . The s p e c i e s r e s p o n s i b l e f o r c o l l e c o r c o a t i n g on i r o n s u l p h i d e i s f e r r i c e t h y l x a n t h a t e ; f e r r o u s i o n s were found not capable of r e a c t i n g w i t h xanthate i o n s . The nonex is tence of f e r r o u s e t h y l x a n t h a t e has been conf i rmed o n l y r e c e n t l y i n a s tudy r e p o r t e d by Samsonova (122). I t was found t h a t f e r r o u s ions are f i r s t o x i d i z e d t o the f e r r i c form and then a s t a b l e f e r r i c e t h y l x a n t h a t e i s produced. A hydroxy x a n t h a t e , F e ( O H ) ( E t X ^ appears t o be formed by the i n t e r a c t i o n o f Fe(0H)2+ and xanthate ions i n n e u t r a l o r very m i l d l y a c i d i c s o l u t i o n s and t h i s compound might a l s o be expected to c o n t r i b u t e t o the d e p r e s s i o n o f i r o n s u l p h i d e m i n e r a l s i n f l o t a t i o n . . . L i t t l e i n f o r m a t i o n i s a v a i l a b l e i n l i t e r a t u r e about f e r r i c e t h y l x a n t h a t e i n comparison w i t h o ther heavy metal x a n t h a t e s . T h i s i s m a i n l y due t o an u n j u s t i f i e d b e l i e f t h a t dixanthogen i s t h e o n l y s p e c i e s r e s p o n s i b l e f o r f l o t a t i o n o f i r o n s u l p h i d e s . The r o l e o f f e r r i c e t h y l x a n t h a t e i n f l o t a t i o n system i s t h e r e f o r e c o m p l e t e l y i g n o r e d . F e r r i c e t h y l x a n t h a t e i s s o l u b l e i n o r g a n i c s o l v e n t s . The dixanthogen i s o l a t e d from a c o l l e c t o r coated i r o n s u l p h i d e minera l , i s contaminated w i t h f e r r i c e t h y l x a n t h a t e . The i n f r a r e d s p e c t r o s c o p i c s t u d y i n d i c a t e s t h a t both compounds g i v e almost s i m i l a r s p e c t r a and t h i s l e d t o the i d e n t i f i c a t i o n o f o n l y d i x a n t h o g e n . \ (140) The present study shows t h a t f e r r i c e t h y l x a n t h a t e i s a s t a b l e compound at pH 2.5 to 3 .5 and i s a s s o c i a t e d w i t h some d i x a n t h o g e n . I t s chemical nature i s changed o n l y i f pH c o n d i t i o n s are changed from a c i d i c pH values to b a s i c ones. The v a r i a t i o n s i n f l o t a b i l i t y o f i r o n s u l p h i d e m i n e r a l s t h e r e f o r e can be a t t r i b u t e d to the changes i n the chemical nature o f f e r r i c e t h y l x a n t h a t e . The Mossbauer s t u d y conf i rms the e x i s t e n c e of a s t a b l e f e r r i c e t h y l x a n t h a t e i n a c i d i c pH values and the changes i n i t s chemical nature i n b a s i c s o l u t i o n s . 7.9 THE FORMATION OF FERRIC ETHYLXANTHATE AND DIXANTHOGEN The o x i d a t i o n o f xanthate by f e r r i c ions and r e d u c t i o n of dixanthogen by f e r r o u s ions are c o n s i s t e n t w i t h the reac t ion= Fe3+ + 2 X ~ t X 2 + F e 2 + 7.1 F e r r i c xanthate format ion occurs i n d e p e n d e n t l y : Fe3+ + 3X~ + F e ( X ) 3 - — 7 . 2 The r e a c t i o n s 7.1 and 7.2 predominate i n a c i d i c s o l u t i o n s . The r e a c t i o n s which i n v o l v e complexed f e r r i c i o n s , as F e ( 0 H ) 2 + , have a s i m i l a r form: F e ( 0 H ) 2 + + 2X" •-»• F e ( 0 H ) + + X £ 7 .3 2X~ + F e ( 0 H ) 2 + - F e ( 0 H ) ( X ) 2 7.4 For c a t i o n s such as F e 3 + which have r e l a t i v e l y n o n l a b i l e water m o l e c u l e s , OH s u b s t i t u t i o n i s a r e l a t i v e l y slow p r o c e s s . T h i s appears t o be governed by the r a t e of h y d r o l y s i s o f the c o o r d i n a t e d water m o l e c u l e s . The presence o f OH ions however, weakens the water molecules i n the c o o r d i n a t i o n sphere of f e r r i c i o n i n p e r m i t t i n g e a s i e r e n t r y o f the i o n i c l i g a n d . (141) \ Another mechanism p o s t u l a t e d by B u l t o and M i l l e r (124) i s t h a t metal ions complex w i t h the t h i o l . T h i s complex can then be o x i d i z e d under atmospher ic c o n d i t i o n s to o t h e r s p e c i e s i n c l u d i n g d i s u l p h i d e s . The o b s e r v a t i o n s do not a l l o w a d e f i n i t e mechanism to be f o r m u l a t e d . However, i t i s found t h a t the r a t e o f o x i d a t i o n o f x a n t h a t e to dixanthogen i n t h i s .system i s pH dependent. The present s tudy i n d i c a t e s t h a t the r a t e i s h i g h at pH 2 . 5 to 3 . 7 , i . e . , a l e v e l of pH at which ions are not s u b j e c t . t o h y d r o l y s i s . SUMMARY AND CONCLUSIONS A study was made of the mode of f o r m a t i o n of heavy metal xanthates and t h e i r d i s s o l u t i o n and decomposi t ion behaviour as a f f e c t e d by a wide range o f pH and temperature . The r e s u l t s i n d i c a t e d t h a t the heavy metal xanthates undergo v a r i o u s pH dependent decomposi t ion r e a c t i o n s . The s i g n i f i c a n t , res ul ts o f t h i s study as a p p l i e d to the metal xanthates of l e a d , copper and i r o n , are summarized as f o l l o w s : (1) The p r e c i p i t a t i o n o f l e a d , copper and i r o n xanthates i n a homogeneous system may not occur u n t i l a f t e r the s o l u b i l i t y product i s reached. The development o f t u r b i d i t y i n such systems may be i n h i b i t e d by complex f o r m a t i o n or by the a d s o r p t i o n o f one of the. i o n i c spec ies o f the system a t the s o l i d / s o l u t i o n i n t e r f a c e of the-metal xanthate n u c l e i . (2) The ra te o f d i s s o l u t i o n o f metal xanthates i n aqueous s o l u t i o n s - j S pH and temperature dependent. (3) In the d i s s o l u t i o n study the v a r i a t i o n s i n the l e v e l o f c o n c e n t r a t i o n o f xanthate and metal ions a t v a r i o u s values o f pH and temperature i n d i c a t e the occurrence o f v a r i o u s decomposi t ion r e a c t i o n s . The i n i t i a l pH values determine the type of decomposi t ion r e a c t i o n . (4) A d d i t i o n a l r e a c t i o n s take p lace between metal and h y d r o x y l , xanthate and hydroxyl or carbonate ions which l e a d to the f o r m a t i o n of metal s u l p h i d e s , hydrated o x i d e s , and c a r b o n a t e s . The e x i s t e n c e of these compounds has been conf i rmed by v a r i o u s a n a l y t i c a l t e c h -n i q u e s . (5) The UV s p e c t r o s c o p i c s tudy i n d i c a t e s the presence (143) o f complex s p e c i e s o f copper such as Cu(X) i n s o l u t i o n s . The presence o f t r i t h i o c a r b o n a t e has been detec ted i n f e r r i c e t h y l x a n t h a t e s o l u t i o n s r i c h i n xanthate i o n s . (6) A t pH 10.5 and 25°C complexed l e a d ions o x i d i z e xanthate ions to dixanthogen which co-adsorbs on undecomposed l e a d e t h y l x a n t h a t e . The presence o f d ixanthogen has been conf i rmed by s p e c t r o -s c o p i c methods. (7) C o n t r a r y to the r e p o r t e d e x i s t e n c e o f s t a b l e c u p r i c x a n t h a t e , the e l e c t r o n paramagnetic resonance and X - r a y p h o t o e l e c t r o n s p e c t r o s c o p i c d e t e r m i n a t i o n s conf i rmed cuprous e t h y l x a n t h a t e to be the s t a b l e compound.. (8) Ferrous ions were found not to r e a c t w i t h xanthate ions to form f e r r o u s e t h y l x a n t h a t e . (9) The a b i l i t y o f f e r r i c ions to o x i d i z e xanthate to d ixanthogen i s a t maximum over the pH range o f 2.5 to 3 . 7 . 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(150) Appendix A C r y s t a l S t r u c t u r e o f : Potassium E t h y l x a n t h a t e -Lead E t h y l x a n t h a t e -and F e r r i c E t h y l x a n t h a t e . C o n f i g u r a t i o n o f : Surface l ead e t h y l x a n t h a t e and mixed f i l m s of bulk l e a d e t h y l x a n t h a t e and d i x a n t h o g e n . Proposed model of r e a c t i o n s of xanthates i n aqueous s o l u t i o n . (151) s Pb B S Pb— C,H,0—C—S—.'b s S Pb— Galena surface which is different from the bulk lend ethyl xanthate CH..O- C—r -1 "b- S—C—OC.H, I I" Two chemical s p e c i e s , s u r f a c e xanthate and b u l k xanthate i d e n t i f i e d on galena s u r f a c e ( A f t e r R. G. G r e e n l e r , J . Phys. Chem. 67, 2121-2126 (1963) . ) R e p r e s e n t a t i o n o f a proposed noncmolecular f i l m o f PbSSCOR on galena ( A f t e r H . Hagihara & T. S a k u r a i , Proceedings IVth I n t . Cong. Sur face A c t i v e Substances , B r u s s e l s , 1964) . 4K IV +. 4R0CS + 0 + 4H90 2 2 * A 4K + 40H + O + 4CS + 4R0H 2 2 II 4K + 40H + III I \ + 4K + 40H VI V / / v 4ROCS H + 0 + 2(ROCS ) 2 2 + 2H 0 2 Proposed r o d e ! o f r e a c t i o n s o f xanthates i n aqueous s o l u t i o n s and f o r m a t i o n o f d ixanthogen ( A f t e r A . Pomianowski and J . ', - j a , Canadian J . Chem. V o l . 4 1 , 2219 (1963) . ) P b Proposed c o n f i g u r a t i o n o f xanthate d ixanthogen l a y e r s bonded through van der U'aals ~orces ( A f t e r M . S . Prasad and S .R . Rao, IXth I n t . M i n e r a l P r o c e s s i n g Cong. Prague , C z e c h o s l o v a k i a 157 (1970) . (152) CS»: A : 4o @ ^ , © O f e o a 0 % 0 p 6 0 f 2 A The crystal structure of potassium xanthate viewed along (100). (After F. Mazzi and C. Tadini: Z. K r i s t . , 118 (5/6), 389, (1963).) v S{4) (a) Molecular dimensions of the independent ligand of t r i (• -ethylxanthate)iron(III) (b) The co-ordination sphere about the iron„ atom. Dimensions are: a=2.326, b=2.308A; ^aa'=93.9, <Cbb'=94.2, ^ b ' = 9 8 . 5 , <a'b=164.1°, <ab=75.5°. (After ^ V/3 Y W ' ^ Hoskins & B. P. Kel ly , Chem. Commun. ..^m^-W /' 45 (1970).) C A I ^ 0(2) C{4) •5 i 3 )T53 C{2 Atom distances and bond angles of lead ethylxanthate. (After H. Hagihara, Acta. Cryst. 21, 350 (1966).) Representation of the configuration of atoms in the unit cel l of lead ethylxanthate, Small dots denote projections of atoms on the plane y=0. (After H. Haqihara Acta Cryst. 21, 350 (1966).) (153) APPENDIX B C a l c u l a t i o n o f g f a c t o r i n case o f C u + + i o n (3d^ c o n f i g u r a t i o n ) from e x p e r i m e n t a l l y observed EPR s p e c t r a , shown i n F i g . 15(3 ) . The resonance c o n d i t i o n f o r EPR s i g n a l i s g i v e n by the e q u a t i o n : hv = g g 3H < In the p r e s e n t s tudy a resonance frequency v o f 9.591 GHz w i t h a resonance f i e l d o f 3306 gauss was used . The p o s i t i o n o f l i n e 2 and. 3 g ives a s e p a r a t i o n 35.72 gauss from the e x p e r i m e n t a l l y s e t c o n d i t i o n o f EPR s p e c t r o m e t e r . The va lue o f H i s t h e r e f o r e 3306 - 35.72 = 3270.28 gauss . This va lue o f H can be now used to c a l c u l a t e g g by _ hv _ /hv . _v -9 e BH " V H = 0.71449 x- pj-where v i s now i n GH* and H i s i n K i l l o g a u s s . Equat ion (2) w i t h v = 9.591 GHz and H = 3.2703 K i l l o g a u s s g ives g = 2 .0954. 

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