Solvent extraction in the winning of copper, nickel and cobalt

SOLVENT EXTRACTION IN T H E WINNING OF

COPPER, NICKEL AND COBALT

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SOLVENT EXTRACTION IN THE WINNING OF COPPER, NICKEL AND COBALT

TER VERKRIJGING VAN DE GRAAD VAN DOCTOR IN DE TECHNISCHE WETENSCHAPPEN AAN DE TECHNISCHE HOGESCHOOL DELFT, OP GEZAG VAN DE RECTOR MAGNIFICUS, PROF. IR. B.P.TH. VELTMAN, IN HET OPENBAAR TE VERDEDIGEN TEN OVERSTAAN VAN HET COLLEGE VAN DEKANEN OP DONDERDAG 10 NOVEMBER 1983 TE 16.00 UUR

p - 2 5 2 . S ' }

PROEFSCHRIFT

DOOR

ABRAHAM JOHANNES VAN DER ZEEUW, GEBOREN TE SCHIEDAM, SCHEIKUNDIG INGENIEUR

DIT PROEFSCHRIFT IS GOEDGEKEURD DOOR DE PROMOTOREN

PROF. IR. H.J. ROORDA

EN

Aan

Anneke, E v e l i n e en E r i k en de nagedachtenis van m i j n Ouders.

DANKBETUIGING

De D i r e c t i e van het KONINKLIJKE/SHELL LABORATORIUM t e Amsterdam ben i k e r k e n t e l i j k voor de ruime gelegenheid d i e m i j steeds geboden i s om t e p u b l i c e r e n of i n het openbaar t e spreken over g e d e e l t e n van het werk dat i n d i t p r o e f s c h r i f t i s verzameld.

ACKNOWLEDGEMENT

I am indebted t o the CANADIAN INSTITUTE OF MINING AND METALLURGY, the ELSEVIER SCIENTIFIC PUBLISHING COMPANY, the INSTITUTION OF CHEMICAL ENGINEERS, the INSTITUTION OF MINING AND METALLURGY, and the SOCIETY OF CHEMICAL INDUSTRY f o r p e r m i s s i o n t o reproduce the papers used i n t h i s t h e s i s and o r i g i n a l l y p u b l i s h e d under t h e i r c o p y r i g h t .

CONTENTS INTRODUCTION, SURVEY OF THE THESIS. PART ONE A. B. C. D. PART TWO PAPERS A 1. 4. C l a s s i f i c a t i o n of SX methods f o r m e t a l s . Solvent e x t r a c t i o n i n the copper i n d u s t r y .

Composition and mode of a p p l i c a t i o n of some commercial r e a g e n t s . References to PART ONE.

Study of the hydrogenation of the VERSATIC a c i d s a l t s of copper, n i c k e l and c o b a l t .

Metals e x t r a c t i o n w i t h c a r b o x y l i c a c i d s . I . Composition of complexes w i t h n i c k e l , c o b a l t ( I I ) and i r o n ( I I I ) .

Metals e x t r a c t i o n w i t h c a r b o x y l i c a c i d s . I I . E f f e c t of temperature on the e x t r a c t i o n of Cu, N i , C o ( I I ) , Zn, F e ( I I I ) and C o ( I I I ) . P u r i f i c a t i o n of z i n c c a l c i n e l e a c h s o l u t i o n s by exchange e x t r a c t i o n w i t h the z i n c s a l t of VERSATIC a c i d . B 1. S e l e c t i v e copper e x t r a c t a n t s of the 5 - a l k y l - 2 - h y d r o x y p h e n y l a l k y l ketoxime type. 2. Hydrocarbon s o l v e n t d i l u e n t s i n hydroxy-oxime s o l v e n t e x t r a c t i o n p r o c e s s e s .

3. Organic and p h y s i c o - c h e m i c a l aspects of p r o p e r t i e s of hydroxy-oxime e x t r a c t a n t s .

4. K i n e t i c s and mechanism of copper e x t r a c t i o n w i t h 5 a l k y l 2 -hydroxyphenyl a l k y l ketoximes.

Ideas and p r a c t i c e i n the d e s i g n of s o l v e n t e x t r a c t i o n r e a g e n t s . C 1 PART THRE A B C D

H i s t o r y of the author's involvement i n SX. Comments to the papers.

The f u t u r e .

References to PART THREE. NOTES added a f t e r c o m p l e t i o n of the t h e s i s . SUMMARY / SAME NV ATT ING

INTRODUCTION

L i q u i d / l i q u i d e x t r a c t i o n of metals ( e i t h e r as ions or s a l t s ) from an aqueous i n t o an o r g a n i c phase has been observed a l r e a d y long ago. In 1842 P e l i g o t found that uranium could be e x t r a c t e d from n i t r i c a c i d w i t h e t h e r . D e s p i t e v a r i o u s other examples found i n l a t e r years the p o s s i b i l i t i e s remained l a r g e l y unobserved u n t i l H. F i s c h e r i n t r o d u c e d 'dithizone'' as a s e l e c t i v e a n a l y t i c a l reagent f o r v a r i o u s metal ions i n 1924. "Dithizone'' complexes o f t e n p r e c i p i t a t e d and g r a v i m e t r i c methods were then used f o r t h e i r quant-i t a t quant-i v e d e t e r m quant-i n a t quant-i o n . In other cases however the complexes could be ex-t r a c ex-t e d i n ex-t o o r g a n i c s o l v e n ex-t s and ex-then deex-termined s p e c ex-t r o p h o ex-t o m e ex-t r i c a l l y . From then on l i q u i d / l i q u i d e x t r a c t i o n (or s o l v e n t e x t r a c t i o n , SX, i n the f u r t h e r t e x t ) became a very important t o o l i n the hands of the a n a l y t i c a l chemist, and t h i s has been so ever s i n c e .

As a general term, l i q u i d / l i q u i d e x t r a c t i o n or s o l v e n t e x t r a c t i o n would be taken to cover such d i f f e r e n t processes as f u r f u r a l e x t r a c t i o n of aromatics i n petroleum r e f i n i n g , e x t r a c t i o n s w i t h s u p e r c r i t i c a l CO2 i n food technology and pharmaceutical c h e m i s t r y , and l i q u i d metal - l i q u i d s l a g exchange

r e a c t i o n s i n m e t a l l u r g y ^ . However, f o r the present purpose the terms s h a l l be used i n the more r e s t r i c t e d meaning d e f i n e d i n the opening paragraph. The process can then be d e s c r i b e d as one i n which an i n o r g a n i c phase

c o n t a i n i n g a s o l u t e i s i n t i m a t e l y contacted w i t h an o r g a n i c phase w i t h which i t i s i m m i s c i b l e , i n order to t r a n s f e r the s o l u t e i n some form i n t o the o r g a n i c phase. To t h i s end the o r g a n i c phase may or may not c o n t a i n an e x t r a c t a n t . Once the goal i s achieved the c o n t a c t i s terminated and the phases are separated. Often t h i s process of e x t r a c t i o n i s f o l l o w e d by i t s r e v e r s e , i n which the s o l u t e - l o a d e d o r g a n i c phase i s contacted w i t h a second i n o r g a n i c phase to t r a n s f e r the s o l u t e i n t o the l a t t e r . T h i s i s o f t e n r e f e r r e d to as " s t r i p p i n g '1 or " b a c k - e x t r a c t i o n " .

Nowadays SX of metals f i n d s a p p l i c a t i o n i n a m u l t i t u d e of f i e l d s , from q u a n t i t a t i v e and q u a l i t a t i v e a n a l y s i s of t r a c e m e t a l s , v i a waste water p u r i f i c a t i o n , to l a r g e s c a l e metal p r o d u c t i o n .

F i r s t i n d u s t r i a l use of SX of metals dates back to the Manhattan p r o j e c t f o r the p r o d u c t i o n f o r pure uranium compounds. During and a f t e r World War I I SX as a u n i t o p e r a t i o n was f u r t h e r developed and y i e l d e d advanced methods

f o r the recovery of uranium; hafnium, z i r c o n i u m and some other r e l a t i v e l y low-volume metals'. The great i n d u s t r i a l breakthrough i n base metals came i n the mid s i x t i e s , when i t became p o s s i b l e to apply SX i n the winning of copper, to p u r i f y and c o n c e n t r a t e the copper s o l u t i o n s p r i o r to e l e c t r o -winning .

Although from a t e c h n o l o g i c a l p o i n t of view SX of metals can be considered a u n i t o p e r a t i o n , i t s p o s i t i o n as a l i n k i n a c h a i n of o p e r a t i o n s which should l e a d u l t i m a t e l y to the w i n n i n g , i n one form or another, of the pure m e t a l ( s ) r e q u i r e s f i n e a d a p t a t i o n to the other processes i n v o l v e d .

FEED CIRCUIT FEED EXTRACTANT CIRCUIT LOADED EXTRACTANT FEED PREPARATION (ORE LEACHING, MATTE DISSOLUTION, ETC. ) BACK-EXTRACTION CIRCUIT STRIP LIQUOR METAL PRODUCTION (ELECTROWINNING, DIRECT REDUCTION, SALT CRYSTALLIZATION)

BARREN EXTRACTANT STRIP SOLUTION

F i g . 1

A simple SX c i r c u i t i n i t s context

In i t s ( i d e a l l y ) completely c y c l i c o p e r a t i o n the o r g a n i c e x t r a c t a n t phase comes i n t o contact w i t h i n o r g a n i c feed and b a c k - e x t r a c t i o n phases which d i f f e r g r e a t l y .

F a c t o r s l i k e c o n c e n t r a t i o n and nature of feed i m p u r i t i e s , c o n c e n t r a t i o n of the m e t a l ( s ) wanted, flow r a t e of the f e e d , p o s s i b i l i t y of b a c t e r i a l or fungoid growths, e t c . , w i l l i n f l u e n c e the a t t i t u d e of the o p e r a t i o n s manager on items i n which he has some l i b e r t y : c h o i c e of reagent, reagent c o n c e n t r a -t i o n , c h o i c e of d i l u e n -t , r a -t i o be-tween o r g a n i c and i n o r g a n i c phase volumes. They w i l l however a l s o c o n f r o n t him w i t h some " f a c t s of l i f e " , l i k e r a t e and q u a l i t y of phase s e p a r a t i o n s throughout the p r o c e s s , presence of " c r u d " (a muddy s e m i - s o l i d c o n t a i n i n g q u i t e h i g h reagent and d i l u e n t c o n c e n t r a t i o n s , which tends to c o l l e c t at the i n t e r f a c e i n the s e t t l e r s and to i n c r e a s e i n

volume w i t h time, thus n e c e s s i t a t i n g the o p e r a t o r to shut down h i s p l a n t at i n t e r v a l s f o r c l e a n i n g ) , e t c .

The o f t e n r a t h e r severe h i g h l y a c i d i c c o n d i t i o n s used i n the s t r i p p i n g o p e r a t i o n put h i g h demands on the s t a b i l i t y of the reagent. Requirements of p u r i t y on the i n o r g a n i c b a c k - e x t r a c t i o n s o l u t i o n which proceeds to f u r t h e r metalwinning o p e r a t i o n s o f t e n d i c t a t e c r i t e r i a of reagent s e l e c t -i v -i t y . I n v e r s e l y , -i n cases where t h -i s s e l e c t -i v -i t y cannot be a c h -i e v e d , a bleed stream from the b a c k - e x t r a c t i o n c i r c u i t may be necessary to keep some c o n t a m i n a t i o n at an a c c e p t a b l e l e v e l of c o n c e n t r a t i o n .

From the d e s i g n e r s ' p o i n t of view the u n p r e d i c t a b i l i t y and o f t e n a l s o the c h a n g e a b i l i t y of feed f a c t o r s such as i n d i c a t e d above, t o g e t h e r w i t h an u n s a t i s f a c t o r y l e v e l of knowledge on the reagent's performance and p r o p e r t i e s puts l i m i t a t i o n s on the accuracy w i t h which p l a n t can be designed. Other l i m i t i n g c o n d i t i o n s are b e i n g put to d e s i g n e r and o p e r a t o r by two more p r o p e r t i e s i n h e r e n t to the reagents used. F i r s t l y , many of the r e a c t i o n s

i n SX p r a c t i c e occur between two i m m i s c i b l e phases and between (hydrated) metal i o n s and l a r g e l y or t o t a l l y n o n - i o n i z e d reagent m o l e c u l e s . T h i s makes

such r e a c t i o n s i n h e r e n t l y slow. A c h i e v i n g e q u i l i b r i u m takes c o n s i d e r a b l e time, and more o f t e n than not stage e f f i c i e n c i e s f a l l s h o r t of 100 %. Hence p l a n t d e s i g n must be adapted to t h i s f a c t . Secondly, e s p e c i a l l y the c h e l a -t i n g -type of SX reagen-ts have r a -t h e r h i g h m o l e c u l a r weigh-ts (LIX 65 N: 339). In o r d e r to ensure h a n d l a b i l i t y of the s o l u t i o n s , reagent c o n c e n t r a t i o n s cannot be i n c r e a s e d too much. The s t o i c h i o m e t r y of the r e a c t i o n s i s o f t e n ( f o r a b i v a l e n t metal) 1 i o n to 2 molecules of the reagent. F r e q u e n t l y some e x t r a f r e e reagent i s needed to keep the complexes i n s o l u t i o n . Hence l a r g e volume streams of reagent s o l u t i o n s are o f t e n necessary to achieve a good e x t r a c t i o n .

The i m p o s s i b i l i t y per se, at l e a s t at an a c c e p t a b l e c o s t , to run the v a r i o u s c i r c u i t s i n v o l v e d f u l l y c y c l i c and s e l f - c o n t a i n e d may cause problems of an environmental n a t u r e , which have to be r e c o g n i z e d by p l a n t d e s i g n e r , reagent s u p p l i e r and p l a n t o p e r a t o r a l i k e .

REFERENCE

1. Rosenbaum, J.B., P r o c . AIME Meeting on H y d r o m e t a l l u r g y , Chicago 1973, p. 169. AIME, New York 1973.

SURVEY OF THE THESIS

In the f i r s t p a r t a survey w i l l be given of the v a r i o u s methods of SX f o r metals, i n d i c a t i n g e x i s t i n g and p o t e n t i a l a p p l i c a t i o n s f o r each method i n a c t u a l metal-winning p r a c t i c e . C o n s i d e r i n g the enormous number of papers, books, conference proceedings e t c . no attempt w i l l be made to achieve completeness. In t h i s p a r t a l s o some i n f o r m a t i o n w i l l be g i v e n on the composition of v a r i o u s reagents which a r e , or have been, a v a i l a b l e on the market and on t h e i r most u s u a l modes of a p p l i c a t i o n .

The second p a r t c o n t a i n s the f u l l t e x t of the author's papers on s e v e r a l aspects of SX of metals.

In the t h i r d p a r t a h i s t o r i c overview of the development of the author's i n t e r e s t i n the f i e l d of SX and r e l a t e d areas w i l l be g i v e n . A l s o comments are p r o v i d e d to the papers p r e s e n t e d , which have been made necessary by the progress of s c i e n c e i n the f i e l d . At the end a r a t h e r s p e c u l a t i v e view to the f u t u r e of SX i s g i v e n , together w i t h a b r i e f comparison of SX w i t h some r e l a t e d processes.

PART ONE

A. CLASSIFICATION OF SX METHODS FOR METALS

Solvent e x t r a c t i o n f o r metals can be c l a s s i f i e d i n 4 c a t e g o r i e s : 1. SX by means of s a l t f o r m a t i o n w i t h a n i o n s ,

2. SX by means of s a l t f o r m a t i o n w i t h c a t i o n s , 3. SX by means of c h e l a t i o n ,

4. " r e a l " SX.

These c a t e g o r i e s w i l l be d i s c u s s e d i n the above sequence. 1. SX by means of s a l t f o r m a t i o n w i t h anions

Most metal ions are capable of forming s a l t s w i t h s u i t a b l e a c i d s . I f the a c i d can be chosen such that both the a c i d and i t s metal s a l t are s o l u b l e i n an o r g a n i c phase but i n s o l u b l e i n water, SX of the metal i o n from an aqueous medium i s , at l e a s t i n p r i n c i p l e , p o s s i b l e .

S u i t a b l e a c i d s may be c a r b o x y l i c and s u l f o n i c a c i d s of reasonably h i g h m o l e c u l a r w e i g h t s , d i - e s t e r s of phosphoric a c i d , mono-esters of phosphonic a c i d s , e t c . :

R- ZOOH -PO(OH)

I

R

Amongst the c a r b o x y l i c a c i d s three types have been s t u d i e d o f t e n : h i g h l y branched a l i p h a t i c a c i d s : R' R" C-—COOH CH3 c y c l o - a l k y l s u b s t i t u t e d a l i p h a t i c a c i d s : VERSATIC a c i d s ( S h e l l ) (example) (CH.)

-2 n COOH naphthenic a c i d s ( S h e l l and other

f u n c t i o n a l i z e d a l i p h a t i c a c i d s : -COOH Br a-bromolauric a c i d ( I s r a e l i M i n i n g I n s t i t u t e ) 10

Of these, VERSATIC a c i d s f i n d the w i d e s t a p p l i c a t i o n a l s o i n hydrometal-l u r g i c a hydrometal-l processes.

Of the phosphoric a c i d d e r i v a t i v e s i t s d i - e s t e r w i t h 2-ethylhexanol has been s t u d i e d most f r e q u e n t l y , and i t i s a l s o a p p l i e d i n p r a c t i c e . I t can be found i n the SX l i t e r a t u r e under a number of names and a b b r e v i a t i o n s , a.o. d i - ( 2 - e t h y l h e x y l ) phosphoric a c i d , b i s - ( 2 - e t h y l h e x y l ) phosphoric a c i d , and o f t e n as DEHPA or D-2EHPA.

In p r i n c i p l e the r e a c t i o n between the a c i d s d e s c r i b e d s o f a r and the m e t a l i o n i s a simple s a l t f o r m a t i o n . Hence, f o r c a r b o x y l i c a c i d s :

M eX + + x R-—COOH < > (R COO) Me + x H+

aq - x org aq Apart from formal o b j e c t i o n s one might have a g a i n s t w r i t i n g H+, t h i s

equation i s g r o s s l y s i m p l i f i e d , as w i l l come to be d i s c u s s e d i n p a r t t h r e e of t h i s t h e s i s . N e v e r t h e l e s s the g e n e r a l i d e a i s v a l i d : a c i d i t y i s gener-ated, and the r e a c t i o n i s an e q u i l i b r i u m one.

I t f o l l o w s t h a t the r e a c t i o n i s pH dependent, and t h a t each metal i o n i s e x t r a c t e d best at an own s p e c i f i c pH v a l u e . Roughly i t can be s t a t e d t h a t f o r any metal the pH of optimum e x t r a c t i o n f o r normal n o n - f u n c t i o n a l i z e d c a r b o x y l i c a c i d s (e.g. VERSATIC or naphthenic a c i d s ) i s t h a t at which the hydroxide of the metal s t a r t s to be formed. For such an a c i d an e x t r a c t i o n / pH sequence f o r a number of important metal ions i s f o r example:

F e3 + C u2 + Z n2 + N i2 +/ C o2 + M n2 + F e2 + C a2 + M g2 + N a+/ K+

2 « pH >• 8 For a c i d s having a g r e a t e r s t r e n g t h , l i k e a-bromolauric or s u l f o n i c a c i d s , the sequence remains l a r g e l y the same, but the s c a l e s h i f t s to lower pH values and might get somewhat compressed. For an a c i d l i k e DEHPA, which

2+

shows a s e l e c t i v i t y f o r Zn , t h i s i o n s h i f t s to lower pH v a l u e s and . . . 2+

changes p o s i t i o n w i t h e.g. Cu .

An i m p l i c a t i o n of the pH dependence i s t h a t i n g e n e r a l the e x t r a c t i o n of a metal i o n w i t h such a reagent consumes a n e u t r a l i z i n g agent i f one aims f o r complete r e a c t i o n . This i s of course a cost f a c t o r , and up to now t h i s has been a h i n d r a n c e f o r a r e a l breakthrough of c a r b o x y l i c a c i d e x t r a c t i o n of base m e t a l s .

In g e n e r a l i t w i l l not be economic to e x t r a c t metals of which the optimum pH value of e x t r a c t i o n l i e s above 6. In p r a c t i c e t h i s means t h a t i n the above sequence SX by c a r b o x y l i c a c i d s might be f e a s i b l e f o r metals up to

.2+ 2+ 2+ N i /Co and perhaps Mn

The f a c t t h a t each metal has i t s own pH of optimum e x t r a c t i o n i m p l i e s t h a t q u i t e o f t e n s e p a r a t i o n s between two or more metals are p o s s i b l e by a d j u s t -ing the pH of o p e r a t i o n . Two cases are i l l u s t r a t e d i n f i g u r e s 1 and 2. In f i g . 1 the pH "gap" between the two metals i s so wide t h a t a complete s e p a r a t i o n can be achieved i n one stage by keeping the pH at the v a l u e i n d i c a t e d . The f i r s t metal A i s completely e x t r a c t e d , whereas metal B remains t o t a l l y i n aqueous s o l u t i o n . E x t r a c t i o n of Fe"^+ (A) and Cu^+ (B)

from s u l f a t e s o l u t i o n s i s t y p i c a l f o r t h i s case.

t pH 1" pH

f i g . l f i g . 2

F i g . 2 i s s l i g h t l y more complicated. At the pH where A i s e x t r a c t e d b e s t , some B i s a l r e a d y c o - e x t r a c t e d . In many cases t h i s problem can be overcome by u s i n g a m u l t i - s t a g e c o u n t e r c u r r e n t o p e r a t i o n . The s m a l l amount of B which i s c o e x t r a c t e d i n the f i r s t stage i s then g r a d u a l l y r e p l a c e d i n the f o l l o w

-2+ -2+

ing stages by A. The e x t r a c t i o n of Cu (A) and N i (B) from s u l f a t e s o l u t i o n .2+ 2+ . . .

i s t y p i c a l . For the couple N i and Co the d i f f e r e n c e i n optimum pH of e x t r a c t i o n has a l r e a d y become so s m a l l t h a t an uneconomically l a r g e number of stages would be r e q u i r e d to accomplish a s a t i s f a c t o r y s e p a r a t i o n . A p p l i c a t i o n s i n p r a c t i c e

SX of copper and n i c k e l from aqueous streams c o n t a i n i n g p l a t i n u m group metals (PGM) was u n t i l r e c e n t l y a p p l i e d at Rustenburg (South A f r i c a ) w i t h VERSATIC a c i d . T h i s a c i d has a l s o been considered f o r the s e p a r a t i o n of

c o b a l t and n i c k e l contained i n h i g h l y concentrated ammonium s u l f a t e s o l u t i o n s obtained a f t e r a p p l i c a t i o n of the S h e r r i t - G o r d o n r e d u c t i o n of c o b a l t / n i c k e l s o l u t i o n s . 1 I n Japan Sumitomo use VERSATIC a c i d f o r the simultaneous

2

e x t r a c t i o n of c o b a l t and n i c k e l . " The metals a r e then s t r i p p e d together w i t h aqueous HC1, and s e p a r a t i o n i s then accomplished by s e l e c t i v e e x t r a c t i o n o f the c o b a l t o c h l o r i d a t e complex w i t h t r i - i s o o c t y l a m i n e . A l s o i n Japan, VERSATIC a c i d i s used i n a complicated m u l t i - s t a g e s e p a r a t i o n process f o r r a r e e a r t h m e t a l s .

A process which i s now being s t u d i e d by L u r g i and approaches commercial-i z a t commercial-i o n commercial-i s the removal of f e r r commercial-i c commercial-i o n s from z commercial-i n c s u l f a t e e l e c t r o l y t e , u s commercial-i n g an exchange r e a c t i o n w i t h the z i n c s a l t of VERSATIC a c i d ^'^'^ •

2 F e3 + + 3 ZnV„ f > 2 FeV-, + 3 Z n2 +

aq 2 org *= 3 o r g aq DEHPA i s used i n the e x t r a c t i o n of z i n c from v a r i o u s s o l u t i o n s at r a t h e r low pH.^Two processes u s i n g DEHPA have been developed f o r the s e p a r a t i o n of c o b a l t from n i c k e l . The f i r s t , ^ c a r r i e d out a t normal temperature, has

8 •

been p i l o t e d and subsequently s h e l v e d . The second one, which a p p l i e s higher temperatures, i s now o p e r a t i o n a l at Matthey Rustenburg R e f i n e r s i n South A f r i c a . I t i s a v e r y i n t e r e s t i n g p r o c e s s , i n t h a t i t uses the temperature-dependent t r a n s i t i o n of C o2 from t h e o c t a h e d r a l s i x c o o r d i n

-q . 2+ a t i o n t o the t e t r a h e d r a l f o u r - c o - o r d m a t i o n . ' The f o u r - c o - o r d i n a t e d Co

i s much more s e l e c t i v e l y e x t r a c t e d than the s i x - c o - o r d i n a t e d i o n .

A phosphonic a c i d e s t e r i s used by Nippon M i n i n g to e x t r a c t c o b a l t s e l e c t -i v e l y from n -i c k e l s u l f a t e s o l u t -i o n s . ^ S e p a r a t -i o n between c o b a l t and n i c k e l i s much b e t t e r than f o r DEHPA. The formula of the product i s

R~—0 y Q

R = 2 - e t h y l h e x y l OH

Even b e t t e r prospects f o r the s e p a r a t i o n of c o b a l t from n i c k e l have been opened by the announcement of p h o s p h i n i c a c i d s by Cyanamid ^

V

These have a p p a r e n t l y even b e t t e r s e p a r a t i o n f a c t o r s i n favour of c o b a l t than the phosphonic a c i d s .

2. SX by means of s a l t f o r m a t i o n w i t h c a t i o n s

Some m e t a l - c o n t a i n i n g anions may be e x t r a c t e d i n t o o r g a n i c l a y e r s by s u i t a b l e c a t i o n i c s p e c i e s , such as l o n g - c h a i n a l i p h a t i c t e r t i a r y or second-ary amine s a l t s , ammonium or s u l f o n i u m compounds, e t c . The most w i d e l y known examples are the A l a m i n e / A l i q u a t range (Henkel) and the almost

i d e n t i c a l Adogens (Sherex C h e m i c a l s ) :

(iso-C0H,_,),,N Alamine 336

( i s o - CgH1 7)3N+- < : H3 C l " A l i q u a t 336

The most i n t e r e s t i n g category of m e t a l - c o n t a i n i n g anions that may be 2-e x t r a c t 2-e d w i t h th2-es2-e compounds ar2-e th2-e compl2-ex h a l i d 2-e s : F 2-e C l . , CoCl. ,

- 2 - 2 - 4 4

CuCl,, CdCl. , ZnCl, and some o t h e r s . J 4 4

2-The r e a c t i o n sequence of the e x t r a c t i o n i s i l l u s t r a t e d f o r C o C l ^ beloxtf. Co + + 4 C l " 2 > C o C l ? "

aq aq 4 aq

2 R.N+ C l ~ + C o C l2" < > (R,N+)„ C o C l ? " + 2 C l "

4 org 4 aq 4 2 .4 org aq Although both r e a c t i o n s are e q u i l i b r i a , the second one l i e s f a r to the r i g h t . The f i r s t one i s s t r o n g l y dependent on the C l c o n c e n t r a t i o n . Therefore the o v e r a l l r e a c t i o n i s [ C l ] dependent, i n about the same way as the c a r b o x y l i c a c i d e x t r a c t i o n i s [ H*] dependent. Hence the metals concerned can be put on a [ C l ] s c a l e :

C d2 + B i3+ F e3 + Z n2 + C u2 + C o2 + Fe 2 + M n2 +

0« [ C l ~ ] , M

With r e s p e c t to s e p a r a t i o n s e t c . the same c o n s i d e r a t i o n s are v a l i d as d i s c u s s e d p r e v i o u s l y f o r c a r b o x y l i c a c i d e x t r a c t i o n s , but now of course r e l a t e d to [ C l ] . A v e r y a t t r a c t i v e aspect of t h i s type of r e a c t i o n i s that ( s i n c e the o v e r r i d i n g f a c t o r i s [ C±~~] ) back-extraction of the metal from the e x t r a c t a n t can be c a r r i e d out by d e c r e a s i n g the c h l o r i d e concen-t r a concen-t i o n i n concen-the aqueous phase, i n oconcen-ther words q u i concen-t e o f concen-t e n s concen-t r i p p i n g w i concen-t h p l a i n water i s s u f f i c i e n t .

A p p l i c a t i o n s i n p r a c t i c e

2+ . . In the sequence g i v e n above N i i s m a n i f e s t l y absent: under normal c o n d i t i o n s

2+ . . .

N i does not form a n i o n i c h a l i d e complexes. This marked d i f f e r e n c e w i t h 2+ 2+ .2+ Co p r o v i d e s an e x c e l l e n t means of s e p a r a t i n g Co from N i i n c h l o r i d e medium w i t h v e r y h i g h s e l e c t i v i t y .

I t i s t h e r e f o r e understandable that s e v e r a l v a r i a t i o n s of t h i s s e p a r a t i o n 13

have found t e c h n i c a l a p p l i c a t i o n s i n the metal-winning i n d u s t r y . F a l c o n b r i d g e N i k k e l v e r k i n Norway apply the p r i n c i p l e t o two d i f f e r e n t

2+ s o l u t i o n s : Adogen 281 (a secondary amine) i s used to e x t r a c t Cu and

2+

Co from a c h l o r i d e n i c k e l matte leach l i q u o r , and t r i - i s o o c t y l a m i n e

2+

(Alamine 336 ?) i s used to e x t r a c t Co from a s o l u t i o n of impure n i c k e l hydroxide i n aqueous HC1. Société Le N i c k e l (now Minemet) use Adogen 381

2+

(a t e r t i a r y amine) to e x t r a c t Co from impure n i c k e l e l e c t r o l y t e . Nippon M i n i n g use " t r i o c t y l a m i n e " f o r the same purpose. Métallurgie Hoboken-O v e r p e l t f i n d s e v e r a l a p p l i c a t i o n s f o r Alamine 336.

The Zincex process of Tecnicas Reunidas uses a secondary amine

(Amberlite LA2) f o r e x t r a c t i n g z i n c (and s m a l l amounts of other metals that form h a l i d e complexes, m a i n l y copper, cadmium and i r o n ) from t h e i r complex s u l f i d e l e a c h i n g s o l u t i o n .

14 . .

In the n u c l e a r i n d u s t r y Alamine 336 or s i m i l a r products are of use i n the p u r i f i c a t i o n of p l u t o n i u m - c o n t a i n i n g s o l u t i o n s .

3. SX of metals by means of c h e l a t e formation

C h e l a t i n g agents have a v a i l a b l e a s a l t - f o r m i n g and an e l e c t r o n - d o n a t i n g f u n c t i o n i n one molecule. The s a l t - f o r m i n g f u n c t i o n i s i n most cases a group c o n t a i n i n g a c t i v e hydrogen: a l i p h a t i c or p h e n o l i c OH groups, c a r b -o x y l i c a c i d gr-oups, t h i -o l -or s u l f -o n i c a c i d gr-oups. The e l e c t r -o n - d -o n a t i n g f u n c t i o n may be any atom or group which i s able to complex w i t h metal ions through lone e l e c t r o n p a i r s :

Apart from the combination of s a l t - f o r m i n g and e l e c t r o n - d o n a t i n g c a p a c i t y i n one m o l e c u l e , s e v e r a l other c r i t e r i a must be met by a "good" c h e l a t i n g agent. The most important one i s r i n g s i z e : the r i n g formed by the metal i o n , the s a l t - f o r m i n g f u n c t i o n , the e l e c t r o n - d o n a t i n g group and a l l the atoms i n between should be f i v e - or six-membered.

The net chemical r e a c t i o n between an a p p r o p r i a t e ( a r b i t r a r i l y b i v a l e n t ) metal i o n and a c h e l a t i n g reagent can, s i m p l i f i e d , be g i v e n as:

2 RH + M e2 + < > MeR„ + 2 H+

org aq • 2 o r g aq

In a schematic s t r u c t u r a l way i t can be p i c t u r e d as:

I t w i l l be c l e a r t h a t c h e l a t i n g reagents w i l l o n l y form complexes as

shown i n t h i s equation w i t h metal ions t h a t are keen to absorb the e l e c t r o n s donated by the reagent. Such metal ions almost a l l have p a r t l y empty i n n e r d - e l e c t r o n s h e l l s .

In most c h e l a t i n g reagents used i n a n a l y t i c a l chemistry or i n d u s t r y the s a l t - f o r m i n g f u n c t i o n has a r e l a t i v e l y low a c i d i t y . Reagents w i t h a l c o h o l i c or p h e n o l i c OH groups are o f t e n used. In f a c t the a c i d i t y of these groups i s so low t h a t the remarkable s t a b i l i t y of many c h e l a t e s cannot be e x p l a i n e d on t h a t b a s i s alone. I t i s the e l e c t r o n - d o n a t i n g f u n c t i o n which i s respons-i b l e f o r the s t r e n g t h of the complexes.

Towards metals which do not accomodate the e l e c t r o n - d o n a t i n g f u n c t i o n the c h e l a t i n g reagents behave l i k e (very) weak a c i d s , forming normal s a l t s at the expected h i g h pH v a l u e s .

I t w i l l be c l e a r from the i n t r o d u c t i o n t h a t an important s t i m u l u s f o r SX came from the needs of a n a l y t i c a l c h e m i s t r y . A v e r y l a r g e number of o r g a n i c compounds w i t h c h e l a t i n g p r o p e r t i e s have been proposed over the years to s a t i s f y these requirements, and many s t i l l f i n d a p p l i c a t i o n s i n t h i s f i e l d . Two v i r t u e s have been of e x t e n s i v e use here. F i r s t l y , the a b i l i t y of the reagents to complex a metal i o n s e l e c t i v e l y or even s p e c i f i c a l l y from a mixture allowed the s e p a r a t i o n and 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 of such a metal i n p r e f e r e n c e of other ones, i n dependence on r e a c t i o n c o n d i t i o n s . Secondly, many c h e l a t e s have v e r y s p e c i f i c l i g h t a b s o r p t i o n s , which can be used f o r t h e i r d e t e r m i n a t i o n by s p e c t r o p h o t o m e t r i c methods.

A f t e r a p p r o p r i a t e chemical a d a p t a t i o n some of the compounds can be made to serve i n i n d u s t r i a l a p p l i c a t i o n s . Such c a t e g o r i e s have to meet at l e a s t the f o l l o w i n g c r i t e r i a :

s o l u b i l i t y i n s u i t a b l e o r g a n i c d i l u e n t s , s t a b i l i t y upon storage and i n use,

a c c e p t a b l e p r o p e r t i e s w i t h r e s p e c t to t o x i c i t y e t c . , r e v e r s i b l e c h e l a t i o n p r o p e r t i e s ,

a c c e p t a b l e c o s t performance t o the user.

Compounds that s a t i s f y these c r i t e r i a and a r e or have been a v a i l a b l e i n commercial q u a n t i t i e s f a l l i n f o u r c l a s s e s : a l i p h a t i c hydroxy-oximes C

C-I

I I

< 3

8-hydr oxy qu ino 1 ine s

LOO

C-I C-I

I J

The n e t chemical r e a c t i o n g i v e n e a r l i e r i n t h i s s e c t i o n i s i n many r e s p e c t s v e r y s i m i l a r t o that g i v e n f o r the e x t r a c t i o n of a metal i o n w i t h a c a r b -o x y l i c a c i d : i t i s an e q u i l i b r i u m , and pH dependent. F-or such a r e a c t i -o n t o be a p p l i c a b l e i n the metal-winning i n d u s t r y i t i s r e q u i r e d t h a t the e x t r a c t i o n i s r e v e r s i b l e under p r a c t i c a b l e c o n d i t i o n s . Because of the remarkable s t a b i l i t y o f many of the c h e l a t e s they are o f t e n formed a t low pH v a l u e s , and one can e a s i l y go t o f a r : a t o l u e n e s o l u t i o n of 1,2-dioximino 4 - a l k y l c y c l o h e x a n e e x t r a c t s copper from 2N H^SO^ ^\ which means that the r e a c t i o n i s i r r e v e r s i b l e under a c c e p t a b l e c o n d i t i o n s .

However, i f the proper c h o i c e of reagent can be made, the e x t r a c t i o n can o f t e n be c a r r i e d out almost or completely without n e u t r a l i z a t i o n of the a c i d i t y generated. This e x p l a i n s why SX by c h e l a t i o n i s so popular i n the i n d u s t r y . Using one of the commercial reagents a v a i l a b l e , e x t r a c t i o n o f copper f o r i n s t a n c e can be c a r r i e d out d i r e c t l y from the s o l u t i o n s coming from a l e a c h i n g o p e r a t i o n a t a pH of 0.5 - 2, because the copper complexes are s t i l l s t a b l e at the lower end of the above range.

A p p l i c a t i o n s i n p r a c t i c e

By f a r the most important a p p l i c a t i o n i s the e x t r a c t i o n of copper from moderately a c i d i c s o l u t i o n s . S e v e r a l hundreds of kT/y of copper are being produced v i a SX. S e c t i o n B of p a r t one of t h i s t h e s i s w i l l be devoted to t h i s a p p l i c a t i o n .

As a l r e a d y i n d i c a t e d metal ions that w i l l r e a c t w i t h c h e l a t i n g agents o f t e n 2+ 2+

have o n l y p a r t i a l l y f i l l e d d - s h e l l s . N i and Co a l s o belong to t h i s category and many c h e l a t i n g reagents t h e r e f o r e w i l l r e a c t w i t h these i o n s , b e i t mostly at c o n s i d e r a b l y h i g h e r pH v a l u e s than w i t h copper. P r a c t i c a l

2+ 2+ a p p l i c a t i o n of c h e l a t i n g e x t r a c t i o n t o systems which c o n t a i n N i and Co

2+

i s s e r i o u s l y hampered by the f a c t t h a t Co complexes i n c o n t a c t w i t h a i r . . 3+ 16,17

are v e r y r a p i d l y o x i d i z e d to Co complexes which are extremely 17 18 2+

d i f f i c u l t to decompose . ' Co a c t s e f f e c t i v e l y as a p o i s o n f o r c h e l a t i n g reagents. Many methods of r e c o v e r i n g a p a r t l y poisoned reagent have been

2+, 2+ 19,20 devised to enhance the f e a s i b i l i t y of SX f o r N i /Co systems

i n c l u d i n g b a c k - e x t r a c t i o n of the c o b a l t w i t h c o n c e n t r a t e d HC1, concentrated H SO. a t e l e v a t e d temperatures, concentrated s a l t s o l u t i o n s , r e d u c t i o n of

2 4 3+

the Co w i t h c o b a l t powder, e t c . Apart from being o f t e n a g g r e s s i v e f o r the reagent, these methods were found by us to be a t best o n l y p a r t i a l l y s u c c e s s f u l . The o n l y method known to date which i s r e a l l y s u c c e s s f u l i s

. . . . 16,18 p r e c i p i t a t i o n of the c o b a l t w i t h HjS.

The b e s t way t o cope w i t h the c o b a l t problem i s to a v o i d i t . I n ammoniacal medium C o2 + i s very e a s i l y o x i d i z e d t o C o3 +, which i s v i r t u a l l y not e x t r a c t e d

21 . 2+ by c h e l a t i n g agents. Therefore d e l i b e r a t e o x i d a t i o n of Co c o u l d be c o n s i d e r e d . Whether t h i s s o l u t i o n i s a c c e p t a b l e depends on the o v e r a l l economics.

A p p l i c a t i o n s of c h e l a t i n g e x t r a c t i o n i n the winning of other metals are r a r e . Matthey Rustenburg are b u i l d i n g a p l a n t a t t h e i r Royston (U.K.) s i t e i n which Pd w i l l be e x t r a c t e d from a PGM s o l u t i o n i n aqueous HC1 w i t h a s o l u t i o n of a hydroxy-oxime. M e t a l l u r g i e Hoboken-Overpelt have patented a process

f o r the e x t r a c t i o n of Ge w i t h LIX 63, an a l i p h a t i c hydroxy-oxime.

Rhône-Poulenc have a process i n o p e r a t i o n i n which G a3 i s e x t r a c t e d w i t h

. . 23 an a l k y l s u b s t i t u t e d 8-hydroxyquinolme d e r i v a t i v e .

4. " R e a l " SX of metal ions

In t h i s method both the metal i o n and the c o u n t e r i o n are e x t r a c t e d from the aqueous phase. The reagents used do n o r m a l l y not c o n t a i n c a t i o n o g e n i c or anionogenic f u n c t i o n s , but do have a v a i l a b l e lone e l e c t r o n p a i r s , through which they form weak complexes w i t h the metal i o n s . Because of the absence of f u n c t i o n s i n the reagents the metal ions must take t h e i r own c o u n t e r i o n s .

Well-known reagents f o r " r e a l " s o l v e n t e x t r a c t i o n are h i g h e r a l c o h o l s , ketones, e t h e r s , phosphate e s t e r s , e t c . Sometimes 8diketones are e r r o n -e o u s l y r-eckon-ed to b-elong to t h i s cat-egory as w -e l l . In f a c t th-ey ar-e w-eak c h e l a t i n g agents, because they r e a c t i n the enol form, w i t h the second c a r b o n y l oxygen a c t i n g as the e l e c t r o n - d o n a t i n g f u n c t i o n .

P r a c t i c a l a p p l i c a t i o n s

From the beginning of the i n d u s t r i a l a p p l i c a t i o n of SX of metals t r i -b u t y l phosphate has -been i n use f o r the e x t r a c t i o n of uranium compounds

24 i n the n u c l e a r i n d u s t r y , and t h i s i s s t i l l so.

B. SOLVENT EXTRACTION IN THE COPPER INDUSTRY

By i t s d e f i n i t i o n a SX process needs s o l u t i o n s to work on, and w i l l y i e l d s o l u t i o n s as i t s end product. From the l a t t e r the metal or metal s a l t may then be won u s i n g methods which are known: c r y s t a l l i z a t i o n t o g i v e metal s a l t s , e l e c t r o w i n n i n g or d i r e c t r e d u c t i o n t o produce the m e t a l , e t c . I n c l u s i o n of a SX step may be warranted i f a sequence of processes a t some stage y i e l d s an aqueous metal s a l t s o l u t i o n which i s too d i l u t e or (and) too impure t o proceed d i r e c t l y t o a metal winning stage, o r t o be t r e a t e d otherwise or disposed of. Such d i l u t e or (and) impure s o l u t i o n s may i n the copper winning p r a c t i c e a r i s e f o r i n s t a n c e :

1. through d i r e c t l e a c h i n g of o r e s , 2. through l e a c h i n g of f l o t a t i o n t a i l i n g s , 3. through n a t u r a l l e a c h i n g , as mine w a t e r s ,

4. as waste streams, e l e c t r o w i n n i n g bleed streams, e t c . , 5. a f t e r d i s s o l u t i o n of scrap metal e t c .

1. SX a f t e r d i r e c t l e a c h i n g of copper ores

Use of SX on s o l u t i o n s obtained through d i r e c t l e a c h i n g of s u l f i d i c copper 13 25

o r e s , mainly c h a l c o p y r i t e , was pioneered by A r b i t e r ' a t Anaconda's Butte Montana p l a n t . The o r e , a f t e r c o n c e n t r a t i o n , was leached w i t h ammonia and a i r to give an ammoniacal copper s u l f a t e s o l u t i o n , which was then e x t r a c t e d w i t h a s e l e c t i v e copper e x t r a c t a n t (LIX 64 N). The process has o n l y been i n

26

o p e r a t i o n f o r a s h o r t p e r i o d , and was c l o s e d down i n 1979, p a r t l y f o r economic reasons and p a r t l y because of l e a c h i n g problems w i t h one of the m o d i f i c a t i o n s of c h a l c o p y r i t e .

D i r e c t l e a c h i n g of o x i d i c copper ores i s planned by Codelco ( C h i l e ) i n t h e i r Chuquicamata mine. The ore i s very pure, and the r e s u l t i n g s o l u t i o n s w i l l h a r d l y c o n t a i n other metal i o n s , so t h a t SX w i l l serve mainly as a concen-t r a concen-t i o n sconcen-tep. A major problem i n p r a c concen-t i c e may be a r a concen-t h e r h i g h conconcen-tenconcen-t of c o l l o i d a l s i l i c a .

2. SX a f t e r l e a c h i n g of f l o t a t i o n t a i l i n g s

In the d r e s s i n g of p o r p h y r i c ores a f l o t a t i o n o p e r a t i o n takes a predominant p o s i t i o n . I t aims a t producing an ore concentrate which can be used d i r e c t l y i n a p y r o m e t a l l u r g i c a l step. Separating the l a s t q u a n t i t i e s of ore from the gangue i s d i f f i c u l t , not o n l y because of the low absolute amounts but a l s o

because the v a l u a b l e s remaining w i t h the gangue have a l e s s pronounced s u l f i d i c , r a t h e r more o x i d i c c h a r a c t e r which makes them l e s s amenable to simple f l o t a t i o n procedures. I n p r a c t i c e t h e r e f o r e a " c u t - o f f " grade i s maintained: m a t e r i a l w i t h a lower q u a n t i t y of v a l u a b l e s i s dumped or s t o r e d . In the past c u t - o f f grades used to be r a t h e r h i g h . However, w i t h time ever lower grade copper ores were c o n s i d e r e d worth mining, so at present many o l d t a i l i n g s dumps are regarded as worthwhile sources f o r copper. Leaching of these dumps i s being c a r r i e d out or planned f o r the f u t u r e at many copper mines i n the w o r l d . Two main types o f l e a c h i n g can be d i s t i n g u i s h e d : heap or dump l e a c h i n g i n which the l i x i v i a n t ( o f t e n d i l u t e ^SO^ or r e c y c l e d r a f f i n a t e from the SX o p e r a t i o n ) i s s i m p l y dosed onto the t a i l i n g s heaps and the copper-enriched a c i d i s tapped, and a g i t a t i o n l e a c h i n g i n which the d i s s o l u t i o n o f the copper i s achieved by a g i t a t i o n (e.g. i n Pachuca's). The l a t t e r system i s used i n the b i g g e s t copper SX p l a n t i n o p e r a t i o n , ZCCM's C h i n g o l a p l a n t i n Zambia.

3. SX on mine waters

In some p l a c e s a combination of n a t u r a l c o n d i t i o n s e x i s t s which leads to d i s s o l u t i o n o f copper from ores w i t h o u t human a c t i o n . Important p o t e n t i a l a p p l i c a t i o n s , which may come t o r e a l i z a t i o n i n the (near) f u t u r e , are at B o u g a i n v i l l e a (Papua New Guinea) and E l Teniente ( C h i l e ) .

4. SX on waste streams e t c .

The e l e c t r o w i n n i n g b l e e d stream from Phelps Dodge's E l Paso r e f i n e r y used t o be worked up by SEC Corp. They e x t r a c t e d copper from t h i s s o l u t i o n w i t h L I X 64 N, then made the s o l u t i o n s t r o n g l y a l k a l i n e w i t h ammonia, and

13 e x t r a c t e d n i c k e l w i t h the same reagent. 5. SX on scrap metal s o l u t i o n s

I m p e r i a l Smelting Processes a r e o p e r a t i n g an e x t r a c t i o n of copper from 27

ammoniacal s o l u t i o n s of z i n c dross i n t h e i r Avonmouth p l a n t . Although the o r i g i n a l setup was f o r L I X 65, i t i s now b e l i e v e d t h a t they have r e -designed the p l a n t f o r LIX 54. The advantage of the l a t t e r (a diketone) i s t h a t c o - e x t r a c t i o n of ammonia i s markedly l e s s .

In 1979 Brookside M e t a l s i n the U.K. c l o s e d down a p l a n t i n which copper 28

had been e x t r a c t e d from s i l v e r n i t r a t e s o l u t i o n s w i t h SME 529. Very c a r e f u l r e g u l a t i o n of pH was necessary i n t h i s p r o c e s s . I f pH was allowed to f a l l below 1, i n c r e a s i n g amounts of copper c o u l d not be s t r i p p e d from

the o r g a n i c reagent. In c o - o p e r a t i o n between the owners and S h e l l i t was e s t a b l i s h e d t h a t t h i s was due to n i t r a t i o n of the copper complex i n the

. . 29 p o s i t i o n ortho to the p h e n o l i c group. This r e s u l t e d i n the f o r m a t i o n of a complex of an extremely s t r o n g reagent, d i s p l a y i n g the corresponding r e s i s t a n c e towards aqueous a c i d .

S e v e r a l other p r o j e c t s based on the d i s s o l u t i o n of scrap metal have been s t u d i e d , but the present economic s i t u a t i o n i s not f a v o u r a b l e f o r t h e i r r e a l i z a t i o n , and most plans have been shelved.

Economics of SX

The t o t a l c o n t r i b u t i o n of SX to the world's copper p r o d u c t i o n i s sub-s t a n t i a l . Thisub-s may be i l l u sub-s t r a t e d by the f o l l o w i n g ( f a i r l y comprehensub-sive) l i s t of copper SX p l a n t s i n o p e r a t i o n , and t h e i r e s t i m a t e d p r o d u c t i o n .

ZCCM, C h i n g o l a , Zambia 80,000 tpa Anamax, Twin B u t t e s , A r i z o n a (USA) 40,000 " Ranchers B l u e b i r d , A r i z o n a 7,000 " Cyprus Bagdad, A r i z o n a 7,000 " Cyprus Johnson, A r i z o n a 5,000 " C i t i e s ' S e r v i c e , A r i z o n a 15,000 " I n s p i r a t i o n , A r i z o n a 30,000 " Kennecott Ray, A r i z o n a 20,000 " Duval B a t t l e Mountain, Nevada (USA) 4,000 "

P i n t o V a l l e y , New Mexico (USA) ? Noranda Lakeshore, A r i z o n a 30,000 "

Cananea, Mexico 20,000 " Cerro Verde, Peru 25,000 " Centromin, Peru 5,000 " Lo A g u i r r e , C h i l e 20,000 "

Worldwide, on a t o t a l copper p r o d u c t i o n i n 1980 of 7 x 10^ tons, t h i s makes some 4.5 Z. However, l o c a l l y the c o n t r i b u t i o n s may be much h i g h e r : i n Zambia 12 - 15 % of the copper i s produced u s i n g SX methods, and i n the USA t h i s f i g u r e i s approaching 10 %.

Numerous f a c t o r s determine the o v e r a l l economics of a SX process as p a r t of a metal-producing o p e r a t i o n . I n many cases the v e r y c o s t l y mining and ore d r e s s i n g , heavy c o n t r i b u t o r s to the f i n a l product c o s t s , are s u p e r f l u o u s . Costs of l i x i v i a n t s may be s u b s t a n t i a l i f the o p e r a t i o n stands on i t s own. M o s t l y however the SX i s p a r t of a l a r g e s c a l e p r o d u c t i o n s i t e where

H^SO^ i s e a s i l y obtained by c o n v e r s i o n of SO^ from the p y r o m e t a l l u r g i c a l o p e r a t i o n .

Often a p r e - n e u t r a l i z a t i o n step i s necessary p r i o r to SX to n e u t r a l i z e excess a c i d , or to p r e c i p i t a t e e x c e s s i v e amounts of e.g. i r o n s a l t s . I f the n e u t r a l i z i n g agent ( o f t e n lime) has to be t r a n s p o r t e d over long d i s t a n c e s t h i s may be a heavy c o s t f a c t o r .

Energy consumption per u n i t of product i n a S X / e l e c t r o w i n n i n g p l a n t i s some 4 times h i g h e r than i n a " c o n v e n t i o n a l " p y r o m e t a l l u r g i c a l / e l e c t r o -r e f i n i n g o p e -r a t i o n .2^ However, i n p l a c e s w i t h cheap energy t h i s i s not

a problem.

Losses of reagent by p h y s i c a l means (entrainment) and decomposition cannot be completely avoided. Such l o s s e s range from 20 ppm t o t a l s o l v e n t ( i . e . reagent + d i l u e n t ) i n the aqueous r a f f i n a t e of a new, w e l l - o p e r a t e d p l a n t to 100 ppm or more i n an o l d one. C o n s i d e r i n g t h a t a p l a n t l i k e ZCCM's

3 . -Chingola o p e r a t i o n produces about 3000 m of r a f f i n a t e per hour, i t i s c l e a r t h a t the a b s o l u t e c o s t s of l o s t reagent are h i g h . The f a c t t h a t i n most o p e r a t i o n s the r a f f i n a t e i s r e c y c l e d to the l e a c h i n g does not improve

the s i t u a t i o n v e r y much: i n the l e a c h i n g most of the reagent contained i n the aqueous phase disappears i n t o the l e a c h i n g r e s i d u e or i s decomposed and cannot be recovered.

A l l i n a l l however i t can be s t a t e d t h a t most SX p l a n t s have shown con-s i d e r a b l e c o con-s t advantage over c o n v e n t i o n a l procecon-scon-secon-s. For i n con-s t a n c e , ZCCM'con-s c o s t s f o r copper produced through SX are i n the US $ 0.45 - 0.55 per pound b r a c k e t , a g a i n s t proceeds of US $ 0.85/lb. T h i s makes SX the o n l y p r o f i t a b l e p a r t of the o p e r a t i o n : " c o n v e n t i o n a l " copper at ZCCM c o s t s around

US $ 0.90/lb.*

S i m i l a r c o n s i d e r a t i o n s h o l d f o r most p l a n t s i n o p e r a t i o n , and the r e a l i z a t i o n of more new p r o j e c t s i s i n f a c t o n l y hindered by l a c k of c a p i t a l .

Mutual i n f l u e n c e s of SX and other p a r t s of metal-winning processes

I n c l u s i o n of SX i n an i n t e g r a t e d metal-winning process may have consequences f o r both upstream and downstream p a r t s of such a p r o c e s s , and the o p e r a t i o n of the SX p a r t i n t u r n may be i n f l u e n c e d by the way i n which other process p a r t s are conducted.

Upstream process p a r t s

F l o t a t i o n reagents o r r e s i d u e s t h e r e o f which may be present i n (e.g.) the f l o t a t i o n t a i l i n g s may end up i n the aqueous feed t o the SX p r o c e s s . Such contaminations almost i n v a r i a b l y do great harm to the process o f l a y e r s e p a r a t i o n i n the s e t t l e r p a r t of the SX p l a n t . A l s o r a t e s of e x t r a c t i o n might be decreased.

Some ores c o n t a i n c o n s t i t u e n t s which d i s s o l v e , p r o p e r l y or c o l l o i d a l l y , i n the l e a c h i n g l i q u o r . A prime example i s SiO^, which i n some cases may a t t a i n a h i g h c o n c e n t r a t i o n and s e r i o u s l y i n h i b i t l a y e r s e p a r a t i o n . Moreover voluminous h i g h l y a d s o r b i n g p r e c i p i t a t e s o f h y d r a t e d s i l i c a may be formed, which g i v e r i s e t o severe s o l v e n t l o s s e s .

In some cases a p r e - n e u t r a l i z a t i o n step has t o be c a r r i e d out p r i o r to SX. A v e r y common n e u t r a l i z i n g agent i s l i m e . O b v i o u s l y CaSO^ w i l l be formed, which shows a well-known tendency to s u p e r s a t u r a t e d s o l u t i o n s . Consequently gypsum p r e c i p i t a t e s may be generated and a g a i n l a y e r separ-a t i o n w i l l s u f f e r .

Downstream process p a r t s

The use o f SX leads t o contamination of the downstream aqueous phases. F i r s t l y , both the reagents used and the d i l u e n t s show a c e r t a i n ( u s u a l l y low) degree of s o l u b i l i t y i n water. Secondly, incomplete l a y e r s e p a r a t i o n causes mutual entrainment o f the phases. The degree of the l a t t e r can t o an extent be r e s t r i c t e d by adequate process o p e r a t i o n , but never f u l l y excluded. I f the r a f f i n a t e i s not r e c y c l e d but disposed o f as waste water i t may be necessary t o b r i n g the l e v e l o f such contaminants down i n order to compel w i t h r e g u l a t i o n s and environmental c o n s i d e r a t i o n s .

I f the aqueous stream c o n s i d e r e d i s a s t r i p l i q u o r , meant to be processed f u r t h e r i n an e l e c t r o w i n n i n g o p e r a t i o n , i t i s a l s o necessary to keep o r g -a n i c cont-amin-ation -a t -a low l e v e l . I f t h i s i s not done p r o p e r l y , the c-athode metal v e r y o f t e n shows " o r g a n i c b u r n i n g " . The v e r y t h i n l a y e r of o r g a n i c phase f l o a t i n g i n the e l e c t r o l y s i s c e l l s causes d i s c o l o u r a t i o n and c o n t -amination of the p a r t of the cathode which i s i n c o n t a c t w i t h the o r g a n i c . A technique o f t e n used to d i m i n i s h the r i s k of o r g a n i c b u r n i n g i s a i r f l o t a t i o n : a stream of a i r i s used to d r i v e the e n t r a i n e d o r g a n i c phase to the s u r f a c e of the aqueous l a y e r , from which i t i s skimmed o f f as com-p l e t e l y -as com-p o s s i b l e b e f o r e the aqueous stream e n t e r s the e l e c t r o w i n n i n g u n i t .

In e l e c t r o w i n n i n g c e l l s i n which a h i g h c u r r e n t d e n s i t y i s a p p l i e d one o f t e n f i n d s " a c i d m i s t " . Due to the h i g h r a t e of gas e v o l u t i o n a b l a n k e t of h i g h l y c o r r o s i v e and v e r y d i s a g r e e a b l e a c i d d r o p l e t s i s maintained over the c e l l . V a r i o u s means of r e s t r i c t i n g t h i s phenomenon are used. One of these i s a d d i t i o n of " a n t i m i s t agents". One of the types of products used f o r t h i s purpose are aromatic s u l f o n i c a c i d s . Because of t h e i r c h a r a c t e r they d i s p l a y a c e r t a i n s o l u b i l i t y i n o r g a n i c phases. Since n o r m a l l y s o l u t i o n s from e l e c t r o w i n n i n g o p e r a t i o n s are r e c y c l e d , the o r g a n i c reagent s o l u t i o n s may take up such s t r o n g l y a c i d i c compounds from the aqueous phases.

31 Losses of reagent through a c i d h y d r o l y s i s may then r e s u l t . S a f e t y aspects

SX i n v o l v e s h a n d l i n g of h i g h l y inflammable p r o d u c t s . I t t h e r e f o r e r e q u i r e s a complex system of s a f e t y measures of a nature which i s not per se common to the metal-winning i n d u s t r y . A v e r y important v a l u e i n t h i s r e s p e c t i s the f l a s h p o i n t of the d i l u e n t . A few years ago the uranium SX p l a n t at Rossing (Namibia) was s e v e r e l y damaged by a f i r e caused, amongst o t h e r s , by the use of a d i l u e n t w i t h too low a f l a s h p o i n t .

C. COMPOSITION AND MODE OF APPLICATION OF SOME COMMERCIAL REAGENTS 1. Commercial forms

Anionogenic reagents are mostly s o l d as v i r t u a l l y pure compounds i n a n o n - d i l u t e d form. An e x c e p t i o n are naphthenic a c i d s which are impure because of t h e i r o r i g i n . They u s u a l l y c o n t a i n c o n s i d e r a b l e amounts of n e u t r a l compounds, mostly hydrocarbons, and i t i s customary to i d e n t i f y naphthenic a c i d s by t h e i r a c i d v a l u e , i . e . the number of m i l l i g r a m s of KOH r e q u i r e d to n e u t r a l i z e the a c i d c o n t a i n e d i n one gram of the impure m i x t u r e . This f i g u r e i s then q u i t e s t r a i g h t f o r w a r d l y found back i n the product d e s c r i p t i o n .

Cationogenic and " r e a l " SX reagents are a l s o u s u a l l y s o l d as pure compounds w i t h o u t d i l u e n t s .

Most c h e l a t i n g reagents are s o l d i n a more or l e s s d i l u t e d form. The d i l u e n t s are mostly hydrocarbons ( k e r o s i n e f r a c t i o n s ) or h i g h e r a l c o h o l s or a l k y l p h e n o l s .

2. Modes of a p p l i c a t i o n

Anionogenic reagents are used i n s o l u t i o n s i n hydrocarbon d i l u e n t s , i n a c t i v e matter c o n c e n t r a t i o n s t y p i c a l l y r a n g i n g from 0.1 to 2 M. Dependent on the p a r t i c u l a r r e a g e n t s , the d i l u e n t and the process i t i s sometimes necessary to add a m o d i f i e r , t h a t i s a c o - d i l u e n t of a more p o l a r c h a r a c t e r

than the main one. T y p i c a l examples are cases where l a y e r s e p a r a t i o n needs improvement, or i n which the metal complexes might p r e c i p i t a t e . A l c o h o l s and a l k y l p h e n o l s are the most w i d e l y used m o d i f i e r s . In pH dependent e x t r a c t i o n s a d d i t i o n of such compounds o f t e n causes a decrease i n s e l e c t -i v -i t y and a s h -i f t of the opt-imum pH range to h -i g h e r v a l u e s .

C a t i o n o g e n i c reagents are n o r m a l l y a p p l i e d i n h i g h l y aromatic d i l u e n t s , sometimes i n combination w i t h a m o d i f i e r , e.g. a h i g h e r a l i p h a t i c a l c o h o l . A l t e r n a t i v e l y c h l o r i n a t e d hydrocarbons may be used as the s o l e d i l u e n t . A c t i v e matter c o n c e n t r a t i o n s i n use are t y p i c a l l y <; 0.5 M.

" R e a l " SX reagents are used as such, or mixed w i t h hydrocarbons or other d i l u e n t s .

C h e l a t i n g reagents are mostly used i n hydrocarbon s o l u t i o n s , c o n c e n t r a t i o n s t y p i c a l l y between 2 and 15 % a c t i v e m a t t e r , or 0.05 to 0.5 M. I t may be necessary to add a m o d i f i e r .

3. Survey of commercial copper c h e l a t i n g reagents

As a l r e a d y i n d i c a t e d f o u r types of c h e l a t i n g reagents f o r copper are or have been a v a i l a b l e : 2 types of hydroxy-oximes, h y d r o x y q u i n o l i n e s , and d i k e t o n e s . T h e i r s t r u c t u r a l groups can be found back i n compounds t h a t have been known i n a n a l y t i c a l c h e m i s t r y f o r y e a r s :

OH S \

N-CH,— C—CH C—CH, 3 II 2 || 3 N " \ "N—OH > ^ N 0 0

X0 H OH

benzoin oxime s a l i c y l a l d o x i m e 8-hydroxy- a c e t y l a c e t o n e (cupron) q u i n o l i n e

(oxine)

Such simple compounds and t h e i r metal c h e l a t e s are o f t e n not v ery s o l u b l e . By s u i t a b l y s u b s t i t u t i n g them w i t h s u f f i c i e n t l y long a l k y l chains the m o l e c u l a r weights can be i n c r e a s e d , so t h a t both the reagent and the complexes a c q u i r e an a p p r o p r i a t e l e v e l of s o l u b i l i t y i n o r g a n i c d i l u e n t s . T h i s p r i n c i p l e was f i r s t s u c c e s s f u l l y used by General M i l l s Inc. i n t h e i r product L I X 63. Over the years a number of reagents have become a v a i l a b l e , which a r e d i s c u s s e d below. 3.1 Oxime reagents . . 32 LIX 63 5,8-diethyl-6-hydroxy-7-oximinododecane C„HC 0oH | 2 5 | C.H„ CH — CH C CH -C.H. 4 9

| 1

This product e x t r a c t s copper from aqueous s o l u t i o n s of pH > 3 at a h i g h r a t e . However, t h i s pH range was not a t t r a c t i v e to the copper-winning i n d u s t r y . Since n o r m a l l y copper-bearing a c i d i c l e a c h l i q u o r s have pH v a l u e s of < 2 use of L I X 63 would n e c e s s i t a t e a d d i t i o n of n e u t r a l i z i n g agents. At present L I X 63 i s m a i n l y used as an a c c e l e r a t o r f o r other Henkel p r o d u c t s , as d i s c u s s e d below.

The former mining chemicals d i v i s i o n of General M i l l s Inc. i s now the p r o -p e r t y of Henkel (USA). The -products a r e s o l d under the Henkel l a b e l .

LIX 65 N 2-hydroxy-5-te rt-nonylbenzophenone oxime 3 3 t-C„H

'9 19

This compound met the requirements of the copper i n d u s t r y w i t h r e s p e c t to pH: i t s a c t i v i t y s t a r t s to be a t t r a c t i v e as low as pH 1.5. I t s r a t e of e x t r a c t i o n f o r copper at t h i s pH l e v e l however i s too low a t normal temp-e r a t u r temp-e . T h i s c o u l d btemp-e improvtemp-ed by m i x i n g LIX 65 N and LIX 63. Thtemp-e b l temp-e n d i s commercially known as LIX 64 N. In cases where i t i s p o s s i b l e or d e s i r a b l e to c a r r y out SX of copper at h i g h e r temperatures than normal, say up to 50° C, LIX 65 N alone can be used q u i t e w e l l .

E a r l y products c o n t a i n e d LIX 65 N and LIX 63 i n a molar r a t i o of about 4 : 1 . T h i s changed r a p i d l y over the y e a r s , and the p r e s e n t commercial product p r o b a b l y c o n t a i n s about 3 % of LIX 63, at an a c t i v e LIX 65 N content of 1 M.

In the e a r l y days of LIX technology a grade LIX 64 has been i n e x i s t e n c e . I t c o n t a i n e d LIX 63 and 5-dodecyl-2-hydroxybenzophenone oxime. I t was soon superseded by the much b e t t e r LIX 64 N.

35

LIX 70 a b l e n d of 2-hydroxy-3-chloro-5-tert-nonylbenzophenone oxime

and LIX 63. With r e s p e c t to pH f u n c t i o n a l i t y LIX 70 i s a much s t r o n g e r reagent than LIX 65 N, due to the i n f l u e n c e of the CI s u b s t i t u e n t . I t i s a c t i v e down to pH 0.5 and hence r e q u i r e s r a t h e r s t r o n g a c i d to r e l e a s e i t s complexed copper. Moreover, i t i s not a v e r y f a s t reagent. With the aim to reduce the complexing power to a more a c c e p t a b l e l e v e l and to improve the r a t e s of e x t r a c t i o n and s t r i p p i n g v a r i o u s blends of LIX 70, LIX 65 N and LIX 63 have been proposed (LIX 71, LIX 73^ ) , but n e i t h e r has been a b l e to match the commercial and t e c h n i c a l success of LIX 64 N.

LIX 64 N 34

SME 529 2-hydroxy-5-tert-nonylacetophenone oxime

With r e s p e c t t o pH f u n c t i o n a l i t y S h e l l M e t a l E x t r a c t a n t 529 i s a s l i g h t l y s t r o n g e r reagent than LIX 65, and i t has f a s t e r k i n e t i c performance than LIX 64 N. I t i s s o l d as a 50 % a c t i v e matter s o l u t i o n i n a hydrocarbon d i l u e n t .

Acorga P 5000 s e r i e sX

. 37 base compound: 2 - h y d r o x y - 5 - t e r t - n o n y l s a l i c y l a l d o x i m e

This i s an extremely potent reagent which e x t r a c t s copper a t pH v a l u e s as low as 0.5. Consequently i t w i l l r e l e a s e the complexed copper o n l y i n c o n t a c t w i t h h i g h l y c o n c e n t r a t e d a c i d , which i s an unacceptable p r o p o s i t i o n i n r e l a t i o n t o p r e s e n t day e l e c t r o w i n n i n g p r a c t i c e . I C I have d e v i s e d

38

f o r m u l a t i o n s m o d i f i e d w i t h nonylphenol which a r e more e a s i l y s t r i p p e d , at the c o s t of o n l y a l i m i t e d and t h e r e f o r e a c c e p t a b l e l o s s of pH f u n c t -i o n a l -i t y . The P 5000 range of e x t r a c t a n t s can be c h a r a c t e r -i z e d as f a s t reagents. C u r r e n t l y the range comprises:

name r a t i o base compound/nonylphenol P 5100 1/1 P 5200 1/2 P 5300 1/3 The products a l s o c o n t a i n s m a l l q u a n t i t i e s of a hydrocarbon d i l u e n t . The base compound, P 5000, i s not s o l d as such. R e c e n t l y a product PT 5050 has appeared, which i s p r o b a b l y a b l e n d of P 5000 m o d i f i e d w i t h t r i d e c a n o l .

Acorga i s a 50/50 j o i n t v e n t u r e between Anglo American and I C I .

LIX 617, LIX 622, e t c .

39 base compound(s): 5 - t e r t - a l k y l - 2 - h y d r o x y s a l i c y l a l d o x i m e

t-R

OH

Under above and other codenames v a r i o u s products are around. They may d i f f e r i n c h a i n l e n g t h of the a l k y l s u b s t i t u e n t , or i n c o n c e n t r a t i o n of a c t i v e matter. They are presumably a l l m o d i f i e d w i t h a h i g h e r a l c o h o l Our a n a l y s i s has shown LIX 622 to be 5 t e r t d o d e c y l 2 h y d r o x y s a l i c y l -aldoxime w i t h t r i d e c a n o l as m o d i f i e r and a k e r o s i n e d i l u e n t .

Compounds of the v e r y s i m i l a r formulas proposed by Henkel and ICI/Acorga are the s u b j e c t s of a mutual law s u i t by these companies i n the USA. Recent i n f o r m a t i o n i s that t h i s case has i n f i r s t i n s t a n c e been won by I C I . The consequences of t h i s r e s u l t cannot e a s i l y be estimated.

40 Acorga P 17 2-hydroxy-5-tert-nonylphenyl b e n z y l ketoxime

T h i s product has o n l y been a v a i l a b l e f o r a s h o r t time. I t was comparable to SME 529 w i t h respect to pH f u n c t i o n a l i t y , but was slower i n a c t i o n . I was superseded by the P 5000 range.

3.2 H y d r o x y q u i n o l i n e d e r i v a t i v e s Kelex 100/120

Base compound:

41 7 - ( l - e t h e n y l - 3 , 3 , 5 , 5 - t e t r a m e t h y l h e x y l ) - 8 - h y d r o x y q u i n o l i n e

This i s a very s t r o n g and f a s t reagent. The s t r e n g t h of the copper complex makes m o d i f i c a t i o n f o r improved s t r i p p i n g necessary. A s h l a n d / S h e r e x ^ a v e achieved t h i s by b l e n d i n g the pure compound ( s o l d as Kelex 100) w i t h nonylphenol. Thus, a blend of 20 % Kelex 100 and 80 % nonylphenol was s o l d as Kelex 120.

The products have never a t t a i n e d a good p o s i t i o n i n the market, and have now been withdrawn. They had b a s i c a l l y two drawbacks.

F i r s t l y , as an " o x i n e " d e r i v a t i v e the base compound i s not very s e l e c t i v e , and w i l l complex many metals. E s p e c i a l l y i n the area of copper w i n n i n g , where s e l e c t i v i t y over F e3 + i s very i m p o r t a n t , the K e l e x reagents have

3+ . 4; problems. "Oxine" complexes w i t h Fe are stronger than those w i t h copper,

and the same i s probably t r u e f o r the complexes w i t h the Kelex reagents. 2+ 3+

The s e l e c t i v i t y obtained f o r Cu over Fe i n the p r a c t i c a l use of Kelex i s t h e r e f o r e of a k i n e t i c n a t u r e , i n s t e a d of thermodynamic, as w i t h the hydroxy-oximes.

Secondly, the b a s i c q u i n o l i n e n i t r o g e n tends to form a s a l t w i t h s u l f u r i c a c i d used i n s t r i p p i n g . This n e c e s s i t a t e s an e x t r a o p e r a t i o n to recover the reagent a f t e r copper s t r i p p i n g .

3.3 Diketone reagents LIX 54 43 Presumably l - ( 4 - a l k y l p h e n y l ) - 4 , 4 , 4 - t r i f l u o r o - 1 , 3 - d i o x o b u t a n e — CH„ C CF, 2

I f

T h i s product has been developed e s p e c i a l l y f o r ammoniacal l i q u o r s and i s presumably being used i n I m p e r i a l Smelting P r o c e s s e s ' p l a n t i n Avonmouth (UK). The advantage of d i k e t o n e reagents i n general i s t h e i r very low ammonia c o - e x t r a c t i o n .

A p p l i c a t i o n of d i k e t o n e reagents f o r e x t r a c t i o n of copper from a c i d i c l i q u o r s i s not f e a s i b l e , because under such c o n d i t i o n s the r a t e of r e a c t i o n i s v e r y slow.

K e l e x used to be a r e g i s t e r e d t r a d e mark of Ashland O i l Comp. T h e i r mining chemicals b u s i n e s s was r e c e n t l y taken over by S c h e r i n g . The products are s o l d under the Sherex l a b e l .

Hostarex DK 16

Presumably l - ( d i - i s o p r o p y l p h e n y l ) - 1 , 3 - d i o x o b u t a n e ^

i s o - C3H7

i s o - C3H7

C CH2 C CH3

No p r a c t i c a l uses of t h i s product a r e known. As LIX 54, i t i s e s p e c i a l l y recommended f o r ammoniacal l e a c h l i q u o r s .

4. C h e l a t i n g reagents without present or past commercial s t a t u s In the course of the years some reagents have been proposed, mainly by General M i l l s Inc/Henkel, which have never achieved even a temporary commercial s t a t u s . Two of these are d i s c u s s e d b r i e f l y below.

LIX X18A 39 An a l i p h a t i c hydroxy-oxime w i t h formula R' C OH N OH

i n which presumably R = R" = n-C^Hg and R' = n-CgH^. (See a l s o paper B 3 i n p a r t two of t h i s t h e s i s ) . This reagent was not s p e c i f i c a l l y designed f o r copper e x t r a c t i o n , but r a t h e r f o r c o b a l t / n i c k e l s e p a r a t i o n from s u l f a t e medium. I t has never been a s u c c e s s , p r o b a b l y m a i n l y because of the c o b a l t problems a l r e a d y d i s c u s s e d .

45 LIX 34, an 8 - s u l f o n a m i d o q u i n o l i n e d e r i v a t i v e of formula

HN-SO,

I t i s o u t s t a n d i n g i n i t s v i r t u a l l y t o t a l i r o n r e j e c t i o n , but i s slow and could not be a c c e l e r a t e d w i t h the common a c c e l e r a t o r s .

Hostarex i s a r e g i s t e r e d Hoechst trademark.