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t lydrometal lurgy 29 ( 1992 ) 1-45

Els e v ie r Sc ie nc e Pub l i s he r s B .V., Am s te r da m

he leaching o f sulphide m inerals in ch loride

m e d i a

J.E. Du trizac

M ineral Sciences Laboratories CANM ET Energ y M ines and Resources Canada Ottawa Ont.

Canada

(Rev ised version accepted N ovem ber 15, 1991 )

ABSTRACT

Du tr izac, J .E., 1992. The leaching of sulphide minera ls in chlor ide me dia. In: W.C. Coop er and D.B.

Dreis inger (E ditors) , Hy drom etallurgy, Theo ry and Practice . P roceedings of the Ernest Peters In-

te rna t iona l Sympos ium. ttydrometailurgy 29: -45.

Recent s tudies on ~he ferr ic chlor ide and cupric ch lor ide leaching ofchalc opy rite , galena and sphal-

er ite are reviewed. A lthough the chlor ide leaching ofcha lcopy rite concentrates has been proven at the

dem onstra tion plant scale , the leaching reaction is dif f icult . In contrast , galena dissolves rapidly in

FeCI.a me dia, an d both the leaching rate and lead solub ili ty increase s ignificantly with increasing chlo-

r ide concentration. The hydrometallurgical treatment of lead concentrates seems to be technically

feasible. The sph alerite leaching rate is strongly affected by its solid solution iron conten t, and leach-

ing processes for iron-r ich zinc concentrates could probably be developed. T he imp ortance of inter-

m ediate sulph ide phases and insoluble reaction prod ucts on the leaching of sulphides is discussed. In

addition , i t is postulated that a t least par t of the elemental sulp hur reaction produ ct is formed v ia the

oxidation of dissolved HaS. The ab ili ty of chlor ide leaching processes to generate e lemental sulp hur

while leaving pyr ite largely unaffected m akes them especially useful tbr the treatm ent of pyr it ic com-

plex sulphides. Th us, recent chlor ide leaching technologies for complex sulphides are a lso reviewed.

I N T R O D U C T I O N

T he l each ing o f cop per from su lph ide ore d epos i t s occu rs natura lly; a s ear ly

as 1086 C hinese m eta l lurg i s ts were recover ing copper from the natura l dra in -

age waters o f such dep os i t s [ l ] . S im i lar operat ions w ere carr ied out on a large

sca le as ear ly as 1737 to ex trac t copper from the ac id waters a t R io Tin to

Spa in . Natura l weather ing processes l iberated both copper and i ron from the

c o p p e r -b ea r i n g p y r it e o re s a n d th e c o p p e r w a s r e c o v er e d b y c e m e n ta t i o n o n

iron . Subse quen t natura l evapo rat ion o f the so lu t ions in the stream bed s dur-

ing the dry season a l low ed ferrous su lphate to be recuperated as a by-produ ct .

Cor r e s ponde nc e to : J .E . Du t r i z a c , M ine r a l Sc ie nc e s La bo r a to r i e s , CANM ET, Ene r gy , M ine s

a nd Re s ou r c e s Ca n a da , 555 Boo th S t r e et , O t t a wa , On t . K I A 0G l , Ca na da .

030 4 - 3 86X /92 /$0 5 .00 © 1992 E l se v ie r Sc ie nc e Pub l i s he r s B .V. Al l r igh t s r e s er ve d .

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2 J E DUTRIZAC

Large-scale heap leaching of calcined ore began in 1876, and the heap leach-

ing techn ique was soon ex tend ed to un roas ted, low-grade pyri tes [2 ] . Th e

leaching of metal l ic gold in cyanide media to prepare solut ions sui table for

gold e lec tropla ting has been em ployed s ince the mid-19th century . In 1887-

1888, M acA rthur and the two Forrest brothers extende d the cyanide leaching

technique to low grade gold ores and the ta i l ings from gold gravi ty circui ts

[3 ] . M ost ini t ia l app licat ions used vat leaching. Today, vario us cyan ide

leaching techniques t rea t a roun d 500,000,000 t / y r of ore , averaging about 5

ppm Au, to prod uce a ppro xim ately 2,500 t of gold. This is certainly the larg-

est single applicat ion of m od ern leaching technology [ 4 ] .

At abou t the sam e t ime as the cyanide p rocess w as bei~;g deve loped , Bayer

discovered tha t a luminum could be ext rac ted f rom bauxi te by leaching in

NaOH media unde r p ressure and tha t pure a luminum hydrox ide cou ld be

prepared by seeding the cooled pregnant solut ion. This discovery la id the

foundat ions o f pressure- leaching technology and a lso paved the way for the

rapid expansion of the electrolyt ic a lum inu m indus try [ 5 ] . Today , the Bayer

process t reats abo~,t 90,000,000 t /y r ofb aux ite , co ntaining approx imately 40%

AlaO3 making this the largest single applicat ion of pressure leaching

technology.

Vat leaching and heap leach ing meth od s w ere widely used to reco ver cop-

per from o xide ores during the 19th and ea rly 20th centuries. Th e solubi l ized

copper was recovered ei ther by cem enta t ion on iron or by direc t e lectrolysis

[ 6 ] . As meth od s to extract co ppe r selectively from the p regn ant so lut ions did

not exist until recently, early op era tion s w ere restric ted to relatively high-grade

ores or to ores having low soluble iron conten ts. W ith the adv ent of mod ern

solvent extract ion technologies, this constraint has been removed, and the

leach-s olven t extraction-electr ,~w inning process is widely used to t reat ev en

low grade oxidized copper ores. Current ly, aro un d 10% of the w orld 's copper

product ion o f 9 ,000,000 t /y r or ig ina tes from leaching opera t ions , and in the

U.S.A. i t is as high as 25%. Short ly after the tu rn of the century, bo th carno ti te

and pi tchblende ores were be ing leached for uran ium an d /o r radiu m produc-

t ion [ 7 ] , and these leaching techn iques w ere develope d into the soph ist icated

method s which now account for al l the wor ld 's uranium prod uct ion of 40,000

t /yr .

The diversi ty, scope and ingenuity of the e arly leaching processes are per-

haps surprising. Equally surprising is the fact that these same processes,

essent ial ly unal tered in principle , current ly account for most of the world 's

product ion of Au, AI and U. I t i s a l so remarkable tha t most of the above

leaching processes a re based on oxidized feeds and tha t mo st employ low

cost H2SO4 or N aOH med ia . Ear ly e ffor ts were m ade to leach the com m on

base metal sulphides directly, but the resul ts w ere disappoint ing . Th e need to

supply la rge amounts of oxidant for the oxida t ion of the sulphide ion was

diff icul t in an era lacking high shear mixing and tonnage oxygen. For eco-

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L E C H I N G S U L P H I D E M I N E R L S I N C H L O R I D E M E D I

3

n o m i c r e a s o n s , t h e p r a c t i c a l c h e m i c a l o x i d a n t s f o r b a s e m e t a l s u lp h i d e s w e r e

l i mi t ed t o f e r r i c i on and a i r . I n i t i a l s t ud i es s howed t ha t f e r r i c s u l pha t e s o l u -

t i ons g ave l owe r leach i ng r a t e s t han f e r ri c ch l o r i de m ed i a [ 8 ] , bu t e f f o r t s t o

u s e h o t c o n c e n t r a t e d F e C l s - H C l m e d i a r e s u l t e d i n s e v e r e e q u i p m e n t c o r r o -

s i o n a n d o t h e r p r o b l e m s w h i c h w e r e n o t w e l l u n d e r s t o o d a t t h e t i m e . A s a

r e s u lt , th e l e a c h i n g p r o c e ss e s d e v e l o p e d f o r su l p h i d e o r e s u s u a l ly i n v o l v e d a

r o a s ti n g s te p t o c o n v e r t t h e s u l p h id e to a n o x i d e . T h u s , th e d e v e l o p m e n t o f

t he e l ec t r o l y t i c z i nc p r oces s was bas ed en t i r e l y on r oas t ed s pha l e r i t e f eeds

[91.

T h e b r i e f h i s to r i c a l r e v ie w p r e s e n t e d a b o v e i n d i c a t e s t h a t l e a c h in g i s a m a -

j o r h y d r o m e t a l l u r g i c a l a c t iv i ty w h i c h is l ar g el y b a s e d o n o x i d i z e d f ee d s.

T h e a b u n d a n t s u l p h i d e o r e s o f c o p p e r , l e a d a n d z i n c a r e tr a d i t io n a l l y t r e a t e d

by r oas t i ng and s m e l t i ng t echno l og i es. A l t hough t hes e t echno l og i es have m an y

a d v a n t a g e s , th e y a r e n o t w i t h o u t t h e i r i n h e r e n t l im i t a t i o n s . C u r r e n t e n v i r o n -

m e n t a l r e g u l a ti o n s d e m a n d n e a rl y c o m p l e t e S O2 c a p t u r e in a n y p y r o m e t a l -

l u r g i ca l ope r a t i on . A l t hough t he t echno l ogy t o cap t u r e SO2 ex i s t s , i t s i mp l e -

m en t a t i on c om m on l y r e s u lt s i n h i gh cap i ta l and ope r a t i ng cos ts . I t i s e s t i m a t ed

t h a t i t c o s t s a n a d d i t i o n a l U S $ 0 . 1 7 / k g C u f o r A m e r i c a n c o p p e r s m e l t e r s t o

co nf o r m t o cu r r e n t SO2 em i s s i on s t a nd a r d s [ l 0 ] . A f u r t he r d i f fi cu l ty i s t ha t

t h e m a r k e t in g o f th e H SO4 is c o u p l e d w i th t h a t o f t h e m e t a l ; d e p e n d i n g o n

t he geo gr aph i ca l l oca t i on o f t he p l an t , t he l i nkage can c r ea t e m a j o r d i f f icu l -

t ie s . Lad l e t rans f e r s , launder s~ e t c ., a ll c r ea t e i n - p l an t hyg i en e p r ob l em s w hi ch

are t echnica l ly d i f f i cu l t to r esolve .

L e a c h i n g t e c h n o l o g i e s f o r s u l p h i d e f e e d s o ff e r m a n y p o t e n t i a l a d v a n t a g e s

ov er s m e l t i ng p r oces s es [ l l , 12 ] , an d t hes e i nc lude :

( l ) F o r m a t i o n o f e l e m e n t a l s u l p h u r o r s o lu b l e s u l p h a t e s u ch th a t S O2

e m i s s io n s a r e e n t i r e l y a v o i d e d .

( 2 ) Ab i l i ty t o tr ea t l ow g r ade o r h i gh l y comp l ex f eeds .

( 3 ) P y r i te is o f t e n i n e r t .

( 4 ) V i ab l e a t e i t he r a s ma l l o r l a r ge sca le .

( 5 ) P o t e n t i a l f o r lo w e r c a p it a l c o s t s a n d i n c r e m e n t a l p l a n t a d d i t i o n s .

( 6 ) P o t e n t i a l ly e a s i e r t o i n s t r u m e n t a n d c o n t r o l .

( 7 ) G r e a t e r f l e x ib i li ty in p r o d u c t p u r i t y a n d f o r m .

Se t aga i ns t t hes e s t r eng t hs a r e s eve r a l d i s adv an t ag es [ 11 ]

( 1 ) T h e n e e d t o d e m o n s t r a t e a s i g n i f i c a n t a d v a n t a g e o v e r e x i s t i n g

t echno l og i es .

( 2 ) T h e y a r e o f t e n e n e r g y in t e n s i v e b e c a u s e o f t h e h i g h s p e c if ic h e a t o f

w a t e r a n d t h e u s e o f e le c t r o c h e m i c a l t e c h n o l o g ie s .

( 3 ) W a t e r p o l l u t i o n p r o b l e m s .

( 4 ) R e c o v e r y o f A u a n d A g b y - p r o d u c t s is d i ff ic u l t a n d r e q u i r e s a d d i t i o n a l

p r oce s s i ng s t eps .

S t e a d y p r o g r e s s, h o w e v e r , i s b e i n g m a d e o n t h e l e a c h i n g o f su l p h i d e f e ed s ,

a n d m a n y o f t h e t r a d i t i o n a l d i f f ic u l ti e s a re b e i n g o v e r c o m e . F o r e x a m p l e , th e

c o r r o s io n p r o b l e m s w h i ch p l a g u e d t h e e a rl y d e v e l o p m e n t o f m a n y l e a ch i n g

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4 J E DUTRIZAC

p r o c e s se s h a v e b e e n l ar g el y r e s o l v e d t h r o u g h t h e u s e o f e n g i n e e r e d p l a st ic s

a n d t h o u g h t fu l ly s e le c te d m e t a l li c a n d c e r a m i c c o m p o n e n t s . A l th o u g h c o m -

m e r c i a l l e a c h i n g p r o c e s s e s f o r s u l p h i d e f e e d s a r e l i m i t e d i n n u m b e r , R & D

ac t i v i t ie s r em a i n r e l a t ive l y s tr ong . Th us , t he p u r p os e o f t h i s r ev i ew i s t o s u r-

v e y t h e r e c e n t d e v e l o p m e n t s a s s o c i a t e d w i t h s u l p h i d e l e a c h in g , a n d e s p e c ia l ly

t he us e o f ch l o r i de m ed i a f o r s uch l each i ng p rocess es~

CHLORIDE LE CHING PROCESSES FOR CH LCOPYRITE CONCENTR TES

N u m e r o u s l e a c h in g p ro c e s se s h a v e b e e n a d v o c a t e d f o r c o p p e r s u l p h i d e o re s

a n d c o n c e n t r a te s . D u t r iz a c a n d M a c D o n a l d [ 8 ] h a v e r e v i e w e d t h e e a r l y lit-

e r a t u r e o n t h i s s u b je c t. F e r r ic c h l o r i d e o r c u p r i c c h l o r i d e p r o c e s s i n g o f c o p p e r

c o n c e n t r a t e s o f f e r s s e v e r a l p o t e n t i a l a d v a n t a g e s r e l a t e d t o s u l p h u r c o n t r o l ,

m e t a l p u r i f i c a t i o n / r e c o v e r y o p t i o n s a n d p r o c e s s e c o n o m i c s . D e s p i t e t h e

p o t e n t i a l a d v a n t a g e s o f t h e c h l o r i d e p r o c e s s in g r o u t e f o r c o n v e n t i o n a l c h a l -

c o p y r i t e - r i c h c o p p e r c o n c e n t r a t e s , t h e t e c h n o l o g y r e m a i n s v e r y m u c h i n t h e

de ve l op m en t a l s tage . Neve r t he l e s s , s ign i f i can t p r ogr es s has been m ad e [ 12 ] ,

a n d s o m e o f t h e r e c e n t a d v a n c e s i n t h is a r e a a r e n o t e d b e lo w .

A b o u t 2 0 y e ar s a g o, b o t h t h e U .S . B u r e a u o f M i n e s [ 1 3 ] a n d M I N T E K

[ 1 4 ] d e v e l o p e d r e la t iv e l y s i m p l e f lo w s h e e t s fo r t h e t r e a t m e n t o f c h a l c o p y r i t e

c o n c e n t r a te s . L e a c h i n g w a s c a r r i e d o u t in a s in g l e s ta g e n e a r t h e b o i l i n g p o i n t

o f t h e f er ri c c h l o r i d e l e a c h i n g m e d i u m ( a r o u n d 1 05 ° C ) ; h i g h c o p p e r e x tr a c -

t i o n s w e r e r e a l i z e d b y g r i n d i n g t h e c o p p e r c o n c e n t r a t e t o 9 5 % - 3 2 5 m e s h

a n d b y p r o l o n g i n g t h e l e a c h in g t im e u p t o 8 h . T h e i n v e s t ig a t o r s r e c o g n i z e d

t h a t m e t a l r e c o v e r y a n d i ro n d i s p o s a l w e r e k ey f a c to r s. T h e B u r e a u o f M i n e s

e l e c tr o w o n c o p p e r p o w d e r d i r e c t ly f r o m t h e c u p r o u s c h l o r i d e s o lu t io n ', M I N -

T E K r e s e a r c h e r s u s e d s o lv e n t e x t r a c ti o n w i t h L I X - 6 4 N t o c o n v e r t t h e c u p r ic

c h l o r id e t o a s u lp h a t e m e d i u m f o r c o n v e n t i o n a l e l e c t r o w i n n i n g . B o t h re -

m o v e d i ro n b y a n o x i d a t i o n - h y d r o l y s i s r o u t e . F i n e g r i n d in g w a s c o n s i d e re d

a n e c e s s a ry f i rs t s te p i n b o t h p r o c e ss e s. A n e c o n o m i c e v a l u a t i o n o f t h e B u r e a u

of Mi nes ' p r oce s s [ 15 ] i nd i ca t ed cap i t a l cos t s ( 1975 US ) fo r an o u t p u t o f

5 4 ,0 0 0 t C u / y r o f 2 8 , 0 0 0 , 0 0 0 a n d o p e r a t in g c o s ts o f 0 . 2 2 / k g C u .

C om i nc o [ 16 ] ca r r i ed o u t s m a l l sca le t e s t w or k a nd de ve l op ed a f e r ri c ch l o -

r id e p r o c es s f o r c o p p e r c o n c e n t r a t e s w h i c h w e r e g r o u n d t o 9 7 % - 3 2 5 m e s h .

L e a c h i n g w a s c a r r ie d o u t c o u n t e r c u r r e n t l y i n tw o s ta g e s, b o t h o f w h i c h o p e r -

a t e d at 9 5 ° C . R e t e n t i o n t i m e s o f 9 - 1 2 h w e re r e q u i r e d t o a c h i e v e 9 9% C u

e x t r a c t i o n f r o m s o l u t i o n s c o n t a i n i n g 5 0 - 2 0 0 g / l F e C l 3 . T h e l o n g r e t e n t i o n

t im e s w e r e p r o b a b l y a c o n s e q u e n c e o f t h e 9 5 ° C t e m p e r a t u r e u s e d . A s w ill b e

s een la t e r, t he l each ing o f cha l co pyr i t e i s s t rong l y t em pe r a t u r e dep end en t , an d

s ig n i fi c a n t a d v a n t a g e s a r e g a i n e d b y l e a c h in g n e a r t h e s o l u t io n b o i l i n g p o i n t

( i. e. , > 1 05 ° C ) . T h e s p e n t i r o n c h l o r i d e l e a c h s o l u t i o n w a s r e g e n e r a t e d u n d e r

p r e s su r e a t 1 3 5 - 1 6 5 ° C , a n d e x c e s s i ro n w a s p r e c i p i t a t e d a s F e 2 0 3 i n t h e i r o n

o x i d a t i o n s t e p . I n t h e C o m i n c o p r o c e s s , t h e h o t - f i l t e r e d l e a c h s o l u t i o n w a s

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LEACHING SULPHIDE MINERALS IN CHLORIDE MEDIA

t r e a t e d w i t h e x c es s c o p p e r m e t a l t o r e d u c e a ll t h e c o p p e r t o t h e c u p r o u s s t a t e .

P u r e c u p r o u s c h l o r i d e c ry s t a ls w e r e f o r m e d o n c o o l i n g t h e s o l u t i o n . C o p p e r

p o w d e r w a s p r o d u c e d b y h y d r o g e n r e d u c t i o n o f t h e c u p r o u s c h l o r id e , w i th

t h e e v o l v e d H C g a s b e i n g u s e d in t h e i r o n o x i d a t i o n a u t o c l a v e . T h e C o m i n c o

p r o c e s s r e c o g n i z e d t h e n e e d t o m a k e h i g h p u r i t y c o p p e r d i r e c t l y , a n d a l s o

s o u g h t t o a v o i d t h e h i g h c o s ts o f e le c t r o w i n n i n g .

A f t e r e x p e r i m e n t i n g w i t h c o p p e r e l e c t r o w i n n i n g d i r e c t l y f r o m a n i r o n

c h l o r i d e le a c h s o l u ti o n , t h e C y p r u s M e t a l l u r g ic a l C o r p . ( C y m e t ) d e v e l o p e d

a p r o c e s s b a se d o n a tw o - s t ag e c o u n t e r c u r r e n t l ea c h in a F e C I 3 - C u C I 2 - N a C I

m ed iu m [ 17 ,18 ] . Th e co nce n t r a t e was l each ed fo r 3 h i n each s t age a t 98 °C

t o a c h i e v e a c o p p e r r e c o v e r y o f 9 9 % . T h e p r e g n a n t s o l u t i o n c o n t a i n e d 1 0 0 -

1 50 g / l C u a n d 1 1 0 - 1 6 0 g / l F e . A f : e r t h i c k e n i n g a n d f i l t ra t i o n , t h e s o l u t i o n

w a s v a c u u m c o o l e d t o a r o u n d 4 0 ° C t o c r y s ta l li z e a b o u t h a l f o f t h e c o p p e r a s

CuCI . The CuCI c rys t a l s were cen t r i fuged , washed , d r i ed , and then r educed

wi th H2 in a f l u id i zed bed roas t e r a t 500°C. Sand was used in t he f l u id bed

r e a c t o r t o p r e v e n t s i n t e r in g o f t h e ch a r g e , a n d t h e C u - s a n d p r o d u c t w a s s u b -

s e q u e n t l y m e l t e d to y i e l d b a r c o p p e r . T h e s p e n t l e a c h in g s o lu t i o n c o n t a i n i n g

a p p r o x i m a t e l y 5 0 g / l C u a n d 1 1 0 - I 6 0 g / l F e w a s r e o x i d i z e d a t 9 5 ° C w i th 0 2

and HCI f rom the f lu id bed r eac to r . A bou t 3 h was r equ i r ed to r eox id i ze the

s o l u t i o n a n d c o n t r o l i r o n b y t h e p r e c i p i t a t i o n o f s o d i u m j a r o s i t e a n d fl

F e O . O H . T h e C y m e t p r o c e s s w a s e v a l u a t e d i n a s m a l l c o n t i n u o u s p i l o t p l a n t

t r e a t i n g a b o u t 2 0 t / d a y o f c h a l c o p y r i t e c o n c e n t r a t e . A ll p a r ts o f t h e p r o c e s s

were t echn ica l ly f ea s ib l e and a l l co r ros ion p rob lems were appa ren t ly ove r -

com e . How ever , s i l ve r was ex t ens ive ly so lub i l ized in t he l each ing c i rcu i t , and

unfo r tuna te ly , m uch o f t he s i lve r r epo r t s i n t he CuC c rys t a l s and , t hence , t o

the me ta l l i c coppe r . The s imi l a r behav iour o f s i l ve r and coppe r i n ~ :oncen-

t r a t ed ch lo r ide m ed ia i s a con t inu ing con ce rn in all cop pe r l each ing p rocesses.

The Cymet p rocess demons t r a t ed on a p i lo t s ca l e t ha t h igh coppe r l each ex -

t r ac t ions were ach ievab le and tha t co ppe r cou ld be success ful ly r ecove red f rom

c h l o r i d e m e d i a b y n o n - e l e c t ro w i n n i n g p r o ce s se s . T h e C y m e t p i l o t p l a n t w a s

c losed in 1982 , and the p rocess has no t been deve loped fu r the r s ince tha t

t ime

T h e c h l o r i d e h y d r o m e t a l lu r g i c a l p r o c e s s f o r t r e a ti n g c h a l c o p y r i t e c o n c e n -

t ra t e s d e v e l o p e d b y th e D u v a l C o r p o r a t i o n a n d k n o w n a s th e C L E A R p r o ce s s

( C o p p e r L e a c h i n g E l e c t r o w i n n i n g a n d R e c y c l e ) o p e r a t e d f o r a p e r i o d o f s ix

y e a r s a n d u l t i m a t e l y a t t a i n e d a n o u t p u t o f 1 00 t C u / d a y [ 1 9 -2 1 ]. A s s h o w n

in F ig . 1, a two- s t age cou n te rc u r r e n t l each w as used to ach ieve h igh ove ra l l

cop per ex t rac t ions . Th e f i r s t s tage was car r ied o ut a t 105 °C w i th 20 g / I CuC I : ,

4 g / l F e C I 3 , 8 0 g / l N a C I a n d 4 4 g / I K C I . D u r i n g p r o c e s s d e v e l o p m e n t , i t

b e c a m e a p p a r e n t t h a t h i gh t o ta l c h l o r id e c o n c e n t r a t i o n s a l l o w e d h i g h e r l e ac h

t e m p e r a t u r e s t o b e u s e d w i t h c o n c o m i t a n t l y h i g h e r e x t r a c ti o n s . T h e p r i n c i p a l

l each ing r eac t ions were f e lt t o be :

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LE CHING SULPHIDE MINER LS IN CHLORIDE MEDI 7

a co l l e ct ion be lt . A t the anode , h a l f o f the cu p rous ions a re ox id ized to cup r ic

ch lor ide , which is recyc led to the second-s tage leach . The re levant reac t ions

are:

C u + + e - -- C u °

Cu + _ e-_ ~C u 2+

( c a t h o d e ) ( 7 )

( a n o d e ) ( 8 )

T h e C L E A R d e m o n s t r a t i o n p l a n t s h o w e d t h a t c h l o r id e l e ac h in g p r o ce s se s

cou ld ach ieve h igh coppe r ex t rac t ions f rom cha lcopyr i t e concen t ra te s wi th -

ou t SO2 emis s ions. Few co r ros ion p rob lem s were encoun te red in the l e ach ing

an d m ate r ia ls ha ndl in g par ts o f the p lan t ; sk i ll fu l use of f ib re -re inforced p las -

t i c s and t i t an ium adequa te ly con ta ined the ch lo r ide so lu t ions . Al though the

e lec t rowinn ing reac t ion i s supposed to gene ra te on ly Cu and

C u C 1 2 . s o m e

Cl2

gas was evolved . This c rea ted in -p lan t hygiene problems as wel l as ex tens ive

co r ros ion o f the ce llhouse bu i ld ing . Ca re fu l con t ro l o f the CuC l concen t ra t ion

and the e lec t ro lys is paramete rs a re necessary to avoid Cl2 genera t ion . Fur-

the rm ore , the e lec t row on coppe r c rys tal s con ta ined m os t o f the s i lve r l e ached

f rom the concen t ra te , and e f fo r t s to remove the s i lve r s e lec t ive ly f rom the

leach l iquors were no t success fu l . The copper produc t the re fore required fur-

ther re f in ing . On the o ther hand , the e lec t rowon copper c rys ta ls were re la -

t ive ly coarse , and c ou ld be han d led a nd m e l ted w i thou t s ign if i can t ox ida t ion .

The j a ro s i t e - Fe O .O H -su lph ur l each re s idue was d iges ted wi th a sma ll am ou n t

o f H2SO4 to fo rm an e f fec tive so il cond i t ione r ( I ron -S u l ) fo r the na tu ra l ly

a lka l ine so ils in the A m erican south w es t [22 ] .

T h e C L E A R d e m o n s t r a t i o n p l a n t is a m a j o r m i le s to n e i n t h e d e v e l o p m e n t

o f ch lo r ide l e ach t e chno log ie s. T he l arge con t inuous s ca le o f ope ra t ion dem -

on s t ra te d the genera l v iab i l ity of the ch lo r ide rou te for a re frac tory su lphide

such as cha lcopyr i te . The process ing cos ts were US 0 .6 0 /k g Cu in the ea r ly

1980 ' s , and such cos ts were compet i t ive wi th those then charged by loca l

sme l te r s . The CLEAR demons t ra t ion p lan t a l so i l lu s t ra ted the need fo r fu r -

the r work on so lu t ion pu r i f i c a t ion and by -p roduc t r e cove ry , and fo r be t t e r

m e tho ds o f con t ro l l ing the anode and ca thod e reac t ions in ch lo r ide e lec tro -

w inn ing c ircu it s. Th e C LE AR d em on s t ra t io n p lan t was c lo sed in 1982, p re-

sum ab ly because o f low coppe r p r ice s.

M inem e t Reche rche p i lo ted

a CuCI2

leach ing process which addressed som e

of the p rob lem s iden t i f i ed in the Cy m e t and CLE AR op e ra t ions [ 23 ]. Leach -

ing is ca rr ied ou t counte rcurren t ly in two s tages a t about 100°C us ing a 3 h

re ten t ion t ime in each s tage. The so lu t ion con ta in s 50 g / l Cu E+ and 250 g / l

NaC l . Cu ex t rac t ion i s m ore than 98% and the re is a lso fo rma t ion o f , p red om -

inant ly e lementa l , su lphur . The c la r i f ied pregnant so lu t ion is t rea ted by so l -

ven t ex t rac t ion w i th LIX-65N . O xygen is in jec ted in to the so lu t ion to conve r t

the co ppe r to the C u E+ s tate , which is the spec ies ex t rac ted . T he ac id re leased

by the ex t rac t ion o f the Cu E+ ion is u t i l ized in the C u + oxid a t ion reac t ion .

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8 J E DUT RIZAC

The loaded o rgan i c i s s c rubbed t o r emo ve ch lo r ide and is t hen s t r ipped w i th

H2SO4 to yie ld a convent iona l CuSO4-H2SO4 e lec t rowinning so lu t ion . Si lver

is not ex t rac ted wi th the Cu 2+ ions and accu m ula tes in the ra f fina te . Presum -

ably , it could be recove red as a s i lver - rich prod uct f rom the so lu t ion , b ut de-

ta il s of the s i lver recovery opt ion s h ave not b een presented .

The p r inc ipa l adv an t age o f t he M inem et appro ach is t ha t h igh pur i t y cop-

per is recovered in com pact form f rom a su lphate e lec tro ly te us ing wel l-proven

technologies . Al though the theore t ica l energy requi rement for the p la t ing of

copper f rom a cupr ic su lphate so lu t ion i s cons iderably h igher than tha t for

depo s i t ion f rom a cuprous ch lor ide e lec tro ly te , the m eta l prod uc ed is of a

h igher pur i ty . U nless ma jor ad van ces a re m ad e in ~ i,e pur i f i ca t ion of chlor ide

leach so lu t ions an d in the cont ro l of the qua l i ty o f the e lec t ro lys is produ ct ,

the t rans i t ion to a copper su lphate e lec t ro ly te may be a prac t ica l so lu t ion to

the coppe r q ua l i ty a nd s i lve r r ecove ry p rob l em s i n ch lo ride hydrom eta ll u rgy .

In a somew ha t s imi l a r ve in , the H enke l Corpo ra t i on [24 ] has deve loped a

mixed o rgan i c e : a r ac t an t t o t r ans f e r coppe r f rom a ch lo r ide leach ing med ium

to a conven t iona l

CuSO4 H2SO4

e lec t rowinning so lu t ion . In pr inc ip le , the

solvent ext rac t ion c i rcui t can be incorpora ted in any fe r r ic chlor ide l eaching

process pro vid ed tha t an excess of Fe 3+ is ma inta ine d in the preg nan t so lu-

t ion to ensure tha t a ll the co ppe r i s present as CuCl2. Such con d i t i ons can be

easi ly achieved in any o t the processes descr ibed abo ve by adjus t in g the ra t io

o f l i x iv i an t t o concen t r a te . T he f ir st com po nen t (d i- isodecy l e st e r o f py r id ine

dicarboxyl ic ac id) of the m ixed organic , ex t rac t s the neut ra l CuCI2 species

f rom the concent ra ted ac id ic l eaching medium. The reagent i s se lec t ive for

copper such tha t mos t impur i t i es , inc luding s i lver , remain in the ra f f ina te .

Presumably , a s i lver - r ich product can be prepared f rom such a so lu t ion by

cem en tat io n, s ta tphide pre cipi ta t ion, e tc. After s i lver recovery, the raff inate is

subjec ted to ox ida t ion hydrolys i s to regenera te the FeCI3 l ix iv iant and to pre-

c ip i ta te excess i ron . Chlor ine gas genera ted e l sewhere in the process i s the

pr inc ipa l oxidan t . Th e copper - loaded organic phase i s contac ted w i th a Na OH

solut ion a t pH 2 .2 to wash ou t a ll the chloride . D ue to the c lose pH cont ro l in

th i s ope ra t ion , the copp er i s t ransfer red f rom the f ir s t reagent to the che la t ing

ext rac tant (L 1X 860 ) an d the c hlor ide ions l ibera ted in the process a re al so

removed dur ing wash ing . The aqueous phase f rom the wash ing ope ra t i on i s

d i rec ted to a convent iona l ch lor -a lka l i ce l l to regenera te the NaOH and to

pro vide CI_~ for the i ron o xid at io n s tep. F inal ly, the load ed e xtra ctan t is con-

tac ted wi th spent H,~SO4-CuSO4 e lec t ro ly te to ext rac t the copper as copper

sulphate . U l t imately, the cop per is recovered as high-pu ri ty catho de using, well

es tabl ished cop per e lec t row inning technologies [ 25 , 26 ] .

The gene ra l d i sadvan t ages o f th i s type o f approach a r e well known. T he re

is a need for a la rge so lvent ex t rac t ion op era t ion an d the co ppe r m us t be e lec-

t rowon f rom the h ighe r va l en t cupri c s ta te . F ur the rm ore , i n t he Henke l op -

t ion, there is a req uire m en t fo r a separate elect rolysis s tep to gen erate C12 an d

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LE CHING SULPHIDE MINER LS IN CHLORIDE MEDI 9

NaOH. These gene ra l d i sadvan t ages mus t , however , be we ighed aga ins t t he

s ignif icant benef i ts o f producing c om pact , h igh-pur ity copp er ca thodes as well

as a s i lver by-p roduc t .

A somewha t d i f f e r en t l each ing- so lven t ex t r ac t i on -e l ec t rowinn ing ap -

proa ch i s fo l lowed in the Cu prex p rocess [ 27 , 28 ] . Chalcop yr i te -con ta in ing

concen t r a t e s a r e l eached i n FeCl3 me d ia t o y i e ld e l emen ta l su lphur an d d i s-

so lved C uCl2 . I t is im po r tan t tha t excess FeCl3 i s presen t to en sure tha t a ll the

copp e r is p re sen t i n t he d iva l en t f o rm:

CuFeS2 + 4FeCI3 ~C uC I2 + 5FeCI2 + 2S °

C uF eS , + 3FeCI3 --, Cu CI + 4FeCI2 + 2S °

CuC I + FeCI3 ~ CuCI2 + Fe C b

9 )

lO)

l l )

I t i s wel l es tabl i shed tha l eq . (11) heavi ly favours CuC 2and FeCI2 al-

thou gh there is , of course , an e qu i l ibr ium am ong the v ar ious spec ies [29 ] .

Af ter l iquid-sol ids separa t ion , the so lu t ion i s cooled , t rea ted wi th CaCl2 to

p rec ip i t a t e gypsum and t hen con t ac t ed w i th ACORGA CLX50. Neu t r a l cu -

pr ic chlor ide i s se lec tive ly ext rac ted an d there i s no n eed to adjus t the p H of

the so lu t i on dur ing ex t r ac t ion . Af t e r s c rubb ing to r em ove m inor imp ur i ti e s ,

the load ed organic is s t r ipped wi th water a t 65 °C to produ ce an aq ueous CuCl2

solu t ion con ta in ing > 100 g / l C u 2+. T he so lu t ion i s e lec tro lyzed in the M et -

c lor ce ll orig ina l ly dev elop ed by Tecnicas R eun idas a nd charac ter ized by the

use of a ca t ion-se lec t ive m em bra ne [ 30 ] .

Al thou gh the pr inc ipa l e lec t rode reac t ions a re the depo s i t ion o f cop per

p o w d e r a n d t h e e v o lu t i o n o f C 2 gas, som e o f the cupr ic ion i s a lso reduce d to

the cup rous s ta te. T hus , i t is necessary to oxid ize the ca tholy te and ext rac t the

r ema in ing coppe r i n a s epa ra t e so lven t ex t r ac t i on ope ra t i on ( r e fo rming )

us ing a h igh o rgan i c / aqueous r a t i o . The l oaded o rgan i c f rom the r e fo rming

s tage is mixed wi th the organic feed to the pr inc ipa l so lven t ex trac t ion (S X )

circui t .

Th e C uprex p roces s en joys seve ra l advan t ages . H igh pur i t y coppe r pow der s

a re p roduc ed a t h igh cu r r en t e ff ic ienc ie s (94% ) and w i th an ene rgy consu mp -

t i on o f 2.66 kW h/k g Cu . The s i lve r con t en t o f t he coppe r is < l ppm and , i n

fact , the C uprex process should a l low the recovery of a h igh-grade s i lver by-

product f rom the copper -deple ted ra f f ina te . The SX c i rcui t i s re la t ive ly

s t ra ight forward an d do es not involve in-c i rcui t pH cont ro l . On the o ther han d,

the overa l l f lowsheet is com plex and the ion-se lec t ive me m bra ne cells may be

di f f icu l t to m ainta in in a p lant envi ro nm en t . Cr i ti cs might a rgue tha t the Cu-

prex process suffers a doub le d i sadvan tage : e lec t rowinn ing is car r ied out f rom

the cupr ic s ta te and par t i cu la te cop per i s produ ced. I t is und ers too d, how ever ,

t ha t e f fo r ts a r e be ing m ade t o p roduce rod d i r ec tl y f rom the coppe r pow der s

( t h e C O N F O R M p r o c e s s ) a n d s u c h d e v e l o p m e n t s c o u l d h e l p t o o v e r c o m e

these cr i t ic isms.

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i 0 J E D U T R I Z A C

T h e G r e a t C e n t r a l M i n e s ( G C M ) h y d r o c o p p e r p r o ce s s a ls o p r o d u c e s p ar -

t i cu l a t e copp e r , bu t doe s no t u se so lven t ex t r ac t ion p u r i f i ca t ion [ 31 ] . As wi th

m any ch lo r ide l each ing p rocesses , the i n i t i a l s t ep inv o lves f ine g r ind ing o f t he

c o n c e n t r a t e , t o 8 0 m i n u s 2 8 p m . A s s h o w n i n F i g . 2 , t h e g r o u n d c o n c e n t r a t e

is t h e n l e a c h e d i n a F e C l a - N a C l s o l u t i o n t o e x t r a c t 9 9 o f t h e C u a n d 93 o f

the Ag. Lea ch ing i s ca r r i ed ou t co un te rcu r r en t ly i n two s t ages so tha t t h e p reg -

n a n t s o l u t i o n c o n t a i n s o n l y c u p r o u s c h l o r i d e a n d f e r ro u s c h l o ri d e . I m p u r i t y

con t ro l i s e f f ec t ed by r ecyc l ing pa r t o f t he oxyhydro lys i s i ron p rec ip i t a t e t o

the second- s t age l each . Th e ch lo r ide so lu t ion i s e l ec t ro lyzed in a d i aph ragm

c ell t o y i el d a g r a n u l a r c o p p e r p r o d u c t a n d t o r e g e n e r a t e a p o r t i o n o f t h e F e C l3

l ix iv iant :

C u C I + H + + e - - ~ C u ° + H C I

FeCI2 + HC I-~ FeCI3 + H + + e -

C u C I + H C i -~ C u C I2 + H + + e -

( ca tho de ) ( 12 )

( an od e ) ( 13 )

( an od e ) ( 14 )

A b o u t 8 5 o f t h e c o p p e r is p r o d u c e d i n t h e m a i n e l e c t r o w i n n i n g c e lls , a n d

t h e r e m a i n d e r i s r e c u p e r a t e d f r o m a s t r i p p e r c e ll w h i c h t r e a t s th e c a t h o l y t e

b l ee d f ro m t h e m a i n c e ll s. T h e m a g n i t u d e o f t h e c a t h o l y t e b l e e d i s g o v e r n e d

b y t h e n e e d t o m a i n t a i n t h e i r o n a n d w a t e r b a l a n c e s i n th e c e ll. T h e s o l u t io n

Ir)n

Residue

Ground

opper

C°nc~f~r°

. ] L _ l c o , , ,

. L

== L _ _ _ S L vE R

L E A C H I E L E C T R O W lN N I N G J

~ e s i d u eo r

gold

r ecovery

F ANOLYTE I

~

Copper ,m

roduc t

Fig . 2 . Schem a t ic tl ow shee t f o r t he G r ea t C en t r a l Mi nes G C M ) hyd r ocop pe r p roces s f o r cha l-

copyr i t e con cent ra tes , a f te r [ 31 ].

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L E C H I N G S U L P H I D E M I N E R L S IN C H L O R I D E M E D I

f rom the ano ly te chambers i s sub jec ted to tu rbo -ae ra t ion to regene ra te the

so lu t ioa ; no i ron p rec ip i t a te s in th i s ope ra t ion :

2FeCI2 + ½02 + 2 H C I~ 2FeCI3 + H 2 0 ( 15 )

T he cha lcop yr i te leach process so lub i l izes al l the i ron in the C uFeS2 as well

a s 0 -1 2% o f the i ron p re sen t a s py ri t e. T he excess iron i s r em ove d by oxyhy-

d ro lys is o f a b leed s t ream us ing a W ooda l l D uck ham sp ray roa ste r, and the

res idue is discharged:

2FeCI2

~ ½02

+ 2 H 2 0 - , F e 2 O a + 4H C 1

2 Fe CI3 + 3 H E O - , F e 2 0 3 + 6 H C I

1 6 )

( 1 7 )

Th e G C M process ha s been eva lua ted o n a la rge l abo ra to ry scale . Based on

the labora tory sca le da ta , opera t ing and cap i ta l cos ts for a p lan t t rea t ing 850

t / d ay o f 23% Cu c once n t ra te we re deve loped ; the cos t fo r the ch lo r ide le ach -

i ng r o u t e w a s c o m p a r e d t o t h os e f o r t h e I n c o a n d N o r a n d a s m e l ti n g t e c hn o l -

og ie s. Fo r the pa r t i cu la r s it e cons ide red , the cap i ta l cos t o f the G CM proces s

w a s 1 5 7 , 0 0 0 , 0 0 0 a s c o m p a r e d t o 6 4 , 0 0 0 , 0 0 0 - 1 2 5 , 0 0 0 , 0 0 0 f or t h e t w o

sme l t ing op t ions . The ope ra t ing cos t s o f a l l th ree rou te s we re comparab le .

Th e G C M process remo ves s i lve r f rom the p regnan t le ach so lu t ion wi th so l id

i o d i d e, b u t d e ta i ls o f t h e A g r e m o v a l / r e c o v e r y p r o ce s s h a v e n o t b e e n p u b -

l ished . The GCM process , which is s t i l l be ing deve loped , ach ieves h igh cop-

pe r ex t rac t ions , r e cove rs s i lve r , and p roduces a pa r t i cu la te coppe r p roduc t .

As the p roces s ha s no t been ope ra ted on a con t inuous p i lo t p lan t s ca le , the

qua l i ty o f the coppe r p ro duc t r em a ins unce r ta in . C lea rly , the GC M process is

mos t su i t ed to spec i f i c s i t e s whe re the marke t ing o f H SO4 from a sme l te r

wo u ld be p roh ib i t ive .

CHALCOPYRITE ACTIVATION

T h e a c t iv a t i o n t e c h n i q u e s s u m m a r i z e d i n T a b le 1 c a n b e d i v i d e d i n t o th r e e

general categories : changing the chalcopyri te to other sulphides by ad ding or

rem ov in g Cu , Fe o r S , c a talyz ing the reac t ion wi th t r a ce s o f Ag , and p rom ot -

ing the ra te by f ine g r ind ing an d /o r indu ced l a t ti c e s t ra in . Fo r e conom ic rea -

sons , it i s doub t fu l w he th e r conve r t ing the cha lcopyr i t e to o the r phase s in a

separa te o pera t ion w i ll p ro ve a t t rac t ive . S i lver ca ta lys is seem s to be e ffec t ive

in fe rr i c su lpha te so lu t ions , bu t no t in ch lo r ide m ed ia . In any even t , quan t i -

t a t ive s i lve r recove ry a t low cost wou ld be needed to m ake th i s op t ion com -

merc ia l ly a t t r a c t ive and , a s no ted above , s i lve r recove ry i s a con t inu ing

conce rn in a ll ch lo r ide l e ach ing p roces se s deve loped to da te .

C onv en t ion a l f ine g r ind ing cu r ren t ly g ives good copp e r ex t rac t ions in ac -

cep tab le re ten t ion t imes . F ine r g r ind ing in tower mi l l s , fo r example , cou ld

fu r the r a ccele ra te bo th the ra te and the ex ten t o f l e ach ing and cou ld p rov id e

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  2 J.E. DUTRIZAC

T A B L E

Act iva t ion m e thods fo r cha lcopyri t e

Me t h o d Re f er en c es Co mm e n t s

Ac t iva t ion wi th 32 ,33

su lphur

Ac t iva t ion wi th 34

covelli te

Act ivat ion with 35

copper

Act ivat ion with 36,37

iron

Act ivat ion with 38

carbon

Act ivat ion by 39

su lphur r emova l

with H2

Activat ion by 40

su lphur r emova l

in vacuum or in

inert gas

Act ivat ion by 4 ,42

silver catalysis in

solut ion

Mechanical 43,44

act ivat ion

Pyr i t e and va r ious C u-S phases (n uku ndam i te , ida i te , bo rn i te ,

covel l i te , e tc . ) formed. Signif icant improvement in ra te and

ex ten t o f Cu l eaching no ted . E nhanced Fe re jec tion a s py r i t e.

Cove l l i t e reac ts to fo rm b orn i t e an d pyr it e . Rap id copper l each ing

and good i ron re jec t ion a ch ieved in CuSO4 leach .

Reac t ion fo rms Cu2S and FeS ; hence h igh so lub le Fe

conc entra t io ns rea l ized dur in g leaching. Signif icant ra te increase

d u r i n g O 2 - H 2 5 0 4

leaching.

Form s Cu2S o r Cu in add i t io n to FeS . Co pper i s r ecovered by

FeCi3 leaching or f lo ta t ion.

A ct ivated carbo n increases the leachin~ ra te in ferric sulpha:e

m ed ia by up to 400%.

Born i t e and FeS fo rmed ; FeS rem oved by ac id l each ing . Born i te

p rodu c t shou ld be am enab le to ch lo r ide leach ing .

Trea tme n t a t ~ 800°C fo rms in te rm ed ia te so l id so lu t ion , bo rn it e

and FeS . Enhanced l each ing ra te s no ted in a n H 2 5 0 4 - O 2 system.

Low co ncen tra t ions o f Ag +great ly accelera te leaching in ferr ic

sulph ate m edia , but have n o effec t in chlor ide solut ions .

Extensive gr indin g resul ts in mark ed increase in leaching ra te in

ferr ic sulphate or H202 so lut ions . S imila r effect l ike ly in chlor ide

m edia . Effect seems to be due to b oth the par t ic le s ize and la t tice

dis tor t ions in the chalcopyri te .

addi t iona l f l ex ib i l i ty in the l eaching s tage . A l so , i t would be des i rable to de -

v e l o p im pr o v e d m e tho d s / ' o r r e m o v i ng the fe w pe r c e nt o f the c o a r se , s lo w l y

d i s s o l v ing pa r t i c le s f r o m the f i ne l y g r o und c o nc e n tr a te s . A l tho ug h no t c r i ti c a l

to the s uc c e s s o f c h l o r i de l e a c h i ng , a c t i v a t io n o f the c o ppe r c o nc e n tr a te s by

f ine gr i nd ing c o u l d i m p r o v e the o v e r a l l e c o no m i c s o f the pr o c e s s by r e duc ing

the s iz e o f the l e a c h i ng s e c t io n . N e v e r the l e s s , the r e s e e m s to be l it t le c o m m e r -

c ia l interes t in ac t iva t ing the cha lcop yr i te pr ior to l eaching , desp i te the

n u m b e r o f f u n d a m e n t a l s t u d i e s o f th i s a sp e c t .

P R O D U C T R E C O V E R Y A N D P U R I T Y

I n m a ny o f the pr o c e s s e s c it e d a bo v e , the r e a r e s e r io us p r o b l e m s r e l a te d to

the pur i ty o f the c o ppe r pr o duc t . P r o duc t pur i ty de pe nds to s o m e e x te n t o n

the c o nc e ntr a te be i ng tr e a ted . H o w e v e r , e l e m e n ts l i ke A g , P b , A s a nd Sb , a re

a ll so l ub l e i n c o nc e ntr a te d c h l o r i de m e d i a [4 5 , 4 6 ] a nd a ll re po r t to s o m e

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LE CHING SULPHIDE MINER LS IN CHLORIDE MEDI 3

e x t e n t t o t h e f i n a l c o p p e r p r o d u c t . B o t h t h e C y m e t a n d C o m i n c o p r o c e s s e s

u t il iz e C u C l p r e c i p i t a t i o n t o e l i m i n a t e m a n y o f t h e o b j e c t i o n a b l e i m p u ri ti es ~

S i lv e r , h o w e v e r , r e p o r t e d t o t h e C u C l c r y s ta l s a n d t r a c e s o f o t h e r e l e m e n t s

w i ll p r o b a b l y a l so c o - p r e c i p i t a t e i f t h e i r c o n c e n t r a t i o n s i n t h e l e a c h i n g m e -

d i u m a r e h i g h . C o n s e q u e n t l y , C u C 1 p r e c i p i t a t i o n , b y i t se lf , is o r o b a b l y n o t a n

a d e q u a t e p u r i f i c a t i o n p r o c e s s f o r y i e l d i n g h i g h p u r i t y c o p p e r . I n m o s t i n -

s t ance s a so l u t i on pu r i f i ca t i on s t ep w il l be r equ i r ed . S o l ve n t ex t r ac t i on ~ ne t h -

o d s a r e b e i n g d e v e l o p e d t o p r o d u c e a p u r e c o p p e r - b e a r in g s o l u ti o n , a n d t h e

d e v e l o p m e n t o f s u c h t e c h n o lo g i e s s h o u l d b e e n c o u r a g e d .

T h e p r i n c i p a l b y - p r o d u c t s i n m o s t c o p p e r c o n c e n t r a t e s a r e s il v e r a n d g o l d .

S i lv e r g e n e r a l ly d i s s o lv e s m o r e s lo w l y t h a n c o p p e r w h e n c h a l c o p y r i t e c o n c e n -

t r a t e s a r e le a c h e d , a l t h o u g h t h e e x t e n t o f si lv e r d i s s o l u t io n d e p e n d s o n t h e

m i n e r a l f o r m o f t h e s i l v e r in t h e c o n c e n t r a t e [ 4 7 , 4 8 ] . A l t h o u g h s o m e o f t h e

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 r e s u lt i n a l o w - c o p p e r c h l o r i d e s o l u t io n c o n t a i n -

i n g m o s t o f t h e s il v e r, th e s i l v e r r e c o v e r y m e t h o d s t h e m s e l v e s h a v e n o t b e e n

w e l l de f i ne d . U n l i ke s i l ve r , go l d is v i r t ua l l y i n so l ub l e in ch l o r i de m ed i a un l e s s

a v e r y h i g h o x i d a t i o n p o t e n t i a l i s m a i n t a i n e d b y C l 2 H 2 0 2 etc . [49, 50 ] .

G o l d c a n b e r e c o v e r e d f r o m t h e le a c h r e s i d u e b y c o n v e n t i o n a l c y a n i d e le a c h -

i ng , b u t t h e c y a n i d e c o n s u m p t i o n is e x c e s si v e b e c a u s e o f t h e h i g h e l e m e n t a l

s u l p h u r c o n t e n t a n d g o l d e x t r a c t i o n s a r e g e n e r a ll y lo w . T h i o u r e a l e a c h i n g h a s

b e e n u s e d t o r e c o v e r g o l d f ro m s u l p h u r - b e a r i n g l e a c h r e s id u e s [5 1 ] . G o l d

r e c o v e r ie s o f 6 0 - 8 5 % w e r e re a li ze d , b u t t h i o u r e a c o n s u m p t i o n s w e re 3 0 k g / t

r e s i d u e . D u e t o t h e f a c t t h a t g o l d i s s u c h a n i m p o r t a n t e c o n o m i c f a c t o r i n

m o s t c o p p e r o p e r a t i o n s , t h e r e c o v e r y o f th e p r e c io u s m e t a l f r o m t h e c h l o r i d e

l e ac h r e s i d u e w ill r e q u i r e m o r e a t t e n t i o n .

SULPHUR GENERATION AND CONTROL

O n e o f th e p r i n c ip a l a d v a n t a g e s o f t h e c h l o r id e l e a c h i n g r o u t e i s t h e t o t a l

a v o i d a n c e o f S O2 e m i s s io n s . N o t o n l y d o e s t h is r e s o lv e c o n c e r n s a b o u t S O 2

a i r p o l lu t i o n , b u t i t a l so s e p a r a t e s m e t a l p r o d u c t i o n f r o m s u l p h u r i c a c i d m a n -

u f a c t u r e . In t h e U .S . B u r e a u o f M i n e s ' p r o c e s s [ l 3 ] o n l y a s m a l l a m o u n t

o f s u l p h a t e w a s f o r m e d a n d p y r i t e in t h e c o p p e r c o n c e n t r a t e w a s l ar g e ly u n -

a f f e c t e d d u r i n g l e a c h i n g . I t w a s p r o p o s e d t o r e c o v e r t h e e l e m e n t a l s u l p h u r

r e a c t io n p r o d u c t u s i n g a n a m m o n i u m s u l p h id e l e ac h , w i th s u b s e q u e n t a c id i -

f i c a ti o n t o p r e c i p i t a t e th e s u l p h u r . I n t h e M I N T E K p r o c e s s [ 1 4 ] , le ss t h a n

5 % o f t h e t o t a l o x i d i z e d s u l p h i d e i o n r e p o r t e d a s S O 4 ; o v e r 9 5 % e l e m e n t a l

s u l p h u r p r o d u c t i o n o c c u r r e d . C o m i n c o [ 1 6 ] n o t e d t h a t e l e m e n t a l s u lp h u r

w a s th e d o m i n a n t r e a c t io n p r o d u c t i n th e i r p r o ce s s a n d p r o p o s e d t o r e c o v e r

t h e s u l p h u r b y f l o t a t i o n . E l e m e n t a l s u l p h u r r e c o v e r i e s r a n g i n g f r o m 7 5 % t o

9 0 % w e r e r e a l iz e d . T h e C u p r e x [ 2 7 ] , G C M [ 3 1 ] a n d H e n k e l [ 2 4 ] p r o c e s s e s

a ll n o t e d m o s t ly e l e m e n t a l s u lp h u r f o r m a t i o n , a l t h o u g h th e p r e c is e a m o u n t o f

S O 4 g e n e r a t e d w a s n o t p r e c i s e ly d e f i n e d a n d m a y d e p e n d o n t h e m i n e r a l o g i -

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14 J E DUTRIZAC

c al c o m p o s i t i o n o f t h e c o n c e n t r a t e t e s te d . I n t h e G C M p r o c e s s [ 31 ] e l e m e n -

t a l s u l p h u r w a s r e c o v e r e d b y p r e s s u r e fi l tr a t i o n a t 1 5 0 ° C , b u t o n l y 6 0 - 7 0 o f

t h e s u l p h u r w a s r e c u p e r a t e d . I n t h e C u p r e x p r o c e s s [ 2 7 ] , s u l p h u r w a s

r e c o v e r e d b y f l o t a ti o n f o l lo w e d b y m e l t i n g - f i l t r a t i o n o f t h e f l o t a t i o n c o n c e n -

t r a te . D i f f i c u lt ie s w e r e n o t e d w i th t h i s a p p r o a c h , h o w e v e r , a n d s u l p h u r le a c h -

in g m e t h o d s w e r e b e i n g e x a m i n e d . A ll s t u d ie s h a v e r e p o r t e d t h a t t h e s u l p h u r

is c o n t a m i n a t e d b y a n u m b e r o f i m p u r i t ie s , n o t a b l y s e l e n iu m , w h i c h s u b s ti -

t u t e s fo r su l ph u r .

I n c o n t r a s t , t h e C y m e t p r o c e s s [ 1 8 ] , w h i c h l e a c h e s c h a l c o p y r i t e c o n c e n -

t r a te s a t 9 8 ° C i n 1 6 0 g / l F e 3+ a n d 1 5 0 g / l C u 2+ m e d i a , r e p o r t e d 2 5 S O 4

f o r m a t i o n . T h e r e a s o n f o r t h e s i g n if ic a n t l e v e l o f S O 4 g e n e r a t i o n i n t h a t p r o -

c es s is n o t k n o w n , b u t m a y b e r e la t e d t o t h e c o n c e n t r a t e u s e d . T h e C L E A R

process [21 ] so lub i l ize s cop pe r by l each i ng i n i t i a ll y a t 10 5°C an d subse -

q u e n t ly a t 1 4 0 ° C in a n o x y g e n a t e d C u C I 2 - F e C I 3 m e d i u m . T h e h i g h t e m p e r -

a t u r e o x i d a t i o n s te p is p r e s u m a b l y r e s p o n s ib l e f o r t h e 1 5 - 2 5 S O 4 f o r m e d in

t ha t p rocess .

C o m i n c o [ 5 2 ] r ec e n t ly r e v i e w e d b o t h t h e p h y s i c a l s e p a r a t i o n a n d l e a c h in g

m e t h o d s a v a i l a b l e t o r e c o v e r s u l p h u r f r o m l e a c h r e s i d u e s . P h y s i c a l s e p a r a -

t io n m e t h o d s , s u c h a s h o t f i lt r a ti o n , p e l l e t i z a t io n a n d f l o t a ti o n , r e c o v e r p a r t

o f t h e e l e m e n t a l s u l p h u r , b u t t h e i r e f fe c t iv e n e s s d e p e n d s o n t h e n a t u r e o f t h e

l e a c h r e s i d u e . T h e s e p r o c e d u r e s , h o w e v e r , c o u l d b e e m p l o y e d i n a n o v e r a l l

s u l p h u r r e c o v e r y f l o w s h e e t t o r e m o v e a s i g n i f ic a n t f r a c t i o n o f th e s u l p h u r

e a r l y i n t h e p r o c e s s i n g s e q u e n c e . I t w a s p o s s i b l e t o l e a c h t h e s u l p h u r c o m -

p le te ly u s in g l im e w a t e r s lu r ry , ca r b it o l, a m m o n i u m s u l p h it e a n d a m m o n i u m

su l ph i de so l u t i ons . A l l fou r r eagen t s e f f ec t i ve l y l eached t he su l phu r f rom t he

r e s id u e , b u t c a r b i to l p r o d u c e d t h e p u r e s t s u l p h u r p r o d u c t . D r y i n g o f t h e re s -

i d u e w o u l d , h o w e v e r , b e r e q u i r e d p r i o r t o t h e u s e o f c a r b i to l , o r a n y o r g a n i c

reagent .

A n u m b e r o f f u n d a m e n t a l s t u d i es h a v e b e e n c a r r i e d o u t o n t h e F eC I3 o r

C uC I_ , l each i ng o f r e l a t ive l y p u re cha l cop yr i t e [ 8 , 12 ] . M os t o f t he i nves t iga -

t io n s r e p o r t e d > 9 0 , a n d o f t e n > 9 5 , e l e m e n t a l s u l p h u r g e n e r a t io n . F o r

exam pl e , R a v i e t a l. [ 53 ] r ecen t l y ob se rv ed 99 .5 S° f o r m a t i o n d u r i n g c h a l-

c o p y r i t e l e a c h in g a t 9 7 ° C . M a j i m a a n d c o - w o r k e r s [ 5 4 , 5 5 ] a l so o b s e r v e d

d o m i n a n t e l e m e n t a l s u l p h u r f o r m a t i o n d u r i n g t h e l ea c h in g o f c h a l c o p y r it e

a n d n o t e d s i g n if i c a n t v a r i a t io n s i n t h e m o r p h o l o g y o f t h e s u l p h u r . M o s t r e-

c e n tl y , D u t r i z a c [ 5 6 ] s t u d i e d t h e r e l a t iv e a m o u n t s o f e l e m e n t a l s u l p h u r a n d

s u l p h a t e g e n e r a t e d d u r i n g t h e F eC I3 le a c h i n g o f p u r e c h a l c o p y r i t e . A t t e m p e r -

a t u r e s < 1 0 0 ° C , m o r e t h a n 9 5 S° t b r m a t i o n w a s c o n s i s t e n t ly a c h i e v e d , t o -

g e t h e r w i t h < 5 S O~ g e n e r a t i o n . T h e r e l a t iv e a m o u n t s o f S° and SO 4 w ere

no t a f f ec t ed by l each i ng t i m e s a s l ong a s 90 h , by FeC I~ co nc en t r a t i on s a s h i gh

as 2 .0 M o r b y H C I c o n c e n t r a t i o n s t o 3 . 0 M . I t w a s n o t e d t h a t t h e p r e s e n c e

o f a i r o r O 2 i n th e l e a c h r e a c t o r h a d n o e f f e c t o n t h e a m o u n t s o f S° and SO 4

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LEACHING SULPHIDE MINERALS IN CHLORIDE MEDIA 5

formed . I t was con firme d that e lem ental sulphur i tself is not a t tacked by FeCI3

solut ions be low the sulphur mel t ing point [ 57 ] .

Fol lowing the earl ier wo rk of M ajim a and co-workers [ 54 55 ] i t was shown

that the sulphur m orphology was s t rongly a f fec ted by par t ic le size re tent ion

t im e an d the leaching condi t ions used [ 56 ] . The e lem enta l sulphur agglom-

erates and coats the in dividual cha lcopy ri te part ic les as noted in Fig. 3.

Al though the sulphur coa t ings probably make the leaching somewhat more

di ff icul t the agglom era t ion cer ta in ly impro ves the th ickening and f i l t ra t ion

pro pert ies o f the leach residues. This is probab ly the caus e of the good f i lt ra-

t ion rates noted by al l invest igators despi te the often f ine part ic le sizes in-

volved. F igure 4 show s the sulph ur layer form ed on a 50 ILtm chalcop yri te

part ic le leached for 24 h at 95 °C. T he ent ire surface of the chalco pyri te is

covered w i th sm al l par t ic les and in te rgrown m asses of e lementa l sulphur . O f

note how ever is the presenc e of m an y 15 ~tm euhe dral sulphur crystals sim-

i la r to those observed by M aj ima an d co-workers [ 54 55 ] . The d evelop m ent

of large well-formed sulphur crystals suggests that s ulphu r is depo si ted from

the leaching m edium . The ac tua l reac t ion sequence m ust involve a t least in

par t var ious d issolved

H 2 S

species:

Fig. 3. Secondary electron micrograph of 30 ~m chaicopyri te part icles leached for 8 h at 95:C

in 0.1 3I FeCI3 solut ion. Th e p art icles are sulp hu r coated an d are agglom erated into large masses

by the su lphur f rom [56 ] .

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16 J.E. DUTRIZAC

Fig. 4. Secon dary e lec t ron m ic rog raph of 50 ~ tm cha lco pyr i te pa r t ic les leached fo r 24 h in O. I M

FeCI.~ med ia a = su lphu r-coa ted cha lcopy r i te ;

b

s u lp h u r c ry st a l s w i th g ro wth fe a tu re s f ro m

[561.

C uF eS , + 4H C I= .C uC i2 + FeC I2 + 2 H.,S ),,~.,olvcd

2 H~S

di ,~, ,, l~.d +

4F eC h ~) 4FeCI ., + 4H CI + 2S °

CuFeS2 + 4FeCI3 -~ CuCI2 + 5FeCI2 + 2S ° 20 )

T h e d i s s o l v e d H 2 S s p e c ie s f o r m e d a t t h e s u r f a c e o f t h e c h a l c o p y r i t e d i ff u s e

f ro m t h e r e a c t i o n i n te r f ac e a n d a r e o x i d i z e d b y f e r r ic i o n s. S u c h a m e c h a n i s m

r e ad i ly e x p l a i n s th e f o r m a t i o n o f S° a s d i sc re t e g lobu le s on the cha l copyr i t e

s u rf ac e , t h e p r o t r u d i n g g l o b u l a r g r o w t h o f t h e s u l p h u r a n d , o f c o u r s e , th e n u -

c l e a t i o n a n d g r o w t h o f e u h e d r a l s u l p h u r c r y s t a l s . A s o m e w h a t s i m i l a r a n d

m o r e d e t a il e d m e c h a n i s m o f s u l p h u r f o r m a t i o n w a s a ls o a d v a n c e d b y L o t e n s

a n d W e s k e r [ 5 8 ]. T h e y p r o p o s e d t h a t t h e s u l p h i d e i o n i n th e c h a l c o p y r i t e

w a s o x i d i z ed a t t h e s u l p h i d e s u r fa c e t o S + , w h i c h w a s s u b s e q u e n t l y h y d r o -

lyzed to

H 2 S : O 2 :

CuFeS2 + Fe 3+ -~ Cu FeS . S + + Fe 2+ 21 )

2 S + + 2 H 2 0 - ~ H 2 S 2 0 2 + 2 H + 2 2 )

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L E A C H I N G S U L P H I D E M I N E R A L S I N C H L O R I D E M E D I A 7

2H 2 SaO 2 --*H2SO3

+ H 2 0 + 3S°

H2SO3 1-

2H2 S--, 3 H 2 0 + 3S°

( 2 3 )

( 2 4 )

Signif icant is the fact , however, that the proposed react ions predict only

75% S° format ion, wh ereas the exp er imen ta l evidence indica tes a h igher de-

gree of sulphur generat ion. Possibly react ion of the sulphi te with dissolved

H2S spec ies ( the reac t ion in eq . ( 24) ) could account for the rem ainde r of the

e lemen ta l sulphur formed.

M ost FeCl3 and CuC l2 leaching processes generate som e soluble sulphate .

The sulphate probably originates from the superficial oxidat ion of the sul-

phid es prior to leaching (e .g., PbSO 4 on galena ) or by the sulphide leaching

react ion i tself. A lthough l it tle sulphate originates from chalcopyri te leaching,

the dissolut ion of associated minerals such as pyri te can contr ibute signif i -

cant sulphate . Elemental sulphur is stable in chloride media at 100°C, but

becom es mo re reac t ive above i ts m el t ing point. Sulphate format ion, accord-

ingly , becom es m ore prevalent in those processes employing e leva ted tem per-

atures: up to 25% SO4 form ation was obse rved in the CLE AR process.

In most chloride processes, sulphate is control led by the addit ion of cal-

c ium chlor ide to the solution to prec ip i ta te some form of ca lc ium sulphate

(CaSO4 2H20, CaSO4 1/2H 20 or CaSO4) . Sulphate can a lso be cont rol led

by prec ipi ta t ion o f ja rosite - type com pou nds, and the technique is espec ial ly

useful a t h igher leaching tempera tures . Both sodium jarosi te

(NaF e3(SO 4)2(OH )6) and po tass ium ja ros it e (KFe3(SO4)E(OH )6) have

been em ployed [ 18, 21 ] . D utrizac [ 59 ] inv est igated several sulphate control

techniques, which included the precipi tat ion of calcium sulphate , lead sul-

phate , barium sulphate , sodium jarosi te and potassium jarosi te . Lead sul-

pha te enjoys a considerable solubi li ty in conc entrated ch loride med ia so this

com pou nd was not useful for sulphate cont rol . Ja rosi te prec ipi ta tion requi red

a relat ively low acid con centrat ion a nd a high tem pe ratu re to be effective; a

low te rm inal sulphate concent ra t ion could not be achieved. I f a min or c i rcu-

lat ing load of sulphate ( l 0 g/ l SO 4) is a llowable in the p rocess, how ever, po-

tassiu m jarosi te pre cipi tat ion is an effect ive meth od o f sulphate control , as in

the C LEAR process . Bar ium chlor ide addi t ions prec ipi ta te BaSO4, and the

react ion proceeds nearly stoichiometrical ly. Sulphate concen trat ions < 0.1 g /

I can be ach ieved. The presence of excess BaCI2 resul ted in th e precip i tat ion

of BaCI2' H 20 during th e cooling of the solut ion, howev er, and this phase ad-

versely affected the f i l tra t ion o f the leach residue. A ddit ion of CaCI2 effec-

t ively control led sulphate; prov ided th at an excess of CaC12 was present, final

dissolved sulphate concent ra t ions o f 1-3 g SO4/1 could be m ainta ined. I t was

conc luded that the be st overal l sulph ate control st rategy involved precipi-

ta t ion of calcium sulphate .

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18 J.E. DUTRIZAC

F U N D A M E N T A L S O F T H E F E R R IC C H L O R I D E L E A C H I N G O F C H A L C O P Y R I T E

A grea t dea l of fund am enta l research on th e FeCl3 leaching of cha lcopyr i te

has been ca r r ied ou t an d rev iews o f the re levan t pub l ica t ions p r io r to 1984

have been pub l ished [ 8 , 12 ] . The m ore re cent in ves t iga t ions carr ied out to

e luc ida te the reac t ion o f cha lcopyr i t e in fe r r i c ch lo r ide media a re summa-

rized in Table 2.

M any e lec trochemica l stud ie s have shown the rap id in i ti a l fo rm a t ion o f a

th in a rou nd 3 nm ) su lph ide l aye r on the cha lcopyr i t e dur ing d i sso lu tion .

Park er et a l. [ 61 ] desc ribed th is as a m etal-d eficie nt poly sulp hide . Biegler

and H orne [ 65 ] pos tu la ted the se lect ive d issolu t ion o f i ron f rom the cha lco-

pyri te to fo rm a covell i te-like phase:

C u F e S 2 - ~ 0 . 7 5 C u S - i - 0 . 2 5 C u 2 -I-

Fe 2+

2 5 )

+ 1.25S° + 2 . 5 e -

In the i r s tud ies on the ga lvan ic coup ling o f cha lcopyr i te and pyr i te , M urr

and Mehta [63 ] iden t if i ed cove l li te C uS ) , cha lcoc it e Cu2S ) , born i t e

CusFeS4) , cuban i te CuFe2S3) and e lemen ta l su lphur by e lec t ron d if frac -

t ion of the reac t ion sca les. Th ese pro ducts form ed by the gen era l ized reac t ion:

C u F e S 2 -- , C u i _,v F e l _ y S 2 _ : -I- x C u 2 -i-

yF e 3+

2 6 )

+ z S ° + 2 x + 3 y ) e -

Al though i t is cer ta in tha t th in scales of su lphide form on ch a lcopyr i te dur-

ing leaching, i t has not been conclus ive ly es tabl ished tha t the 3 nm layers

significantly affect the m acro scop ic leaching of the cha lcopy ri te . Th at is, it is

not es tabl ished tha t the sulphid e layer pass iva tes the e nt i re surface in such a

way tha t the overa l l leaching ra te i s contro l led by the d issolut ion o f the in ter-

media te phase . The poss ib i l i ty exis ts tha t the bulk leaching reac t ion could

proceed s imu l taneous ly in two or m ore para l le l pa ths :

CuFeS2 + 2F e 3+ --,CuS + 3Fe 2+ + S °

C uS + 2Fe a+ - ,C u 2+ + 2Fe 2+ + S°

CuFeS2 + 4 F e 3+ --,Cu 2+ + 5F e 2+ + 2S °

2 7 )

2 8 )

2 9 )

F U N D A M E N T A LS O F T H E C U P R I C C H L O R I D E L E A C H I N G O F C H A L C O P Y R I TE

Var ious fundam enta l s tud ie s on the reac t ion o f cha lcopyr i te wi th

C u C I 2

media have been repor ted , and a sum m ary o f the re levan t in fo rm a t ion i s g iven

in Table 3.

Tab le 3 ind ica te s a num ber o f incons is t encie s in the rep or ted pa ram e t r i c

depen dencies for the leaching of cha lcopyr i te in

C u C I 2

m edia . In th is regard ,

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LEACHING SULPHIDE MINERALS IN CHLORIDE MEDIA

19

TABLE 2

Recent fund ame nta l s tud ies on the leaching ofcha lco pyr i te in

F e C I

me dia

Mater ia l Reference Conclus ions

Natura l cha lcopyr ite 54

single crystal

Na tural chalcopyrite 55

single crystal

Natura l h igh pur i ty ,

ma ssive chalcopyrite

Natura l cha lcopyri te sawn

mass ive and pow ders

(pur i ty no t g iven)

Natura l m ass ive

cha lcopyr i te

Natura l m ass ive

chalco pyrite , free of

microsco pic inclusions

60,61

62,63

64

65

Sized, high purity natural 66

chalcopyrite

Leach ing is 2 t im es faster in

F e C l

than in Fe(SO4)~.5

me d ia

Linear leaching k ine t ics

Act iva t ion energy 69 kJ /m ol

R ate c~ [

F e C l a

] 0.5

Rate increases sign ifican tly wi th 0 -2 M NaCi

concentra t ions

Rate indepen dent of [

F e C l ]

in 0-1.0 M range

Elec trochemica l mechanism ad vanced

Kin etics controlled by one-electron transfer

Theo ry ex plains effect of tem perature , FeCla, FeCI2

Theo ry does no t explain the effect of NaCl

CuCI2 form ed during leaching accelerates

leaching rate

Elec trochemica l s tud ies showed format ion of ~ 3 nm

sulphide f i lm

Impo r tance o f CuCl2 reac t ion produc t shown

Catalysis by Ag2S explained

Electrochem ical effects shown to be im portant in bacter ial

leaching of chalcopyrite

Galva nic in te rac t ions with pyr i te demon s tra ted

Electrochem ical studies suggested sulphide inte rm ediale

phases

Electro-oxidation of C uFeS2 gives Fe 3+ directly

Electrochem ical s tudies showed an a nodic prew ave to

produce a ~ 3 nm su lphide in te rmedia te

Subse quen t leaching involves the thin sulphide

in te r me d ia te

Predicts th at a ll chalcopyrites should leach at same rate

Leaching s tudies showed that the C uCl2 reaction p roduct

prom oted the FeCl3 leach

R at e a [ FeC I3 ] 0.3-0.4

Rate increased s lightly with [ HC ]

FeCI2 s lightly inhibited the reaction

Tota l Cu ex trac t ion depends on NaC concentra t ion

d i f f e r en t mechan i sms may p reva i l above and be low 80°C . Low concen t r a -

t ions of Cl adverse ly a f fec t the reac t ion , but the ra te may be chlor ide-

insens i t ive a t h igher > 2 M Cl ) chlor ide concent ra t ions . M ost workers hav e

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20 J E DUTRIZAC

T A B L E 3

R e c e n t fu n d a m e n ta l s tu d ie s on th e l e a c h in g o fc h a l c o p y r i t e i n C u CI2 m e d ia

Ma te r i a l R e fe re n c e C o n c lu s io n s

Sized cha icop yr i te 67 L inea r leach ing k ine t ics

c o n c e n t r a t e c o n ta in in g In d e p e n d e n t o f s t i r r in g sp e e d s > 4 0 0 rp m

2 7 -3 0 % C u H ig h a c t iv a t io n e n e rg y , 1 35 k J /m o l

R a t e in d e p e n d e n t o f [ C u C I : ]

R a te i n d e p e n d e n t o f [C I ]

E lec t rochemica l iy cont ro l led reac t ion

Sized cha lcop yr i te

c o n c e n t r a t e c o n ta in in g

c.80% chalcopyrite;

total Cu = 34%,

t ot al F e = 2 5 %

U ns ized c ha lcopy r i te

c o n c e n t r a t e c o n ta in in g

26% Cu

68

29

Natura l cha lcop yr i te c rys ta ls 69

. 38

~tm chalcopyrite

c o n c e n t r a t e s c o n ta in in g 2 7 -

32% Cu

70

Parabol ic leach ing k ine t ics

A c t iv a t io n e n e rg y 71 k J /m o i a t > 8 0 ° C

A c t iv a t io n e n e rg y 3 3 5 k J /m o l a t < 8 0 ° C

R a te i n c re a ses w i th r a t i o o f C u C I2 /C u C

Rate increases wi th [CI]

Dif fus ion cont ro l led a t > 80 °C

P o s tu l a te s C u S | b rm a t io n a t h ig h C u + / C u 2+ r a t io s

H ig h [C l ] f a v o u r s re a c t io n

Rate l inear fo r f i r s t 200 h , bu t acce le ra tes thereaf te r due

to su r f ac e ro u g h e n in g

A c t iv a t io n en e rg y 8 2 k J / to o l

Ra te i ncr eas es as [CuC I2 ]o. 54

Rate decreases as [Cu CI] -o .5

Rate increases

w i t h [ N a C ] t o

-,, 2 M , bu t is insensit iv e

to h ig h e r c o n c e n t r a t i o n s

Rate e lec t rochemica l ly cont ro l led by But le r -Volm er

e q u a t io n

Linear k ine t ics

R a te i n d e p e n d e n t o f [C u C I2 ] w h e n 0 2 sp a rg in g u se d

Rate increases wi th [Ci] to 90 g / i

R a te i n d e p e n d e n t o f su r f a c e a r e a o f c h a l c o p y r i t e

R a t e m a x i m u m a t 8 5 ° C

observed l inear kinet ics together with a moderately high act ivat ion energy.

All workers noted that e lemental sulphur is the dominant , i f not exclusive,

sulphidic react ion produ ct . T here is a large bod y of data w hich suggests that

the CuCI2 leach, a t high tem pe ratu res and high Cl con centra t ions, is e lectro-

chemica l ly cont rol led [60, 61] , and there i s good agreement be tween the

mixed potent ial in cupric ch loride m edia an d the leaching rate [ 71 ] . That

CuCI2 solut ions are m ore effect ive than FeCI3 m ed ia is a t t r ib ute d to the fact

tha t the Cu 2 /Cu couple i s fas te r and m ore reversib le than the Fe 3 /Fe 2

couple on a chalcopyri te surface in chloride m ed ia [ 61 ] .

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L E C H I N G S U L P H I D E M I N E R L S IN C H L O R I D E M E D I 2

C H L O R I D E L E A C H I N G P RO C E SS E S F O R L E A D C O N C E N T R A T E S

G alena (PbS ) is the on ly lead su lph ide m ine ra l o f any com merc ia l signi fi -

cance . Ga lena conce ntra tes a re readi ly processed by pyrom eta l lurgica l m eth-

ods , but problem s pers is t wi th fugi tive SO2 em iss ions f rom some ope ra t ions ,

an d a l l p lants a re conc erned wi th poten t ia l in-plant hygiene problem s caused

by Pb, Cd, TI , e tc . In addi t ion , the capi ta l cos t of replac ing obsole te lead

sme l te rs is h igh, an d the fu ture of smal l, ind epe nde nt smel te rs i s in do ubt .

Hy drom eta l lurgica l process ing offers som e prom ise of resolving these prob -

lems and nu m erous deve lopm enta l and fundam enta l s tud ie s on the leach ing

and recove ry o f lead have been ca r r i ed ou t .

Al though som e work has been don e o n the reac t ion of ga lena in fe rr ic su l -

ph ate m edia , tha t ap proa ch is l imi ted to processes in tend ing to leave the lead

as insoluble PbSO4 in the leach residue . D ue to the m od era te ly h igh solubi li ty

of PbCI2 in concen tra ted chlor ide m ed ia [ 72 , 73 ] and the potent ia l to recov er

a pu re PbCI2 in te rm edia te produ ct by cool ing the hot PbCl2-concentra ted leach

solut ion , mos t processes have been chlor ide based. Al l ear ly inves t iga t ions

no ted t ha t galena is easi ly oxidized by ei theJ FeCI3 or CuCI2 med ia, and tho se

early invest ig ations ha ve bee n revie we d [ 8, 12 ] .

Ear ly low-tem pera ture leaching processes inc luded tho se d eveloped by the

H e c l a M i n i n g C o m p a n y [7 4 ] , C o m i n c o L i m i t e d [7 5 ] a n d H a z e n R e se a rc h

[76] . Low temp era tu re l eaching i s ca r r i ed ou t a t a rou nd 40°C in FeCI3 o r

CuCI2 med ia to co nve r t ga lena to PbCI2, which rem ains in the leach res idue .

Th e residue is sepa rated from the p rim ary leach solution and is then re-leached

in h ot con centra ted br ine to solubi lize the PbCI2 se lec tive ly . Pure PbC I2 is

subseque nt ly prec ip i ta ted by cooling the solution:

4 0 ° C

PbS + 2FeC I3 ~ (PbCI2),olid + 2FeCI2 + S° (30)

(PbCl2)~olid + 2C1 - 95 °C (PbCI~-)~o~tio. (3 1 )

25 °C

(PbCI24- )solution ' (PbC 12)solia+ 2C 1- ( 32 )

Th e a dvantage o f the low-tem pera ture leaching opt io n is tha t i t is re la t ive ly

se lec tive fo r l ead an d impur i ty p rob lem s a re m in imized . T he d i sadvan tages

are tha t s i lver i s not ent i re ly ext rac ted and the d issolut ion o f some of the im-

pur i ty e lem ents canno t be en t ire ly avo ided .

Both the U.S. B ureau of Mines [ 77 ] an d M inem et R echerche [ 78 ] ha ve

dev eloped high temp era tu re leaching processes based o n FeCI3. High lead ex-

t rac t ions were cons is tent ly rea l ized toge ther wi th predominant ly e lementa l

su lphur fo rma t ion :

P b S + 2FeCI3 ~ PbCI2 + 2FeC12 + S° (33)

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LE CHING SULPHIDE MINER LS IN CHLORIDE MEDI

3

L e a d

C o n c e n t r a t e

~ esidueTreatment- - - - ~ e r i g h t S o

P b C l2

C r y s t a l l i z a t i o n

t

P b C l s

I C o p p e r I ~ C uO

C e m e n t

|

F e° ] . S o l u t i o n B l e e d

~

Re s idue

e t

J A q u e o u s

L e a d

- I l e c t r ° l y s i s I

J e r r i c I

I R e g e n e r a t i o n ~

~ P b M e t a l

Fig . 5 . Sche mat ic f lowshee t for the St . Joe fe r r i c ch lor ide l each process fo r ga lena conce nt ra tes

f rom [ 80 ] .

t ion of lead occurred . Fina l ly , the so lu t ion w as regenera ted w i th chlor ine gas ,

which could be recovered f rom the e lec t ro lysis cells of a com m erc ia l opera t ion .

Al though the Leadex process [30] developed by Tecnicas Reunidas i s

nominal ly based on aqueous Cl2 leaching, i t can a lso be v iewed as a d i lu te

FeCl3 leach in which the l ixiviant is continuously regenerated by Cl2 gas . A

s imilar process was a lso adv ocated by the U.S. Bure au o f Mines [ 81 ] . In the

Leadex process, leaching is carr ied ou t for 2 .5 h a t 90 °C in a so lu t ion con ta in-

ing 2-10 g/ l Fe 3+ and 200 g/ l Cl; the redox potent ia l i s contro l led a t 55 0 mV.

Impur i t i e s , inc lud ing Ag and B i, a re rem ove d by ceme nta t ion wi th a sma l l

quan t i ty o f z inc dus t . N ex t , lead i s r ecove red by cem enta t ion on shea red z inc

ca thodes in a trom m el . Lead i s to ta lly remo ved f rom the so lu tion and sepa -

ra tes c leanly f rom the z inc . The lead form s smal l pe lle ts which are mel ted an d

cas t in to ingots. Th e resul ting z inc c hlor ide solut ion is t rea ted by solvent ex-

t rac t ion to p roduce a pure 70 g / l Zn so lu t ion fo r e lec t ro lysi s in the com pan y ' s

Metclor cel l . Chlorine gas from the zinc electrolysis cel l is employed in the

leaching opera t ion . Th e process has been eva lua ted on a l kg P b /h p i lo t p lant

which ran for ove r 600 h , and achiev ed 99 Pb recove ry as a 99 .97 Pb

produc t . S ilver recove rie s were a rou nd 94 and su lphur was p roduc ed by

f lo ta t ion of the leach res idue . Z inc is used to cem ent the lead an d the overa l l

ene rgy consu m pt ion i s 2 .33 kW h/k g Zn , o r abou t 0 .9 kW h/k g Pb , a va lue

wh ich is not excessive.

Al though d evelop ed for copper , the Dex tec process can a lso be used to re -

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  4 J E D U T R I Z A C

c o v e r le a d f r o m l e a d c o n c e n t r a t e s [ 8 2 ], a n d m a y b e p a r t i c u l a r l y u s e fu l fo r

d e l e a d i n g c o p p e r c o n c e n t r a t e s p r i o r t o s u b s e q u e n t s m e l t i n g . I n r e g a r d t o t h e

l a t t e r a p p l i c a t i o n , B o l i d e n M e t a l l a n d D e x t e c o p e r a t e d a 3 m d i a m e t e r b y 4

m h i g h p i l o t c e ll f o r a b o u t l y e a r . T h e c e ll w a s o p e r a t e d i n a b a t c h m o d e u s i n g

10- 12 h / d a y cyc l es . I n t he an od e , o r s lu r r y , pa r t o f t he ce l l, l ead w as se lec -

t iv e l y s o l u b i li z e d a t 9 0 ° C i n a 2 5 0 g / l N a C l e l e c tr o l y t e m a i n t a i n e d a t a p H o f

a r oun d 1 .5 w i t h H C1. A va r i e t y o f d i s so l u t i on r eac t i on s a r e p r oba b l y i nvo l ved :

Pb S + 2FeC I3 --, PbCI2 + 2FeC I2 + S°

P b S + 2 H C I -- , P b CI2 + H 2 S

P b S - 2 e - -~ P b 2+ + S°

( 3 8 )

( 3 9 )

( 4 0 )

Any H S

e v o l v e d e i t h e r w o u l d b e o x i d i z e d b y f e r ri c c h l o r id e o r w o u l d p r e -

c i p i t a te d i s s o l ve d Ag , Cu , Zn , e t c . I n t h i s rega r d < 1% of t he co pp er , z i nc and

i ro n i n t h e c o n c e n t r a t e w a s s o l u b il iz e d . T h e l e a d c o n c e n t r a t i o n o f t h e s o l u t i o n

w a s 2 0 g / l P b , a n d t h e l e ad m i g r a t e d t h ro u g h t h e d i a p h r a g m a n d w a s d e p os -

i t e d a s c o a r s e c r y s t a l s a t t h e c a t h o d e . C o n c e n t r a t e s c o n t a i n i n g 1 0 - 2 5 % C u ,

4 - 2 0 % P b , 4 - 3 0 % Z n a n d 1 0 0 - 2 0 , 0 0 0 p p m A g w e r e s u cc e ss fu ll y t re a t e d .

O v e r a l l l e a d r e c o v e r i e s w e r e 9 3 % a n d t h e e n e r g y r e q u i r e m e n t w a s 0 . 6 - 0 . 7

k W h / k g P b . D u r i n g th e p il o t p r o g ra m , v a r i o u s i m p r o v e m e n t s w e r e m a d e t o

t h e ce ll d e s ig n , a n d it w a s e s t i m a t e d t h a t t h e c a p i t a l c o s t o f a 3 0 , 0 0 0 t / y r l e a d

r e fi n e ry w o u l d b e ( 1 9 8 6 U S $ ) $ 1 0 , 0 0 0 ,0 0 0 a n d t h a t t h e o p e r a t i n g c o st s,

e x c lu s iv e o f c a p i t a l c h ar g e s, w o u l d b e $ 0 . 2 7 / k g P b . A l th o u g h t h e D e x t e c p r o -

c e s s w o u l d p r o b a b l y r e q u i r e e x t e n s i v e d e v e l o p m e n t t o c o n t r o l a l l t h e i m p u r -

i t i e s p r es en t i n conven t i ona l l ead concen t r a t e s , i t appea r s t o o f f e r a v i ab l e

m e a n s o f d e - le a d i n g c o p p e r c o n c e n t ra t e s w i th t h e c o n c o m i t a n t p r o d u c t i o n o f

a m a r k e t a b l e l e a d p r o d u c t .

M o s t o f t h e l e a d l e a c h in g p r o c e s s e s d e v e l o p e d t o d a t e a d v o c a t e t h e p r e c ip -

i ta t io n o f a P b C l2 i n t e r m e d i a t e p r o d u c t . S u c h a s t e p i m p r o v e s t h e f i n a l p u r i t y

o f t h e l ea d m e t a l a n d p r o v i d e s a s u r g e c a p a c i t y b e t w e e n t h e le a c h in g a n d

m e t a l r e c o v e r y o p e r a t i o n s . A l t h o u g h t h e M i n e m e t p r o c e s s i n i t i a l l y p r o p o s e d

e l e c t r o w i n n i n g d i r e c t l y f r o m t h e p u r i f i e d l e a c h s o l u t i o n , t h e l a t e s t d e v e l o p -

m e n t s o f t h a t p r o c e ss i n c o r p o r a t e a n i n t e r m e d i a t e P b C l2 c r y s ta l l iz a t i o n s t ep .

O n l y t h e D e x t e c p r o c e s s p r o p o s e s l e a d r e c o v e r y d i r e c t ly f r o m t h e l e a c h so l u-

t io n , b u t it is d o u b t f u l i f t h a t o p t i o n w o u l d b e v ia b l e f o r d i r t y l e ad

concen t r a t e s .

A l th o u g h t h e H a z e n R e s e a r c h p r o c es s [ 7 6 ] e m p l o y e d H 2 r e d u c t i o n o f t h e

PbCl 2 c r ys t a l s , mos t p r oces s es u t i l i ze e l ec t r o l ys i s t o r ecuper a t e t he l ead and

r e g e n e r a te a n o x i d a n t . S N C I n c . a n d C A N M E T r e c e n t ly r e v i e w e d P b C I 2 e le c -

t r o l y s i s t e c h n o l o g i e s a n d o f f e r e d a c o n c e p t u a l d e s i g n f o r a n e l e c t r o w i n n i n g

ce ll [ 83 , 84 ]. S even f us ed s a l t and e l even aq ue ou s e l ec t ro l ys i s ce l ls wer e eva l -

ua t ed . I t was con c l uded t ha t t he r ecover y o f l ead by e i t he r fus ed s a l t o r aqu eou s

e l e c t r o l y t i c p r o c e d u r e s h a d b e e n d e m o n s t r a t e d a t a p i l o t s c a l e . T h r e e p r o -

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c e ss e s w e r e f o u n d t o b e p a r t i c u l a r ly a d v a n c e d f o r c o m m e r c i a l a p p l i c a t io n : t h e

U . S . B u r e a u o f M i n e s m o n o - p o l a r f u s e d s a lt ce ll , A l c o a s b i -p o l a r f u se d s a l t

ce ll an d M ine m et s aq ueo us e l ec t ro lys i s ce ll . Ov e ra l l , i t was f e lt t ha t t h e fused

s a l t c e l l s w e r e s i m p l e r t o o p e r a t e , p r o d u c e d a m o l t e n p r o d u c t a n d p r o b a b l y

h a d l o w e r o p e r a t i n g c o s ts . F o r a s m a l l s c al e o p e r a t i o n , t h e B u r e a u o f M i n e s

m o n o - p o l a r c e ll, w h i c h is s h o w n s c h e m a t i c a l ly in F i g . 6, w o u l d s e e m t o b e t h e

p r e f e r r e d o p t i o n . F o r a l a rg e l e a d p r o d u c e r , h o w e v e r , t h e b e t t e r e c o n o m i c s o f

b i -po la r ce l l e l ec tro lys is cou ld be a t t r ac t ive . Rega rd le s s o f t he e l ec tro ly t ic rou te

fo l lowed , t he pu r i ty o f t he PbCl2 c rys t a l s i s a key f ac to r fo r the sm oo th a nd

e f f i c i en t op e ra t io n o f t he ce ll . I ron an d su lph a te i n t he PbCI2 c rys t a ls a r e o f

p r inc ip a l conce rn . I ro n causes a r educ t ion in t he cel l cu r r e n t e f f i ci ency , an d

t h e a c c u m u l a t i o n o f s u lp h a t e n e c e s s i t a te s t h e f r e q u e n t b l e e d i n g o f e l e c t ro l y t e

t o p r e v e n t i m p u r i t y c r y s t a ll i z a ti o n o n t h e e l e ct r o d es . I r o n c o n t a m i n a t i o n c a n

be e l im ina te d by g ood wash ing o f t he PbC12 c rys t a l s [ 80 ] , and SO4 can be

c o n t r o l l e d b y t h e p r e s e n c e o f C aC I2 i n t h e l e ac h a n d t h e r a p i d c r y s t a ll i z a ti o n

o f t h : P b C