A Comparison of Alkali and Acid Methods for the Extraction of Gold From Low Grade Ores

8/4/2019 A Comparison of Alkali and Acid Methods for the Extraction of Gold From Low Grade Ores

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PergamonM#wrals Engineer#tg, Vol . 9 , No. 10, pp. 1 033-1 047. 1996Copyr i gh t 1996 P ub l i she d by E l se v i e r S c ie nc e L t dPr inted i ll Grea t Br i ta in. Al l r ights r eservedP I h S 0 8 9 2 - - 6 8 7 5 ( 9 6 ) 0 0 0 9 6 - 9 0 8 9 2- 6 87 5 /9 6 $ 15 .0 0+ 0.0 0

A C O M P A R I S O N O F A L K A L I A N D A C I D M E T H O D S F O RT H E E X T R A C T I O N O F G O L D F R O M L O W G R A D E O R E S

S . V U K C E V I CA J P a r k e r C o o p e r a t i v e R e s e a rc h C e n t r e f o r H y d r o m e t a l l u r g y ,

M u r d o c h U n i v e r s i t y , M u r d o c h W A 6 1 5 0 , A u s t r a l i a(Received 1 February 1996; accepted 12 July 1996)

A B ST R A C TAlternative alkali and acid methods for gold extraction from low grade copper-goldores/tailings were studied. Several ores/tailings which originate from South and WesternAustralia were treated by cyanide, ammonia-cyanide, bromine and sulphuric acid, toachieve optimal reactant concentration for the selection of gold over copper. The validityof these systems was compared according to the gold leaching kinetics and other relevantcriteria. It was found that different solubility o f copper minerals and characteristics ofpredominant gangue minerals presented in the ores/tailings have a significant effect onboth the concentration of copper in the solution and the consumption of the reactants.Selective copper precipitation occurs from ammonia-cyanide leach solutions, whichexplains the apparent selectivity of this system for gold.Leaching an ore consisting of1.5% Cu as CuFeS2, Cu2S and Cu5FeS4 with 0.55 kg/t NaCN and 3 kg/t NH3allowed89% gold extraction with only 200 ppm o f copper remaining in solution. The sameconcentration of cyanide and a lower concentration of ammonia (2.2 kg/t NH3) werefound to be optimum for achieving 85 % extraction of gold from tailings consisting o f1.15%Cu as Cu2S, Cu20 and CuS. The ammonia addition in the cyanide system leadsto the production of Cu(II)NH 3 species during the oxidising of gold metal to Au(CN)2- .Copper precipitates mostly as Cu(OH)2, CuO, Cu20 and CuCN. Gold is leached asAu(CN) 2- by chemical reactions involving Cu(1) cyanides present in the system.Copper tailing containing 700-800 ppm Cu as CuFeS2 and CuS, was leached withsulphuric acid as a pre-treatment step. This step was found to be beneficial as only 30ppm Cu remained in solution after ammonia-cyanide leaching. Leaching of the tailing inan acid bromine solution showed much faster kinetics o f gold extraction with no worsecopper selection compared to the alkali systems.Copyright 1996 Published by Elsevier Science LtdKeywordsGo l d o re s ; t a il i ngs ; l e a c h i ng ; p roc e s s op t i mi sa t i on ; c ya n i da t i on

I N T R O D U C T I O NCya n i da t i on ha s b e e n t he s t a nda rd p roc e s s f o r go l d r e c ove ry s i nc e c ya n i de wa s f i r s t ly a pp l ie d a s a n op t i ma ll i x i v i a n t fo r go l d , ne a r l y a c e n t u ry a go . H ow e ve r , t he re a re a num be r o f o re s wh i c h c on t a i n c ya n i de -c onsu mi n g c ons t i t ue n t s o t he r t ha n go l d . Mo s t i mpor t a n t a re the d i f f e re n t su l ph i de mi ne ra l s o f i ron , c oppe r ,a r s e n i c a nd a n t i mo ny . In sp i te o f the wo rk t ha t ha s be e n done i n t he a re a o f va l o r i s a t i on o f t he se o re s ,

1 0 3 3


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1034 S. Vu kcevicpa r t i c u l a r l y i n a t t e mpt s t o r e du c e t he r e a c t i v it y o f c e r t a i n c oppe r mi ne ra l s i n c ya n i de so l u t i on , l i tt l e succ e s sha s be e n a c h i e ve d . The on l y me t h od o f e nsu r i ng c ons i s t e n t l y good g o l d r e c ov e ry i n t he se s i t ua ti ons wa st o e mpl oy h i gh c ya n i de c onc e n t ra t i on a nd t o t o l e ra t e h i gh c ya n i de c onsumpt i on .T h e a l t e r n a t i v e p r o c e s s o f s e l e c t i v e g o l d l e a c h i n g f r o m c o p p e r - g o l d o r e s , u s i n g t h e a m m o n i a - c y a n i d esys t e m, o f fe r s l ow c ya n i de c onsumpt i on . Th i s p roc e s s wa s f i r s t pa t e n t e d i n 1901 [1 ] . S i nc e t he n , al i t e ra t u re r e v i e w o f t he a pp l i c a t i on o f a mmoni a -c ya n i de fo r go l d l e a c h i ng re ve a l s t wo wi de l y s e pa ra t e dpe r i ods o f a c t i v i t y , t he f i r s t be fo re t he 50 ' s [2 -4 ] a nd t he s e c ond i n t he l a s t t e n ye a r s [5 -13 ] .W h i l e t h e c h e m i s t r y o f t h e a m m o n i a - c y a n i d e s y s t e m h a s b e e n b e t t e r u n d e r s t o o d i n m o r e r e c e n t ti m e s [ 1 3 ]t he l i te ra t u re show s t he re i s s t il l some d i s a g re e me n t a bou t go l d d i s so l u t i on [14 ] . M ore o ve r , t he re i s a la c ko f sys t e ma t i c r e se a rc h i n t o d i f f e re n t o re p roc e s s i ng m e t hods u s i ng the a mm oni a c ya n i de l e a c h sys t e m.S l i gh t l y d i f f e re n t k i ne t i c s a nd me c ha n i sm o f go l d l e a c h i ng a re c a use d by spe c i f i c ge o -phys i c a l a nd ge o -c he mi c a l c ha ra c t e r i s t i c s o f na t u ra l mi ne ra l s wh i c h fo l l ow go l d . T he y a re a l so c a use d by t he t a il i ngsc h a r a c te r i st i cs i n f lu e n c e d b y t h e t y p e o f m i n e r a l d r e ss i n g e m p l o y e d f o r c o p p e r c o n c e n t r a t io n o f c o p p e r - g o l do re s . Th e a dso rp t i on c ha ra c t e r i st i c s o f t he ga ngue mi ne ra l s i n t he a pp l ie d go l d o re a l so a f fe c t t he k i ne ti c sa n d m e c h a n i s m o f g o l d le a c h in g .The re a re on l y t wo ope ra t i ng p l a n t s u s i ng t he a mmoni a c ya n i de l e a c h sys t e m. One i s a suc c e s s fu l sma l ls c a l e t ai l i ng t r e a t me n t p l a n t on t he P a r i s Dum p ne a r Ka l goo r l i e , Aus t ra l ia , w h i c h s t a r t e d i n 1986 [15 ] a ndt he o t he r i s t he f i r s t ma j o r c omme rc i a l ope ra t i on a t Aj k j ou j t i n Ma ur i t a n i a [16 ] , wh i c h i s now unde rgo i ngt e c hno l og i c a l i m prov e me n t [ 17 ].Ano t he r p roc e s s i s t he a c i d p roc e s s i n go l d me t a l l u rgy , u s i ng b romi ne go l d e x t ra c t i on . The re su l t s o fre se a rc h i n t o t h i s p roc e s s ( r e v i e we d du r i ng t he l a s t t e n ye a r s [18 -21 ] ) show muc h fa s t e r k i ne t i c s o f go l dl e a c h i ng t ha n i n c l as s i ca l c ya n i da t i on . G o l d re c ove r i e s f rom Br p re gna n t so l u t i ons u s ing d i f f e re n t s e pa ra t ionme t ho ds ( c a rb on a d so rp t i on , i on e xc ha ng e , so l ve n t e x t ra c t i on ) c a n be 99 .9 9 % [ 19 ]. One m ore a dva n t a geo f t h i s a l t e rna t i ve p roc e s s l ie s i n t he f a c t t ha t the t ox i c i t y o f c ya n i de i s now ra i s i ng som e e nv i ronme n t a lc onc e rns a nd t hus a l t e rna t i ve l i x i v i a n t s fo r go l d a re o f i nc re a s i ng i n t e re s t .The p re se n t work s t ud i e s bo t h a l ka l i a nd a l t e rna t i ve a c i d me t hods fo r go l d e x t ra c t i on f rom l ow g ra dec o p p e r - g o l d o r e s.T h e a p p l ic a b i li t y o f t h e a m m o n i a c y a n i d e s y s te m o n l o w g r a d e c o p p e r - g o l d o r e s i s r e s e a rc h e d o n s e v e ra lo re s / t a i l i ngs wh i c h o r i g i na t e f rom S o u t h a nd W e s t e rn Aus t ra l ia . T he pos s i b i l it y o f b rom i ne go l d e x t ra c t i oni n l ow c oppe r so l ub l e c oppe r -go l d o re ha s be e n i nve s t i ga t e d a nd c ompa re d t o a l ka l i l e a c h i ng .In a dd i t i on , su l phur i c a c i d l e a c h i ng a s a p re - t r e a t me n t s t e p due t o c oppe r s e l e c t i on wa s s t ud i e d . Th i s i s o fspe c i al i n t e re s t fo r t he e mp l oym e n t o f c l a s s ic a l c ya n i da t i on a s t he ne x t s te p i n CIP a nd / o r R IP p roc e s se s .

M A T E R I A L S A N D M E T H O D SR a w ma t e r i aL ,R a w m a t e r i a l 1 ( R M 1 ) . A c o p p e r - g o l d ta i li n g w h i c h i s d e p o s i te d in t o d a m s a n d o r i g in a t e s f r o m c o p p e rf l o t a t ion o f s e ve ra l o re s . I ts c he mi c a l c ompo s i t i on wa s (% we i gh t ) : 50 % F e , 4 .3 % S i , 3 .1% S a nd 1 .5 ppmA u a n d 7 0 0 - 8 0 0 p p m C u . M i n e r a l o g i c a ll y th e t a il in g c o n si s te d p r e d o m i n a n t l y o f m a g n e t i t e ( 7 0 - 8 0 % ) ,s i l i c a t e s (10% ) , su l ph i de s , ha e ma t i t e , goe t h i t e a nd s i de r i t e (10% ) . Coppe r i s p re se n t p re domi na n t l y a s ac ha l c opyr i t e (CuF e S 2) a nd t o a muc h l e s se r e x t e n t a s a c ove l l i t e (CuS ) . Muc h o f t he go l d oc c u r re d a si nc l us i ons o f na t i ve go l d i n c ha l c opyr i t e .

R a w m a t e r i a l 2 ( R M 2 ) . A c o p p e r - g o l d o r e . T h e c h e m i c a l c o m p o s i t io n w a s 5 to 1 0 p p m A u a n d 1 . 5 %Cu. M i ne ra l og i c a l l y t he s a mpl e c ons i s t s ma i n l y o f qua r t z wi t h sma l l e r a moun t s o f ka o l i n i t e , ha e m a t i t e a ndgoe t h i t e . The c opp e r mi ne ra l s a ppe a re d a s c ha l c opyr i t e (CuF e S 2) , c ha l c oc i t e (Cu2S ) a nd bo rn i t e (CusF e S 4) .The go l d d i s t r i bu t i on c ons i s t e d o f na t i ve go l d , mos t l y l i be ra t e d .


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Extraction of gold from low grade ores 1035R a w m a t e r i a l 3 (R M 3) . A c o pp e r -g o l d t a i li ng f rom t he f l o ta t i on c onc e n t ra t i on o f c oppe r o re . I ts c he mi c a lc om pos i t i on wa s 1 .15 % Cu a nd 4 to5 ppm Au . M i ne ra l og i c a l l y t he s a mpl e c ons i st e d ma i n l y o f qua r t z a ndka o l i n i t e wi t h sma l l e r a moun t s o f f e r rug i nous ox i de s a nd py r i t e s . The c oppe r mi ne ra l s a ppe a re d a sc ha l c oc i t e (Cu2S ) , c up r i t e (Cu20) a nd t o a muc h l e s se r e x t e n t a s c ove l l i t e (CuS ) a nd ma l a c h i t e( C u C O 3 x C u ( O H ) 2 ) .Th e pa r t i c l e s i z e o f r a w ma t e r i a ls w a s 9 0 % l e s s t ha n 74/ ~m.

E X P E R I M E N T STh e s l u r ry , 5 0% w/ v , w a s t r e a te d i n bo t h sys t e ms us ing bo t t l e ro l l i ng a nd a g i ta t i on t a nks (300 rpm) , unde ra mbi e n t t e mpe ra t u re . In t he c a se o f go l d l e a c h i ng by c ya n i de , a e ra t i on oc c u r re d t h rough t he u se o f ape r fo ra t e d l i d . pH , Eh a nd t he so l u t i on c om pos i t i on we re c on t ro l l e d du r i ng a l l t he p roc e s se s .The p roc e s se s wh i c h we re r e se a rc he d a re a s fo l l ows : go l d a nd c oppe r c ya n i de e x t ra c t i on , s e l e c t i ve go l da n d c o p p e r a m m o n i a - c y a n i d e e x t r ac t i o n , c o p p e r l ea c h in g b y s u l p hu r i c a c id a n d g o l d a n d c o p p e r e x t r a c t io ni n b r o m i n e s o l u t io n .The a l ka l i p roc e s se s s t a r t e d a t pH 11 wi t h spon t a ne ous de c re a se t o a bou t 10 (o r l e s s whe n p roc e s se s i na g i t a t i on t a nks we re run ) due t o va r i ous r e a c t i ons suc h a s c ya n i de ox i da t i on o r c a rbon d i ox i de a dso rp t i onf r o m t h e a t m o s p h e r e .The a c i d p roc e s se s we re run unde r pH 1 .5 t o 2 .5 .R M I - w a t e r s l u r r y h a s n a tu r a l a c id i ty o f p H = 2 . 4 , w h i l e R M 2 h a s p H 7 . 5 a n d R M 3 h a s p H 5 . 4 .C h e m i c a l a n a l y s i s o f t h e c o m p o n e n t s o f t h e s lu r r yS o l u t i o n a n a l y s i s . G o l d f r o m t h e l e a c h e d s o l u t i o n w a s d e t e r m i n e d b y A t o m i c A b s o r p t i o n S p e c t r o m e t r yus i ng o rga n i c s e l e c t i ve e x t ra c t i on i n DIBK so l u t i on . The c ha nge o f c oppe r c onc e n t ra t i on wa s de t e rmi ne db y t h e m e a s u r e m e n t o f t o t al c o p p e r b y A t o m i c A b s o r p t i o n S p e c t r o m e t ry .Re s i du e a n a l ys i s . G o l d a na l ys is wa s c a r r i e d ou t by t r e a t me n t o f t he r es i due a f t e r l e a c h i ng , u s i ng d i ge s t i oni n a qua re g i a . Th i s w a s do ne pa ra l l e l t o the so l u t i on a na lys i s . The se pa ra l le l a na l yse s we re e spe c i a l lyi mpo r t a n t i n the o re s a mpl e s i n wh i c h a c oa r se g ra de e f fe c t wa s e mp ha s i s e d , a s i n RM 2 .T h e c a l c u l a t i o n a n d p r e s e n t a t i o n o f g o l d a n d c o p p e r r e c o v e r y . The re su l t s o f go l d e x t ra c t i on a rep re se n t e d i n bo t h fo rms d i re c t l y a s c onc e n t ra t i on i n l e a c h i ng so l u t i on ( i n ppm un i t s ) a nd / o r i n % o f go l de x t ra c t i on . T he l a s t fo rm p re se n t s t he e f f i c i e nc y o f t he l e a c h i ng p roc e s s , c a l c ua l t e d us ing b o t h so l u t i on a ndre s i due go l d a na l yse s t o a c h i e ve t he h i ghe s t pos s i b l e a c c u ra c y .The a na l ys i s o f c oppe r e x t ra c t i on i s ba se d on c oppe r c onc e n t ra t i on i n t he l e a c h i ng so l u t i on . Th i sc onc e n t ra t i on shows d i re c t l y t he a pp l i c a b i l i t y o f t he so l u t i on fo r s e l e c t i ve go l d r e c ove ry .

R E S U L T S A N D D I S C U SS IO NThi s w ork i s a i me d a t p re se n t i ng a nd d i sc us s i ng go l d e x t ra c t ion f rom t h re e r a w m a t e r ia l s a s we l l as c op pe rre mo va l f ro m l e a c h so l u t i ons . A l ka li a nd a c i d le a c h i ng p roc e s ses a re e mp l oye d . T he op t i mi sa t i on o f t hep roc e s se s a nd a c ompa r i son o f t he m a c c o rd i ng t o va l i d i t y c r i t e r i a a re s t ud i e d .

C y a n i d e l e a ch i n gA funda m e n t a l s t udy on he t e roge nou s e qu i l ib r i um, k i ne t i c s and me c ha n i sm o f go l d l e a c h i ng i n t heA u - C u - N a C N - H 2 0 s y s te m w a s u n d e r ta k e n r e ce n tl y u s in g t h e H S C ( e n t h a l p y - e n t r o p y - h e a t c a p ac i ty )


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1036 s. Vukcevicc h e m i s t r y c o m p u t e r p r o g r a m p r o d u c e d b y O u t o k u m p u O y R e s e a r c h . T h i s s t u d y e x p l a i n s t h e p r o d u c t i o no f g o l d - c y a n i d e b y t h e r e a c ti o n o f g o l d w i t h f r e e c y a n id e :2 A u + 4 C N - + 1 /2 0 2 + H 2 0 = 2 A u ( C N ) 2 - + 2 O H - 5 G = - 4 6 . 8 6 k c al /m o l (1 )Coppe r i n c ya n i de so l u t i on p roduc e s Cu( I ) c ya n i de s wi t h t he s t a b i l i t i e s a s fo l l ows :S pe c i e s CuC N C u(CN)2 - Cu(CN)32 - Cu(CN)43 -AG , kc a l / mo l 25 .88 83 .11 129 .90 180 .71The se c ya n i de s a re r e spons i b l e fo r t he go l d l e a c h i ng i n t he a bse nc e o f t r e e c ya n i de i n t he so l u t i on , unde rc ond i t i ons s imi l a r t o indus t ry u s ing 0 .01 t o 0 .03 mol N a CN , a s the fo l l owi ng re a c ti ons show:A u + 2 C u ( C N ) 4 3 - + 1 / 40 2 + 1 / 2 H 2 0 = A u ( C N ) 2 - + 2 C u ( C N ) 3 2 - + O H - A G = - 4 2 . 6 8 k c al /m o l ( 2)2 A u + 4 C u ( C N ) 3 2 - + 1 / 2 0 2 + H 2 0 = 2 A u ( C N ) 2 - + 4 C u ( C N ) 2 -

A u + C u ( C N ) 2 - + 1 / 4 0 2 + 1 / 2H 2 0 = A u ( C N ) 2 - + C u + + O H -

+ 2 O H - A G = - 6 9 . 3 2 k c a l / m o l(3 )

A G = - 4 8 . 8 9 k c a l / m o l ( 4 )F i g u r e 1 p r e s e n ts t h e l o g ( m o l ) - m o l s t ab i li ty d i ag r a m . T h e c o n c e n t r a t io n o f p r o d u c t s a t ( th e o r e ti c a l)e qu i l i b r i um s t a t e s , e xp re s se d i n mo l , i s c a l c u l a t e d us i ng t he a moun t o f r a w ma t e r i a l s i n t he sys t e m.Af t e r a c h i e v i ng a s t a te o f e qu i l i b r ium, c opp e r s t a r ts t o p re c i p i ta t e f rom t he so l u t i on , a s t h i s e xpe r i me n t a lw ork sh owe d , a c c o rd i ng t o t he fo l l owi ng re a c t ions :C u (C N ) 2 - + 1 /4 0 2 + O H - = C u O + 2 C N - + 1 /2 H 2 0 A G = - 2 2 . 1 2 k ca l/ m ol

2 C u( CN ) 2 - + 2 O H - = C u 20 + 4 C N - + H 2 0 A G = - 1 8 . 2 9 k c a l / m o lC u (C N ) 2 - + 1 /2 0 2 = C u C N + O C N - A G = - 8 0 . 5 2 k ca l/m o l

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_Z _.c ( C N ) 3 ( - 2 a )

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F i g. 1 L o g ( m o l ) - m o l d ia g ra m f o r th e A u - C u - N a C N - H 2 0 a t 2 5 C ;[ A u ] = 5 x 1 0 - 5 m o l ; [ C u ] = 2 x 1 0 - 1 t o o l; [ N a C N ] = 10 - 3 t o o l; [ 0 2 ] = 1 0 - 3 t o ol


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Extraction of gold from low grade ores 1037Th e e xpe r i me n t a l op t i mi sa t i on o f t he Na CN c onc e n t ra t i on wa s a i me d a t a c h i e v i ng go l d e x t ra c t i on a t a l e ve lm o r e t h a n 6 0 % . T h i s l e d to v e r y h i g h C u c o n c e n t r a t i o n i n th e s o l u ti o n o f 1 0 0 0 p p m C u a n d l o w C upre c i p i t a t i on ,w he n a n i n it i a l 1 .5% C u wa s p re se n t i n t he sys t e m [22 ] .T h e r m o d y n a m i c a l l y , w h e n C u - m i n e r al s a re c y a n is e d , C u ( C N ) 2 - i s p r o d u c e d w i th m o r e n e g a t i v e A G v a l u et h a n A u ( C N ) 2 - . A l s o , c o p p e r c o n c e n t ra t i o n i n th e s y s t e m is m u c h h i g h e r t h a n g o l d an d k i n e t ic s o f c o p p e rc ya n i d a t i on i s f a s t e r . I t is und e rs t ood t ha t c onc e n t ra t i on o f Cu i n so l u t i on p l a ys a s i gn i f ic a n t ro l e i n go l de x t ra c t i on . Th i s c on c e n t ra t i on de pe nds on t he t ype o f Cu mi ne ra l u se d a nd i t s so l ub i l it y . W he n 1 .5 % o ft he i n i ti a l Cu i n t he fo rm o f d i f f e re n t mi ne ra l s wa s d i l u t e d t oge t he r wi t h 10 ppm o f Au p ow de r , t he h i ghe s tc onc e n t ra t i on i n so l u t i on wa s p roduc e d w he n C u2 0 a nd Cu2S mi ne ra l s we re t r e a t e d . The so l ub i l i t y o f Cuf ro m C uO a nd e sp e c i a l ly CuF e S 2 is muc h l ow e r (Ta b l e 1 ). Con se que n t l y , t he l owe s t go l d e x t ra c t i ono c c u r r e d w h e n C u 2 0 w a s l e a c h e d .

TA BLE 1 S o lu b i l i t y o f cop p er f rom d i f f eren t min era l s ,l each ed w i th 1 .6 g / ! N aC N in p res en ce o f go ld

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757 I- - 708"1-5 - - 4 278-6-2 - - 4 25

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T h e p r e l i m i n a r y t e s ts o f l e a c h in g o f o r e s i n cy a n i d e s o l u ti o n s f o r 2 4 h o u r s s h o w e d l o w s o l u b i li t y o f c o p p e r( 2 5 % ) f r o m R M 1 , b u t h i g h s o l u b il it y ( 7 3 % ) f r o m R M 2 a n d 8 0 % f r o m R M 3 , u n d e r h i g h l y c o n c e n t r a t edN a C N s o l u t io n ( T a b l e 2 ) . T h e r e a s o n f o r t h is i s t h a t R M 1 c o n s is t s m o s t l y o f C u F e S 2 w i t h l o w C uc o n c e n t r a t i o n an d t h e R M 2 a n d R M 3 h a v e h i g h C u c o n c e n t r a t io n w i t h m o r e s o l u b l e m i n e ra l s a p p e a r in g(Cu2S , C u2 0 , CuS ) . H i gh go l d l e a c h i ng is e xp l a i ne d by t he p re se nc e o f h i gh f r e e c ya n i de i n the sys t e m,a c c o rd i ng t o r e a c t i on (1 ) .

TA BLE 2 C op p er an d go ld l each in g f rom ores u s in g cyan id e s o lu t ion sN a C N ,

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Th e sa me c op pe r so l ub i l i t y f rom R M 1 wa s foun d by l e a c h i ng wi t h o t he r r e a c t a n ts , suc h a s we a k e r c ya n i deso l u t i ons (Ta b l e 2 ) , su l phur i c a c i d a nd b romi ne so l u t i ons . Mos t o f t he d i s so l ve d c oppe r c ome s f rommi ne ra l s i n t he o re o t he r t ha n c ha l c opyr i t e .A d e c r e a s e o f N a C N c o n c e n t r a ti o n r e s u lt e d in a d e c r ea s e o f C u a n d A u . B e l o w 1 . 65 k g / t N a C N , o n l y 1 7% A u a n d 4 % ( 6 5 0 p p m ) o f C u w e r e e x t r a c te d f r o m R M 2 . W h e n m e t a l li c C u w a s l e a c h ed u n d e r t h e s a m ec o n d i t i o n s , 5 0 0 p p m o f C u i n s o lu t i o n an d l e ss t h a n 2 0 % o f A u w e r e f o u n d .Th i s i nd ic a t e s t ha t h i gh c o ppe r c onc e n t ra t i on a c h i e ve d by l e a c h i ng RM 2 a nd RM 3 , a nd c ons e que n t l y lowl e ve l o f go l d e x t ra c t i on , c a use h i gh c y a n i de c onsump t i on . To a n a l yse s e l e c ti ve go l d le a c h i ng a t l owe rre a c t a n t c onsum pt i on , a l t e rna t i ve l e a ch i ng me t ho ds a re c ons i de re d i n t he fo l l owi ng s e c t ion .


6/15

1038 S. Vu kcevicS u l p h u r i c a c i d l e a c h in g w i t h c y a n i d e p o s t - t r e a t m e n tR M 1 w a s t r e a t e d w i t h s u l p h u r i c a c i d s o l u t io n c o n c e n t r a ti o n s f r o m 2 . 5 t o 1 0 % H 2 S O 4 . T h e c o n c e n t r a t i o no f c o p p e r f o u n d i n t h e s o l u t io n c a n b e s e en i n T a b l e 3 . I n t h e n ex t p r o c e s s - - c y a n i d a t i o n , o n l y 1 5 - 3 0 p p mC u w a s l e a c h ed . A f t e r a c i d p r e - t re a t m e n t , g o l d w a s l e a c h e d w i t h s e v e r a l u n it s l es s e x t r a c ti o n ( 6 8 % ) , t h a nw h e n t h e a c i d tr e a t m e n t w a s n o t e m p l o y e d . T h e r e f o r e , h i g h e r c y a n i d e c o n s u m p t i o n f o r g o l d l e a c h i n g o fa c id p r e - t r e a t e d m a te r i a l c a n b e o f f s e t w i th v e r y goo d se l e c t iv i t y o f go ld o ve r c o ppe r a s a fi na l r e su l t .

T A B L E 3 E f fe c t o f p r e - tr e a tm e n t o f R M 1 w i t h H 2 S O 4o n l e a c h in g o f c o p p e r w i t h 1 .6 5 g /I N a C N

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C y a n i d e - a m m o n i a le a ch in gK i n e t i c s a n d m e c h a n i s m . T h e s t u d y o f t h e k i n e t i c s a n d m e c h a n i s m o f s e l e c t i v e g o l d l e a c h i n g i n t h ec y a n i d e a m m o n i a s y s t e m s h o w s d i f f e r e n t m o d e l s f o r g o l d s e le c t i o n o v e r c o p p e r [ 1 3 ] . R e s e a r c h h a s s h o w nt h a t a m m o n i a a p p e a r s t o c a t a l y s e t h e a n o d i c d i s s o l u t io n o f g o l d w i t h c y a n i d e [ 1 3] a n d o t h e r e l e c t r o c h e m i c a lr e s e a r ch h a s s h o w n t h a t a m m o n i a g r e a t l y s u p p r e s s es t h e a n o d i c h a l f re a c t io n [ 1 4 ] . T h e s e , a n d o t h e r r e s u l t s[ 8 , 9 , 1 3 , 1 4 ] , a r e b a s e d o n t h e t h e r m o d y n a m i c c o n s i d e ra t i o n o f o n l y t e n s p e c ie s , a n d s o m e a r e o b t a i n e dus ing c onc e n t r a t i ons o f r e a c t a n t s no t a pp r op r i a t e t o a pp l i c a t ion in i ndus t r y . A r e c e n t s tudy [ 22 ] w a s a im e da t c o n s i d e r i n g t h e k i n e t i c s a n d m e c h a n i s m o f s e l e c t i v e g o l d l e a c h i n g u n d e r c o n d i t i o n s a p p r o p r i a t e t oindus t r i a l a pp l i c a t ion . Th i s s tudy i s a l so ba se d on the t he r m odyna m ic a na ly s i s o f 120 d i f f e r e n t spe c i e s ,w h i c h w e r e c h o s e n f r o m a d a t a b a s e c o n s i s t in g o f 5 6 0 0 s p e c i e s ,u s i n g t h e H S C c h e m i s t r y c o m p u t e r p r o g r a mm a d e b y O u t o k u m p u R e se a rc h O y .T h e E h - p H d i a g r a m s o f t h e s t ab i l it y o f A u a n d C u s p e c ie s a r e s h o w n i n F i g u r e s 2 an d 3 . T h e a r e a o f t heh i g h e s t s t a b il i ty o f A u ( C N ) 2 - e x i s ts u p t o p H = 6 . 5 , a n d a t l o w e r E h a r e a s c o m p a r e d t o t h e s y s t e m w i t h o u ta m m o n i a [ 2 2 ] . T h e m o s t i m p o r t a n t ro l e o f a m m o n i a i s th e p r o d u c t i o n o f C u - N H 3 s p e c i es .

T h e p r i o r it y o f th e e x i s te n c e o f re l ev a n t s pe c ie s i n t h e A u - C u - C N - N H 3 - H 2 0 s y s t e m a nd t h e e f fe c t o f C Na n d N H 4 c o n c e n t r a t i o n w e r e a n a l y s e d b y t h e m e t h o d e x p l a i n e d a b o v e a n d i t w a s t b u n d t h a t a f t e r C u C Na n d A u ( C N ) 2 - t h e m o s t t h e r m o d y n a m i c a l l y p r o b a b l e s p e c ie s i n t hi s s y s t e m a r e C u - N H 3 s p e c i es .T h e C u - N H 3 i o n s a r e p r o d u c e d b y t h e a d d i t i o n o f a m m o n i a d u r i n g t h e o x i d a t i o n o f g o l d m e t a l t oA u ( C N ) 2 - b y c h e m i c a l r e a c ti o n i n cl u d i n g C u ( I ) c y a n i d e f r o m t h e s y s t e m :A u + C u ( C N ) 2 - + 4 N H 3 + 1 / 2 0 2 + H 2 0 = A u ( C N ) 2 - + C u (N H 3 ) 42 + + 2 O H - A G = - 3 4 . 6 7 k c a l/ m o l (8 )T h e y a r e a l s o i n c l u d e d i n C u p r e c i p i ta t i o n b y d e c o m p o s i t i o n o f C u ( N H 3 ) 4 2 + a c c o r d i n g t o t h e r e a ct i o n :C u ( N H 3 ) 4 2 + + 2 O H - = C u ( O H ) 2 + 4 N H 3 A G = - - 9 . 3 4 k c a l / m o l ( 9)T h i s s t u d y c o n f i r m s , t h e r e f o r e , t h e p o s i ti v e ro l e o f a m m o n i a i n t h e c y a n i d e s y s t e m , a s it h e l p s b o t h c o p p e rp r e c ip i t a t i on a nd go ld l e a c h ing . P r oc e s s op t im i sa t ion w a s unde r t a ke n he r e t o f i nd the be s t r e a c t a n t


7/15

Extraction of gold from low grade ores 1039c o m p o s i t i o n f o r t h e s e l e ct i o n o f g o l d o v e r c o p p e r b y t h e l e a c hi n g o f na t u ra l o r e s R M 1 t o R M 3 . A l t h o u g ht h is s y s t e m i s m u c h m o r e c o m p l i c a te d , w i t h th e i n v o l v e m e n t o f m a n y o t h e r e l e m e n t s , t h e b a s ic m o d e lde ve l ope d i n [22 ] i s r e l e va n t . /

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F i g .3 C u s p ec ie s in E h - p H d i ag r a m f o r t he A u - C u - N a C N - N H 4 C 1 - H 2 0 s y s te m a t 2 5 C ;[ A u] = 5 x 1 0 - S m o l ; [ Cu ] = 2 . 4 x 1 0 - 1 m o l ; [ N aC N ] = 3 . 4 x l 0 - 2 m o l ; [ N H 4 C 1 ] = 4 x 1 0 - 2 m o l ; [ O 2 ] = 1 0 - 2 t oo l


8/15

1 0 4 0 S . V u k c e v i c

O p t i m i s a t i o n . W h e n R M 2 w a s l e a c h ed w i t h 1 . 6 5 k g / t N a C N , 1 7% o f g o l d w a s e x tr a c t ed . T h e a d d i t io no f 1 .1 k g / t o f N H 3 i n th i s s y s t e m i n c r e a se s g o l d l e a ch i n g f r o m 1 7 to 6 0 % a n d d e c r e a s e s c o p p e rc o n c e n t r a t i o n i n l e a c h s o l u t i o n f r o m 6 5 0 t o 4 3 0 p p m d u e t o p r e c ip i t a ti o n .H o w e v e r , t h e a d d i ti o n o f 0 . 7 9 t o 1 .1 k g / t o f N H 3 i n th e s a m e c y a n i d e s y s t e m f o r R M 1 , i n cr e a se d g o l de x t r a c t i o n b y o n l y 1 0 - 2 0 % . T h i s w a s f o l lo w e d b y a 1 7 % d e c r e a s e i n c o p p e r c o n c e n t r a t io n i n t h e s o l u t io n ,f r om 180 to 150 ppm .T o c o n f i r m t h e d i f f e r e n c e w h i c h a m m o n i a c a u s e s i n th e c y a n i d a t i o n o f th e s e t w o m a t e r i a l s , a s y s t e m a t i co p t i m i s a t i o n o f b o t h s y s t e m s w a s d e v e l o p e d . T h e r e s u l t s s h o w t h a t t h e i n f l u e n c e o f t h e c y a n i d ec o n c e n t r a t i o n i s s u p e r i o r , c o m p a r e d t o t h e a m m o n i a f o r R M 1 ( F i g u r e 4 a n d F i g u r e 5 , b o t h o b t a i n e d u n d e re igh t d i f f e r e n t l e a c h ing c ond i t i ons ) , w h i l e R M 2 l e a c h ing i s c ha r a c t e r i s e d by a m or e s ign i f i c a n t i n f lue nc eo f N H 3 ( F i g u r e s 6 a n d 7 , b o t h o b t a i n e d u s i n g e i g h t e e n d i f f e r en t l e a c h i n g c o n d i t i o n s ) .

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F i g . 4 E f f e c t o f a m m o n i a a n d c y a n i d e o n g o l d l e a c h i n g f r o m R M 1 , a f t e r 2 4 h o u r s

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9/15

Extraction of gold from low grade ores 1041

F i g . 6 E f f e c t o f a m m o n i a a n d c y a n i d e o n g o l d l e a ch i n g f r o m R M 2 , a f t e r 2 4 h o u r s

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F i g . 7 E f f e c t o f a m m o n i a a n d c y a n i d e o n c o p p e r l e ac h i n g f r o m R M 2 , a f t er 2 4 h o u r sT h e p r e s e n c e o f 3 k g / t N H 3 a l lo w s 8 9 % A u e x t r a c t io n f r o m R M 2 o r e , u n d e r o n l y 0 .5 5 k g / t N a C N (F i gu re 6 ) . T he c onc e n t ra t i on o f c opp e r i n so l u t i on unde r t he s a me c ond i t i ons i s 200 ppm, wh i c h i s aq u a r t e r o f t h e c o p p e r f o u n d b y l e ac h i n g in 2 k g / t N a C N s o l u ti o n w i t h o u t a m m o n i a ( F i g u r e 7 ) . A l t h o u g ha mmoni a i n t h i s sys t e m ha s a s i gn i f i c a n t ro l e i n e nha nc i ng go l d l e a c h i ng a c c o rd i ng t o r e a c t i on (8 ) i t a l sos t r e ng t he ns t he p re c i p i t a t i on o f C u(O H) 2 ( r e a c t i on (9 ) ) .


10/15

1042 s. Vuk cevicU s i n g t h e s a m e a m o u n t o f c y a n i d e , 0 . 5 5 k g / t a n d 2 . 2 k g / t N H 3 , t h e g o l d f r o m R M 1 i s l ea c h e d w i t h a ne x t r a c t io n o f n o t m o r e t h a n 7 3 % . A l t h o u g h t h is l o w c y a n i d e c o n c e n t r a ti o n w a s d e s i r a b le f o r l o w C uc o n c e n t r a t i o n ( 11 1 p p m ) , g o l d c o u l d n o t b e l e a ch e d d u e t o t h e h ig h a d s o r p t i o n o f g a n g u e m i n e r a ls a n d i tsl o w i n i t ia l c o n c e n t r a ti o n ( 1 .5 p p m ) . A l s o , t h e c o n c e n t r a t io n o f 2 . 2 k g / t o f a m m o n i a w a s n o t e n o u g h t od r i v e r e a c t i o n ( 8 ) to t h e r i g h t . G o l d c a n b e s u c c e s sf u l ly l e a c h e d ( 8 5 - 9 0 % ) o n l y w i t h a h i g h l e v e l o f c y a n i d ec o n c e n t r a t i o n ( 1 . 6 5 k g / t ) f r o m t h i s o r e . I n t h i s c as e , a l o w l e v e l o f a m m o n i a c o n c e n t r a t io n i s d e si r a b l e( < 1 .1 k g / t ) . A h i g h e r l e v e l o f a m m o n i a d i ss o l v e s C u - c o m p o u n d s a l r ea d y p r e c i p i ta t e d a n d t h e r e f o r einc r e a se s t he C u c onc e n t r a t i on in so lu t ion ( F igu r e s 4 a nd 5 ) .C o p p e r r e m o v a l . A n a n a l y s is o f th e c o p p e r r em o v e d f r o m t he l e a ch i n g s o lu t io n i n th e a m m o n i a c y a n id esys t e m show s tha t a m m on ia ha s s ign i f i c a n t i n f lue nc e on i t .S i m i l a r i ty i n t h e s h a p e o f b o t h d i a g r a m s , F i g u r e 7 ( t h e e ff e c t o f a m m o n i a a n d c y a n i d e o n c o p p e r l e a c h in gf r o m R M 2 , a f t e r 2 4 h o u r s ) a n d F i g u r e 8 ( t h e e f f e c t o f a m m o n i a a n d c y a n i d e o n c o p p e r l e a c h in g f r o m R M2, a f t e r 10 m inu te s , bo th ob ta in e d u s ing e igh te e n d i f f e r e n t le a c h ing c ond i t i ons ) , i s f ound . The pa r t s o f t he setw o d i a g r a m s r e l a t e d to t he a r e a o f low c ya n ide c onc e n t r a t i ons ( 0 . 55 k g / t N a C N ) , a r e ne a r ly i de n t i c a l( a b o u t 2 0 0 p p m C u p r e s e n t i n t h e s o l u t i o n ) . H o w e v e r , i t r e q u i r e d 2 4 h o u r s t o a c h i e v e s i g n i f i c a n t c o p p e rp r e c ip i t a t i on in the a r e a o f h igh c onc e n t r a t i on o f le a c h ing r e a c t a n t s ( t he " ne a r e r r i gh t " a r e a o f thed i a g r a m s - - F i g u r e 7 ) .

F i g . 8 E f f e c t o f a m m o n i a a n d c y a n i d e o n c o p p e r l ea c h i n g f r o m R M 2 , a f t e r 1 0 m i n u t e sTo r a t i on a l i s e t he se f i nd ings t he i n flue nc e o f a m m o n ia a t the h ighe s t l e ve l o f c ya n ide ( 2 kg / t ) , w a si n v e s t i g a t e d ( F i g u r e 9 ) . W i t h o u t a m m o n i a , a h i g h c o p p e r c o n c e n t r a t i o n w a s f o u n d i n s o l u t i o n a f t e r 1 0m inu te s . I t is m uc h h ighe r a f t e r 24 hou r s . The u se o f a m m on i a t o 1 . 5 kg / t de c r e a se s t he f i nal C uc onc e n t r a t i on in so lu t ion , bu t i t is s ti l l h ighe r a f t e r 24 hou r s t ha n a f t e r 10 m inu te s . S uc h a h igh in i ti a l l e ve lo f c y a n i d e ( 2 k g / t ) c a u s e d h i g h c o p p e r c o n c e n t r a t i o n i n s o l u ti o n d u e t o t h e h i g h c o n c e n t r a ti o n o f c o p p e ri n R M 2 a n d t h e p r e s e n c e o f C u 2 S ( h ig h s o l u b l e m i n e r a l f o r m ) . T h i s r eq u i r e s m o r e a m m o n i a t o a c h i e v ea s o l u t i o n c o m p o s i t i o n s u i t a b le f o r d e c o m p o s i t i o n o f C u ( N H 3 ) 4 2 + t o C u ( O H ) 2 a n d a l o n g p r o c e s s o fo x i d a t i o n o f C u ( I ) t o C u O . T h e s e c o n d i t i o n s a r e l a b e l l e d a s 5 a n d 6 i n F i g u r e 9 a n d c o r r e s p o n d t o t h e" n e a r e r r i g h t " a r e a i n F i g u r e 7 a n d F i g u r e 8 .


11/15


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F i g . 9 E f f e c t o f a m m o n i a o n c o p p e r r e m o v a l u n d e r c o n s t an t N a C N ( 2 k g / t );W hi t e ba r s : C u i n so l u t i on a f t e r 10 mi nu t e s ; B l a c k ba r s : C u i n so l u t i on a f te r 24 hours ;

T h e l i n e : ch a n g e o f t h e a m m o n i a a m o u n t

V a l i d i ty c r i t e r i a . T h e r e a re t h r e e i m p o r t a n t c r it e r ia f o r t h e a s s e s sm e n t o f t h e a m m o n i a - c y a n i d e p r o c e s s :t h e e f f i c i e n c y o f g o l d e x t r a c ti o n , t h e s e l e ct i v it y o f g o l d o v e r c o p p e r a n d t h e c o n s u m p t i o n o f t h e r e a ct a n ts .A c c o r d i n g t o t h e s e c r it e r ia , a m m o n i a - c y a n i d e l e ac h i n g s h o w s g o o d p o s s i b i li ti e s f o r a p p l ic a t io n w i t h R M2 a n d R M 3 . H i g h g o l d e x tr a c t i o n f o r b o t h R M 2 a n d R M 3 ( 8 5 - 9 0 % ) i s a c h i e v e d u s i n g o n l y 0 . 5 5 k g / t ,2 . 2 - 3 k g / t N H 3 a n d 6 - 1 0 k g / t N a O H ( t o ac h i e v e t h e r e q u ir e d p H 1 1 ). G o o d r e s u lt s i n t h e r e m o v a l o f t h ec o p p e r a r e a c h i e v e d a n d 1 0 0 - 2 0 0 p p m C u r e m a i n e d i n th e f in a l l e a ch i n g s o l u ti o n a ft e r 2 4 h o u r s .G o l d e x t r a c t i o n f r o m R M 1 is o f t h e s a m e h i g h v a l u e ( 9 0 % ) a n d t h e r e m a i n i n g c o p p e r i n t h e s o l u t i o n is150 ppm, und e r 1 .65 kg / t N a CN a nd 0 .79 kg / t N H 3 . The se r e su l ts ba s i c a ll y s a t is fy t he c r i t e r i a .T o a n a l y s e b o t h c o p p e r r e m o v a l a n d g o l d e x t r a c t io n f r o m R M 1 , th e s a m e o p t i m i s e d s o lu t i o n c o m p o s i t i o nf o r R M 2 a n d R M 3 , o f 0 . 5 5 k g / t N a C N a n d 2 . 2 k g / t N H 3 w a s e m p l o y e d . T h e r e m a i n i n g c o p p e r i n th eso l u t i on i s l ow , s i mi l a r t o t he RM 3 l e a c h ing re su lt s . H ow e ve r , Au e x t ra c t i on e f f ic i e nc y fo r RM 1 und e rt he r e se a rc he d c on d i t i ons i s a bou t 70% , t he s ame re su l t be i ng ga i ne d i f u s i ng me re l y 1 .65 kg / t N a CN( w i t h o u t t h e a m m o n i a ) !F r o m t h e p o i n t o f v i e w o f e c o n o m y o f re a c ta n t c o n s u m p t i o n f o r th e l e a c h in g o f R M " I , t h e r e i s n o c r u c i a ld i f f e r e n c e b e t w e e n u s i n g t h e s e t w o s y s t em s : c y a n i d e a n d a m m o n i a - c y a n i d e . F r o m t h e s e l e c ti v i ty p o i n t o fv i e w , t he i nvo l ve m e n t o f a mm oni a i n RM 1 c ya ni de " l e a c h i ng is a dva n t a ge ous , a s Cu i n so l u t i on d rops f rom1 8 0 t o 1 11 p p m . H o w e v e r , t h e h i g h a c id i t y o f th e R M 1 - w a te r s l u r r y r e q u i r e d 3 - 5 t i m e s m o r e N a O H f o rl e a c h i n g t h a n f o r l e a c h i n g o f R M 2 o r R M 3 , w h e t h e r c y a n i d e o r a m m o n i a - c y a n i d e w a s e m p l o y e d .G o l d a n d c o p p e r e x t r a c t i o n w i t h b r o m i n eT h e m a i n r e a s o n f o r e m p l o y i n g b r o m i n e l e a ch i n g is t h e h i g h a c id i ty o f R M l - w a t e r s l u r r y , p H 2 . 4 . T h el e a c h in g s o l u t i o n w a s p r e p a r e d w i t h a B r2 an d N a B r m i x t u re .


12/15

1044 s. VukcevicTh e k i ne t i c s o f bo t h g o l d a nd c o ppe r l e a c h i ng us i ng a c i d i c p roc e s ses i s sl i gh t ly d i f f e re n t c om pa re d t o t hea l ka li p roc e s se s . Ta b l e 4 shows t he f ir s t hou r o f go l d l e a c h i ng fo r t h re e d i f f e re n t c ompos i t i ons o f b rom i neso l u t i on . The s a me va l ue s o f go l d e x t ra c t i on a f t e r 24 hours w e re found a s a f t e r one hour . In f a c t, 90 % o fe x t ra c t e d go l d i s a c h i e ve d a f t e r 5 mi nu t e s .

T A B L E 4 G o l d e x t r a c ti o n w i t h b r o m i n e

T i m e , h r s0 . 2 5

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Gol d i n so l u t i on , ppm,0.7 5 ml /1 2 .5 ml /1

0 . 4 7 0 . 8 80 . 5 5 0 . 8 7

5 ml/11.11.1

Th e a na l ys i s o f k ine t i c s o f c opp e r l e a c h ing shows t ha t fo r t he l owe r c onc e n t ra t i ons o f 0 .75 a nd 2 .5 m lBr2 / 1 , c oppe r c onc e n t ra t i on i n t he l e a c h i ng so l u t i on i nc re a se s du r i ng 24 hours t o 180 ppm, bu t s t a gna t e sa t t he s a me va l ue a f t e r on l y 5 mi nu t e s u s i ng 5 ml Br2 / 1 .Th e op t i ma l c on d i t i ons fo r th i s sys t e m a re whe n a b rom i ne c onc e n t ra t i on o f l e ss t ha n 2 .5 ml /1 is e mp l oye dt o a c h i e ve a n a c c e p t a b l e l e ve l o f 140 ppm Cu a f t e r 5 mi nu t e s .C omp arin g th e l each in g s ys temsW he n c ons i de r i ng bo t h a l ka l i a nd a c i d l e a c h i ng , a dd i t i ona l va l i d i t y c r i t e r i a a re r e qu i re d : go l d l e a c h i ngk i ne t i c s , r e s i s t a nc e o f t he e qu i pm e n t t o t he c o r ros i ve a c t ion o f t he c omp one n t s a nd t ox i c i t y o f c ya n i de .Th e fa s t e s t l e a c h i ng i s a c h i e ve d by us i ng the b rom i ne so l u t i on , a s 90% o f go l d i s e x t ra c t e d a f t e r 5 m i nu t e s .A h i g h g o l d e x t r a c t i o n o f 8 7 % i s a c h i e v e d i n t h e a m m o n i a - c y a n i d e s y s t e m f o r R M 1 . C o m p a r e d t oc ya n i da t i on on l y , a ne g l i g i b l e h i ghe r r e a c ta n t c onsum pt i on o f c ya n i de oc c u r re d wi t h t he u se o f a su l phur i ca c i d p re t r e a t me n t a nd re su l t e d i n 68 % o f go l d l e a c h i ng i n pos t -c ya n i da t ion .Th e k i ne t i c s o f go l d e x t ra c t i on fo r t he r e se a rc he d ma t e r i al RM 3 i s p re se n t e d i n F i gu re 10 . Un de rop t i mi se d a m mo ni a -c y a n i d e l e a c h ing , 85 % o f go l d e x t ra c t i on is a c h i e ve d , (uppe r c u rve ) . A u wa s l e a c he dby p r odu c t i on o f Au(C N) 2 - a c c o rd i ng t o r e a c ti on (8 ). Co ppe r c onc e n t ra t i on i n so l u t i on wa s l ow , < 100p p m . U n d e r n o n - o p t i m i s e d a m m o n i a - c y a n i d e l e a ch i n g , 6 5 % o f g o l d e x t r a c ti o n i s a ch i e v e d ( lo w e r c u r v e ) .A h i gh l e ve l o f c ya n i de c on c e n t ra t i on c a use d h i gh c onc e n t ra t i on o f Cu i n so l u t i on a nd a mm oni a wa s no t" p o w e r f u l e n o u g h " d u r i n g o x i d a t i o n o f A u m e t a l t o A u ( C N ) 2 - .Co ppe r r e ma i n i ng i n so l u t ion a f t e r 24 hours o f l e a c h i ng us ing d i f f e re n t re a c t a n ts i s p re se n t e d i n F i gu re 11 .On l y c ya n i de l e a c h i ng wa s e m pl oye d unde r l e a c h i ng c ond i t i ons 1 a nd 9 . Und e r c ond i t i on 1 , t hec o n c e n t r a t io n o f C u a f t er 2 4 h o u r s i s e x tr e m e l y l o w ( 3 0 p p m ) a s H 2 SO 4 p re - t r ea t m e n t w a s e m p l o y e d . W i t ht h e s a m e a m o u n t o f c y a n i d e ( c o n d i t io n 9 ) , 1 80 p p m o f C u w a s d e t e rm i n e d . W i t h a d d i ti o n o f a m m o n i a ,l ow e r l e ve l s o f Cu c on c e n t ra t i on we re de t e rm i ne d , c ond i t i ons 2 t o 8 , F i gu re 11 .F o r t he pu rp ose o f C IP o r R IP go l d l e ac h i ng , t he be s t sy s t e m fo r RM 1 i s c ya n i de l e a c h i ng wi t h su l phur i ca c i d p re t r e a t me n t . In e x i s ti ng go l d te c hno l ogy , a c t iva t e d c a rbon fo r go l d r e c ove ry i s u se d . C a rbon re a d i l ya dso rbs a mm oni a a nd t he Cu-c ya n i de spe c i e s wi t h li t tl e d i s c r i mi na t i on ove r Au-c ya n i de . T hus i t is pos s i b l et o s e l e c t i ve l y a dso rb go l d f rom so l u t i on us i ng a c t i va t e d c a rbon p rov i de d t he c onc e n t ra t i on o f c oppe r i ns o l u t io n is l o w , < 2 0 0 p p m a p p r o x i m a t e l y . T h e r e f o r e , a m m o n i a - c y a n i d e le a c h in g c a n b e r e c o m m e n d e df o r R M 2 a n d R M 3 .To a c c e p t b romi ne l e a c h i ng a s a n a l t e rna t i ve p roc e s s , c ruc i a l c ha nge s i n i ndus t ry a re r e qu i re d . Howe ve r ,t he se r e su l t s i nd i c a t e s i gn i f i ca n t l y f a s t e r k i ne ti c s o f go l d l e a c h i ng c om pa re d t o c ya n i da t i on .


13/15


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7 8 9F i g . 11 Co ppe r r e m a i n i ng i n so l u t ion (b l a c k s t ri p ) a f t e r 24 hours o f l e a c h i ng unde r d i f f e re n t c ond i t i ons :

c o n d i t i o n n u m b e r p r e s e n t s t h e a m o u n t o f N a C N ( b l a c k - w h i t e s t r ip ) a n d N H 3 ( w h i te s t r ip )

C O N C L U S I O N S

Va l i d i t y c r i t e r i a fo r bo t h a l ka l i a nd a c i d p roc e s se s o f go l d l e a c h i ng f rom non-c onve n t i ona l go l d o re s a re :go l d e x t ra c t i on , s e l e c t i v i t y o f go l d ove r c oppe r , r e a c t an t s c onsumpt i on , go l d l e a c h ing k i n e t i c s , r e s i s ta nc eo f t h e e q u i p m e n t t o t h e c o r r o s i v e a c t io n o f t h e c o m p o n e n t s a n d t o x i c i ty o f c y a n i d e .


14/15

1046 S. Vu kcev icT h e a p p l i c a t i o n o f a c y a n i d e l e a ch i n g s y s t e m o n t h e R M 2 a n d R M 3 a c ts t o b o t h e x t ra c t 6 0 0 t o 8 0 0 p p mC u in so lu t ion a nd su pp r e s s g o ld l e a c h ing to a m a x im um o f 17 % , a t a c ya n ide c on c e n t r a t i on o f 1 .65 kg / t .Th i s i s be c a use o f t he h igh l e ve l o f C u p r e se n t i n t he se o r e s , a s w e l l as t he p r e se nc e o f h igh c o ppe r so lub lem i n e r a l s C u 2 0 a n d C u 2 S . T h e r e i s a h i g h e r t h e r m o d y n a m i c p o s s ib i l i ty o f p r o d u c t i o n o f C u ( C N ) 2 - f r o mC u- m ine r a l s t h a n the A u( C N ) 2 - i n t he sy s t e m . A l so , t he k ine t i c s o f C u c ya n id a t ion i s f as t .R M 1 is c h a r a c te r i s e d w i t h l o w e r c o p p e r c o n c e n t r a ti o n a n d l e ss s o l u b l e c o p p e r s u l p h id e m i n e r a ls ( m a i n l yC u F e S 2 ) . T h e r e f o r e , a l o w e r c o p p e r c o n c e n t r a t i o n i n a le a c h in g s o l u t io n o f 1 8 0 p p m , a n d c o n s e q u e n t l yh i g h e r g o l d e x t r a c t i o n o f 7 0 % h a v e b e e n a c h i e v e d u n d e r t h e s a m e c y a n i d e c o n c e n t r a t i o n o f 1 . 6 5 k g / tN a C N . T h i s c o n c e n t r a t i o n a l l o w e d a n o p t i m a l c o n c e n t r a t i o n o f C u ( I ) c y a n i d e s r e s p o n s i b l e f o r o x i d i s i n go f g o l d m e t a l t o A u ( C N ) 2 - .W h e n s u l p h u r i c a c id p r e - t re a t m e n t i s e m p l o y e d f o r R M 1 , f o l l o w e d b y c y a n i d a t i o n w i th 1 . 65 k g / t N a C N ,a h igh ly s a t i s f a c to r y c oppe r s e l e c t ion w i th 30 ppm C u in so lu t ion i s a c h i e ve d . The go ld i s l e a c he d w i th6 8 % o f e x t r a c t io n .T h e e m p l o y m e n t o f a n a m m o n i a - c y a n i d e s y s t e m re s u l te d i n c l e a r b e n e fi t s fo r R M 2 a n d R M 3 a n d s o m ebe ne f i t f o r R M 1 , w he r e t he r e a r e be t t e r pos s ib i l i t i e s w i th t he u se o f a c id sy s t e m s .A s a r e s u l t o f t he o p t i m i s a t i o n o f t h e s y s t e m c o m p o s i t i o n o f R M 2 l e a c h i n g , a d e c r e a se i n t h e c o n c e n t ra t i o no f c y a n i d e i n s o l u t io n t o 0 . 5 5 k g / t i s a c h i ev e d b y u s i n g 3 k g / t o f a m m o n i a . T h i s r e s u l te d i n 8 9 % e x t r a c t io no f g o l d a n d a r e s id u a l 2 0 0 p p m o f c o p p e r i n th e s o l u t io n . U s i n g t h e s a m e c o n c e n t r a t i o n o f c y a n i d e , R M3 r e q u i r es a n e v e n l o w e r a d d i t i o n o f a m m o n i a , a t 2 . 2 k g / t , t o r ea c h 8 5 % e x t r a c t io n o f A u a n d a b e t t e rs e l e c ti o n o f C u w i t h 1 00 p p m r e m a i n i n g i n s o l u t io n . T h e a m m o n i a a d d i t io n i n th e c y a n i d e s y s t e m a l l o w st h e p r o d u c t i o n o f C u ( I I ) N H 3 spe c i e s , w h ic h a r e r e spons ib l e f o r in t e ns ive c opp e r p r e c ip i t a t i on a nd go ldl e a c h in g . C o p p e r p r e c i p i ta t e s m o s t l y a s C u ( O H ) 2 , C u O , C u 2 0 a n d C u C N . G o l d i s le a c h e d a s A u ( C N ) 2 -by c he m ic a l r e a c t ions i nc lud ing C u( I ) c ya n ide s p r e se n t i n t he sy s t e m .

T h e o p t i m i s a t i o n o f R M 1 l e a ch i n g i n t h e a m m o n i a - c y a n i d e s y s t e m , r e s u l t e d in t h e re q u i r e m e n t o f a h i g h e rl e v e l o f c y a n i d e , 1 . 65 k g / t , b u t l o w e r a m m o n i a , 0 . 7 9 k g / t , w h i c h a l l o w s 9 0 % A u e x t r a c t i o n a n d 1 5 0 p p mC u i n s o l u t i o n .L e a c h i n g i n b r o m i n e s o l u t i o n s h o w s m u c h f a s t e r g o l d e x t r a c t i o n k i n e t i c s w i t h n o w o r s e c o p p e r s e l e c t i o nc o m p a r e d t o t h e a l k a li s y s t e m s . T h e r e f o r e b o t h r e s e a r ch e d a c id s y s t e m s ( s u l p h u r i c a c i d p r e - t re a t m e n t a n db r o m i n e l e a c h i n g ) a r e r e c o m m e n d e d a s b e t t e r t e c h n o l o g y f o r R M 1 , c o m p a r e d t o t h e a l k a l i p r o c e s s e s .O n t h e o t h e r h an d , t h e a m m o n i a - c y a n i d e s y s t e m c a n b e u s ef u l l y e m p l o y e d f o r th e l e a c h in g o f R M 2 a n dR M 3 a s t h e y h a v e s i m i l a r m i n e r a l o g y .

A C K N O W L E D G M E N T ST h e a u t h o r g r a t e f u l l y a c k n o w l e d g e s s u p p o r t f r o m t h e A u s t r a l i a n R e s e a r c h C o u n c i l a n d t h e A J P a r k e rC o o p e r a t i v e r e s e a rc h C e n t r e f o r H y d r o m e t a l l u r g y . T h e P a r k e r C e n t r e w a s e s t a b l is h e d a n d i s su p p o r t e d b yt h e A u s t r a l i a n G o v e r n m e n t u n d e r t h e C o o p e r a t i v e R e s e a r c h C e n t r e s ' P r o g r a m .T h e a u t h o r w i s h e s t o a c k n o w l e d g e A / P r o f . D . M u i r , f o r hi s g e n e ro u s h e l p a n d u s e fu l s u g g e s t i o n s , a n d J.B idd le a nd T . K om osa f o r t he i r t e c hn ic a l a s s i s t a nc e .

i .2 .

R E F E R E N C E S

H u n t , B . , US Patent No. 689,190, (Dec . 17 1901) .J a r m a n , A . & B r e r e to n , E . L e G a y , L a b o r a t o r y e x p e r im e n t s o n t h e u se o f a m m o n i a a n d i tsc o m p o u n d s i n c y a n i d i n g c u p r i f e r o u s o r e s a n d t a i l in g s , Trans.lnst. Min. and Metall. XIV, 2 8 9 - 3 3 4( 1905) .


15/15

Extraction of gold from low grade ores 1047,

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2 0 .

2 1 .2 2 .

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