Heap Leaching Gold Mining

 

I NTRO DUCTION TO EVALUATII ON DESIGN EVALUAT DESI GN A N D OPER OF PR ECPRO IOUJECTS S ME MET TAL H EATION AP L LEA EACHI CHING NG Editors

Dirk Di rk J.A. va n Zyl Welsh Engineering Inc. Denver, Colorado

Ian

P G

utchison

Steffen Steff en Robertson and Kirs Kirste ten n Colorado) Color ado)Inc Inc Denver, Colorado

J e a n E . Kiel E Kiel

Associates Denver, Colorado

Soc iety of Minin g Engineers Inc. Littleton Colorado

1988

 

Copyright

O 1988 by

the

Society of of M in in g Engineers Engineers

Inc

United S t a t e s o A m e r i c a by Cushing-Malloy Inc. Ann Arbor Michigan rinted in the

All rlght rlghts s resewed. resewed. This book or parts pa rts thereof thereo f may not be reproduced In any form wlthout permlsslon p ermlsslon of the publisher.

Library of

ongress Cat Catalo alog g Card Card Number Number 88 60773

IS N 0

87335 074 X

 

  hapter

Or e Prepar ation Crush Crushing ing and Agglo Agglomerati meration on G e n e E McC lelland and Dirk van Zyl

5.1

INTRODUCTION

Heap 1 1e e ac ac h c y a n i d a t i o n t e c h n i q u e s p po ossess c o n s i d e r a b l e p o t e n t i a l f o r ex plo ita tio n o f lo ow w - g ra ra de o r e ess , s m a llll o r e b o od d ie i e ss,, m iin ne str ip wa ass te te a an nd t a i l i n g ma ter ia ls wh he e re re f i n e g r i n d i n g i s n o t n e ecc e ess sa s a rryy f o r g o oo od e x t r a c t i o n . F o r heap n g t o b e s u c c e s ssff u l , ore mu uss t e x h hii b i t c e r t a i n c h a r a c t e r i s t i c s , a s 1 e a c h i ng previou sly discu uss s e d in C Ch ha ap p te te r 1 Primary among the necessary ore ch ara ct eri st ic s i s t h a t the ore m mu u sstt h ha ave g go o o d p e r n iie e a b i llii t y a f t e r b e eii n g c rru ush he ed or tr e at ed an nd d stacked i n t o h he eaps i u n i f or or m d i s t r i b u t i o n o f t he c ya ni de l e a c h s o l u t i o n i s t o b e a acc h ie i e vve ed d.. G ol o l d a n d s i l v e r o r e s c o n t a i n i n g e x cce e s ssii ve ve a am m o unts o f c l a y s o r f i n e s g e n e r at a t ed e d b y c r u s h i n g a r e sso ome o f t h e m o oss t d i f f i c u l t t o t r e a t s u c c e s s f u l l y b byy heap 1e 1e a c h i n g . T h e p re re s e en n c e o f e x c e s s i v e am o unts o f s l i m e s (gen eral ly c la ss if ie d as min nu us 5 50 0 -m - m iicc ro ro n o r 2 27 70 T y l e r m me e sh s i e v e s i z e p a r t i c l e s ) i n tth he heap l e a c h f e e ed d w i l l s lo l o w t h e p e r c o l a t i o n f l o w o f tth he lea acc h s o l u t i o n , c a u s e c h a n n e l i n g , o r p r o d u c e d o rrm mant o r unle ea a c h e d a rre eas w i t h i n the he ea ap p.. T h i s m ma ay r e s u l t i n u n rre e a s o n a b l y l o n g l e a c h i r l g p e r i o d s and p po oo orr e x t r a c t i o n s . I n e x tr tr e m e c as as e ess , t h e c l a y s o r s l i m e s c a an n comple tely se ea al the ore h he eap, c a u s i n g t h e l e a c h s o l u t i o n t o r u n o f f t h e s id i d e s o f t h e heap r a t h e r t h a an n t o p e n e t r a t e t he he o re heap. The p r o b l e m o f h e ea ap le ac hin g ores con taini ng fi ne s ca an n b be e agg grr a avv a tte ed dur ing stac king an nd d preparation o f the ore h he eaps, b e c a u s e n a t u r a l s o r t i n g o f c o a r s e an an d f i n e m a t e r i a l o c c u r s d u r i n g t h e sse e s tte e p s ( JJo oh a an ns o on n, 197 78 8 )).. T h i s

phenom enon r e s u l t s i n a c o n c e n t r a t i o n o f o r e f i n e s a t t h e c e n t e r o f i n d i v i d u a l o r e p i l e s a n d a c o n c o m i t an a n t c o n c e n t r a t i o n o f l a r g e r r o c k ffrr a g gm me en n ts t s on t h e l o w e r s l op op e s a an nd ba ass e o f t h e p i l e s . When t h e i n d i v i d u a l p i l e s w i t h i n t h e h e ea ap a r e l e v e l e d o f f p r i o r t o i n s t a l l a t i o n o f t h e s p r i n k l i n g ssyy s t e m w wh hich d e li v e r s t h e l e a c h s o l u t i o n , a d d i t i o n a l s e g rre e g a t io i o n o cccc u rrss a ass t h e f i n e s s i f t tth h ro ug h t h e c o a r s e r o r e p a r t i c l e s . The s e g r e g ga a t iio o n r e s u l t s i n l o c a l i z e d a rre e a s o r zones w ed pe ab bc e i l , yp. e rAcso laa tci on n ns eq uwennwcce 1e ahc ht h seo l cuot ia or ns se f oiltlho wm atrrk hk e e d pdai t hf e or ef n cl ee sa s it n r ep se irsmt ae na gs e dqoue aer,d t htth herro o1 ueg gh ar o r e r e g i o n s a n d b y p a s s i n g o r b a r e l y w e t t i n g a rre ea ass t h a t c o n t a i n l a r g e am am o u n ts o f f in e s o r s l i m es . E f f e c t i v e u t i l i z a t i o n o f m a rrg g in in al g go o ld l d and s i l v e r r e s o u r c e s t h r o u g h h e a p l e a c h p r o c e s s i n g r e q u i r e s t h e d e vve e lo lo p pm men ntt o f n ne ew m et et h o od ds i n orde r t o achie evv e m mo o r e u n iiff or or m s i z e d i s t r i b u t i o n d u r i n g o r e h he eap p r e p a r a t i o n an a n d b e t t e r s l m e c o n t r o l d u r i n g 1eaching. 1 eaching. 8

 

ORE PREPARATION

R U S H I N G AND AGGLOMERATION

9

As briefly disc uss ed in the p r e ce ce d in g c h a p t e r, r, a g g lo l o m e r at at io n p r e t r e a t m e n t h a s b e e n s h o w n t o b e e f f e c t i v e f o r t h e e x p l o i t a t i o n o f lo lo w - gr ad e m a t e r i a l s w h ic ic h d i s p l a y p o o r p e r c o l a t i o n c h a r a c t e r i s t i c s . I n some c as a s es es , a g g l o m e r a t i o n - h e a p 1e 1 e a c h i n g i s t h e o n l y v i a b l e p r o c e s s i n g t e c h n iiq q ue f o r a p ro r o b le l e m f e ed e d . H o w e v e r , c r u s h i n g c i r c u i t s a nd n d a g g l o m e r a ti t i n g sy s y sstt e ms ms a r e c a p i t a l i n t e n s i v e , a n d s h o u l d n o t be b e i n c o r p o r a t e d i n t o a co c o mm m m er e r c iia al operation unless a b s o l u t e l y ne n e ce c e ss s s ar ar y . C a r e f u l a t t e n t i o n s h ou l d be g i v e n t o d e t e r m i n i n g t h e r e qu i re m e n t f o r a g g l o m e r a ti o n p r e t r e a t m e n t f o r a p a r t i c u l a r fe e d b e f o r e c o m m i t t i n g i t t o t h e c o m m e r ci ci a l o p e r a t i o n . This chapter p r o v i d e s so so m e g u i d e l i n e s f o r t h e e f f e c t i v e a nd n d e co c o no n o mi m i c u s e o f a g g lo l o m e ra r a t i o n s y s t e m s, s, a s w e l l a s a b r i e f h i s t o r y o f t h e d ev e v el e l o pm p m e n t o f a g g l o m er e r a t iio o n t e c hn h n ol o l o gy gy . A g gl g l o m e ra r a ttii on o n a nd n d b a l l n g o f c r u s h e d o r e t o p rro o du d u ce c e a p or o r o us u s a nd n d m or ore u n i f o r m fe fe e d m a t e r i a l f o r h e a p l e a c h i n g i s a v i a b l e m ethod f o r t r e a t i n g c l a y e y o r e s . I n t h e m i d - 1 9 7 0 s t h e U. U.S. B u r e a u o f M i ne n e s (U ( USBM) i n Re Re no, N ev ev a d a , b eg e g an an an a g g l o m e r a t i o n p r e t r e a t m e n t r e s e a r c h p rro o gr gr a am m t o a 1 l o w t h e c o m me m e rrcc iia al e x p l o i t a t i o n o f t h e s e p o o r l y p e r c o l a t i n g f e ed m a te r i a l s . P r i o r t o t h i s , l i t t l e a t t e n t i o n h a d be b e e n g i v e n t o s uc u c h m e th t h o ds ds f o r i m p r o v i n g u n i f o r m p e r c o l a t i o n f l o w o f l e a c h s o l u t i o n s t h r o u g h s i l v e r a n d g o ld l d o r es e s . H o w e v e r , t h e g e n e rra al i d e a o f o r e a g g l o m e r a t i o n w as as a d v an a n c ed e d a nd nd , b e f o r e t h e US USBM r e s e a r c h p r o g ra ra m .

t o so some e x t e n t ,

r e s e a r ch ch e d w e l l

I n 19 1 9 0 5 , T. T.C. S c r u t t o n d e v e lo l o p e d a u n iq iq u e t e c h n i q u e f o r o b t a i n i n g r a p i d v a t l e a c h i n g o f a c l a y e y o r e i n w h i c h t h e g o l d wa wa s f i n e l y d i s se s e m i n at at e d ( D or r a n d B o s qu q u i, i , 1 9 5 0 ) . S c r u t t o n s t e c h n i q u e c o n s i s t e d o f r o l l i n g t h e o r e do do w n a c h u t e i n c l i n e d a t 60 6 0 d e g re r e e s t o f o r m a gg g g llo o m e rra a tte e s o r b a l l s r e a d i l y p e rm r m ea e a bl bl e t o t h e c y a n id id e s o l u t i o n . H o w e v e r , t h e s e a g gl g l o m e ra r a te te s l a c k e d r i g i d i t y and, t o e n su s u r e go g o o d p e r c o l a t i o n l e a c h i n g a n d w a s hi hi n ng g , t h e y c o u l d n o t be be be bedded i n l a y e r s mo m o r e t h a n t h r e e f t deep. f t h i s d e p t h wa was e xc x c e e d e d , d i f f i c u l t i e s wo w o ul ul d b e e x p e r i e n ce c e d i n o b t a i n i n g u n i f o r m l e a c h i n g an a n d w a s h i n g , r e s u l t i n g i n r ed ed uc ed g o l d r e c o v e ry r y . S he h e pa p a rrd d an a n d S k i n n e r ( 1 9 3 7) 7) , s t u d i e d t h e a d d i t i o n o f l i m e and c ar ar b o n d i o x i d e o r c a l c i u m c a r b o n a t e t o g o l d - b e a r iin ng ta il in gs t o form a g g l o m e r at at e s s u i a b 1 e f o r v a t 1 e a c h i ng. S a t i s f a c t o r y p e r c o l a t i o n f l o w r a t e s w er e r e a c h i e v e d i n 90 9 0 --g g ra r a m s c a l e e x p e r i m e n t s , b u t t h e r e a g e n t r e q u ir i r e m e n t s w er er e prohibitive. A g gl g l o m e ra r a t i on o n a nd n d p e l l e t i z i n g h av a v e b e e n u s e d i n o t h e r segm ents o f t h e m i n e r a l i n d u s t r y . T h i s t e c h n i q u e wa wa s f i r s t us us e d s u c c e s s f u l l y a r o u n d 1 9 1 1 f o r p e l l e t i z i n g i r o n o r e s ( D a v i s a nd n d Wade, 1 95 9 5 1; 1 ; E n g l i s h a n d F rra a ns n s , 1 97 9 7 7) 7) . Since t h a t t i m e , a g g l o m e r a t i o n a nd n d p e l 1 e t i z i n g ( o r b r i q u e t t i n g ) h av av e b e e n w i d e l y a do d o pt p t e d f o r c o n s ol o l i d a t i o n o f f i n e s f o r m an a n y o t h e r m a t e r i a l s s u ch ch a s m a n g a ne s e ,

u o r s p a r , a nd n d p h o s p h a t e s . T h e se se m a t e r i a l s h a avv e be b e en e n p e l 1 e t i z e d t o c on o n s ol ol i d a t e f i n e p a r t i c l e s i n t o 1 a r g e , d en e n s e , a nd n d m e c h a n i c a l l y s t r o n g m asses, p r i n c i p a l l y t o p r e v e n t d u s ti n g p r o bl e m s d u r i n g f u r n a c i n g o p e ra t io n s . fl

T h e o b j e c t i v e o f t h e U S B M s i n v e s t i g a t i o n s i n t h e 1 9 7 0 s was t o e v a l u a t e p a r t i c l e a g gl om e ra ti on p r o ce d ur es f o r i m p ro v i ng f l o w r a t e s i n th e heap l e a c h c y a n i d a t o n p r oc o c e s s. s . T he h e c o n c e p t wa was t o i n v e s t i g a t e p rro o c e d u r e s w he h e rre e by b y 1o 1 o o se k n i t , p o ly l y m er e r 1 e a g g l o m e r a t e s c o u l d be b e fo f o rrm m e d t h a t w er e r e h i g h l y p er e r me m e ab a b lle e to s o l u t i o n f l o w a n d y e t m e c h a n i c a l1 l 1 s t a b 1 e d u r i n g t h e 1 e a ch i n g se q u e n ce . T h r e e i m p o r t a n t a g g l o m e r a t i o n p a r a m e t e r s w e re r e d e t e r m i n e d f r om o m t h e USBM s w or o r k f o r s u c c es e s s fu fu l a g g l o m e r a t i o n p r e t r e a t m e n t o f c rru u s he h e d o r e s w i t h p oo oo r perc olati on ch ar ac ter ist ics . T h e p a r a m e t e r s w er er e : 1 ) q u a n t i t y o f b in d e r  

7

P R E C I O U S M ET ET L H E

P L E C H IN IN G P R O J E C T S

t ) a dd d d ed ed t o t h e d r y f e e d ; 2 ) a m o u n t o f m o i s t u r e a ad dded ( p o r t l a n d c e m e n t) b i n d e r / o r e m i x t u r e ; a n d 3 ) t h e c u r i n g p e r i o d r e q u i r e d t o f o r m c a llcc iu iu m s b r i d g i n g . T h e i n v e s t i g a t i o n r e v e a l e d t h a t m os o s t c r us us h he ed o orr e s ( f i n e r i n c h ) c o u l d be b e e f f e c t i v e l y a g g llo o m er er a att e ed d b y m i x i n g 10 Ib s o f p o r t l a n d

t o th e il cate tha n cce ement

p n o i( s5t u kr eg/ g / mct) to) n t oe nf t d or yf af ee ebo at t te, r mo er c hc ay n a an ni cid i da el l y s ot ul umt bi ol inn g t ot h ea f i enra l t o m beodut u,t 1w2e twt ieni gg h w t i pt he rc r cwea n nt w e t t e d m i x t u r e t o e f f e c t a g g llo o m e ra r a t i o n , and c u r i n g f o r m ore t h a n e i g h t h o u r s b e f o r e a p p l y i n g c o n v e n t i o n a l h ea ea p l e a c h i n g t e c h n i q u e s ( H He e iin n en en , e t a a1 1 1979; M c C l e l l and a n nd d E i s e l e , 1 9 8 2 ). ).

.

T h e a g g l o m e r a t i o n t e c h n o l o g y d e v e l o p e d b y t h e U S M was r a p i d l y a d o p t e d by t h e p r e c i o u s m e ta l p r o d u c t i o n i n d u s t r y . T h e f i r s t p i o t - s c a l e c o l urnn p e r c o l a t i o n l e a c h i n g t e s t s o n a g g lo l o m e r a te t e d f ee e e ds d s w er e r e p e r f o rrm m e d i n 19 19 78 78 . T h e i n i t i a l p i l o t - s c a l e h e a p l e a c h t e s t on o n c ru r u ssh h ed and ag gl o om m e ra r a te t e d o r e was c o nd n d u cctt ed e d i n e a s t e r n N ev ev a d a i n 1 97 9 7 9. 9. The f i r s t c o m m e err c iia al a ag g g lo l o m e r a ti ti o n n-- h e ap ap l e a c h o p e r a t i o n p o u r e d b u l l i o n i n l a t e 1980. M any o p e r a t o r s h a avv e s i n c e a d o p t e d t h e t e c h n o l o gy g y f o r p r o d u c i n g p r e c i o u s m e ta ta l s f r o om m t h e i r lo ow w -g - g ra ra d de e or e d e p o s iitt s , m i ne ne w a ass te t e ss,, a n d m i l l e d t a i l i n g s m a t e r i a l s . 52

GGLOMER TION

PRINCIPLES

T h e b a s i c o b j e c t i v e o f a g g lo l o m e r a t i q g p re r e c i o u s m e ta t a l o r e s f o r h ea ea p l e a c h i n g i s t o p ro r o d uc u c e p or or o ou u s o r e w h ic i c h w i l l be s t a b l e when h a n d l e d , s t a c k e d , a n d p e r c o l a t e d w i t h l i x i v i a n t . As p r e v i o u s l y d iiss cu c u ssss ed e d , e x c e s s i ve ve f i n e s i n a an n o r e ca c a n l e a d t o r e d u c t i o n i n he h e a p p e r m e a b i l it it y , as well as increased c h a n ne n e l in in g , and b l i n d i n g . A s o m e w h a t s i m i l a r a p p l i c a t i o n o f t h e g e n er e r al al p r i n c i p l e o f a g g l o m e r a t i o n i s i n t h e p r o v e n p r oc o c ed ed u urr e o f s o i l s t a b i l i z a t i o n f o r r o a d c o n s t r u c t i o n ie., the mixing o f ro oa a d pa pavem ent m a t e r i a l s w i t h s t a b i l i z i n g a g e en n ts ts t o i m mp p ro ro v e t h e i r s t r e n g t h a nd n d c o n s t r u c t i o n b e h a v i o r ) . C e m e n t, l i m e , f l y - a s h , a s p h a l t , a n d o t h e r c h em e m i ca c a ls l s (e (e.g., calcium s i l i c a t e ) ha avv e b e e n u s e ed d f o r s ta bi li z at io n . A mo mo u un nts u s e d i n r o a d c o n s t r u c t i o n u s u a l l y r a n ge ge fro m 5 t o 1 0 p e r c e n t b y w e eii g h tt.. cl ea r th a t su ucc h h i g h p er e r ce ce nt a ag g es e s o f a d d i t i v e s a r e n o t e co c o n om o m ic ic a all f o r l e a c h pu p u rrp po oss e ess . O p t i m i z a t i o n i s t h e r e f o r e i m p o r ta ta n t .

is h ea p

t

W i t h r e g a r d t o o r e a g g llo o m er e r a t iio o n , s i m i l a r m a t e r i a l s t o t h o s e u sse ed i n r o a d c o n s t r u c t i o n w o rk r k ( i .e .e . , c em e m e nt n t a n d f l y - a s h ) h a vve e b e e n u s ed ed w i t h s o om me s uc u c cce e ss s s . A l l o f t h e s e b i n d e r s h av a v e i n common t w o i m p o r t a n t p h y s i c a l / c h e m i c a l e ff ec ts wh hii c h a cccc o u un n t i n l a r g e p a r t f o r t h e s uc ucc e s s w i t h w h hii c h t h e y h a v e b e e n used :

T h e e xxcc ha h a ng n g e o f s od o d iiu u m c a t i o n s i n t h e o r e c l a y particles w I t h c a l c i u m c a t i o n s fr o om m t h e b i n d e r , t h e rre e b y i m p r o v i n g t h e w o r k a bi 1 i y a n d p e r m e a b i l i y o f c l a y m a t e r i a l s ; and The c e m me e n t iin n g ( o r p o z z o l a n i c ) a c t i o n o f b i n d e r , t h e rre eby ad di ng s t r e n g t h t o t h e a gg g g llo o m e rra a tte ed materials. s h o u ld b be e n o tte e d h er e r e t h a t t h e d i f f e r e n t b i n d e r s m ay v a r y in effectiveness, de ep p en e n di d i n g o n t h e o r e i n q u e s t io io n a an nd t h e p a r t i c u l a r n e e ed ds o f e ac ac h a g g l o om m e r a t iin n g s y s te t e m . F o r ex e x a m pl pl e , l i m e i s v e r y e f f e c t i v e i n o b t a i n i n g t h e sso o d iu iu m c a t i o n ex e x ch ch a n ng g e r e a c t i o n ; h o w ev ev e r , t h e s t r e n g t h o b t a i n e d f rro om l i m e a n d t h e r a t e a t w h i ch ch s t r e n g t h i nc r ea s es a r e b o th l o w er f o r l i m e t h a n f o r c em e m en e n t a nd n d so som e t y p e s o f f l y - a s h . De ep p en e n di di n g o n t h e o r e t y p e , t h e c a t i o n It

 

7

O R E P R E P A R A T I O N C R U S H IIN N G A N D A G G L O M E R A T IO IO N

e xxcc h ha an ng ge re ac ti on m ma ay o r m a ayy n o t b be e mo orr e i m p o r t a n t t h a n s t r e n g t h a n nd d r a t e of reaction. I t i s , t h e re f or e , i m po rt an t t o c a r e f u l l y i n v e s t i g a t e t h e b e ha vi or o f o r e w i t h r es pe ct t o b i n d e r . Two b a s i c p a att h hw wa ayy s f o r s u c c e ssss f u l p r e c i o u s m e t a l o r e s . Th e ess e a r e :

agglomeration

cca an

b be e

identi ied

A g g l o m e ra r a t i o n o f f i n e s o n t o c o a r sse e crushed ore a an n d w a sstt e ; A gg g g lo lo m me e ra r a ti ti o n o f f i n e s i n t o s t a b l e b a l l s .

for

and

F i g u r e 5 . 1 sh o w s s c he he m a att ic i c s o f t h e a g g l o m e rra a t iio on effe ct s. I n the l a t t e r i n s ta n c e ( f i n e s a g g gll o m e ra r a ti ti n g i n t o s t a b l e b a l l s ) t h e f i n e s c a n b e s i l t a an nd sa n nd d pa rt ic le s o r they ca an n c o n t a i n h i g h p e rc r c en e n ta ta g e ess o f c l a y ( ex ex a am m p lle es b a an nd c on F i g u r e 5 5.. 1 ) . M o od d e r a t e t o m o d e r a t el el y h i g h q u a n t i t i e s o f b i n d e r a r e r e q u i r e d fo r the ag gg g lo l o m e rra a ti ti o n o f f i n e s a an n d t a i l i n g s i n t o s t a b l e b a l llss . Specific p r o j e c t s exem pl i f y i n g t h i s t y p e o f a g gg glo om mera att io io n a r e d i s c u uss s e ed d i n Sub bcc h ha a p tte e rs rs 5.6 t h r o u g h 5.8. When

fine

m a t e ri a l

such

as

ta il in gs

with

no

or

l it t le

cl ay

is

a gg g g lo lo m e err a att ed ed , t h e f i n e s a r e b bo ound t o g e t h e r w i t h a b i n d e r s u c h a s p o r t l a n d c e m e n t . C lla ayey o re i s p a r t i c u l a r l y d i f f i c u l t t o l e ac h e f f e c t i v e l y because o f t h e l ow p e r m e a b i l i t y o f c l ay . B e n t o n i t i c c l a y s (so d dii u m m o n t m o r i l l o n i t e ) a r e es pe cia lly a p prr o b lle em . I n t h e g e en ne err a l C i v i l E n g iin n e e rrii n g i n d u s t r y , s u c h c l a y s h av av e been st ab il ized ( i e., w o r k a b i l y and permeab bii 1 y have been i n c r e a s e d ) , s u c c e ssss f u l 1 y u s i n g 1 m e . C a t i o n e xc x c ha ha n ng ge takes pla ce an nd d the so d dii u m r i c h c l a y cch h a n g e s t o a c a l c iiu um r i c h clay. I t is , theref ore , sugg ge e st s t ed ed t h a t clayey ores ca an n be ag gg g llo ome err at a t ed ed b y u s i n g l i m e a an n d p o r t l a n d c em em e en nt a ass b i n d e r s . ''T The l i m e w i l l sta biliz e t h e c l a y m i n e r a ls , w h i l e t h e p o r t l a n d cement w i l l form a s t r o n g b in d e err . In order t o th e clay effectively, the l ime mu uss t cco om e i n c l o s e c o n t a c t w i t h t h e c l a y m i n e r a l s . I n the ca ass e o f a g g gll o m e err a ttii o n o f c r u uss h e d o r e a n d w a ass tte es co nt ai ni ng hi gh p e r ce c e n tta age ess o f f i n e s , t h e f i n e s a r e b bo o u n d t o t h e c o a rrss e p a r t i c l e s ( s e e e exx a m p pll e a o n F i g u r e 5 .1 . 1 ). ). T y p i c a l l y , p o r t l a n d c e m me en ntt c a an n be u s e ed d a s a b i n d e r a nd nd l o w t o mode err a tte ely low qu an tit ies are suf fi ci en t. Su ub b ch ch a ap p te t e r 5.6 d i s c u s s e s s p e c i f i c pro ject s wh hii c h a r e e xxa am p pll e s o f t h i s t y p e o f a g g llo o m e r a t iio on. 5 3

AGGLOMERATORS

This subchapter discusses agglomeration design factors and then goes on t o describe the variou s kinds o f agg gll o m e err a tto o r s w h i cch h h ha ave b e ee en succ es sfu lly u sse ed o on n precious meta all o r e s . A g g llo o m e rra a t iio on design fa ct or s in cl ud e M i l 1 gan,

1983)

Fee d c h a r a c t e r i s t i c s , e .g . p a rt ic le size a an nd p prr e sse en ncc e o f f r a c t u r e s i n p a r t i c l e s . The r e l a t i o n s h i p b be etw e ee en t t h e t i m e t o a g iv iv en a m e t e r , c a n be s t a t e d a s : e x t r a c t i o n a n d D, t h e p a r t i c l e d iia

where C 1 i s a cco o n sstt a n t . Fo orr r a p i d u n i f o r m h i g h p r e c i o u s m e t a l re ecc o v e r y, y , t h e f i n e s t c rru u sh i s t h e r e f o r e d e s ir a bl e . F i ne g r i n d i n g i s i n c o n f l c t w i t h t h e u n i f o r m l y h i g h p e rrm me ea a b ili l y r e q u i rre e m e n ts o f he ea ap lea chin g. Agglomeration m ma akes t h e s e t w o m o orr e c o m p a t i b l e ;

 

72

PR EC IO U S M ET L H E

P LE C H ING ING PR O JEC T S

F T E R AGOLOMERATION

B E F O R E AOQLOMERATION

r

C O A R S E M A T E R I A L W l T H LA R Q E PERCENTA QE FIN NE ES.

a

FINES ARE AQ QLOMERATED ONTO CO AR SE PARTIC C.. L E S , B I N D E ER R SU UC CH A S P O R T L A N D C E M E N T I S USED.

b

F I N E M A T E R I A L . e.g. T A l L l N Q 8 W I TH N O O R L I T T L E C L A Y

b

AQQLOMERATES AR E FORMED BY B l N D l N Q F I N E S T O Q ET H E R W l T H BINDER B UC H AS PO RTLAN D C CE EME EN NT.

C

CLAY MATERIAL WITH META L L OC KE D IN LO W PERME ABILITY MEDIUM.

C

AQQ LOM ERA TES ARE F FO ORMED BY B I N D IN IN Q F I N E S T O Q E T H E R A F T E ER R M O D l F Y lN Q C L A Y P R O P E R T I E S , L I M E A N D P O R T L A N D C EM E N T C CA AN BE USED.

F I G U R E 5.1 GGLOMER

T I O N EFFECTS

 

7

ORE PREPARAT PREPA RATION ION CRUSHING AN AND D AGGLO AGGLOMER MERATI ATION ON

P r oc o c e ssss c o n t r o l , e .g. f e e ed d r a t e and t y p e o f o r e and b i n d e r a d d i t i o n ra te s. O p tim um conditio ns are obtained during stead y-sta te co nd it io ns of op ptt im im u um m feed siz e a an nd r a t e and a t o op p titi m mu um mo ist ure a n d b i n d e r a d d i t i o n r a t e s ( a s d iiss c u uss s e ed d be ell o ow w ). ). O p e err at a t or or c o n t r o l i s v e r y i m p o r t a n t a n d c o n t i n u o u s m o n i t o r i n g m ay b be e requi red are freque nt; an nd d

i

upsets

E q ui u i pm pm e n ntt s e l e c t i o n . The a g g llo omerato orr m u sstt p r o v i d e t h e a g i t a t i o n a nd nd m o t i o n n e e ed d ed ed t o m ma a k e t h e n e c e s ssa a r y g rre ee en n st re ng th f o r c o n s t r u c t i o n o f t h e h e a p . The t h r e e m a j o orr ttyy p e s o f a g g l o m e r a tto ors f o r gold a an n d s i l v e r o r e s a r e b e l t , d ru m a n d p pa an. T h he ese t h r e e a r e ( 1 9 8 3 )).. d i s c u s s e d b e l ow o w . T he d i s c u s s i o n i s t a k e n f r o om m i l 1 gan Other me ett h ho od dss o f a g gg glo om mera att i o on n i n c l ude s t o c k p i l e a g g l o m e r a att i o n , v i b r a t i n g de ecc k , a n d s t e e p l y i n c l n e d c o n vve eyo orr b e1 t s ( C h a am m b e rrll a iin n, 1986). 5.3.1

Be1 t A g g l o m e r a t o r s

B e 1 t - t y p e a g g l o m e r a t o r s u se s e c on o n ve ve y o orr s t o o b t a i n t h e n e cce essa arr y t u m b l i n g and c o m p pa a c ttii o n n.. T h i s a g g l o m e r a t o r t y p e p ro ro d du u ce ce s t h e l e a s t d de eg grr ee ee o f c o om mpaction a n d a g g l o m e r a t i o n o f a n y a g g l o m e rra a t o r c u r r e n t l y i n u se s e . Th e b e l t m a y b be e s t e e p l y i n c l n e d t o i n d u c e r o l l n g o n t h e b e 1 t o r may h a v e m mu u1 t i p l e t r a n s f e r p o i n t s a t w h i c h a g i t a t i o n and c o m p pa a c ttii o n o c c u r . The h i g h e r t h e p e r c e n tta age o f fines, the m mo o re t r a n s f e r p o i n t s a r e needed ( h a r d s i l i c e o u s o r e w i t h f i v e percent 10 00 0 m e sh, t w o t o t h r e e t r a n s f e r s , a n d w i t h 1 0 p e r c e n t o r 1 5 p e r c e n t 1 0 0 m e sh, f o u r t o f i v e t r a n s f e r s ) ( C h ha amb be e rl r l ai a i n, n, 1 9 98 86 6)) . A g g l o m e r a t iio o n may a l s o be i n d du uced d du u rr-- in in g d i s c h a r g e w h he ere t h e o r e r o l l s d do o wn a s t e e p i n c l i n e . F i g u r e 5.2, B el t Ag gg g llo o m e rra a tto o r S iz i n g g,, i l l u s t r a t e s t h e c a p a c i t y o f a t y p i c a l three-drop co on nve eyy o orr a g g l o m e r a t i o on n. Siz ing i s b ba ased on t h e c a r r y i n g c a p a c i t y o f th e b be1 e1 ne ar th e ma maxi ximu mum m spe speed. ed. Fi g ur e 5.3, B e1 t A g g l o m e r a t o r C o s t , i l l u s t r a t e s an e s t i m a t e d b u ud dg ge et co om mp pa a ri r i so so n c o s t o f s u ucc h a an n agg gll om o m e rra a to t o r. r. gg or smee ra rcar tto he ea l c oe nx tt ar ai nc st i ov ne .r y 1 t t l e f i n e mTaht iesr i tayl p ae n do f a acg ogallo uosrh i ysi esl ud ist a gbol oed wph reercei otuhse moer tta 5.3.2

Dr Drum um Ag gl om er at or s

T h e d ru r u m - ttyy p e a g g l o m e r a t o r u s e ess a d r u m t o o b t a i n t h e r e q u i r e d t u m b l i n g and c o m p a acc t iio on fo r agglomeration n.. T h i s t y p e o f e q qu u iip pm me en ntt p r o od du ucc e ess a f a i r l y w id id e s i z e d i s t r i b u t i o n o f a g gg g llo o m er er a att es e s . The g grr ee e e n s t r e n g t h cca an b be e ex ce ll en t d e pe pe n d dii n g o n e q u iip pmen ntt si z e a an nd production r at e. Figure 5.4, Drum A g g lo lo m me e rra a ttii on on Sizing, il lu s tr at es a typ ica l ra ti ng capacity for d rru um

a g g l o m e ra r a t o r s . The f o l l o w i n g e q u a t i o n c a an n a a1 1 so be u uss ed ed t o d e t e r m i n e r e s i d e n c e time i n an agglomerato orr . R a t e o f g r o w t h o f a g g gll o m e err a te te r e a acc h he e s a m a x im u m a t the optimum moisture content:

where T mat erial (rpm), L s i z e and

i s r e q u i r e d r e s i d e n c e t iim me (min nu ute ess ) , A i s t h e a n ng g le l e o f r ep ep o oss e o f ( d e g r e e s )),, S i s t h e s l o p e o f s h e l l ( de de g grr ee e e ss)) , N i s s p e e d o f d r u m Agglomerate i s l e n g t h o f d rru u m ( f t ) , and D i s d i a am m e tte er o f d drr u m ( f t ) . s t r e n g t h i n c rre e a s e s w i t h l o n g e r r e ssii d e en n c e ttii m e ( r e v o l u t i o n s ) .

 

P R E C I OU S M E T L HE

P L E C HI HIN NG PRO JECTS

BELT

WIDTH-IN.

FIGURE

5 2

BELT AGGLOMERATOR SIZING f r o m Mllllgan

1983

 

O R E P R E P A R A T IO IO N C R U S H I N G A N D A GG GG L O M E ER RAT TII O ON N

BELT W IDTH-IN.

FIGUR BELT

QGLOMER from

 

MHIIgan

5.3 T O R COST 1983

PRECIOUS MET L HE

P LE CHING CHING PRO JECT S

DRUM DIAMETER-FT.

FIGUR DRUM

5.4

GGLOMER TOR SIZING from Mllllgan 1 9 8 3

 

ORE PREPARATION

T y p i c a l l y f o r s ca c a le l e -u -u p p,, 4 , t h e slo p pe e o f the sh ell i s remains co ns tan t a ass d do o es es t h e C o s t , ll s t r a t e s t h e t y p i c a l

C R U S H I N G A N D AGGLOMERATION

77

the L t o D r a t i o i s ke ep pt con nss tta a n t between 2 a n d c o ns t an t n e ea a r 7 d e g r ee ee s , and t h e r e s i d e n c e t i m e degree o f lo ad in g . Figu re 5 5.. 5 , Drum A g g l o om m e r a tto or bud dg ge ett c o s t o f d drr u m a g gg g lo lo m e err at a t or o r s. s.

R e c e n t i mp m p rro o ve ve m me en ntt i n t h e d drr u m a g g llo omerator includes the use o f fl e x i b l e r u b b er l i n e r s t o r e d u ucc e c a k i n g w i t h i n t h e d r u m a n d t o e l i m i n a t e l a r g e o v e r s i z e material. 5. 5.3. 3.3 3

Pan Ag gl om er at or s The p pa an n-- ttyy p pe e

d i s k ) a g g llo o m e rra ato orr u sse e s a f l a t i n c l i n e d pan t o o b t a i n t h e

re qu ir ed

tumb bll i n g

an nd d

c o m p a cctt i o n n..

This

eq qu u ip ip m e en nt

p ro ro d du u ce ce s

a

u nifo rm

a g g l o m e r a t e w i t h e x c e l 1e n t g r e e n s t r e n g t h . F i g u r e 5 .6 .6 , Pan A g g l o m e r a t o r Sizing, il lu s tr a t e s a ty pi ca l r at in g f o r p pa an a g gg g lo lo m me e ra r a ti t i on o n . The f o l l o w i n g e q u a t i o n c a n a l s o be u uss e ed d t o sca le up design: C

where

C

=

Em

Constant;

i s Y c a p a c i t y and

D

i s d i am e t e err o f a s h a l l o w d i s k o r p a n .

T h e m a j o r o p e r a t i n g p a rra a m e tte e r s i n t h e p a n a g g llo o m e rra ato orr a r e : 1 a ng n g le le o f d i s k ; 2 ) s p e e d o f d i s k ; 3 ) p o i n t o f m a t e r i a l f ee ee d d;; a n d 4 l o c a t i o n a an nd a m mo o un un t f t h e w a t e r i s s p rra o f water sp prr a ayy . a ye ye d u p po on the la rg er agg gll om o m e rra a te te , t h e f t h e f e e d m a t e r i a l an d t h e w a t e r a gg g g llo o m e ra r a tte e w i l l t e nd n d t o i n c rre e a s e i n si z e . spray loca tion are o on n o r near fi n e ma teria l, the agg gll o m me e ra r a te t e w i l l t en en d t o be small L a r g e r p e l 1e 1e t s a r e f o r m e d i f t h e f e e d a n nd d s p r a y a r e b rro ought clos er t o g e t h e r . Budget c o s t s o f t h i s t y p e o f e eq qu uii p m me en ntt a r e i l l u s t r a t e d i n F i g u rre e 5. 5.7, 7, Pan Aggl ome omera ra t o r Co st.

.

Table 5.1 i s a p ar ti a l l i s t o f supp liers fo r bo ott h d r u m a an nd p pa an a g gl gl o m e err a tto o rs rs . M o oss t h a avv e t h e i r own t e s t i n g f a c i l i t i e s . Be1t a g g l o m e r a t o r s a r e innovatio ns by oper ator s an nd d a ass s u ucc h a r e n o t a v a i l a b l e a s p rre ed de e si s i gn gn e ed d units . 54

OPTIMUM

W

TER

CONTENT

FOR

GGLOMER

TION

The p r o p e r m o i s t u r e c o n t e n t f o r a g g l o m e rra atio on n is d de e te t e rm rm i n ne ed by th e p a r t i c l e s i z e , c l a y c o n t e n t , w e t t i n g c h a r a c t e r i s t i c s , a n d d e s i re re d degree o f c o m p a c ti ti o n d u r i n g a g g l o m e r a t i o n . T h he e m a s s m u s t n o t be s a t u r a t e d , h o ow we evv er er , f o r t h i s d e sstt rro o y s t h e g re re e en n s t r e n g t h . G r e e n s t r e n g t h i s a tte e rm rm a p p l i e d t o t h e s t r e n g t h o f a g g llo ome err at a t e s t o s tta a n d u p t o p r o cce e s s i n g and h a an nd dll i ng ng . su ff ic ie nt g re re e en n st reng th i s r equ ired t o r e s i s t crushing during R Re eap b u i l d i n g . G r e e n strength i s m ma ad e u p o f s t r e n g t h i m p pa a rt ed tension o f the wate err m e n i s c i .

y a binder,

but mostly d du ue t o t h e

s iim m p le le me ett ho ho d o f e s t i m a t i n g t h e p ro ro p pe e r m o iiss t u rre e c o n tte ent fo r a gg g g llo o m e rra a ti ti o n i s t o n i i x a s l u r r y o f t h e o r e i n w a att e r a n d f i l t e r o n a vva ac uu m f i l t e r . The d e w wa a tte e re re d f i 1 e r c a k e w i l l c o n t a i n s l i g h t l y m o re w wa a te te r t h a an n n e ce c e s ssa a r y f o r p r o p e r a g g l o m e r a ttii o n . A n o t h e r t e c h n i q u e f o r e s t i m a t i n g t h e p ro ro pe r m o i s tu r e c o n t en t i s t o o b t a i n t h e w a t e r c o n t e n t vvss . d r y d e n s i t y r e l a t i o n s h i p f o r t h e s o i l b y u s i ng ng a S t a n da da r d P r o c t o r C o om mpa acc ti ti o on n t e s t . The o op p ti t i mu m u m m o i s t u r e cco o n t e n t i s a good estimate f or th e prope err a g g l o m e r a att i o n m o i s t u r e c o n t e n t .  

P R E C IO U S M ET ET A AL L H E A P L E A C H IN IN G P R O J E C T S

04

I

4

10

8

6

12

DRUM DIAMETER-FT.

FIGURE 5 5 DRUM AGGLOMERATOR COST from M l l l l ~ a n 1983

 

ORE PREPARATION CR USH ING AND AGGLOME AGGLOMERAT RATIO ION N

400

300

-

200 -

100-

0 5

10

16 DIAMETER-FT.

20

25

FIGURE

5 6

PAN AGGLOMERATOR COST r o m Mllllgan

1883 )

 

P R E C I OU S M E ET T L HE

0

5

10

P L E C HI N NG G PRO JECTS

15

P A N D IIA A M E T ER ER F T .

20

25

FIGURE

5 7

PAN AGGLOMERATOR SIZING from Mllllgan

1983 )

 

ORE OR E PREPARATION PREPARAT ION CRUSHING AN D AGGLOMERATlON

TABLE 5.1 AGGLOMERATOR SUPPLIERS Acme International Ltd.

G l a t t A i r T e c h n iq iq ue

A R i c West h a rd r d Ave S t o .l l m a n 10t t0n .T.S. T.S. Je nk in to wn PA PA 215-885-7750

A 2 0t t-T -Tn . SSp et eavr e RAdbt .b e l y Ramsey, NJ 201-825-8700

A l l i s -C - C h a l m e rs r s M i n i n g S y s te te m s D i v . A t t n . G eo e o rrg ge Skoro nski Box 512 M i l w a u k e e , W 53201 414-475-2437

L e ge g e nd nd M e t a l 1 u r g i c a l L a b o r a t o r y Attn. Larry 125-T Manuel St. Reno, NV 8 9 5 0 2 702- 786- 3003

Bepex Corp. A t t n . D ave P h i l l i p s M i nn n n e a po po l i s , M N 612-331-4370

MMC/MARS M i n e r a l A t t n . M a r k C a th t h e r/ r / B ob ob H i n k l e Box 128 Valencia, PA 16059 412-898-1551

C a l i f o r n i a P e l l e t M i l l Co. 1800 Fol som S t. Sa San n Fr an ci s co , CA CA 94103 415-431-3800

O B r i e n I n d u s t r i a l E q u ip i p m en e n t Co Co . Attn. Andy Whitaker 1 5 9 6 Hu Hu ds d s on o n A ve v e nu nu e a t N e w h a l l Sa an n Fr a nc is co , C CA A 415- 826- 3033

Dravo Company A t t n . D.W. K e s t n e r One On e 01 e r P l aza P i t t s b u r g , PA 1 5 52 222 412-566-3000

R en neb ur g Sons C o. o. A t t n . J o h n R e n n e b u rg r g / G a rr rr y 2635 Boston St. B a l t i m o r e , M D 21224 302- 732- 1666

D u s t S u p p r e ss ss i o n S y s t e m I n c . A t t n . J a y R e a di di n g 2459-A Charlotte Kansas City MO 816-421-4739 Feeco International Inc. A t tn . L a r r y C l i v e r 3913 Algoma Algoma Rd. Rd. D e pt . A Green Bay, W 5 4 3 0 1 414-468- 1000 Ferro-Tec h Attn. Carl Ho lly Eureka and 5 Ave. (467 Eureka Rd.) W yandot t e, M I 48192 313-282-7300

 

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5.5

AGGLOMERATION O

P L E C H IN IN G P R O J E C T S

CRUSHED ORES AND WASTES

M os os t p r e c i o u s m e t a l o r e s a n nd d wa ass tte es re qu ir e cru sh ing t o min nu us o on ne i n c h ( 2 5 mm) o r f i n e r b e f o r e a g g llo o m e r a t i o n . C r u s h iin ng t o the ess e s i z e s l i b e r a t e s precious m etal v alues an nd d i mp r o ovv e s o v e r a l l r e c o v e r y . C r u uss h iin ng t o a ab bou utt 3 3// 4 i n c h ( 19 1 9 mm) u s u a l l y r e q u i r e s ttw wo stage ess o f c r u s h i n g . A f e e d s i z e o f a b o u utt 3 / 8 i n c h ( 9 mm i s c o n s id e r e d t h e e c o on no om m ic ic m mii n i m u um m, an nd d re qu ir es th re e crushing gs eh se .r . PSr e im sshue ed aarrd on on ne e cs rt au ge c on oa nr yd da a cry r yr uasnhdi n tge ri tsi a ur ys ucar lul sy h ai ncgc o imsp lliui sh ad l l yb y d do oan ej a w u s ionrg as hso ortrat -nhde ea dd cc o on crushers. C rru u ssh he ed d o res ca an n , i n g e n e r a l , b e a g g llo omera att e d b byy m i x i n g 5 t o 1 0 I b s o f port land ce em me en n t p e r t o n (2. 5 t o 5 k g / p pe e r t o n ) o f d r y ffe eed, w e t t i n g w i t h 8 t o 1 6 p e r c en t m o i s t u r e as e i t h e r w a t e r o r s t r o n g c y a n i de s o l u t i o n , m e ch a ni c al ly tum blin g th e wetted mixtur e, an nd d c u r i n g t h e a g g llo omera att e d ffe ee d d u r i n g he a ap p b u i l d i n g p r o cce e d u rre e s . The q u a n t i t y o f c e em me en nt a ad d d e d d u r i n g a g g l o m e r a t i o n u su su a all 1 y p r o v i d e s t h e p r o t e c t i v e a1 k a l n i y r e q u i r e d f o r c y a n i d e l e a c h i n g . A f t e r agglomera tion an nd d he ea ap bu il di ng , lea ch ing i s con nd du ucc t e ed d wi t h conventiona all h e ea ap 1e a c h i u g t e c h n i q u e s . D u r i n g a g g l o m e rra a ti on ,

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ac od ha er sr ee p t oa r tt ihc el e sc o a T r sh ee r a gp ga lro tm i cel rra ea stte nd ruec ae om e sa n pd r o cd du ed dt e a rae coo fa t si nu gf f i o c if e nf itn eg grsr e eanr osu tnrde n tght eh a f t e r c u r i n g t o w i t h s t a n d h a n d l i n g a n d w e t t i n g w i t h m iin n iim m al d e eg g rra a da d a ti ti o on n. Agglomeration o ve v e rc rc o om me ess th e major p rro ob bll e em ms associated with p a r ti c le s e g r e g a t i o n d u r i n g heap b u i l d i n g , f i n e s m i g r a ti o n , and s o l u t i o n c ha n n ne e l iin ng d u r i n g l e a c h i n g b y p r o d u c i n g a p o rro o u ss,, p e err m me ea ab b lle e ffe eed d.. A p er er me a ab b le le f e e d m a t e r i a l s t a c k e d i n a h he eap p e r m i t s t h e u n i f o r m f l o w o f

1e a ch i ng s o l u t i o n a an n d c o n t a c t o f t h e c yya a ni d de e e a ch i n ng g so lut io n wit h the e x po p o s ed ed p r e c i o u s m e t a l p a r t i c l e s , a n d d e ecc re re a ass es es t h e l e a c h i n g t i m e r e q u i r e d t o o b t a i n t a r g e t e d p r e c i o u s m et al r e c o ve r y . The f o l l o w i n g i s a b r i e f d e s c r i p t i o n o f o n e c o n v e n t i o n a l h e a p l e a c h op era tio n (n no o a g g l o m e r a t i o n ) and t h r e e c o m mm me err ccii a all o p e r a t i o n s w h he e rre e crus hing a n d a g g l o m e r a t i o n p r e t r e a t m e n t w a s n e c e s s a rryy f o r t h e s u c c e s s f u l h e a p l e a c h i n g t r e a t m e n t o f t h e o r e . The t h r e e w e err e s e l e c t e d f o r d i s c u s s i o n b e ecc a u s e o f t h e d i v e r s i t y o f the agglomerating eq qu u iip pm me en ntt u sse e d f o r p r e t r e a t i n g t h e o r e . Two o f t h e o p e r a t i o n s h a vve e be ee en p r o d u c in g b u l l i o n s i n c e t h e e a r l y 1 9 8 80 0 s an nd d the i n f o r m a t i o n g i v e n h e r e i n d e s c r i b e s t h e i r o p e r a t i o n s h o r t l y a f t e r s tta a r t - u p . The, t h i r d ope ratio n be eg g a n p r o d u c t i o n i n e a r l y 1 9 8 5 . A l l t h r e e a r e c o n s id id er ed moderate siz ed he ea a p 1e a c hi n g o p e r a t i o n s and t h e i r p r o d u c t i o n r a t e s r a an ng ge e ffrr o m 2,000 t o 3 3,, 5 0 0 t o n s o f o r e p e r d a yy.. 5 6

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conventional gold h he eap l e a c h i n g o p e r a t i o n i s l o c a t e d n ne ea arr t h e g e o g ra p h ic a l c e n t e r o f t h e s t a t e o f N Ne e v a d a . T h e s i l i c e o u s o r e i s m iin ned a t a r a t e o f a b o u t 2 0 , 0 0 0 t o n s p e r d a y (T P D ) u s i n g o p e n - p i t m i n i n g m e ett ho ho d dss . M i n ne ed o r e i s t r u c k e d t o an i n - p i t u n nd de err g grr o ou un nd d primary stand da ard co on ne c r u s he r . Discha rge from th e prim ary crus her (app roxi mat ely fo u r inches, 10 00 0 mrn) i s c o n ve ve y e d t o a s e c o n d a r y s h o r t h e ea ad co on ne crushe r where t i s reduced i n s i z e t o A

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T he o r e v e r y s i 1 ~ C ~ O U Sn d few f i n e s a r e g e ne n e r at at e d by c r u s h i n g t o 3 8 i n c h ( 9 ~nm) C o ns n s e q ue u e n ttll y , a gg g g 1o 1 o m er er a att iio o n p r e t r e a t m e n t i s n o t n ec e c e s sa sa r y f o r c o n t r o l l i n g f i n e s m i g r a t i o n d u r i n g l e a c h i n g . G o l d g rra a de d e a ve v e rra a ge g e s 0 . 0 4 5 o un un ce ce s p er er t o n ( 1 1.. 5 g l i n t ) , a n d so some v i s i b l e g o l d i s p r e s e n t i n t h e f e ee e d. d. C rru u sh s h ed e d o r e i s c o nv nv e eyy e ed d t o an u n d de e rrg g rro o un u n d o r e s t o c k p i l e . L im im e i s ad ad d e d t o t h e o r e a t t h e c o n ve v e y or o r b e f o re re t r e ac a c h es e s t h e o r e s t o c k p i l e . The o r e -1 - 1 irn e m i x t u re r e i s c on o n v e y e d fr om t h e s t o c k p i l e t o a t r u c k l o a d o u t b i n and i s t r a n s p o r t e d t o t h e a s p h a l t p a d by b y t r u c k . H eaps a r e b u i l t t o a h e i g h t o f 40 40 f t ( 1 2 m) b y p u s h i n g up u p t h e a n g l e o f r e po p o s e w i t h a t r a c k e d d oz o z e r. r. O v e r a l l d i m e n s i o n s o f th e h e a p a r e 4 ,8 0 0 f t x 300 f t x 4 0 f t (1,460 m x 9 1 m x 12 m . o n ttii n nu u ou ou s l e a c h i n g o f 1 1.. 2 m i l l i o n t o on ns o f his s i z e h e a p w i l l a l l o w f o r t h e c on ore. i s c on on d du u ct ct e ed d b y a p p l y l n g c y an a n lld d e s o l u t i o n c o n t a i n i n g 1 .0 l b 0 . 5 k g l m t ) o f s o l u t i o n o v e r t h e he he a p s a t a r a t e o f 0. 0. 00 5 g p rn r n / ft ft (0 .0 0 3 l / s / m 2 ) o f h e ea a p s u r f a c e a r e a . W ob o b bl bl e r s p r i n k l e r s a r e u se se d f o r a p p l y i n g 52 s o l u t i o n i n a p a t t e r n t o e n s u r e ma m axlm um c o ve v e r ag a g e an a n d m iin n i m um um e v a p o r a t i o n . t o 55 d ay a y l e a c h c y c l e i s r e q u i r e d t o o b t a i n t a r g e t e d g o l d re r e c ov o v e ry r y , Leached o r e i s re r e m ov ov e d f ro ro m t h e l e a c h p ad ad a n d i s t r u c k e d a s h o r t d i s t a n c e t o t h e t a i l n g s d i s p o s a l a re r e a. a. P r eg e g na na n ntt s o l u t i o n d r a i n s f rro o m th t h e he h e a p a n d f l o w s by by g r a v i t y t o c o l l e c t i o n d i t c h e s . S o f u t l o n i n t h e d i t c h e s f l o w b y g r a v i t y t o a p rre e gn g n an an t solut lo n res erv ol a n d i s pu p um ped t h r o u g h a f i e - s t ag a g e c ar ar b bo on adsorp t I o n c i r c u i t a t a r a t e o f 2,600 gpm ( 1 6 4 1 s he ca c a rrb b on o n a ds d s o r p t lo lo n c i r c u i t c o n t a i n s f r o m 1 5 t o 18 t o n s o f c a r b o n . t o t a l a f 2.7 v o l u m e to t o n s o f ca c a r bo bo n I s e d u c t e d t o t h e s t r l p p l n g r s i r c u l t each day day,, Loaded Loaded ca rb on (120 t o 150 OP OPT A u I s d es es or o r be be d i n a b bo o u t e l g h t b u r s u s 1 n g p re r e s s u r e s t r i p p i n g t e c h n o lo l o g y . D es es or or b be ed carbon I s e c l d w a s h e d and t h e m a l l y r eg e g en e n er er a att e ed d b e fo f o r e b e i n g r e c y c le le d t o t h e a d s o r p t i o n c i r c u i t G o l d v l u e s s t r i p p e d f r o m t h e c a r b o n a r e e le le c t r o w o n o n t o s t e e l w o o l c a th t h o de de s . C a att h ho o de de s a r e r e f i n e d o n s i t e t o p rro o du d u ce c e d o re re b u l l o n , Q s r e b ut p uu rl ll ff oi cna t Il os n .a b o ut

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L ow o w --g g ra r a de d e o r e f r o m the mjna I s dump leac hed a t a run-of-mlne f e e d s i z e . About 600,000 t a n s o f I o n --g g r a d e i s I s a c h e d a t a t i m e on c l a y pad, pad, The The dump l e a c h s i t e ha h a s I t s own c ar a r b on o n ~ d s e r p t i o n c l r c u i t , b u t l oa o a d e d c ar a r b on on i s processed a t t h e m f n e p l a n t s l t a , B a rr r r e n s o l u t i o n fr f r o m t h e c ar ar b o n c i r c u i t i s r ec e c y cl c l e d t o the dump, M u l t i p l e l i f t s o f l o w - g r a d e o r e w i l l u l t i m a t e l y b e p r o c e s s e d a n t h e clay pad Each I l f t I s 60 F t (18 rn i n h e i g gh h tt,, L i f t s a r e b u i l t b y t r u c k d u m pi p i n g from the s u r f a c e o f t h e dump.

Few p r o b l e m s a r e exparlanced w l t h h e a p l e a c h i n g i n t h l s o p e r a tl tl o n , primarily b e c a u s e t h e o r e f s v e r y c l @ a n a n d c o n t a l n s a l m os o s t no c y a n i c i d e s . I t I s r e p o r t a d t h a t t h e k e y t o t h e su s u c c e s s o f t h l s o p e r a t i o n i s t he he e f f i c i e n t s t r l p p l n g taond nd40,0 e00 a c t iTvPaI)t ioo fn crous f he t h de feed. c a rb r b on on , expansion 40r,000 5 6 2

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m a t e r i a l s a r e m i n e d : o l d w a st s t e m a t e r i a l w h i c h was us u s e d f o r m in in e b a c k f i l l ; and v i r g i n o r e a d j a c e n t t o t h e w a st s t e m a t e r i a l . T h e wa w a s t e m a t e r i a l i s mi min e d w i t h f r o n tt - e n d l o a d e r s t o e xp x p o s e t h e v i r g i n o r e . T h e v i r g i n o r e i s d r i l l e d an an d b l a s t e d a nd n d m o v e d b y f r o n t - e n d l o a d e r s . T h e s i l v e r c o n t e n t of o f t h e t wo wo f e e d m a t e r i a l s v a r i e s . T h e c u t o f f g ra r a d e o f f ee e e d t o t h e he heaps i s 1 1.. 0 t r o y o u n c e of of s i l v e r p e r t o n ( a b o u t 3 4 g / m t ) . A p p r o x i m a t e l y 2, 2 ,0 0 0 t o n s p e r d a y o f o r e a r e m i n e d a nd nd a g g l o m e r a t e d T h e m i n e d o r e a nd n d m i n e r a l i z e d w a s tte e a r e mo mov ed f r o m a s t o c k p i l e t o t h e c r u s h i n g p l a n t w h er e r e t h e y a r e c r u s h e d t o a no n o m in i n al a l 1 / 2 i n c h ( 1 2 mm) w i t h t h r e e s t a g e s o f c r u s h i n g a nd nd s c r e e n i n g . R u un n - o f - m in in e o r e i s f e d t o t h e p r i m a r y j a w a nd n d i s d i s c h a r g e d a t a b o u t a 22- 1 1// 2 i n c h ( 3 7 mm) s i z e . S ec e c on on d da a rryy a nd nd t e r t i a r y c r u s h i n g i s d o n e w i t h a s c r e e n i n g c i r c u i t an a n d s h o r t h e a d co cone c r u s h i n g system . L im i m e ( 7 I b s , 3 kkg g , p e r t o n o f o r e ) i s u se s e d a s t h e b i n d e r f o r a g g l o m er e r a t i o n and i s m i x e d w i t h t h e o r e d u r i n g s e c on o n d a ry r y c r u s h i n g . T he c rru u sh s h e d o r e -1 -1 ime m i x t u r e i s c on o n v ey e y e d t o a n u n d e rg r g r o un u n d o r e s t o c k p i l e . Some m o i s t u r e i s s p ra r a y ed ed o n t o t h e o r e o n t h e c r u s h e r d i s c h a r g e c o n vve e y or o r t o d e c rre e as as e d u s t i n g . T h e o r e f r o m t h e u n d e r g r o u n d s t o c k p i l e i s a g gl gl o om m er er a att e ed d on on a r e v er s e b e l t c o n v e y o r d e s i g n e d b y t h e o p e r a t o r s . T h e 4 f t (1.2 m) x 25 f t ( 7 . 6 m ) b e l t a g g l o m e r at a t e s o r e a t a r a t e o f 2 0 t o n s p g r h ou o u rr.. T h e a g g llo o m e r a t i ng n g c on o n vve e yyo or c a n b e s e t a t an a n a n g l e b et et w we e en e n 3 5 a nd n d 45 a n d t h e b e l t t r a v e l s u p w ar ar d w h i l e t h e o r e l n ov ov es es d o ow w n t h e b e1 e 1 t . T he he a n g l e a n d s pe p e e d o f t h e b e1 e 1 t c an an b be e varied t o p r o v i d e t h e d e s i r e d r e t e n t i o n t i m e o f o r e on o n t h e b e l t . W a t e r i s sp sp r a y e d a t s e v e r a l l o c a t i o n s a l o n g t h e l e n g t h o f t h e b e l t and g i v e s t h e agglom e err a t e d f ee ee d a m o i s t u r e c o n t e n t o f b et e t we w e en e n 1 0 a nd n d 1 2 p e r c e n t . A s m a l l a m o u n t o f m o is i s t en e n ed ed f i n e s a d h e r es es t o t h e b e l t and r i d e s u p t h e c o on n v e y or o r . A s c ra ra p e err a t t h e b o t t o m s i d e o f t h e d r i v e r o l l e r e l i m i n a t e s e x c e s s i v e f i n e s b u i l d-up. T h e a g g l o m e r a t e d o r e i s t r a n s p o r t e d t o a s t o c k p i l e b y a r a d i a l arm s t a c k e r . T h e m a t e r i a l f r o m t h e s t o c k p i l e i s tr t r u c k e d 50 5 0 0 f t ( 1 5 0 m) m) t o a 3 /4 /4 a c r e ( 4 , 0 0 0 m 2 ) l e a c h i n g p ad a d a nd n d i s a1 a 1 o we we d t o c u r e d u r i n g heap b u i l d i n g . F i v e h ea ea p pss , e a ch c h c o n t a i n i n g 6, 6 , 0 0 0 t o n s o f a gg g g llo o m er er a att e ed d or e stacked 10 t o 3 ft tl eo a c3. 3 .h4i n gm,) hwihg ihl ,e at rhee l oe tahc ehre dt woon at hr ee ep iad atdh. e Tr hbre r eeei n gh e apprre s paa rrre ee d a fto dr i fl ef ea rcehni nt g st s ot ar ge g ebse in e i no gf removed from the pad. T h e h e a p s a r e s p r a y e d w i t h pH pH 10 1 0 ..5 5 s o l t i o n c o n t a i n i n g tw t w o I b s NaCN p e err t o n ( 1 k g / m t ) a t a r a t e o f 0.0075 g p m /f /f t Y (0.005 l/s/m2). The l e a c h i n g s o l u t i o n p e r c o l a t e s t h r o u g h t h e h e a p , i s c o l l e c t e d o n t h e i m p e r vvii ou ou s l e a ch i n g p a d , a n d d r a i n s i n t o t h e p l a s t i c - l i n e d s o l u t i o n t r e n c h e ss.. T h e l e a c h i n g a n d w a s h i n g c y c l e i s s ev e v en e n da days. T h e l e a c h ed e d r e s i d u e i s t r a n s f e r r e d t o an an a u x i l i a r y l e a c h i n g p a d a nd n d s p ra r a ye y e d w i t h c y a n i d e s o l u t i o n o n e da da y p e r m onth f o r a d d i t i o n a l p r e c i o u s m e t a l e x t r a c t i o n . P r e ci c i ou ou s m et a all v a lu lu es i n t h e pr e eg g na n a nt nt s o l u t i o n a r e r e c o v e r e d b y M e r r i l 1-Crowe z i n c p r e c i p i a t i o n t e ecc h n o l og o g y . The p r e c i o u s - m e t a l - b e a r i n g z i n c p r e c i p i t a t e s a r e r e f i n e d on o n s i t e an a nd y i e l d d o r e b u l l i o n . T h e d o r e i s s h iip p pe p e d t o a n o t h e r f a c i l i t y f o r r e f i n i n g . The b a r r e n s o l u t i o n s a r e r e c y c l e d t o t h e h ea ea p s . H e a p l e a c h i n g w a s u n s u c c e s sf s f u 1 b e f o r e a g g l o m e r a t i o n p r e t r e a t m e n t w as a p p l i e d t o t h e o r e . C o n v en e n t i on o n a l h e a p l e a c h i n g r ec e c o v e re r e d o n l y 37 37 p e r c e n t o f

t h e leac habl e s i l v e r from three i nc h (7 75 5 mm) fe fe e d m a t e r i a l t r e a t e d i n 90 90 d a y 1 e a c h i n g c y c l e s. s . S e v e re r e p e r c o l a t i o n p rro o bl bl e em m s w er e r e e n c ou o u n te t e r ed e d . A g g lo l o m e ra r a t io io n permitted finer c r u sh i n g, w h i c h 1 e ra r a tte ed additional s i l v e r v a llu u es es f o r  

8

O R E PR PR E P A R A T IIO ON CRUSHING AN D AGGLOMERATION

di ss ol ut io n b byy c y an an i d de e. F i n e r c r u s h i n g an d a g g l o om m e r a ttii o n --h heap l ea ch in g i n c r e a s e d s i l v e r r e c o v e r y t o 90 p e err c e n t o f t h e l e a c h a b l e s i l v e r a n d d e ccrr e a ass e d t h e l e a c h i n g t i m e t o seven d a ayy ss.. 5.6. 5.6.3 3

N o r t h er n Nev Nev a ada da Gold He Heap ap Lea c hi ng : 2,50 2,500 0

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adt i oc no u ni nt e rncourrtrhe en rt n d eN Ne ifcohr hs as aesv e rparro ol d du ea drrss , g odlids c b n c y a n i dAant i oonp earn nd ce av andt aa,t iio own h ic yu ecce o vy e raegdi t aa t ni oe w o r e d e p o s i t s e v e r a l m i l e s f ro r o m t h e w o r k i n g m iin ne e.. H i g h e r g r a ad de o re fro m the ne ew w d e p o s i t i s t r a n s p o r t e d t o t h e o r i g i n a l m i l l f o r g o l d r e c o v e r y . O re re c o n t a i n i n g l e s s t h a n 0 . 0 7 t r o y o u n c e g o l d p e r t o n 2 .4 .4 g / m t ) i s h he e a p l e a c h e d a t t h e new s i t e . A vve e ra ra g ge e o r e g r ad ad e f o r t h e h e ea ap m a t e r i a l i s 0 0.. 0 3 4 t r o y o ou u nc nc e g o l d p e r t o n ne ed b byy o p e n - p i t m e ett h ho od dss a an nd i s t r u c k e d t o t h e h e ea ap 1.2 g / m t ) . T h e o r e i s m i n leac hing si t e approximately one-half mil e 0 .8 . 8 k m )f ) f rro o m t h e new p i t . A b bo ou utt 2 , 5 0 0 t o n s p e r d a y o f o r e a r e m iin n e d and h e a p l e a c h e d . T he h e o r e i s c ru ru sh e ed d t o m i nu n u s 5 8 i n c h 1 6 mm) b y a p r i m a r y j a w c r u s h e r an nd d a s e c o n d a ry ry c o on ne crus her. Po rt la nd ce em me en n t t y p e 11 , a t t h e r a t e o f 7 t o 1 0 l b s p e r t o n 3 . 5 t o 5 kkg g /m / m tt)) o f o rre e, i s a ad dded t o t h e o r e a t t h e p r i m a r y j aw crusher discharge co on n vve e y o rr,, a n d i s m i xxe ed w i t h th e or e d ur in g secon nd dary c r u s h i n g . T h e o r e - b iin n d e r m i x t u r e f rro o m sse e cco on nd da arr y c r u s h i n g i s c o on nve eyy e d t o a rt ha ed i as lt a ca kr me r s a t an cd k er re. s uWl ta at ot u rt eh e c omni txet un tr e o af t 9t ht eo d1i 3s c hp ae rr gc e e n te en an st e ri ni sa ssp fpi rra naayye le dm oo ni stto .n d T oh ef or e i s agg gll o m me e rra ate ed d b y c a s c a d i n g do down t h e s i d e s o f t h e c o n i c a l 1 yy - ssh h ap ap e ed d a gg g g lo l o m e rra a te te d o r e s t o c k p i 1e. A d d i ti o n a l t um um bl i n g , su ff ic ie n t t o ef fe ct a g g l o m e r a t i o n , o c c u r s when t h e f r o n t - e n d l o a d e r l o a d s t h e r e a r dum p t r u c k w i t h a g g lo lo m e r a att e s f r o m t h e s t o c k p i l e an an d w wh h en t h e t r u c k d u m p s t h e a g g l o m e r a t e d f e ed ed o n t o t h e a s p h a l t l e a c h i n g p pa a d . The a g g gll o m me e ra t e ed d ore I s cured f o r two t o t h r e e d a y s w h i l e t h e h eap i s b e i n g b u i l t . t 3.7 m F i v e 1 7 ,,0 000 0-- to to n h e ea ap pss , a p p r o x i m a t e l y 1 2 h fg fg h h,, a r e b u i l t o on n t h e l e a c h i n g pa pad. T h r e e h e a p s a r e i n d i f f e r e n t s t a g e s o f t h e l e a c h i n g c y c l e while th e rema aii n iin n g ttw wo a r e e i t h e r b e i ng p r e ep p a re d f o r l e a c h i n g o r b e i n g removed from the pad.

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011 k ag b/m / mo tu)t 0o. 0f 0 3s o ll /ust/i m o n* ). oT hf e pHp o1r0 t -l 1 a 1n ds oce cleumt ien eonnt cad a do dnet da i ndiunrgi n 1g. 0 a g1gbl o Nmae rNa t pf oenr tpor no v i d0 .e5s m o s t o f t h e a 1 k a l i n l t y r e q u i r e d d u r i n g l e a c h i n g , b u t s m a l l q u a n t i t i e s o f NaOH a r e a dd dd e ed d t o t h e b a r re r e n s o l u t i o n t o m a i n t a i n t h e d e s i r e d pH v a l u e . T h e l e a c h i n g and w a ass h hii n g c y c l e i s 20 d a ayy ss.. L e a c h e d r e s l d u e s a r e t r a n s p o r t e d t o a ta il in g s dispo oss a l a r e a . The p re g gn na an n t s o l u t i o n d r a i n i n g f rro om the leaching p pa ad f l o w s b y g r a v i t y t o a rese rvo ir a an nd i s p pu um ped t h r o u g h a s e r i e s o f f i v e c ar ar b o on n adsorp tion tanks f o r rec ov ery o off d i s s o l v e d g o l d vva alue ess . T h e g o l d - l o a d e d , 12 x 3 0 m e ess h , c o c o n u t s h e l l a c t i v a t e d c a rrb b on on i s t r a n s p o r t e d t o t h e o r i g i n a l m i l 1s i t e f o r d e s o r p t i o n b y an an a l k a l i n e a l c o h o l s o l u t i o n . T h e v a llu u e s d e sso o rrb be ed d from th e carbon are e l e c t r o w o n on s t e e l w o oo o l c a th th o od de ess , w h i c h a r e r e f i n e d o n s i t e t o p r o d u ucc e d o r e bullion. hei s o or e p. e r Ca toino vne i nt ai al l hl ey a tpr il ee ad c ch oi nngv ewnatsi o nu an lssu 1e i nc gau oe op rf o tche es s h ti hg eh l o w -g - g r aTd de e. en ni tni o on ap u hcecaeps s 1 f ue la cbhec ein a u tsse c l a y c o n t e n t o f t h e o r e , p a r t i c l e s e g r e g a t i o n, n , and f i n e s m i g r a t i o n , w h i c h resul te d i n leach so lu ti on ch ha an nn ne ell i n g . A g g gll o me m e r a t iio on pretreatme nt increased

 

8

PRECIOUS MET L HE

P LE CHING CHING PROJECT S

g o l d r e c o v e r y b y 60 60 p e r c e n t , w h i l e d e c r e a s i n g t h e l e a c h i n g c y c l e ftft-om 50 50 d a y s t o 2 0 d a y s . E ve v e n w i t h a g g l o m e r a t i o n , some o r e r e t a i n s a p p r o x i m a t e l y 3 0 P e rc r c e nt nt moisture. a nd n d l o n g w a sh s h in i n g p e r i o d s a re r e r e q u i r e d t o r e c o v e r t h e d i s sso o l v ed ed v a l u e s f r o m t h e a g gl g l o m e ra r a t e s. s . T h e l o n g e r wa wa s h hii n ng g c y c l e ex e x t en en d s t h e t o t a l caching c y c l e t o 3 0 d a ys y s f o r some h ea ea p pss . 564

West C e n t r a l Neva Nevada da Gold Heap Heap Leach: 3, 3,50 500 0 Tons Per Day Day

An o p e r a t i o n i n w e s t c e n t r a l N ev ev ad ad a p r o c e s s e s 3 ,5 ,5 0 0 TPD o f c r u s h e d a n d a g g l o m e r a t e d g o l d o r e . O r e i s m in i n e d u s i n g o p e n - p i t m et e t h od o d s. s . D r i l l e d and b l a s t e d o r e i s l o a de d e d b y a f r o n tt - e n d l o a d e r o nt n t o t r u c k s an a n d i s h au a u lle e d ab abo ut 0.5 m i l e s 0.8 km ) t o t h e c r u s h i n g c i r c u i t . p r i m a r y j a w c r u sh s h e r p rodu ces a minus s i x i n c h 1 5 0 mm) f ee e e d. d. The p r i m a r y c r u s h e r d i s c h a r g e i s conveyed a s h o r t d i s t a n c e t o a s e c o nd n d a ry ry s h o r t h e ea a d c on on e c r u s h e r wh w h e r e i t i s r ed ed u c e d i n s i z e t o a n o m i n a l m i n us u s o ne ne i n c h . T he h e c r u s h e d o r e i s v e r y c l a y e y a n d c o n t a i n s a b o u t 25 25 w e i gh g h t pe p e rrcc en en t m i n u s 100 m e s h f i n e s . T h e c r u s h e d o r e i s a g g l o m e r a t e d b y a d d i n g 1 0 I b s p o r t l a n d c e m e n t p e r t o n 5 k g /m / m t ) t o t h e s e co c o n da d a rryy c r u s h e r . W e t t i n g a t s e ve v e rra al l o c a t i o n s w i t h b a r re r e n s o l u t i o n c o n t a i n i n g c y an a n iid d e t o a f i n a l m o i s t u r e c o nt nt e en nt o f 1 0 t o 1 2 w e i g h t p e rc r c e n t , m e c h a n i c a l l y t u m b l i n g i n a th t h r e e -s - s t a g e d ro ro p b e l t a g g l o m e r a t i o n c i r c u i t , a n d c u r i n g i n a s t o c k p i l e f o r t h r e e t o f o u r da d a y s b ef ef o r e being placed on the pad. L e a c h i n g i s c o n du d u c te t e d o n t h e p r i m a r y he h e a p s b y a p p l y i n g c y a ni ni d de e solution c o n t a i n i n g 0.2 I b s NaCN p e r t o n 0 . 1 k g /m / m t ) o f s o l u t i o n a t a r a t e o f 0. 0.0 0 3 gpm per sq t 0 . 0 0 2 1 //ss //m m 3 ) o f he h e ap a p s u r f a c e a r e a . P r i m a r y h ea ea ps ps a r e c o n s t r u c t e d o n a s p h a l t p ad ad s t o a h e i g h t o f 1 2 t 3 .7 m) b y l i f t i n g w i t h a f r o on n tt-- e nd nd loader. t o t a l o f f i v e h e a p s a r e pr p r o ce c e ss s s ed e d a t o n c e . T h re r e e heaps a r e i n d i f f e r e n t s t a g e s o f l e a c h i n g w h i l e o ne n e i s b e i n g re re mo m o ve ve d fr fr o om m t h e p a d , a n d th th e other i s b ei ng b u il t. 2 1 - d a y l e a c h i n g a n d w as a s h iin n g c y c l e i s r e q u i r e d f o r each p r i m a r y h e a p t o a c h i e v e 75 7 5 p e r c e n t g o l d r e c o v er er y . L e a c he h e d r e s i d u e f rro o m t h e p r i m a r y h e a p s i s t r u c k e d t o t h e r e le l e a c h pad a re r e a . R e l e a c h h ea ea p s a r e b u i l t b y t r u c k d u m pi pi n g f r o m t h e h e a p s ur u r fa fa c e t o a h eig ht o f 1 t o 1 2 0 t 3 0 t o 37 m ). ) . S ev e v er er a all m on o n t h s o f r e l e a c h i n g i s r e q u i re re d t o i n c r e a s e t h e o v e r a l l g o l d r e c o v e r y f r o m t h e c ru r u sh s h e d o r e t o 85 8 5 p er e r cce e nt . L o w - g r a d e o r e f r o m t h e m i n e i s p rro o c es e s s ed e d by b y du dump l e a c h i n g a t a r u n - o f m in i n e f e ed e d s i z e . Dumps a r e b u i l t o n c l a y pa pa d s t o a h e i g h t o f 1 2 0 t b y t r u c k d um u m pi pi n ng g f r o m t h e h e a p s u r f a c e . L o ww - gr gr a ad d e o r e r e m a i n s on on t h e pa pa d u n t i l i t b e co m e s u n e c o n o m i c a l t o p r o c e s s a nd nd r e c y c l e s o l u t i o n s . Dump 1e 1e a c h c y c l e s u s u a l l y a r e f rro o m 9 to 14 months. E a ch c h t y p e o f h ea ea p p r i m a r y , r e l e a c h a n d du d u rrrr ~ p) p ) h a s i t s ow own pr pr e eg g na n a nt nt solution reservoirs. l l p r eg e g n a n t s o l u t i o n s u l t i m a t e l y a r e p r o c es e s s ed ed i n a s i n g l e z i n c p r e c i p i t a t i o n c i r c u i t . S O ~ U ~ ~ rOo m~ Sa n y o f t h e p r e g n a n t p o n d s c a n be b e t a k e n d i r e c t l y t o t h e z i n c c i r c u i t o r ca c a n be be d i v e r t e d t o o t h e r h he eaps t o rveiat sy e t op rae gsnuarngte st ao nl uk t i fo t i go hn st.h e P zre r ei ngn g cn a cn ti r csuo il tu. t i oSnosl u tdi or an isn a rby bey gi nr ca re foonr pg rool cd e scsoi nn cge nt ht rr oa u c l a r i f i e d a n d d e a rre e a t ed e d b e f o r e a d d i n g t h e M e r r i l l i t e z i n c d u s t . Th e z i n c c i r c u i t c a n p r o c e s s 6 0 0 gpm 3 7 - 8 1 1 s ) o f p rre e g na n a n t s o l u t i o n . P r e c i p i t a t e s a rre e e ss s s e s a n d a r e r e f i n e d o n s i t e t o p ro r o du d u ce c e d or or e b u l l i o n . r e c o v e r e d i n f i l t e r p rre

 

ORE PREPARATION

CRUSHING AN D AGGLOMERATI AGGLOMERATION ON

7

A to t a l o f 2 2,,0 00 gpm ( 12 1 2 6 1 1 s ) o f p rre egn na ant solu tio n drain s from the v a r i o u s h e a p s . T h e z i n c p r e c i p i t a t i o n c i r c u i t c a n p rro oce ess s o n l y 6 60 00 g gp pm ( 3 37 7.8 l/s). Consequently, i t i s d i f f i c u l t t o o b t a in a g go ood s o l u t i o n b ba a la la n ncc e f o r t h e o p e r a t i o n . E v e n tth hou ug gh solu tio ns ca an n b be e d i v e r t e d f rro om an nyy h he eap a t a s p e c i f i c s o l u t i o n g r a d e , i t i s s t i l l d i f f i c u l t t o o b t a i n a s o l u ti o n balance fr o m a n y g i v e n h ea ea p b e ecc au a u se se a a1 1 1 s o l u t i o n s a r e p ro r o ce c e ss s s ed ed t h r o u g h a s i n g l e z i n c c i r c u i t . T he o p e r a t i o n d o oe es no t h ha av e t o h u t do w n d u r i n g t h e w i n t e r m o n ntt hs hs b ec e c au a u sse e barren so lu ti on s are hea att e d t o 3 0 F S o l u t i o n s a r e h e ea a te te d w i t h a h e a t exchanger circuit. Some p r o ob ble em ms a re in he re nt t o t h i s opera tio n. O r g a n i c com p po ounds c o n ta t a i n e d i n t h e o r e cca au uss e d p rro o b l e m s i n t h e zz-- i n c p r e c i p i t a t i o n c i r c u i t . M o oss t s e v er e r e p r e c i p i t a t i o n p ro r o b lle ems w we e r e e n cco oun ntt e rre e d e a r l y i n t h e p r o j e c t . Go1 d p r e c i p i t a t i o n p ro r o bl b l em em s w e err e m iin n i m i zze ed b byy p r e c i p i t a t i n g t h e d i s s o l v e d o r g a n i c s w i t h b a rrii um um c h l o r i d e . S c a l i n g h ha as b be e e n a m a j o r p rro ob bll e em m the dura tion o f th e pro jec t. Sca ling h ha as b be een c o n t r o l l e d b byy t h e u sse e of d de e s c a lla ant che em m i cca a ls ls . I n s e ve v e rre e ca ass es es , 1 n e s h a avv e t o be p h y s i c a l l y u un np pll ug ug g ge ed usin g a hydroj et. So lu ti on b a l a n c e r em em a i n nss t h e m a j o r p ro r o bl b l em em . T h i s p r o b bll e m c a n o n l y b e s o l v e d b y i n c re a s i ng t h e c a p a c i t y o f t h e z i n c c i r c u i t o r by b u i ld i n g s e ep pa arr a t e s o l u t i o n eer ny vseys y sr yte te m ms eelne awci ht h a tnhde d du he ea ap ier dc .u i t s . hr ea sc o bv e ee s us c cf eo sr s ftuhl e ervve purmopb lle eh m s p e nl ecaocuhn t ecrre 5 7

G G L O ME M E R T IO IO N O F F I N E L Y G GR ROUND T

The o p e r a t i o n

IL IN GS

T h e W e sstt er er n U n i t e d S t a t e s has m ma any t a i l i r l g s m a t e r i a l s f rro om former mi nin g o p e r a t i o n s t h a t c o n t a i n s i g n i f i c a n t p r e c i o u s m e ta t a l v a llu ue ess . M o s t o f tth hese t a i l i n g s r e so u rc e s a r e t o o l o ow w --g grad e o r t o o sm al l t o w a rr an t t h e c a p i t a l e x p e n d i t u r e t o c o n s t r u c t a c o n v e n t iio o na l a g i t a t e d c ya n nii de de l e a c h i n g c i r c u i t ( M c C le l e l lla and, et a a1 1 . , 1 9 85 8 5 ). ) . I n m os os t ca s e ess , the only via ble processing technology f o r thes e feeds i s qg gll o m me e ra ra titi o n n-- he he a ap p 1e a c h i n g . A g g lo lo m e r a att i n g p pa a ra ra m me e te t e rs r s w h iicc h a r e i m p o r t a n t f o r s u c c e s s f ~ ~ rl e a tm tm en t o f c ru r u ssh he ed d ores are eq ua ll y important f o r t a i l ngs agg gll om o m e rra a ti t i on o n w i t h so m e m o d i f i c a t i o n . The b i n d e r n o r m a all l y r e q u i r e d f o r t a i 1 n g s a g g gll om o m e rra a ti t i on on i s a combination o f li m e a an nd c e m e en nt, u s u a l l y 1 10 0 - 1 5 I b s o f e ach p e r t o n o f d r y fe e ed d. M o i s t u r e a d d i t i o n s a r e u s u a l l y h ig h e err , a t f r o m 1 16 6 t o 22 w e i g h t p e r c e n t f i n a l m o i s t u r e . C u r i n g t i m e s i n t h e r an an g ge e of 7 72 2 ho ou u rrss o r l o n g e r a r e r e eq q u i rre ed. Two m e c h a n nii c a l p a r a m e t e r s a r e a a1 1 s o i m p o r t a n t f o r a g g llo o m e rra a t iirr l g t a i l i n g s : M o i s t u r e s h o u l d b e a d d e d a s a n o n - a t o m iizz i n g s p r a y o r a ass d r o p l e t s ; and A r o l l i n g , ra th er than a bo ou un ncc iin ng o r tu um m b l iin ng, ac tio n shou ull d b e imparted t o t h e t a i l i n g s b y t h e a g gg g llo om me e rra a tto o rr.. S o l u t i o n s h o u l d be a d dd ded a ass d r o p l e t s o r c o a r s e s p r a y b be e cca a us us e t h e w a t e r d r op o p i m p a c t i n g t h e d r y f e e d i m m e d i a tte e l y ffo orm s a s m ma a lll l b a l l w h hii cch h a c t s as t h e nucleus for agglomerate growth. f f i n e s p rra ays ar e u uss e ed d , n o n u c lle eus i s fo orr m me ed d.. A g g lo l o m e rra a t o rrss s uc uc h a s drunis, d i s k s , a n d p pu ug m i l l s i m p a r t a r o l l i n g r a t h e r t ha n a b o ou un ncc iin ng (b el ts ) ac tion t o the ta il in gs be eii n ng g ag gg g llo om me e rra a te te d d.. These types of ag gg g l o m e ra r a to t o rs rs are required for ef fe ct iv e t a i l ngs agglomeration.

 

PRE CIO US MET MET L HE

 

P LE CHING CHING PROJE CTS

S e v e r a l c o m m e r c iiaa l - s c a llee t a i l i n g s a g g l o m e r a t io i o nn-- h e a p l e a c h o p e rraa t i o n s h av a v e b e e n s u c c e s s f u l . T h rree e s u c c e s s ffuu l o p e r a t i o n s a r e b r i e f l y d e s c r i b e d bbee lo lo w w.. T h e o p e r a t i o n s , h ow o w eevv er e r , a r e n o t i n c u r r e n t p r o d u c ttii o n . T h e g o 1 d t a i l n g s e a cchh eedd . T h e s i l v e r t a i l i n g s p r o j e c t s w er e c o m mpp l e t e d a n d a l l t h e t a i l i n g s w e r e l ea p r o j e c t w a s s h u t ddoo w n bbee c aauu ssee o f t h e l o w s i l v e r p r i c e ( l e s s t h a n 7 .0 0 p e r o u nc n c e )).. N o n e o f t h e t a i l i n g s f e eedd m a t e r i a l s c o u l d b e e c o n o m i c a l l y p r oocc es e s se se d b y means o t h e r t h a n a g g l o m e r a t i o n - h e a p 1 e a c h i n g . 5.8

EXAMPLES OF T A I L I N G S A G G L O M E R A T I O N

Go1 d A g g l o m e r a t i o n - H e a p L e a c h i n g i n S o u t h - C e n t r a l

Ne vada

t a i l n g s m a t e r i a l f r oom m t h e s o u t h - c e n t rraa l N e v a d a G o l d f i e l d D i s t r i c t was p r o c e s s e d b y a g g l o m e r a t i o n p r e t r e a t m e n t aann d hhee a p 1 e a ch cya n id a t io n . ' T h e t a i l i n g s r e s u l t e d f r oom m a c y an id e m i l l i n g o pe ra ti on t h a t w waas a c t i v e j u s t a f t e r t h e t u r n o f t h e c e n t u r y . T h e o r i g i n a l o r e was h i g h i n s u l f i d e s aann d g ooll d r e c o v e r i e s w e rree l oow w . T h e t a i l i n g s o x i d i z e d f o r a p p r o x i m a t e l y 7700 y ea e a rs r s bbyy n a t u r a l w e a t h e r i n g a nd n d r e s i d u a l s u l f i d e s o x i d i z e d t o s o l u b l e s u l f a t e . T he n a t u r a l pH o f a 5 0 p e r c e n t s o l d s s l u r r y w waas 11.. 7 b e c a u s e o f t h e s o lluu b llee s u l f a t e s . T hhee t a i l i n g s w e r e 6655 p e r c e n t m mii n u s 2200 0 m e s h ( 00.. 07 07 4 rnm) a n d c oonn ta t a 'i' i ne ne d 0 .0 . 0 8 o u nncc e Au p e r t o n ( 22.. 7 g / m tt)) o f t a i l i n g s . T he m a xi m u m g o l d r e c o v e r y b y a g i t a t e d c y a n i d a t i o n w a s 83 p e r c e n t . T h e t a i l i n g s w eerr e m o v e d t o t h e a g g lloo m eerr a ttii n g p l a n t b y a f r o n t - e n d l o ad ad e r a n d d u m p e d i n t o a h o p p er e r . T h e t a i l i n g s w eerr e c on on ve ve ye ye d t o a 88..5 t (2. 6 m) x 22 (6.7 m ) d r u m a g g l o m e r a t o r , w h i c h w waas a m o d i f i e d a s p h a l t k i l n . The dru m t r o t a t e d a t 1 00.. 5 r p m , h aadd a s l o p e t o t h e d i s c h a r g e e nndd o f 4 d eegg r e e s aann d was l i n e d w i t h l o o s e l y f i t t i n g c oonn vvee yyoo r b e l t m a t e r i a l . s p r a y b a r w as s i t u a t e d l e n g t h w i s e i n t h e d rruu m aann d d e l i v e r e d a f a n d r o p l e t s p r a y t h a t c o v eerr ed ed t h r e e f o u r t h s o f t h e l e n g t h o f t h e ddrr u m . A l iim m ee-- ce ce m mee nntt s l u r r y was a p p l i e d t hhrr o u g h t h e s p r a y s yyss t e m t o a d d b i n d e r a n d b r i n g t h e f i n a l m o i s t u r e c o n t e n t o f t h e a g g l o m e r a t e s t o b eett we w e eenn 1 2 a nndd 14 1 4 w e i g h t p e r c e n t . T hhee t o t a l b i n d e r a d d i t i o n w a s 5 0 l b s ( 2 5 k g ) l i m e a nndd 1 0 I b s ( 5 k g ) ccee m e n t p e r t o n ( m tt)) o f d r y f eeee dd.. T h e lar ge lime a dd it io n w waa s r e q u i r e d t o a d j u s t t h e ppH H o f t h e t a i l i n g s f r om om 1.7 t o 10.5. A 1 2 i n c h ( 3 0 ccm m ) w e i r o n t h e i n s i d e o f t h e ddrr u m w waas f o u r t from the d i s c h a r g e e nd n d t o i n c r e a s e f e e d r e t e n t i o n t i m e a n d t o p r e v e n t d iiss c h aarr g e s u r g i n g . T h e a g g l o m e r a t e s d i s c h aarr g e d f r oom m t h e drum t o a t r a n s f e r p o i n t f e e d i n g a r a d i a l a r m s t a c k e r . T h e g r eeee n aagg g lloo m eerr a ttee s w eerr e g e n t l y p l a c e d o n t h e hhee a p b y t h e s t a c k e r a nd c u r e d d u r i n g heap b u i l d i n g . T h e l e a c h ppaa d w as c o n s t r u c t e d b y c om o m pa p a cctt in in g b a r r e n t a i l i n g s i n s i x i n c h l a y e r s a n d c o v e r i n g tthh e m w i t h a t h i n P PV VC l i n e r . T h e h eeaa p s w eerr e b u i l t b y a d j u s t i n g t h e r a d i a l - a r m s t a c k e r t o i t s l o w e s t a nngg le l e , s w e e p i n g a c rroo ssss t h e w i d t h o f t h e p a d , r a i s i n g t h e s t a c k e r d iiss c hhaa r g e e n d oonn e f o o t 3 0 cm), and s we w e eepp in i n g t h e o p p o s i t e d i r e c t i o n a c rroo s s t h e w i d t h o f t h e ppaa d . T h i s pprr oc o c e dduu re re c o n t i n u e d u n t i l t h e hhee aapp was 1 6 t ( 5 m) h i g h . T h e s t a c k e r r e m a i n e d a t 1 6 t ( 5 m ), ) , a n d nnee w a g g l o m e r a t e s w e r e a dddd eedd t o t h e h eeaa p bbyy s w eeee p i n g t h e s t a c k e r a c r o s s t h e w i d t h o f t h e p aadd aann d a l l o w i n g t h e a gggg lo lo m mee ra r a te t e s t o c a sscc ad a d e ddoow n t h e h e aapp . H eeaa p s b u i l t i n t h i s m maa nnnn eerr a v ooii d eedd c o rrnn ppaa ct c t in i n g t h e a g g l oom m e r a t eess . T h e a g g l o m e r a t i n g e q u i p m e n t aann d t h e s t a c k e r w eerr e m moo v e d aass a u n i t b y a d o zzee r b e f o r e a new r o w o f a g g l o m e r a t e s w waas a dddd e d t o t h e l e a c h i n g ppaa d , A w i d t h o f P V C l i n e r was r o l l e d o u t t h e w i d t h o f t h e ppaa d a n d w eell d eedd aass n e c eess s aarr yy,, t o c o n t i n u e h eeaa p b u i l d i n g . T hhee a g g l o m e r a t e s c u r e d f o r s e v e r a l d a y s w h i l e t h e 66,, 4 0 0 t o n h eeaa p w a s b u i l t . 'The hhee a w a s l e a c h eedd b y s p r a y i n g a c y aann i ddee s o l u t i o n c o n t a i n i n g 2 . 0 I b s NaCN per ton k gg// r nntt ) o f s o l u t i o n oonn i t a t a r a t e o f 00.. 0 0 3 g ppm m //ff t2 t 2 ( 0. 0 . 00 00 2

l

 

9

O R E PR PR EPA R A TI O N C R U SH I N G A N D A G G LO MER A TI O N

l /s /s / m3 ). The p r e eg gn na an ntt s o l u t i o n t h a t d r a i n e ed d from th e sloped le ac hi ng p pa ad c o l l e c t e d i n l i n e d d i t c h e s and f lo w ed b y g r a v i t y t o a p r e eg g n a n t s o l u t i o n pond. G o ld l d was r e c o v e r e d f r o m t h e p r e g n a n t s o l u t i o n b y c a r b o n a d s o r p t i o n - d e s o r p t i o n e l ectrowinning g.. Go1 d

re co ve ry

by

agg lom era tio n- he ea ap

c oans su shui nmgp ttici oy nc l ewaw s as0.a7 b o1ubt 2N4aCdays. N per to n w wa 5.8.2

(0 0.. 3 5

1e a c h i n g w wa as k g //m mt)

of

78

per ce nt.

ta i l i n g s .

Th he e

Cyanide l ea ch in g-

S i lv e r Ag gg g lo lo m me e ra r a ttii o on n --H He ea ap Le ea ach hii n ng g i n S o u tth h e a sstt e rrn n California

A t a i l i n g s p i l e fro m a f orm e err f l o t a t i o n o p e r a t i o n i n s o u t h e a s t e r n Ca l o r n i a w as p rro o cce e ssss ed e d b y a g gl gl o m e r a att i o on n-h he eap le ac hi ng t o re co ve r t h e c o n ta ta i n e ed d s i l v e r v a l ue s ( M i l 1 g a n a n nd d En ng gel h a r dt , 1 9 8 83 3 ) . The t a i l n g s w e r e 90 u n ce ce s A Ag g pe r to n (48 per cen t min nu u s 200 m me e s h a n d c o n t a i n e d a n a vve e r a g e o f 1.4 o un g /n / n iti t ) o f t a i l i n g s . The o p e r a t o r s o f t h e p r o p e r t y c o n d du u c tte ed bot h b be e n cch h- an nd d pi lo t- sc al e exp pe e ri ri me n ntt s t o e v a l u a t e a g gg g llo ome err at a t iio on n-- he he a ap p lea ch ing f o r rec ove rin g s i l v e r ffrr o m t h e t a i l i n g s . B e en n ch c h -s - s ca c a lle e r e s u l t s show ed t h a t 63 p e r c e n t o f t h e s il v e r w wa as r e c o vve ere ed d b byy a g i t a t e d c y a n i d a t i o n a n d 7 2 p e r c e n t o f t h e s i l v e r w a s r e c o v e r e d b y a g g l o m e r a ti ti o n - h e a p l e a c h i n g . The l o n g e r 1 1e e a ch in g c y c l e f o r heap leaching allowed the higher recovery. T h e p l a n t was d e s i g gn ned t o agglomera att e a an n d h e a p l e a c h 1 ,,0 00 00 0 to n s p er day o f d r y t a i l i n g s . The t a i l i n g s w we e r e m iin n e d a n d ccrr us us he d t o b r e a k u p t h e l a r g e c hu h u nk n k s o f cce em e en nted m a t e r i a l . The c r u s h e r d i s c h a r g e w wa as c o n nvv e yye ed t o two m ixe rs w he h e re re 3 35 5 I b s o f p o r t l a n d c em em e en nt per to n (1 17 7.5 k g l m t ) o f d r y f e e d w e r e a ad dd de ed as a b i n d e r . T h e b i n d e r an an d f e e d m i x t u r e w we e rre e co on nve eyy ed e d t o a 1 0 t ( 3 m ) x 30 t ( 9 m) d drr um um a g g l o m e r a t o r . A s cr cr a p e err , w h i c h r o t a t e d i n t h e o p p o s i t e d i r e c t i o n t o t h e d r u m , w as s i t u a t e d a l o n g t h e l e n g t h o f t h e d r u m t o p r e v e n t a g g l o m e r a tte e buildup. Wa att e r w wa as a p p l i e d a ass a c o a rrss e s p r a y t h r o u g h a s p r a y b a r s i t u a t e d l e n g t h w i s e i n t h e d rru um . The w a t e r w wa as a d dd d e d a t t h e b o t t o m o f t h e d ru ru m a n nd d m ix ix e ed d w i t h t h e t a i l . i n g s t o b r i n g t h e f i n a l m o i s t u r e c o n t e n t t o 1 2 t o 15 w e i g h t p e r ce c e n tt.. T h e a g g gll om o m e rra a te t e s d i s c h a r g e d ffrr o om m the d drr u m t o a t r a n s f e r p o i n t f e e d i n g a r a d i a l - a r m s t a c k e r . The g grr e ee en ag gg g llo ome err at at e ess w e err e p l a c e d o on n a stockpile by the s t a c k e r an a n d ccu ured fou r d da ay s b e f o r e b e i n g t r a n s p o r t e d t o t h e l e a c h i n g p a ad d. The 1e 1e a ch ch in g p pa a d was c o n s t r u c t e d f ro ro m m o i s t e n e ed d clay ey s i l t m at er ia l c o m pa pa c t e d i n t h r e e l a y e r s . T h e m i d d l e l a y e r w wa as m iixx e d w i t h b e n t o n i t e t o e n s u r e i m p e r m e a b i l i t y o f t h e l e a c h i n g p a d ((vv a n Z y l 19 98 8 4 )).. T h e h e ea aps w e r e b u i l t t o a height o f 13 t ( 4 m) b y a f r o n t - e n d l o a d e r t o a v o i d d r i v i n g o n t h e agglomerates. The h e ea aps w e err e ssp p rra aye ed d w i t h a so lu ti on co nt ai ni ng 2 2..0 l b s N Na aCN p e r t o n ( 1 k g /m t) o f s o l u t i o n a nd a t a r a t e o f 0.01 g p m f t 2 (0.007 l / s / m 2 ) ( M i l l i g a n , 1 9 8 3 ) . The p r e eg gn na an ntt s o l u t i o n c o l l e c t e d i n l i n e d d i t c h e s a n d d r a i n e d b y g r a v i t y t o a pre eg gnan ntt s o l u t i o n p o n d . T h e p r e eg gn na ant so lu ti on c ontai ned an average o f 1 1.. 0 o u n c e Ag p e r t o n ( 3 4 4.. 2 g //m mt) o f so lu ti on a an n d w as p pu um ped t o t h e p r e c i p i t a t i o n c i r c u i t a t a ra te o f 1 15 5 0 g p ~ n (9.5 l / s ) . The s o l u t i o n w wa as c l a r i f i e d , d e a ae era att e d , a n d co co n ntt a acc t e d w i t h z i n c d u s t t o r e ecc o v e r t h e s i l v e r . S il v e r recovery w wa as 7 2 percent af t e r a 2 25 5 day leac hin g a an nd 40 d da a y w a ssh h iin ng cy cle . 5.8 .3

G o lld d Agg gll om o m e rra a ttii on o n --H Hea ap p Leaching i n East Ce ntr al C a l i f o r n i a

A s ma ll t a i l n g s p i l e i s b e i n g p prr o c e ess se se d b y a g g l o m e r a t i o n - h he eap leac hing methods f o r r e c o v e r y o f g o l d and s i l v e r v a all u e s . T h e o p e r a t i o n i s l o c a t e d i n

 

PRECIOUS PRECI OUS MET MET L HE

9

P LE CHING CHING PROJECTS PROJ ECTS

e a s t c e n t r a l C a l i f o r n i a n e a r t h e h i s t o r i c M o th th e r L od e D i s t r i c t . A p p r o x i m a t e l y 1 3 0 , 0 0 0 t o n s o f o l d m i l l e d t a i l i n g s c o n t a i n i n g 0 . 0 7 0 o u n c e s o f g o l d 2.4 g / m t ) a n d 0 . 7 5 o u n c e s o f s i l v e r 2 5. 5 . 7 g / m t ) p e r t o n was a v a i l a b l e f o r p r o c e s s i n g . T h e t a i l i n g s a r e 90 9 0 p e r c e n t m i nu n u s 20 2 0 0 mesh a n d c o n t a i n e x c e s s i v e q u a n t i t i e s o f clayey mine rals. T h e t a i l i n g s a r e m in in e d b y f r o n t - e n d l o a d e r s and a r e t r a n s p o rt e d b y t h e l o a d e r a v e r y s h o r t d i s t a n ce t o a s t o c k p i l e . T a i l i n g s from t h e s t o c k p i l e a r e p us u s h e d by b y a t r a c k e d d o z e r i n t o a h o pp p p er er . The f e e d i s c on o n ve v e ye y e d fr fr om o m t h e h o p pe p e r t o a s i n g l e o ne n e i n c h s c r e e n d ec e c kk.. T h e p l u s on on e i n c h 2 5 mm) c lu l u m p s o f c l a y a r e p u s h e d t o t h e s i d e and a r e a l l o w e d t o a i r d r y f o r s e v e r a l d a y s . T h e a i r d r i e d c l u mp m p s a r e b ro ro ke n u p b y d r i v i n g o v e r t h he em w i t h t h e t r a c k e d d oz o z e r , a n d a r e t h e n p l a c e d b ac a c k i n t o t h e h o pp pp er . M in i n u s o ne n e i n c h m a t e r i a l i s c on on v e y e d t o a 6 t x 22 t 1.8 m x 6.7 m) r u b b e r 1 n e d d ru ru m a g g l o m e r a t i o n . P o r t 1 and cement 2 0 1b/to n, 1 0 k g / m t, t, o f f e e d ) i s ad a d d e d f r o m a c e m en e n t s i l o t o t h e c on o n ve v e yo y o r. r . T h e b i n d e r i s m ix i x ed ed w i t h t h e t a i l i n g s i n t h e f i r s t 1 / 3 o f t h e d r u m . W a t e r i s ad a d d e d i n t h e m i d d l e 1 /3 / 3 of of t h e dr d r u m t o a c h i e v e a f i n a l m o i s t u r e c o n t e n t f o r t h e a gg g g lo l o m e ra r a te t e s o f 1 5 t o 18 w e i g h t p e r c e n t . M e c h a n iicc a l f r e e t u m b l i n g i n t h e l a s t 1 / 3 o f t h e dr d r u n i p r od o d uc u c es es s t r o n g and s t a b 1 e a g g l o m e r a t e s . s i n g l e h e a p o f 75 75 , 0 0 0 t o n s o f a gg g g lo l o me m e ra r a te t e d t a i l i n g s wa w as b u i l t on on a d o u b l e l i n e d c l a y p a d u s i n g a s e r i e s o f c o n v e y o rrss a n d a r a d i a l a r m s t a c k e r . T h e h ea ea p was b u i l t t o a h e i g h t o f 2 4 t 7 .3 . 3 m ). ) . T h e a g g l om o m e r a t ed ed t a i l i n g s w er e r e c u r e d i n t h e h e a p f o r a b o u t o ne n e we week b e f o r e a p p l y i n g l e a c h i n g s o l u t i o n . L e a c h in i n g wa was c o n du d u c t ed e d b y a p p l y i n g c y a n id i d e s o l u t i o n c o n t a i n i n g 2.0 I b s 0.002 NaCN e r t o n 1 k g / m t) t ) o f s o l u t i o n a t a r a t e o f 0 . 0 0 3 gpm p e r s q t /s/m o f h ea e a p s u r f a c e a rre e a. l e a c h c y c l e o f a b o u t t h r e e m on o n t h s was r e q u i r e d t o o b t a i n t a r g e t e d p r e c i o u s m e t a l r e c o v e r y . P r e gn gn an t s o l u t i o n s d r a i n e d b y g r a v i t y f r o m t h e h e ap a p t o a p r e g n a n t s o l u t i o n p on o n d . P r e g n an a n t s o l u t i o n wa was p u m pe d f r o m t h e p o n d t o a s u r g e t a n k o u t s i d e t h e z i n c p r e c i p i t a t i o n c i r c u i t building. r e1 60 i f i e 1d 0 an a nl d/ s )d e aor ef a pt er e d g nb ae nf ot r es oal dudt ii no gn . z i nPcr e dc ui psitt.a tTehse we z ienr ce c i r c u i St o lpuro rtoi coensss ewde re 6 0c l agpr m w r e c o v e r e d i n f i l t e r p r e s s e s an a n d we w e r e p ro r o ce c e s se s e d o n s i t e t o p rro o du du c e d o r e b u l l i o n . T h e d o r e b u l l i o n p rro o d u ce c e d c o n s t i t u t e d a b o u t 65 6 5 p e r c e n t g o l d a nd n d 30 30 p e r c e n t silver. T h e o p e r a t i o n i s c u r r e n t l y b u i l d i n g a n o t h e r pa p a d t o p rro o ce ss t h e r e m a i n in g tai lin gs . F u t u r e p l a n s a r e t o p r o c e s s wa wa s t e m a t e r i a l f r o m t h e o l d m i n i n g o p e r a t i o n b y a g g lo l o m e r a t i o n h ea ea p l e a c h i n g u s i n g t h e p r e s e n t f a c i l i t y . 5 9

CONCLUSION

A g g l o m e r a t i o n p r e t r e a t m e n t o f c r us u s h e d o r e s an a n d wa w a st s t es e s , a n d f i n e l y g r ou ou nd t a i l i n g s h a s be bee n a p p l i e d b y t h e i n d u s t r y f o r t h e s u c c e s s f u l he ap l e a c h i n g o f fe ee e ds ds t h a t d i s p l a y p oo r p e r c o l a t i o n c h a r a c t e r i s t i c s . M any f e e d m a t e r i a l s p e r c o l a t e w e1 1 w i t h o u t a g g l o m e r a t io io n . T h e n ee ee d f o r a g g l o m e r a t i o n f o r a p a r t i c u l a r f e e d s h o u l d be b e d e t e r m in i n e d b e f o r e c o m m i t t i n g a c o m me m e r ccii a l o p e r a t i o n t o t h i s p r o ce s s in g t e ch no lo gy .

 

ORE PREPARATION CRUSHING AN D AGGLOMERA AGGLOMERATI TION ON

5.10

RE FE RE NCE S

Anon An onym ymou ouss (1 98 1) . Pel 1 e t i z i n g a i d s t o m b s t o n e 1e 1e a c h i n g o p e r a t i o n , a nd nd M i n i n g J o u r n a l , V o l . 1 8 82 2, N No o. 1 J a n u a r y .

Enginee ri ng

C h a m b e r l a i n , P .D . (1986), Agglomeration f o r the h he ea ap p lea ch ing o f go ld s i l v e r o r e s , A IM E A n n nu u a l M e e t i n g , New O r l e a n s , P r e p r i n t No. 8 6 --1 10 06 6.

an nd d

Davis, a nd n d H .H . W a d e, (1951). Agglomera tion o f i r o n or e by t h e EW p e l l e t i z i n g p r oc o c e s s , U n iivv . o f M iin n ne n e sso o tta a Institute o f T Te e cch hn no o llo og gyy , M iin ne ess E xp xp . S t a . I n f . Ci rc . N No o. 6 , J a n u ua ary. Dorr ,

JJ..V .N. an nd d F.L. B o s q u i , ( 1 9 5 0 ) . C y a n i d a t i o n a n d c o n c e n t r a t i o n o f g o l d and s i l v e r o r e s , McGra McGraw-Hi w-Hi11 11 Bo Book ok Company, Inc ., New York York..

E n g l i s h , A. a n nd d R.D. Fran nss , ( 1 9 7 7 ) . De evv el e l op op m me en ntt s i n p e l l e t i z i n g , Ch. A g g l om o m e r a ttii o n 7 77 7, Am me e ri r i cca a n I n s t i t u t e o f M i n iin ng, Me ett al a l 1u r g i c a l , P e t r o l e u m E n g i n e e r s , New Y o r kk,, V o l . 1. Hein en, H ..JJ ., ., G.E. Mc C le ll en d an nd d R.E. L fn d s t r o m , (19 79) . p e r c o l a t i o n r a t e s i n h e a p l e a c h i n g o f g o l d - s i l v e r o rre e s , U.S. M i n e s R I 8388. Jo oh han nss o n n,, JJ..R. (1978). Particle Chemical En gi ne er in g Jou rna l,

segregation n,, , . and w h a att Vol. 85 5,, No. 11

t o do

in and

En h a n c i n g Bu urr e a u o f about

it

,

M c C l e l l a n d , G,E, a nd nd J , A . Ei se le, (198 82 2), Im mp p rro o vve em me en ntt s i n h e a p l e a c h i n g t o rec ove r s i l v e r and go ld from lo ow w-g grr a d de e reso ou urce ess , U.S. B ur ur e ea au o f M Mff ne ne s R I 8612. McClelland, G,E,, D.L P o o l , an a n d J ,A , E is el e, (1983). Agg lome ratio n hea ap p l e a c h i n g o p e r a t l o n s f n t h e p r e c iio o u s m e t al s i n d u s t r y , U . S B ur ur e a u o f M f n e s I C 8945, McClelland, D.L. Po ol , A.W. Hun t, and J.A. J.A. Eisele, (1 98 5) . G E A g g l o m e r a t i o n and h ea e a p l e a c h i n g o f f i n e l y g rro ou un n d p re r e c iio o u ss-- m e ett a l - b e ea a rr1 1 ng t a i l i n g s t ' , U S Bureau o f M iin n e s I C 9034, 1985, Millfgan, O.A, May 1 9 83 83 ) , A g g gll o om m e rra ato orr d e s i g n f o r h e a p l e a c h i n g o f g o l d a n nd d s i 1 v e r o r e s , Pr e c So u s M e ta l s Sy Sym mp po o si si u m m,, R e n o . Milligan, D A a n d P,R, En gel ha rdt , (1983), Agglomerate ed d hea ap p le a c h in g a n a cco on nd da a'' s d a r w i n s l l v e r r e c o v e r y p r o j e c t , P re r e sse en ntt ed ed a t S oc, o f Mining E n g i n e e r s A I M E F a l l M e e t i n g and E x h i b i t , S a l t L La a k e City UT, Soc Soc , o f M i n i n g E n g i n e e r s AXME p r e p r i n t 8 3 - 4 3 0 , Shepard, 0.0, a n d C,F, S k i n ne n e r , ( 19 19 3 7 7)) . l l S t a b i l i z i n g a ag g g llo ome err a tte ed slimes f o r cyanide leach hii n g , Am me e rl rl c a n I n s t i t u t e o f M i n i n g and M e t a l l u r g i c a l En g i n e e r s , N e w York Tech, Pub, No, 790, March. v a n Z y l , D. J.A. (1984 4)) . C o n s t r u c t t o n a an nd i n v e s t i g a t i o n o f a c l a y heap l e a c h pad , i n A Au u Ag h e a p a n d dump l e a c h i n g p r a c t i v e ( C h a p t e r 7 , ed. J.B. H i s k e y . S HE -A IME F a l l M e e t iin n g , S a l t l a k e C i t y U ta h , Oc to b e r 1 9 - 2 1 , pp. 59-68.