8/10/2019 Crisocola Amonio

1/1

Leach ing of C hrysoco l la wi th

Ammonia Ammonium Carbonate S o lu t ions

M . M E N A a n d E A . O L S O N

C h r y s o c o l l a w a s l e a c h e d i n s o lu t io n s o f a m m o n i u m h y d r o x i d e a n d a m m o n i u m c a r b o n a t e a s a f u n c ti o n

of t he va r i ab l e s: t emper a t u r e ( 25 t o 55 ~ amm oni a - am mon i um r a ti o ( 0 .0 : 1 .0 t o 1 .0 : 0 .0 ) , t o t a l

amm oni a co ncen t r a t i on ( 0 .25 t o 6 .0 M ) , and pa r t i c le s i ze ( 100 t o 400 mesh) . A m ode l o f t he l each i ng

b e h a v i o r w a s d e d u c e d b a s e d o n : ( 1 ) th e a c t i v at io n e n e r g y o f 6 0 .7 5 k J / m o l e ( 1 4 .5 1 k c a l / m o l e ) f o r

3 M t o t a l NH3 whi ch was depend en t on bo t h t o ta l amm oni a concen t r a t ion and t emp er a t u r e ; ( 2 )

f i r s t -o r de r depend ence o f r a te on [ (NH~ ): CO3]; ( 3 ) dependen ce o f i n i t ia l r eac t i on r a te on r ec i p r oca l o f

pa r t i c le d i ame t e r ; and ( 4 ) mo r pho l og i ca l ev i dence f r om S E M and E D AX measu r ement s o f d i f f us i on

and l each i ng occur r i ng p r i mar i l y i n su r f ace mi c r oc r acks and no t i n t he submi c r oscop i c por es . I n

add i t i on t o t he i mpor t ance o f d i f f us ion t h r ough m i c r oc r acks i n r a te con t r o l chemi ca l r eac t i on a t ac t i ve

sur f ace s i te s t o p r odu ce t he spec i e s , CuNH~ ~ , is a l so i mpor t an t . Onl y a f r ac t ion o f t he Cu a t oms r eac t

t ha t ar e exposed t o li x i v ian t . H i ghe r amm oni a - am mo ni um i on concen t r a t i ons , h i ghe r tempe r a t u r es , o r

mu ch l onge r t imes a r e r equ i r ed f o r mor e r e f r ac t o r y Cu a t oms t o d i s so l ve .

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

C H R Y S O C O L L A , a h y d ro u s c o pp e r si li ca te , C u O .

S iO2 2H : O, f ound i n the uppe r ox i da t i on zones o f copp er

depos i t s , i s commonl y a s soc i a t ed w i t h ma l ach i t e , azur i t e ,

and l i mon i t e . ~ S ampl es va r y w i de l y i n com pos i t i on , bu t

us i ng the abov e f o r mul a chr ys oco l l a has a copp er con t en t o f

36 .18 pc t a s compar e d t o 34 .62 pc t f o r cha l copyr i t e , L a r ge

or e depos i ts o f ch r yso co l l a a r e f ound t h r oughou t t he wor l d ,

some of whi ch a r e p r esen t l y be i ng mi ned . : Unf or t una t e l y ,

chr ysoco l l a is no t ea s i l y concen t r a t ed f o r f r o t h f l o t a t ion l i ke

cha l copyr i t e . T he d i r ec t sme l t i ng o f h i gh g r ade ox i de o r es

has bee n r epo r t ed , 3 bu t such an a l t e r na t i ve wo ul d no t be

app l i cab l e to a ma j o r i t y o f ox i de o r e depos i t s whi ch a r e l ow

gr ade , Hy dr om et a l l u r gy , howeve r , opens t he poss i b il i ti e s o f

exp l o i t i ng such depos i t s .

Chr ysoco l l a has been l eached wi t h va r i ous agen t s l i ke

E DT A 5 and NT A , 6 cyan i de so l u t i ons , 7 '* and amm oni aca l

solut ions .8,9,10 Al tho ugh the s ul fur ic acid lea ching of chry s-

oco l l a has been gen e r a l l y accep t ed a s p r ac t i ca l, t he p r epon-

de r ance o f ca r bona t es i n ce r t a i n o r e depos i t s can cause

t r emendou s i nc r eases i n ac id consum pt i on , t hus c r ea ti ng t he

need f o r a mor e s e l ec t i ve r eagen t f o r such depos i t s. Am mo -

n i a i s an a t t r ac t i ve r eagen t because i t does no t r eac t w i t h

ca r bona t es , and beca use o f it s ease o f hand l i ng , l ow i nven-

t o r y cos t , and amenab i l i t y t o r egene r a t i on . T he NH3- COe-

H,O sys t em was t he r e f o r e chosen i n t he i nves t i ga t i on o f

t he k i ne t i c s o f copper d i s so l u t i on f r om chr ysoco l l a . T he

va r i ab l e s s t ud i ed wer e ammoni a - ammoni um r a t i o , t o t a l am-

m o n i a c o n c e n t r a t i o n , t e m p e r a t u r e , a n d i n i t i a l p a r t i c l e

s i ze . T he r o l e s o f t hese va r i ab l e s i n t e r ms o f l each i ng

r a t e a r e i n t e r p r e t ed us i ng t he r e s i due ana l yses : S E M and

E DAX. S ur f ace a r ea and i n f r a r ed measur ement s a s we l l a s

X- r ay s t ud i e s wer e a l so conduc t ed .

M. MENA, former ly Graduate Student , Depar tment o f Meta l lu rgy and

Metal lu rg ica l Engineer ing , Um versl ty o f Utah , i s now Assistan t Professor

of Extrac t ive Meta l lu rgy, Depar tm ent o f Min ing and Metal lu rgmal Engi-

neer ing , UmversW of the Ph i l ipp ines, Dlhm an, Quezo n Ci ty 3004 , Ph i l ip -

p ine Is lands. F A OLSO N is a Professor o f Meta llu rgy , Depar tm ent o f

Metallurgy and Metallurgical Eng ineerin g, Univers ity of Uta h, Salt Lake

C W, UT 84112.

Manuscr ip t submit ted March 28 , 1984

METALLURGICAL TRANSA CTIONS B

I I . E X P E R I M E N T L

A. Materials

T he chr yso co l l a s ampl es wer e f r om an upgr ad ed o r e f r om

Gl obe , Ar i zona . T he mi ne r a l was g r ound us i ng a F i she r

M or t a r Gr i nde r i n t o f i ve s i ze f r ac t i ons be t ween 100 mesh

and 400 mesh . E ach s i ze f r ac t i on was ana l yzed f o r cop-

pe r us i ng an a t omi c absor p t i on spec t r opho t omet e r , and t he

copper con t en t o f t he s ampl es va r i ed f r om 33 .01 pc t t o

36 .16 pc t , w i t h a s l igh t t endenc y f o r t he chr y soco l l a t o

concen t r a t e i n t he f ine r s ize f r ac t ions . T he co mpo s i t i on and

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

gr av i me t r i c and a tomi c absor p t i on t echn i ques . T h e chemi ca l

f o r m u l a C u O

S i 0 2 " 8 9

was ob t a i ned and based on t h i s

f o r mul a , t he s am pl es con t a i ned 91 pc t ch r ysoc o l l a , w i t h

t he rema i n i ng 9 pc t be i ng f r ee s i li ca . Bo t h X- r ay and i n f r a -

r ed spec t r opho t omet r i c s t ud i e s conf i r med t he p r esence o f

these minerals .

T he l each i ng so l u t ions wer e p r epa r ed f r o m r eagen t - g r ade

a m m o n i u m h y d r o x i d e a n d a m m o n i u m c a r b o n a t e , d is s o l v ed

in dis t i l l ed deionized water , according to the des i red tota l

a m m o n i a c o n c e n t r a ti o n an d a m m o n i a - a m m o n i u m r a t i o. T h e

t o t a l amm oni a concen t r a t i on ( NH3 + NH 2) o f the l each i ng

so l u t i on was va r i ed f r om 0 .25 t o 6 .00 M . T he ammoni a -

a m m o n i u m r a t i o w a s c h a n g e d f r o m 1 : 0 ( p u r e a m m o n i u m

hydr o x i de ca r bona t e in so l u t ion) t o 0 :1 ( pu r e amm oni um

car bona t e i n so l u t i on) . T he ammoni a - ammoni um r a t i o was

de f i ned a s above on t he bas i s o f mol e r a t i o o f ammoni um

hydr ox i de t o ammoni um ca r bona t e i n i t i a l l y added i n t o t he

l each i ng so l u t i on . A 0 .5 : 0 .5 ammoni a - ammoni um r a t i o i s a

ra t io of uni ty,

i.e.

equ i m ol a r r a t i o .

B. Apparatus and Technique

T he l each i ng expe r i ment s wer e conduc t ed i n a r eac t o r

ves se l sys t em cons i s t i ng o f a one l i t e r , unba f f l ed r eac t i on

ke t t l e w i t h a g l a s s cove r hav i ng open i ngs f o r r e f l ux con-

dense r , t he r momet e r , c l osed- sys t em s t i r r e r , and a s ampl i ng

dev i ce w i t h a f r i tt ed g l as s end f o r t he w i t hdr awa l o f 2 .5 ml

a l i quo t s ampl es f o r so l u t i on ana l ys is . T he w hol e sys t em was

i mmer sed i n a wa t e r ba t h equ i pped w i t h a Haake E 2 s t ir r e r-

hea t e r capab l e o f ma i n t a i n i ng t he ba t h a t a s e l ec t ed t em-

pe r a t u r e t o w i t h i n + -0 .03 ~ E xper i m ent s wer e conduc t ed

VOLUME 16B, SEPTEMBER 1985--441

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