CA2023119A1 - Extraction of noble metals with thiourea - Google Patents

Abstract

EXTRACTION OF NOBLE METALS WITH THIOUREA
ABSTRACT OF THE DISCLOSURE
Noble metals (e.g., gold and/or silver) are recovered form ore with an extraction solution containing thiourea. An alkali metal or ammonium bisulfate is used to maintain an acidic pH without the addition of sulfuric acid. The thiourea extraction solution can be rejuvenated and recycled.

Description

2023~19 l~lR~CrlON OF NOI~LE MEr~LS ~ ~OU~

'Ihis is a co~tinua~on-in~art a~plica~don c~f co~e~ding a~ica8on Serial Nc.
3 949119 which was filed on A~gast 15, 1989. ~he dis~as~e ~ ~e application i~
5 hercby incorpQra~d byrefere~c~

0~
Ihe present i~ntio~ relates to the rec~y of g~ld and s~ver ~om an ore by ~trac~on with a~ on solution c~nprisi~g thiourea and an acid~i~g 10 age~t consisting essential}yof an alkali metal and/or ammoDr~bisuh'aee.

B~CKG1~9U~) O~
ide e~trac8on is an old a~d est~ib~ished prwess for ~enng g~ld and si~ ~om ores. Unf~rtunate~y, ~db is aD ~gb difflcult sol~ent to use -~de is hi~hly ~ic, elmiomnentally problema~c, and diEfia~lt to use wi~ ores cont~ copp~ and/or manganese. ~r and manganese contamina~e the cyanide and result iII re~ced yields of ~he desJred metals. A need e cis~ for a~effl~ent ~trac~on solve~lt that does not iIrvol~ cyamde.
'~niourea is an alte~native to cyanide. In thiourea processc~ the orc ~
contacted ~nth a solu~don including thiourea and a number ~ other additi~es under acidic conditions (e.g. at a ~H af about 15 to ~ 6) at an ele~ated temperature.
Sulfuric acid is the mo6t c~non ~cidif~g agent. See, U5. Patent Nos. 4,145,212;
4,342,591; 4,561,947; 4,571,265; and 4,731,113 in addition to Canadian Patent Nos.
1,235,908 and 1,236,3~
Ch' particular i est is Schulze U$. Patent NQ 4,561,947 Whi~h d~beS a tbiourea extraction pro~ss uwng sulfuric acid to maintain the pH. In a~tion to sulfilric acid, the e~action p~s is Qperated to hane a redm potendal of about W~O mV (with a Pt-Ag/AgCI electr~le) in the presenoe o~ both a2~idation and reduction agents. Ihe o:~idation agents are tr~alent iron salts. Sulfur di~ide or a bound prea~sor thereo, su~h as a h~oge~ sulp~itè salt"s purportedly added to pre~e~t the ogidadon of thiourea E~ample l descnbes ~he addition of a so~
bisulfite to reduoe thio~ea a~illiæd during the process. Ihe ~rac~ion efflciency I
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2023~19 descn~d by that e~ e 1 reported remo~al ~ 56.7% o~ the gold alld 165% o ~he sil~r.
~ thc onl~ osare of temperatore, the Schulze pa~ent presents ~ample 1 which uses ~ hot water wa~es of the leachir~ r~due a~ a tempera~e of ~
S C (194- ~) to liberate adsorbed ble metals. Af~ tw~ e e~tra~on eEficiell~y was 85.4% of the g~ld a~ 54.8% o ~he silves. Such .bigh temperatures are not ~red for comme~cial ope~ation due 0~ the large ~mes of feed be~
~eated a~d ~e cost of energy to heat u~ the p~oc~s s~eams. Lawer e~trac~on temperatures are required for ownmercial ~iabl~i~.
The prcoe~ in the S~hulæ patent also results in significant coDs~pffon o~
t~iourea nDtwi~hstan~ing ~e efforts ~o prescrve the thiourea ~m degrada~on. ;~
Because thiourea is e~pe~ lost t~iourea represents a ~xesnng cost w~
Iimits the econ~mic operation of ble metal recov~y. ~idation o~ the t~iourea : ~:
also prohlbi~ the reg~le af the ~raction sohation w~i~ fur~er re~uces the lS economic operation o~ the prooe~ ` .
It would be ~rable to have a thiourea ~raction pr~cess ~hat ~hibits 1 thiourea losses with hi8~ rea~very o~ the nolble metal ~ par~cularly the precious Gro~p ~ meeals of gdd and sil~. ~ .
It w~uld also be des~able to h~ne a ~iourea estraction process that ope~ates at a substan~dally ambient temperature.
` ~ .~'~' ';' SI~RY OF T~ ~lON ~;
It is ~n object of the invention to provide a process for re~ noble, particular~,r group IB, metals ~om ores at high gields ~ an ~id~ing agent ~a~
does not d~grade the ~iourea -It is ano~er object of the iInentio~ to provide a ~ion process that can operate at ambiellt temperature oonditions.
It is anothe~ object of the ~nention to ~ovide a process that can be used in a plant originally designed for cyanide e~traction without slibstantial additional capital ~pense formod~g the e~istingequipment.

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2~23119 In acc~a~oe with these and other objects that will bocome a~p~cnt from ~he d~p~on herein, the proce~ ordiDg to the iI~ve~on com~:
colltac~g an are co~taining nobk: metals with a e~don solution co~pnsmg thiourea and an acid~g agent c~sis~g esse~all~r o~ an alkali metal . ::
S and/or ammomum bisuh'a~c; and :
recov~ at least a po~tion of said noble metals from said e~tractio~
SOhl~i~IL . , , lhe e~traction prooe~ ~ the ~tiol~ us :s aII acid~fgiDg a~pnt that does not degrade the ~hiourea in ~he ~raction sohltioD~ AS a result~ the ertraclion so~ution ca~ be reg~ed thereby making ~e prooess mc~e eso~omical wi~h 1~ thiourea The prooe~s of the i~vention can also be retr~sfit into facili~des previous~r -desiglsed for ~de trea~en~ Ihis ca~ab~ity permit~ con~iion Qf haz~dous ~yanide plan~s without sulxtantial ca~ital e~peDses and without the installation o~
ne waste ~ nent faciliti~

l~.RIl~F DES(~IPI'ION OF TEE Dl~A~INGS :
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Fg~re 1 s~hematicany is a flow diagram o~ a thiourea trea~ent process acc~rding tothe i~nention.

DFrAILEI~ DESC~I~N
lhe present i~ention foa~ses on the relationship betwecn thiourea a~
acid}f~g agent coDsisting essentially of an alkali metal and/ar ammonium `:.
bisulfate. lhe alkali m~tals are, of course, lid~iwn, so~, pot_ rubidi~, `: `
2~ ces~ andf~anaum. For ~he present ~entioD, thebisu~ate æidifging ag~nt is prefe~ably pre&ent as a sodium, potassium, or ammonn~ salt with the complete : `
e~usion ~ sulfuric acid from the e~traction solution. Most prefe~ab~, the ~raction 501ution is also devoid o othe~ stroDg a~idants su~ as hy~rogen per~md~ ,," .,;.~ ,, . ~

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20~3119 Whik not wishing es~ be bound by theo~y, sulfuric acid a~a~s to be respons~b~e fQr tie~ up thiourea ~om the solu~on into cop~ comple2es and haste~ thc degrada~ of the rem~ ~biourea It is thoorizod that when su~ric alid contac~ the subject ore in the c f a thiourea sa~ution, ~e S copp~ f~om the ore is immediat~ en into solu~don in a co~pl~ of u~
coordinat~on ~th the thiourea lhese co~thiourea compl~es may be ~ mo6t of the us~ul ~hiourea ~erebs~ le~ little thiourea for rec~very of ~e 8~ld a~d si~ver.
I~l addition, sulf~ic aad a~pears to cause ~he bre~ of the remainin 10 thiourea whose degradaeion pToducls become iYrwa~ Ihe ~ fo~
o~ ~he thiourea degrada~on pro~ are unlmown at present, but the resul~ af e~imen~ indicate a reduction in the effec~e le~el of thiourea l~e reac~ons of degradation and asidation resolt in large thiourea cons~p~don fa¢ the process.
'Ihe thiourea degrada~oll also limi~; priar art ~trætion prooe~ to a batch 15 operation because the ondizetl e~action solutioll cannot be reused.
Ihe prese~t prooess contemplates the use o~ bisulfaSe anion added as a bisu~a~e salt within a range ~om about 2 to about 80 ~, preferably about 3.4 to about 67 lb. bisuh'ate anionlton ore. Ihe upper and lawer limits ~ these ranges may vaIy somewhat due to the ore and the particular apparatus used. l~y the 20 addition of the bisulfate salt, the pH of the present e~tracdon solution is desirably maintained at less than about 6 ~th a pH fmm ~ibout 1.5 to about 3 bei~g preferred .
The use of bisuh'ate according to the iIIvention elhninates the deleterious effects o sulfuric acid on t~iourea and the attendant thiourea losses. Bisu~ate25 does t pm~ce the copper ac~v.ityproblems or degrade the thiourea l~e sul~uric acid. A~oording~, the ~s realiæs the effec~ o~ thiourea u~hindered l~y delete~.ious ~ide reactio~s and result~ in a e~rac~ion solution that can be recy~led for reuse. Prooesses according to the imrention are ~haracteriæd by an overall thiourea con~umption cf less than about 30 lb/ton, usually less than about ~0 30 Iblton, and even can be operated under c~ditions whi~h e~er.ienoe losses of less . .
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thall abou~ 10 Ib/to~ of ore pro~ lhe rec~very~s is made comm~ally Ihe tempe~at~e o~ the ~esent ~o~ p~ccess is desirably within the ra~e froin about 50 to about 85 F. Su~ law a~tra~on temperanlres repre~ent substanti~l e~ergy _ compared to estraaio~ proce~s operated at higher temp~aturcs. ~is ~ is realized be~ l~ dties o~ solution and ore do DO~ have to be hea~ at all to mu~ ~Ixrve ambient temperature.
On~ ar mor~ t~valent metal salt!; ~ be used to eDhance the ~traction efflciency of ehe thiourea Prefe~red sal~ nc sulfate and fernc ~hlonde.
Ferric sulfate is deirably used for sulphide ores, but femc chlonde is preferab~used~nth ~nide ores.
Fernc saats enhanoe the efficien~ o~ the e~ra~:tion by increasng the osidatioDlreduction potential a the sa}otion. For e~ample, a thiourea s~lution without fe~ric sulfate m~y h~e a reduc~on potential of greater ~a~ ut 70 mY, e.& about 70 95 m~ ~ a Pt-Ag/Aga dec~ode. Addition ~ f~Tic sulfate increases that poten~al to a ~alue grea~er than 100, e.g. within the ran8e fhm about 115-200 mV. Ihe e~rac~on efflcien~r increases ~s the reduction potential increases but, ~1nth the process of the imentio~, the poten~al need not be as high as the 250 650 mV ran~e su~ested by US. 4,561,947 due to the different rea~ion mechani~s i~ ved. For measuring the reduction potentiaL the disclo6ure of 4,561,947 is herein inmrporated by referenoe.
Allother type of ad~ti~ co~temp~ated by the ilIvention is aII alkanolamine of 1~ ca~bon atoms. Methallolamme a~d etha~olamine are pref~red alkanolamines. l'ne alkanolamine is desirab~ added to the e~traction so}ution during or after ~he e2¢raction prooes~ in an amount sufflcie~lt to maintain the e~racted metals in solu~doD, e.~ abo~ 1û Iblton of ~re. Precipitation and reoombination of the e:stracted va}ues are thereby preYented whi~h ~mits effi~ent recove~ om solu~io~iaconventional methods E~p~ary metal recove~y metho~s include ca~on adsorption, ahlminum precipitatioD, and ion ~hange with an alJionic e2~ ge resim Zinc precipitation is ~ot 8 preerred means ~ recovering the e~tracted ~ah~s from ~he ~iourea .
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2023~1~
soluti~ Zillc degrad~ ~he thiourea t~ f ~ thiourea loss~ and inbl~i~g ~c op~a~on o~ the prooess aS a con~uous e~rac~o~ Ihe circumstanccs in which thesc co~vendonal r~v~y proc~ will msmmiise recave~y O~ e e~tracted precious metals is wi~thin the ens~g skill 1~1 wi~
S m~re tha~r~u~ne e~perimentatio~
Af~ reoov~y ~ the metal ~alues, the e~trac~don solu~on ma~ be re~ed to the e~traction zone f~¢ reuse. Such recy~e is ~ot pos~le wi~ proc~es tha~
we~ib~rdegrade the thiourea Ihe preseIIt i~vention ~ venientlJr d~cnbed ~nth refe~ence to the a~ed 10 ~aw~ Ill Fgure 1, an e~raction so~u~don com~ ~i~urea, an al~ali metal or ammonmm bisa~a~e are added to agi~ed lea~ tan~ 1 ~or contact wi~ nolble metal contai~ing ore. Ihe ~ ~ addi~o~ is pr~ferab~r regulated so that thiourea is added to a m~ture ~ wat~ and ~bout 2s% to about so~o solids. Ihe pH is adjus~ to pr~oe acidic condi~o~ h an acid~ing age~t consis~g 15 essentially af an allcali metal or ammoDium bisu~ate to the de~ed range. Uponaddition, e~rac~on will start to o~r via ~he falmation of one or more so}uble orcata~sic metal compl~ Ihe spec~fic structl;re and cllemical nat~e o~ these comple~es are not clearly understood at t~is time.
A ferric salt is desirab~ aWe~ to the ~traction solution to increase the 20 reduction po~eneial to the desired valuc, e.g. to greater than about 70 mV, and ao~lerate ehe e~rac~on prooess.
An al1canolamine such as ethanolamine can be added after a predetermined e~raclion period to keep the e~cted metals in solution. Appropriate amounts of allcano~amine are ~ determinable by no more than routine e~nentatio 25 by one ~vith an ¢~di~y skill le~el in this ar~ E~emplaly e~on periods are about l/2 - ;~bout 4 hou~ although long~ r or shorter penods of time maybe used.E~action solu~ion-11 LS then pæsed to a senss ~ thi<~keners 2~ with c~untercur~e~t flow ~ the o~erflow mate~iaL Solid waste 14 m~ be neutralized with lime ~ar disposaD. ~ract lO from the fi~ ehickener is then passed ~
30 recove~y mne 5 whare metal valu~ are rec~ered in line lS by co~e~tional meana : i ' .
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-20~3~19 C:l~ed ~ru~io~ solu~doll 16 i~ passe~ ery ZDae S a~d stored in soarage ~c 6 f~ re~c na line 17 to lea~ mk 1. AdditioD~l ehiourea s:an be added to make u~ any thi~urea 106t to the e:~raction aDd passing out of the : ~ .
S But fat tlle i~ ation of a reg~e line, th,e ~ and han~ing apparatus f~ ::
treating sJre acc~ffing to the i~don are comenffonal and ma~r alreaa~
loca~d in a facility onginally designed for the plevious ~de rec~s~y proce~ : ~ :~;
A~rdingb, ~here are few imp~ents to ~e c o~rsion ~ a cyanidizadon paant to th~ saf~r tbiourea pro¢ess acc~g to the mvendo~ .

~he foJlswing e~amp~es will sen~ to i~us~aate the present ~entio~ ~ ::
~m~eS 1-6, 100 g ~ Sonora Concentrate (bigh ~) is con~ed ~nth an ~ -~
e~action solution oo~tai~ng sod~um bisulfate. lhe amount of gold ~racted is calculated by comp~ing the amount of gs~ld in the o~e bo~ bef~e and af~
contact ~th the e~ac~on solution. With a~priatc methods for re~ the gold from the ~traction solu~oD, ab~ut 98 99% of the gold ~tracted from the ore by the thiourea can achlaLb ~e rec~ered. ~ ;:
Sono~a conoen~ate is most~r pyrite with small amounts o other metallic ~ides a~d some silicates. Gold and s~r are essential~y ~ee a~d are t :
combi~ed ~ ith the ~te. C~yanide reoovery prooe~ from this ore rec~er abo~t 95% of the gold and about 8~85% of the dlver. lhe present e~amples meas~e o~5r the amount o~ gDld e~tracted ~om the conoentrate.

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2 ~ ~ 3 1 1 9 Ta})l~
Ihiourea E~io~ o~ So~ora Co~cen~at~

2 2S10 2B. 60 48 10 96.7 3 2510 16 60 48 10 9i~

4 3310 1~ 32 10 96.7 : -33 5 3.6B 20 16 10 93.0 :: :
6 ~ 5 73~ 20 16 10 94.0 ~:

l~ampl~7~
E~n~des 7-12 compare the e~traction efficie~lcies and thiourea loses inco~red ~ -using acidiijing ag~llts af sodium bisulfate (iII accordanoe ~nth thc i~en~don), a :
2û solution of 98% su~ic acid, aDd a m~ed agent o~ 98% sulfu~ic acid, hy~}rogen p~de, and sodi~ bis~atc Tniourea 106s is catQ~lated ;~s the amount of ~`-thiourea resIlmed to return the e~action solueion eo its inieial concen~atioD.
Ihe e~raction solu~on u~ed a 5 wt9~o sahtion ~f thiourea wieh 10~ g ore at a solids conoe~ ion o~ 33 vvt~o. From e~nple S, ehis level corre~onds to 3.68 Ib. thiourea/ton o~ ore. Ihe stardng pH values were all wiehin 15 -1.8 aDd endedwithin 2.28 - 2.8. All temperatures v~ere wiehin 74 - 8~ F. Agitation times werewie~ 2 h~s. 'Ihe results are shown in Table æ B~ compa~g the thiourea 106ses, it is rcadily apparent that the present ~rooess e~bits substan~ally lessehiourea loss.
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20~3~9 Table 2 Acidic Ferri~R~ on n~io~rea S Adicic AgE~ SulfatePote~ % L~ '~
E~ ~nt A~ou~t (~ mY) . l~d (~ ore) 7 NaHSO~, 5 g 1~ 172 98 3.
8 NaHSO4 ~5 g lD 168 92.4 4.0 `
9 NaHSO4 S g 15 180 98 3-9 NaHSO4 ~ g 05 60 90 4.8 : :
11 H,~04 2 cc 11 160 89 34.6 ; : :
12 H,~ 2 cc H~02 2 cc 11 165 ~.6 3S2 -- .`
NaHSO, S g .'.' By comp~ ~amples 7-lO~nth ~amples 11 a~ , s~e of the advan~s ~ :.
of the i~ on are ~lustrated F~remost, faz less thiourea and fe~nc su~ate are re~ to pro~ce high recov~ries lhis s~ lraDslates into su}~dal 20 eco~omic advantag~

E~amples 1~1 In e~p~es 13-18, ea~ sohltion contained 10 wt96 thiourea ith 100 g ore 25 at a 33% solids conoentration. lhc pH o~ each s~ution w~s maintained at 1~
with sodium bisuh'ate. Ethanolamine in the amouDt o~0.15 ccw~s added las~ Ihe effect~ of f~c salts arc readi~r seen as enhanci~g thc e~tion process.

Tablc 3 ~ :
Effect of FerTic Salt So~ Fe~ic Reductio~ `

Bisuh'ate Su1fatc Potential Agita~ion All % : .
mV~rtme ~r~ F~racted 13 6 0.0 88 æo 79 14 6 5 125 l.g 88 lS 6 S 123 15 97 `
16 6 1.0 170 1.0 9S
17 6 lD 172 2.0 99.7 18 5 0.75 13Z 1.0 97.7 ' ':

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~he in~:reased dficiencies of femc sal~ ~e illus~ated by a companson o :
G~ample~ 13 an~ 14-18.

' S ~ ~amples lg26, samples contai~g 100 g. ~ ~Dld co~sentrate ~om a high :
su~de ore ~Pere treated ~or the same ~trac~ol~ time wit~ 300 ml a~ a 5 wt%
thiourea solutioD, 15 ~ fer~ic su~ d ~e amouIIt ~f bis~ate or bis~te (in : :-a~l cases tlhe Na~ fo~ the salt was used) ~dicated i~l ~e table.

Table 4 Comparison of Bisu~a~e wîth Bis~te Go~d I eft in Bisulf~e aQ Fltercake Gold E~racted ~5 19 O. (Co~l)1.100 -- ' 1S bi~te 1.041 ~A
21 3D ~ 1.0~4 6.9 Z 6.0 ~ 8 5.6 ~3 læo ~ l.OQ5 6 8 ~4 2.0 bis~ate 0.193 ~5 4.0 ~ 0.182 835 26 8.0 " 0.139 87A
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'Ihe increased efficien~y of thc bisulfate io~ ava that of the bisu~ is ilhlstrated by a ca~parisoll of e~ es 24-26 and 20 23.

E~2cam~es Z7-29: CQm~on of Diffe~ent Bisu~ate Sour~e~

a higb su~ate ore were treated for identica~ times with 300 ml of a 5 ~o thiourea solution, 15 g fe~ic su~ate, and the amount of bisu~ate indicated. The suh'uric -. acid was a 1 Molar solution. The results are in Table 5.

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~ , Tablc S
Companso~ of Different Bis;u~
pH Sta~t E~ 96 loss E~at ~moullt p~ p]H R~ery to~ or~
27 H2SS~, 10 ml 2 45 95.9 173 28 NH~HS04 5 ~ .. 7 94.6 ~5 -` : "
29 NaHSO4 4 ~ 1.8 3~ 942 368 ;
'`' ' Ihe hi~h thiourea loss ill e~ample 29 appc~s to b~ the resol~
uDident~fied ~ental ermr. Compare e~ s 7-lQ

~5 ~er tests w~re d4~ne to dete~mine wheth0 the losses indicated by e~mple 29w~re ac~a~e o~ ~ental em~r. Co~rmation e~m~les 30 33 ~ndicate ~ ~ .
~ample 29 was erroneous.

Table 6~ firmation Tests pH ~ea ~ ``
pH Ag~ Oro 5%TU S~t En~ los~ ~b/ . .
E~ Agc~ Am~mt (d ~ ml) pH pH ~o~e) :
3D NaHSO, 6 100 300 1~ 26 86 :
31 NaHSO~ 4 150 200 ~3 33 ~2 : `
~ NaHSO~ 4 IS0 200 ~3 33 14.6 33 NaHSO; 4 lS0 200 15 ~S 12 E~p~le 34 lln ~n~e 34-37, a 200 g. ore sampde o gald conoentrate ~om a high s~
on was treatal with 400 ml of a 5% thiourea/ sod~n bisu~ate/ferric sulfate solution for 2 ho~ at a pH between about 1.8 to about 2;L lhe e~ tion ~ ~ .
soludon rema~ed ~e gold and si}~er ~ om the ore in the listed p~oenta~ ~ :
After the fiIst e~traction and separation of the metal ~alues, the e~ac~o~
solution was ~he~ed for thiourea conoentration and ~mdadon reduction potelltiaL
Ihiourea was added to return the solution to its oridnal concentratioD~

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2~23119 amount ~thiourea addWwa~ rec~ded as thiourealos~ that~:le. Fernc :`
sulfa~ added a~:r ca~ cy~:lc aS indicatod to mai~tain an ~da~on re~on .
potential o ~ibout 17~185 mY. 1~ ated e~ractioII solution ~vas the~
conta~ vith a ~esh 200 g. ~e sample. Ihis se~oe ~ e:ctrac~on, analysis, S re~ena~oD9 and recy~ was repeated f~3r 9 ~cles (o~ tractio~ and 9 reg,~les). 'Ihe results are ~ Table 7.

Table 7 - Re~e af Sa}udon Sodium F~c Ihioura~ d ~reBis~llfa~e Sulfatc Consump~on E~trætion - 1 200 9 1 3 gæ2 2 200 4 0.1 14 87A
3 200 10 0.25 13 g~A
4 200 9 1 12 89.6 6 200 9 2 11 86.7 7 20~ 9 2 15 87.1 9 200 9 3 26 86.0 ..
~ 200 10 3 16 89.4 Re~e of the tbiourea solution contiru~d to result in hi~h ~traction etEicDencies a~ re~uYenation.

~amg~es 3S 37:
In e~ampIes 3S 37, samples co~taining 100 g. o~ gold cowentrate from a hi~
sulfide ore were treated far identical times with 300 ml ~ a 5% ~biourea so}udoD~ : .
15 g fe~ic su~ate, a~d tlle differen~ amoun~ ammoni~ bisulfate indica~
Tne results obtained by ~arying ~e amounts ~ bisuh'ate are reported m Table 8.

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- ~ :.-'' -`~ 2 0 2 3 1 1 9 Ta~le 8 Varicd Amo~ B.suh'ate 3~ 2.2 93.8 7.1 31; 4A 94.1 3.25 .
37 8.8 95.6 4.13 ~ampl~ ~ ~:
I~ e%am~ 389 the present ~oce~ is co~ared tl~ that o e~ample 1 iu Sc hulæ 4,561,947 in du~icaeed te~ts. A sample af hi~h n ~fide9 gold~ntaiD~g orewas co~ed wi~ a ~iol~rea ~træ~on solution a~ng to US. Pate~t No. . ~ -4,561,~47. Conoe~trated s~furic acid was added to m~tain the pH betwee 1.8 ~ 2.5. ~ bisu~te ~9 added to the ~trastion s~on as directed'by .
t11G Schulze patent. Hot water wa~es were ~ot ~sed to en~le direct comparison i~of the ~ooess wi~h shat af ~e ~rese~t mventiotL
As a:n embodiment of the present prooe~, another samp~e o ~e same ore was contscte~ h thiourea m equal ~t ratio~ So~ bisu~at4 rath~ than su~ic ac~d, was added to maintaiD thc pH betw~:en about 1.8 and 2.5.
lhe results are repartcd in Table 9. ,; ~
2~ Table 9 ~ Companso~ Tes~ .
Con~oneIIt PreselltI~ll~on . US~4.561.947 .
lhiourea ~b/ton are) 184 1~
30 (mllton ore) `~ :
So~ Bis~te -- 21 (Iblt~ ~re) ` ~ `
~Ib/t~nore) ~ ` ~~ `
3~ lhiol~rea Cons~ption . ~.6 0 `~
~tton o~e) `
Golde~trac~on (~3~) 945 Z7.6 94.4 38A :~

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;: .. , . . . ~ . . .

13y ~mp~ thc tests, ;t ~s clear that the a~acen~ ~hiourea consumption in the proce~ ~ US. 4,S61,947 is quit~ 1~JW at the sacr~c~ of ~ra~:tio~ cfficie~

low thiourea loss~, hawwer, the estra~ion effic~en~y rem~ hi~h It is to be unde~ d tha~ e ~amples p~esented ;ibove ~re fo~ illustrating the: i~:n~oD. Ihe ~ fic embodiments of the e~nples are not intended to limit :
~e scope of tlle claimed mventioD.

:''. ' ~

. ~ .

Claims (31)

1. A process for recovering noble metals from ores by extraction, said process comprising:
contacting an ore containing a noble: metal with an extraction solution comprising thiourea and an acidifying agent consisting essentially of an alkali metal and/or ammonium bisulfate; and recovering at least a portion of said noble metal from said extraction solution.

2. The process according to claim 1 wherein said noble metal comprises a precious metal of group IB.

3. The process according to claim 1 wherein said bisulfate is present in said on solution in an amount within the range from about 2.0 to about 80 lb.
bisulfate anion/ton of ore.

4. The process according to claim 3 wherein said bisulfate is present in said extraction solution in an amount with the range from about 3.4 to about 67 lb.
bisulfate anion/ton of ore.

5. The process according to claim 1 wherein said bisulfate is ammonium bisulfate.

6. The process according to claim 1 wherein said extraction solution is at a temperature within the range from about 50° to about 85° F.

7. The process according to claim 1 further comprising:
adding a ferric salt to said extraction solution.

8. The process according to claim 7 wherein said ferric salt is selected from the group consisting of ferric sulfate and ferric chloride.

9. The process according to claim 1 wherein said extraction solution exhibits a reduction potential greater than 70 mV.

10. The process according to claim 9 wherein said reduction potential is within the range from about 70 to about 200 mV.

11. The process according to claim 1 wherein said reduction potential is greater that 100 mV.

12. The process according to claim 11 wherein said reduction potential is within the range from about 115 to about 200 mV.

13. The process according to claim 1 wherein said process exhibits a thioureaconsumption of less than 30 lb./ton of ore.

14. The process according to claim 13 wherein said process exhibits a thiourea consumption of less than 20 lb./ton of ore.

15. The process according to claim 14 wherein said process exhibits a thiourea consumption of less than 10 lb./ton of ore.

16. The process according to claim 1 further comprising:
recycling at least a portion of the extraction solution to the contacting step after the recovering step.

17. The process according to claim 1 further comprising:
adding an alkanolamine to said extraction solution after the contacting step and before the recovering step.

18. The process according to claim 17 wherein said alkanolamine comprises methanolamine or ethanolamine.

19. A continuous process for recovering noble metals from ores, said process comprising:
adding thiourea to a mixture of water and a noble metal containing ore to produce an extraction solution;
adjusting the pH of said extraction slurry with an acidifying agent consisting essentially of an alkali metal or ammonium bisulfate to produce an acidic extraction solution;
adding a ferric salt to the acidic extraction solution;
allowing at least a portion of the noble metals in said ore to be extracted from said ore into said extraction solution;
recovering at least a portion of said noble metals from said extraction solution; and recycling at least a portion of the acidic extraction solution from the recovering step to the contacting step.

20. The process according to claim 19 wherein said bisulfate is ammonium bisulfate.

21. The process according to claim 19 wherein said bisulfate is sodium bisulfate.

22. The process according to claim 19 further comprising:
adding an alkanolamine of 1-6 carbon atoms to said extraction solution after the addition of said ferric salt.

23. The process according to claim 22 wherein ferric salt is ferric sulfate or ferric chloride.

24. A process for recovering a group IB metal from an ore by extraction, said process comprising:
contacting an ore containing a group IB metal with an extraction solution comprising thiourea and an amount of sodium bisulfate that is sufficient to maintain said solution under acidic conditions without addition of sulfuric acid to said solution for a time sufficient to extract said Group IB metal into said solution;
and recovering at least a portion of said group IB metal from said extraction solution.

25. The process according to claim 24 wherein said group IB metal is gold.

26. The process according to claim 24 wherein said extraction solution is at a temperature within the range from about 50° to about 85° F.

27. The process according to claim 24 wherein said process exhibits a thiourea consumption of less than 30 lb./ton of ore.

28. The process according to claim 27 wherein said process exhibits a thiourea consumption of less than 20 lb./ton of ore.

29. The process according to claim 28 wherein said process exhibits a thiourea consumption of less than 10 lb./ton of ore.

30. The process according to claim 24 further comprising:
recycling at least a portion of the extraction solution after the recovering step.

31. The process according to claim 24 further comprising:
adding an alkanolamine to said extraction solution after the contacting step and before the recovering step.

31. The process according to claim 31 wherein said alkanolamine comprises methanolamine or ethanolamine.
33. The process according to claim 24 further comprising:
adding a ferric salt to said extraction solution.
34. The process according to claim 33 wherein said ferric salt is selected fromthe group consisting of ferric sulfate and ferric chloride.