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Estudos, Notas e Trabalhos Online - Tomo 39

"A Study of arious !ethods for yanide #estructionby $%idation of Gold&each 'esidues (rom a South African Gold !ine, and Subse)uent

(lotation of *yrite"

Ana !aria 'ibeiro +otelho de Sousa

&aboratrio do .G! - 'ua da Amieira - //01 S2 !amede de .nfesta

Palavras-chave:Oxidao; Destruio do cianeto; Resduos da Lixiviao do Ouro;

Flutuao de Pirites.

Resumo:Nesta publicao est condensado um estudo eito no !inte" #$ouncil or!ineral %ec&nolo'()* +rica do ,ul* tendo em vista a viabilidade econ-mica da aplicao

de um circuito de lutuao da pirite em meio alcalino numa mina de ouro* uma ve /ue

o circuito tradicional em meio cido* tin&a /uase deixado de ser lucrativo ap-s a descida

drstica veriicada no preo do ur0nio em meados dos anos oitenta.

O estudo consistiu em testar vrios m1todos para a destruio por oxidao do cianeto

contido nos resduos da lixiviao do ouro* resduos estes /ue constituem a alimentao

da lavaria de lutuao* se'uido de um estudo comparativo da lutuao da pirite

aurera em meio alcalino e cido. 2p-s anlise detal&ada dos resultados* oi

recomendada a substituio do circuito de lutuao em meio cido por um circuito em

meio alcalino e cido.

2p-s anlise detal&ada dos resultados* oi recomendada a substituio do circuito de

lutuao em meio cido por um circuito em meio alcalino* depois do tratamento dos

resduos pelo processo Inco,O342ir para oxidao do cianeto. 5ste m1todo era no s-

vivel* como tamb1m mais vanta6oso /ue o tradicional.

Key-words:Cyanide Destruction; 7old Leac& Residues; P(rite Flotation.

Abstract: %&is Paper is t&e summar( o a stud( carried out at !inte" #$ouncil or

!ineral %ec&nolo'()* in ,out& 2rica* envisa'in' t&e economic viabilit( o an al"aline

p(rite lotation circuit* at a 'old mine* in order to replace t&e existin' traditional acidic
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circuit* 8&ic& &ad become barel( proitable 8&en in t&e mid9ei'&ties* t&e uranium prices

decreased to suc& an extent t&at its recover( 8as no lon'er advanta'eous.

%&e 8or" consisted o testin' various met&ods or cyanideremoval b( oxidation o t&e

'old leac& residues* t&e loat plant eed* ollo8ed b( a comparative stud( o al"aline

versus acidic lotation o t&e 'old9bearin' p(rite.

2 replacement o t&e acidic lotation circuit or an al"aline xant&ate lotation ater

cyanideoxidation ollo8in' t&e Inco,O342ir processat p: * 8as recommended* as

t&e latter 8as s&o8n to be not onl( easible but also c&eaper to carr( out.

2 .ntroduction


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%&e Inco,O342ir process8as carried out 8it& t&e addition o Na3,OB>!. L bea"er* in 8&ic&8ere placed B ' o t(pical cyanide leac& residue and mL o a B ppm Na$N

solution #8&ic& corresponds to >C? ppm $N9); > mL o t&is solution 8as diluted into a

3C mL volumetric las" and a $N9determination carried out immediatl(* beore an(

contact 8it& t&e solids. %&e slurr( 8as stirred or 3 min at > rpm* at 8&ic& time a 3C

mL* ali/uot o sample 8as ta"en and iltered* > mL* o t&e iltrate 8as diluted into a 3C

mL volumetric las" and anal(sed or ree $N9. %&is procedure 8as al8a(s ollo8ed or

ever( experiment* beore t&e addition o t&e oxidiin' rea'ents. One minute ater ta"in'

t&is initial ali/uot o slurr(* one o t&e oxidiin' rea'ents 8as added at a "no8n

concentration or lo8. %&e irst ali/uot o 3C mL o slurr( 8as ta"en > min ater t&e

addition o t&e oxidiin' rea'ent* iltered and a'ain > mL diluted to a 3C mL volumetric

las" and anal(sed or ree $N9. ,&ould t&e pea" be too small or non9existent* a dilution

into C or > mL 8ould be done.

C? ppm solution) is s&o8n b( t&e results presented in %ables >

to B and Fi'ures > and 3* 8&ere t&e residual cyanidein solution is plotted a'ainst t&etime ater addition o t&e oxidiin' rea'ents tested; t&e most relevant results ac&ieved

8it& eac& rea'ent 8ere selected* in or to establis& a comparison o t&eir eicienc(.

Table The o%idation of cyanide5ith sodium hypochlorite, measured by the residual

cyanidein solution at a gi6en time, after Na$l addition2

#$A%&I&' () %a(Cl *(+$&I(% ADD,D 1. in /01. %a(2

3 m+ 1/ m+ 1!03 m+ 13 m+ !/ m+

time C%- time C%- time C%- time C%- time C%-


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min2 ppm2 min2 ppm2 min2 ppm2 min2 ppm2 min2 ppm2

>C3 >=> >C3 >C> >==

> ?@ > => > B> > B? > N.D.C ?@ C BC C 3? C N.D. C N.D.

>3 ?@ > B > 3? >B N.D.

3@ ?@ 3C B BB 3?

C 3? >B >

N2#2 - not detected

Loo"in' at %able >* it can be seen t&at an amount o >C mL NaO$l >!* 8as suicient to

oxidie t&e cyanidein less t&an C minutes. Guantities smaller t&an t&e above* 8ere not

suicient to complete t&e oxidation process* 8&ereas 3 mL o t&is solution 8ereenou'& to convert all t&e cyanideinto c(anate* in less t&an > minute.

%&e results or t&e Inco,O342ir process* are s&o8n in %able 3. Hased on t&is process

or cyanideremoval* it 8as decided to use Na3,OBinstead o ,O3and lime* to oxidie

t&e >C? ppm $N9present in t&e slurr(. L4min* > mL Na3,OB>!* completel( oxidied t&e

cyanidein less t&an C minutes and 8it& 3 mL no $N 98as detected ater a period o

3C minutes. %&e eect o copper sulp&ate is also &i'&li'&ted in t&is table.

Table 4The o%idation of cyanide5ith Sodium Sulphite and an air flo5 rate of &7min,

measured by the residual cyanidein solution at a 8no5n time after Na4S3addition2

#$A%&I&' () %a!*(4*(+$C&I(% ADD,D 1. in 3/ m56+ Cu*(72

3 m+ 1/ m+ 1!03 m+ 13 m+ !/ m+

time

min2

C%-

ppm2

time

min2

C%-

ppm2

time

min2

C%-

ppm2

time

min2

C%-

ppm2

time

min2

C%-

ppm2

>C >@ >3B >3B >@

> @ > B > > >3 > >

C @ C @@ C ? C ? C N.D.

>= = >= C@ >B =? >B ?@3= C@ 3B CB 3C N.D. 3B C

BC = =? N.D. C> N.D. C C@

C =C N.D. @B B3

B

>>C B

Peroxidation 8as not eicient as a cyanideoxidant. %&e addition o 3 mL o :3O3BE

could onl( reduce t&e $N9in solution to >B= ppm* and ater an extra > mL addition* ??

ppm 8ere still present in t&e slurr(* 8&ic& means t&at too lar'e a /uantit( o t&is


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rea'ent 8ould be re/uired* placin' t&e processbe(ond an( economic consideration.

%&is process&o8ever* &as proved successul in t&e treatment o 'old mill tailin's at OI

%edi !ine in Papua* Ne8 7uinea [4".

Oonation is an alternative process or cyanide destruction b( oxidation* in

replacement o c&lorination at &i'& p:* 8&ic& is t&e standard met&od or t&e treatment

o 8aste 8aters containin' cyanide[7". ,everal lo8 rates 8ere bubbled t&rou'& t&e

slurr( or dierent time periods. %&e values or t&e residual cyanide* ater oone &ad

been bubbled t&rou'& t&e pulp or a "no8n period o time* are s&o8n in %able B. minutes.

Table 3

The o%idation of cyanideto cyanate 5ith different $:one flo5rates

(8one (42 )lowrate

/04 m+ /03 m+ /09 m+ 107 m+

time

min2

C%-

ppm2

time

min2

C%-

ppm2

time

min2

C%-

ppm2

time

min2

C%-

ppm2

>== >C3 >C> >BC

> >B> > >> > > > >@

B ? B = 3.C C 3.C =>

= C @ = >? = >>3> N.D. > N.D. N.D. N.D.

>C N.D. >C N.D.

N2#2 - not detected

From t&e our met&ods used or cyanide oxidation* it can be seen t&at t&ree*

c&lorination* t&e Inco,O342ir processand oonation produced satisactor( results in

eliminatin' t&e $N9 in solution. ,ubse/uent sta'es o treatment and economic

considerations 8ould be t&e basis or t&e c&oice o t&e met&od to ollo8.


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(ig2 - The $%idation of yanide5ith Sodium ;ypochlorite


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2erorot& @C

L pac&uca 8as used

and t&e air lo8rate 8as C L4min. Na$N 8as added to 'ive a concentration o 3 ppm in

t&e 8ater p&ase. %&e startin' natural p: o t&e pulp varied bet8een . and ?.. %&e

rea'ent consumption durin' pulp conditionin' or bot& acidic #:3,O=) and al"aline #Inco

,O342ir) processses* are s&o8n in %able C.

Table 1'eagent consumption during pulp conditioning for both acidic


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2l"aline 9 Inco,O342ir . $u,O=J @C

,O3J >

$a#O:)3J >@2t t&e end o eac& conditionin' period* t&e slurr( 8as collected into t&ree C L bea"ers

#c.a. B.B L in eac&)* ater 8&ic& lotation too" place in t&e Leeds 2utoloat $ell. %&e cell

8as s8itc&ed on* at an impeller speed o >3 rpm. %&e collector or suite o collectors

8as added ater > min and conditioned or = min* t&e rot&er 8as t&en added and

lotation commenced > min ater rot&er addition b( openin' t&e air at a lo8 o L4min.

One rou'&er concentrate 8as collected or > min* at 8&ic& time a practical completion

o t&e process&ad been reac&ed.


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8it& all t&e ot&er rea'ent combinations and dosa'es led to bot& lo8er 'rades and

recoveries.

%&e 'old recoveries rom t&ese residues 8ere about CE on avera'e* at 'rades o >.C

to >. '4t in t&e p(rite concentrate* t&e 'old remainin' in t&e loat tails 8as less t&an

.?C '4t. 2 summar( o t&ese results is presented in table .

Table ?A summary of the results obtained for gold and pyrite, in three flotation tests run under different conditions2

&ype and period

o.@ >.>B C. ?.3 .?C .3@

2l"aline* 3= & >.C@ >?.CC C>.= 3.3 .C .3B

2l"aline* = & >.C >@.C C>.@ .= .? .B

/2 onclusions

#i) 9 %&e oxidation o cyanide rom 'old leac& residues at p:?* 8as ac&ieved 8it&

NaO$l* t&e Inco,O342ir processand OB.

#ii) 9 2 irst approac& to costs* indicates t&at to treat > tonne o ore 8it& NaO$l 8ould

be almost > times more expensive t&an t&e traditional sulp&uric acid leac& prior to

lotation* 8&ereas t&e Inco,O342ir processusin' ,O3and lime 8ould be 3C to =Ec&eaper t&an t&e :3,O=treatment. ,o t&e considerable dierences estimated or t&e

costs s&ould be suicient to ruled out cyanide destructionb( c&lorination.

#iii) 9 %&e stud( o al"aline lotation ater t&e Inco process8as continued* in order to

optimise t&e sulp&ur 'rades and pulp conditionin' periods. Hetter results 8ere obtained

8it& al"aline t&an 8it& acidic lotation* considerin' t&e same periods o pulp

conditionin'.

#iv) 9 %&e = to 3= &ours conditionin' period prior to t&e loat tests* did not aect t&e

al"aline lotation results si'niicantl(* 8&ereas to ac&ieve similar results* a conditionin'

period o 3= &ours 8as re/uired or acidic lotation. %&is means a 'reat savin' in t&e

costs or compressed air* s&ould t&e Inco process ollo8ed b( al"aline lotation o

p(rite* be implemented.

#v) 9 %&e addition o ,NP as t&e onl( collector or combined 8it& %rocol ,C amine* led

to better results t&an ,.C and >.

'4t.


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12 'ecommendations

$onsiderin' t&e savin's in t&e costs o rea'ents and compressed air durin' al"aline

conditionin' and t&e results rom al"aline lotation* 8&en compared 8it& :3,O=$onditionin'* ollo8ed b( acidic lotation* it 8as recommended to replace t&e existin'

acidic circuit or an al"aline xant&ate lotation at p: * ater t&e application o t&e Inco

,O342ir process* durin' a period o not more t&an = &ours* alt&ou'& 8it& lon'er

conditionin' periods* a sli'&t improvement o t&e overall results 8as ac&ieved.

?C* ,out&

2rican Patent 34B3 and .I. Patent 3?>>BH

Q3. ROHH??@* pp. @B9@?* #>??@)

QB. INORR5* :. 2ND 7R?=* Mol. 3* pp C>?9CB. Publis&ed b( Dep.

$ivil 5n'.* $olorado ,tate niversit(* Fort $ollins* $olorado C3B* .,.2. #>?C)

Q=. 7ROL* !. D.* HR5!5N* V. !. 2ND :OLD5N* %. 5* TOxidation o c(anides in

industrial 8aste 8aters b( ooneT* Cyanide and t&e 5nvironment* Proceedin's o a

$onerence* %ueson* 2riona* December >?=* Mol. 3* pp B=>9B@3. Publis&ed b( Dep.$ivil 5n'.* $olorado ,tate niversit(* Fort $ollins* $olorado C3B* .,.2. #>?C)

QC. D5M,%* 5. 2.* $ON2RD* H. R. 2ND :D,ON* V.* T$ommercial operation o

I%C(>s ,O342ir cyanide removal processT* Cyanide and t&e 5nvironment*

Proceedin's o a $onerence* %ucson* 2riona* December >?=* Mol. 3* pp =@?9=.

Publis&ed b( Dep. $ivil 5n'.* $olorado ,tate niversit(* Fort $ollins* $olorado C3B*

.,.2. #>?C)

$O!O $


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Pyrite %studos+ ?otas e 1ra#alhos+ 1omo 39. nstituto @eolgico e 8ineiro.

AersBo Onlineno site do @8 ;http://www.igm.pt/edicoes_online/estudos/tomo39/artigo5.htm>.

5diWes Online4 5studos* Notas e %rabal&os4 %omo B?4 2 ,tud( o

Marious !et&ods or Cyanide Destructionb( Oxidation o 7old Leac&

Residues From a ,out& 2rican 7old !ine* and ,ubse/uent Flotation o

P(rite
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