Cyanide Measurement and Control for Complex Ores and Cyanide Concentrates P L Breuer1 and J A Rumball 2 ABSTRACT Measuring cyanide in the leach liquors associated Measuring associated with high copper and/or sulfide ores is a non-trivial exercise. It is well known that copper complexes with cyanide and reduces the amount of cyanide available for gold leaching. What is not so well known is that the rhodanine end point overe ov eresti stimat mates es the amo amount unt of cya cyanid nidee av avail ailabl ablee for lea leachin ching g in the presence of copp er er.. Sulfid Sul fidee ions also int interfe erfere re wit with h a rhod rhodani anine ne end poin pointt tit titrat ration, ion, although this is less of a problem as the black silver sulfide precipitate formed clearly indicates to the operator that something is wrong. Thiosul Thio sulfat fate, e, whi which ch form formss rea readil dily y fro from m the alk alkali aline ne oxid oxidati ation on of sulfides, sulf ides, causes an overe overestimat stimation ion of the cyani cyanide de ava available ilable for leachi leaching ng due to the formation of Ag(S2O3)-. The net result of these observations is that rhodanine is rarely of value as an end point indicator in complex solutions. It generally overestimates the amount of cyanide available, providing plant metallurgists with a false sense of security. Potent Pot entiome iometri tricc tit titrat ration ionss are gen genera erally lly much more cap capabl ablee of accurately measuring cyanide in complex solutions. The interfering effect of copper can be resolved and it is even possible to estimate the copper concentration using the inflexions associated with the titration of CN - + Cu(CN)43- versus Cu(CN)32-. Using the potentiometric method sulfide ions can be determined before the cyanide measurement is made due to the formation of AgS2, although the electrode will foul with repeated measurements. Thiosulfate can also be distinguished from cyanide with a potentiometric titration. Rhodanine and potentiometric titrations are both affected by the pH of the liquor. At pH 9.2 half the cyanide will be present as CN - and half as HCN(aq) with only the CN- being titratable. This does not hold in the presence of a buffer active around pH 9. In the presence of sufficient buffer, both the CN- and HCN(aq) are titrated. Ca(OH)+ may buffer the pH when large amounts of lime h ave been added.
INTRODUCTION Cyanide measurement is an important control parameter in the recove rec overy ry of gol gold d fro from m ore oress usi using ng cya cyanid nidatio ation. n. Com Common monly ly,, a silver nitrate titration using a rhodanine indicator end point is employed on mine sites to measure the cyanide concentration of filtered samples. A potentiometric determination of the end point is al also so po poss ssib ible le an and d th this is ha hass bec becom omee th thee ba basi siss fo forr on onli line ne measurement measur ement techniques employed to automat automatee cyanid cyanidee contro controll in some gold plants. The processing of more complex ores and concentrates using cyanidation has generated a new range of issues and challenges in the measurement and control of the cyanide concentration in these processes. The major issues identified are interference from high copper concentrations and the presence of sulfide ions. In some gold plants economics also constrain operation to pH <10. This not only creates OH&S issues with regards to the presen presence ce of HCN(g), but can impact on the cyanide measurement depending on the method used. Understanding the relationship between the various vari ous cyanide measur measurement ement values and the gold disso dissolution lution
process is also very important in ascertaining the appropriate set point for the process. These aspec ts are discussed in this paper.
EXPERIMENTAL PROCEDURES Unless stated otherwise, solutions were prepared from AR grade reagents and deionised water. Rhodanine Rhodan ine titrations titrations were conduct conducted ed with a 5 ml sample, two to three drops of indicator and titrated directly with 0.05 M silver nitrate using a Metrohm 665 Dosimat (for constant addition rate) until the end point was observed. Potentiometri Potentiometricc titrat titrations ions were conducted using a Metrohm 716 Titrino auto-titrator with 0.01 M silver sil ver nitrate nitrate sol soluti ution. on. Samples Samples (1 - 5 ml) were dil dilute uted d wit with h deio de ioni nise sed d wa wate terr to ac achi hiev evee su sufffic icie ient nt vo volu lume me fo forr th thee measure meas urement ment set set-up -up.. All tit titrat ration ionss wer weree rep repeate eated d in at leas leastt triplicate and average values are reported. An amperometric method developed by CSIRO Minerals was also utilised. This method measures the silver dissolution rate at a fixed potential (-0.05 V versus the standard hydrogen electrode, SHE) in filtered solutions or slurries. Gold leach rates and electrochemistry were measured in air satura sat urated ted sol soluti utions ons usi using ng a rot rotati ating ng ele electr ctroche ochemic mical al qua quartz rtz crystal microbalance (REQCM), which is described elsewhere (Jeffrey,, 1998). (Jeffrey
RESULTS AND DISCUSSION Cyanide analysis techniques Cyanide is traditionally measured by titrating with silver ions with the end point determined using a rhodanine indicator. In the case of coloured solutions potassium iodide has been used as an alternate indicator. A refinement to this method is to measure the potential of a silver wire immersed in the titration cup and use the potential inflection at approximately -100 mV (SCE) as the end point. Ion oniic cyanide in solut utiion may al alsso be measured amperometrically (Heath, Rumball and Bailey, 1999) and with a variety of other techniques. Table 1 presents the most common methods used and the species measured by each technique. For gold leaching leaching it is the fi first rst three three meth methods ods that are of interest as these potentially give a measurement of the cyanide avail av ailabl ablee to lea leach ch gol gold. d. It sho should uld also be not noted ed tha thatt onon-sit sitee
TABLE 1 Species measured by various cyanide analysis techniques. Analysis technique Silver nitrate titration – rhodanine or KI indicator Silver nitrat nitratee titrat titration ion – potenti potentiometri ometricc
1.
Resear Rese arch ch Sc Scie ient ntis istt – Go Gold ld Pr Prog ogra ram, m, Pa Park rker er Ce Centr ntree (CS (CSIR IRO O Minerals), PO Box 7229, Karawara WA 6152. Email:
[email protected]
2.
MAusIM MAus IMM, M, Go Gold ld Pr Prog ogra ram m Ma Manag nager er,, Pa Park rker er Cen Centr tree (CS (CSIR IRO O Minerals), PO Box 7229, Karawara WA 6152. Email:
[email protected]
Ninth Mill Operators’ Conference
Amperometric
Species measured CNCN-, S2- and estimate of Cu CN- and estimate of Cu
Flow injection/ligand exchange/ UV digestion
WAD CN, total CN
Distillation
WAD CN, total CN
IC and HPLC
Fremantle, WA, 19 - 21 March 2007
Metal cyanides, CNO-, SCN-, S2-, S2O32-
249
P L BREUER and J A RUMBALL
cyanide measurements are typically reported as mg/L NaCN, whereas samples submitted to analytical laboratories are often reported as mg/L CN-.
Influence of pH Cyanide measurement In gold plants where the economics constrain the leach pH to below ten, both CN- and HCN(aq) exist. The CN /HCN (aq) distribution as a function of pH is described by Equation 1 (pKa = 9.2). Knowing the total cyanide ([CN]T), the ionic cyanide concentration can be calculated using Equation 2 and is graphically shown in Figure 1.
The amperometric technique gave results different from both the calculated ionic cyanide and the titration technique (Figure 2). As this technique is measuring the silver oxidation rate, the ionic cyanide concentration at the electrode surface decreases as ionic cyanide complexes with the oxidised silver. The buffering effect of the carbonate results in some dissociation of HCN(aq), which provides more ionic cyanide for silver oxidation. However, diffusion of ions to and from the surface into the bulk solution minimises the dissociation of HCN(aq) at the electrode surface. Clearly, carbonate has some positive effect on the silver oxidation rate. However, it is dependent on the diffusion rate and thus does not correlate with either the cyanide measured by titration or the ionic cyanide concentration. 100 ) 80 N C a N 60 L / g 40 m (
100 ) 80 N C a N 60 L / g 40 m (
Theoretical ionic cyanide
-
N C 20
Amperometric
Theoretical ionic cyanide Titration
-
N C 20
Titration
0 8.6
Amperometric
8.8
9
9.2
8.6
8.8
9
9.2
9.4
9.6
9.8
10
10.2
CN -
]
[ HCN ]
= 10
(pH − pKa )
(1)
(aq )
[CN ] = [CN] −
T
10
(pH − pKa )
/ (1 + 10
(pH − pKa )
)
(2)
The cyanide measurement by silver nitrate titration (colorimetric or potentiometric end points) follows the ionic cyanide concentration as a function of pH, which indicates HCN(aq) is not measured under these conditions. The amperometric method also gives cyanide measurements that follow the ionic cyanide concentration. This clearly indicates that the oxidation of silver (or gold) is dependent on the ionic cyanide concentration. If the sample pH is increased above 11 before the cyanide measurement, then CN- + HCN(aq) ([CN]T) is measured. For buffered solutions, the cyanide measured by titration is higher than the calculated ionic cyanide (Figure 2). This is because buffering the pH according to Equations 3 or 4 allows further HCN(aq) dissociation without a pH fall that would otherwise stabilise the HCN(aq). In Figure 2, the titration measured the total CN- + HCN(aq) because the buffer concentration was greater than the HCN(aq) concentration. At buffer concentrations less than the HCN(aq) concentration, only the equivalent moles of HCN(aq) to buffer will be measured by titration, in addition to the CN-. +
+ H ⇔ HCO
− 3
(3)
+
Ca(OH) + H + ⇔ CA2 + + H2O
(4)
HCN (aq ) ⇔ H + + CN −
(5) −
Ag + + 2CN − ⇒ Ag(CN)2
250
10
10.2
1 0.4
FIG 2 - Comparative measurement of cyanide in buffered solutions 2(0.1 M KCl, 93 mg/L NaCN, 250 mg/L CO3 ).
FIG 1 - Cyanide measurement as function of pH in unbuffered solutions (0.1 M KCl, 93 mg/L NaCN).
CO
9.8
10.4
pH
2− 3
9.6
pH
0
[
9.4
(6)
Gold leaching So which cyanide measurement is important for gold leaching? The gold leaching process is dependent on both the ionic cyanide and oxygen concentrations. A graphical representation of the gold leach rate as a function of ionic cyanide concentration is shown in Figure 3. For a given oxygen concentration, the gold leach rate is cyanide diffusion limited at ionic cyanide concentrations less than X and oxygen diffusion limited at ionic cyanide concentrations greater than X, where X is known as the critical cyanide concentration.
Cyanide limiting rate e t a r h c a e l u A
Oxygen limiting rate
X -
CN concentration
FIG 3 - Schematic of oxygen and cyanide limiting rates of gold dissolution.
With a decrease in pH, the ionic cyanide concentration decreases, and the gold leach rate can change from oxygen diffusion limited to cyanide diffusion limited. Under cyanide diffusion limiting conditions it would thus be expected that the gold leach rate would decrease with decreasing pH relative to the ionic cyanide concentration. This is shown not to be the case in
Fremantle, WA, 19 - 21 March 2007
Ninth Mill Operators’ Conference
CYANIDE MEASUREMENT AND CONTROL FOR COMPLEX ORES AND CONCENTRATES
Figure 4. The reason for the higher than expected gold leach rate at pH’s <10 was further investigated by conducting electrochemical studies using a REQCM. The increase in gold leach rate was found to be attributed to the generation of OH - ions from oxygen reduction concurrently occurring on the gold surface. The OH- ions react with HCN(aq) which releases more ionic cyanide.
0.0E+00 8
8.5
9
9.5
10
10.5
(mg/L Cu)
2.53E-02
659.1
1241.4
[CuCN(s)]
0.00E+00
0.0
0.0
[HCN(aq)]
1.30E-04
3.5
6.4
[Cu(CN)2-]
1.38E-05
1.6
1.4
0.9
[Cu(CN)32-]
6.99E-02
9896.7
10 275.7
4441.4
[Cu(CN)43-]
5.60E-02
9384.4
10 975.1
3557.8
Titratable cyanide
8.13E-02
10 0
Total copper
1.26E-01
C 60 N ( m 50 g / L 40 N a 30 C N ) 20
2 x ionic cyanide
(mg/L NaCN)
[CN ]
m l 3.0E-05 o m2.5E-05 ( e 2.0E-05 t a r h 1.5E-05 c a 1.0E-05 e l u5.0E-06 A
Calculated ionic cyanide
mg/L 0.0
70
Au leac h rate
[Cu+]
mol/L 2.16E-26
s 3.5E-05
2 -
Species concentration -
) 4.0E-05 1 -
TABLE 2 Speciation of solution containing 22 500 mg/L NaCN + + 8000 mg/L Cu (pH 11).
0.0 0.0
3985.2 8000.0
11
pH
FIG 4 - Effect of pH on gold leach rate measured using a REQCM (0.1 M KCl, 71 mg/L NaCN, air saturated).
Two possible oxygen reduction reactions can take place (Equations 7 and 8). For both oxygen reduction reactions, one mole of hydroxide is produced per electron consumed. Thus, for each mole of Au oxidised one mole of OH- ions is generated from oxygen reduction and hence up to one mole of CN- can be released from HCN(aq). Hence, gold leach rates up to double (based on the solution ionic cyanide concentration) are theoretically possible where the gold leach rate is cyanide diffusion limited. This theoretical maximum gold leach rate is shown as a dotted line in Figure 4 (2 × ionic cyanide, with a maximum of CN- + HCN(aq)), and is only slightly higher than the measured gold leach rates shown in this figure. O2 + 2H2O + 2e− ⇒ H2O2 + 2OH−
(7)
O2 + 4H2O + 4e− ⇒ 4OH−
(8)
Having established the effect of pH on the gold leach rate, the effect of carbonate was determined under cyanide limiting conditions. The gold leach rate measured at pH 9 with 1 g/L CO32- present was found to be 2.86 × 10 -5 mol m-2 s-1, which is 13 per cent faster than without CO32- (see Figure 4). Thus, at pH’s below 9.2 the presence of carbonate may enhance the gold leach rate depending on the diffusion rates prevailing.
7000
9000
6000
8000
) 5000 L / g m 4000 ( ] N 3000 C a N [ 2000
7000 [ C u 6000 ] ( m 5000 g / L ) 4000
Rhodanine Potentiometric Potentiometric Cu
1000
3000
0
2000 0
1
2
3
4
5
6
7
Rate of AgNO3 addition (mL/min)
FIG 5 - Comparison of rhodanine and potentiometric titrations for a + solution containing 22 500 mg/L NaCN + 8000 mg/L Cu .
200
20 mV diff mV
0
Ag+ + 2Cu(CN)32-
Ag(CN)2- + 2Cu(CN)2-
15
Ag+ + 2Cu(CN)43 Ag(CN)2- + 2Cu(CN)32-200 V m Ag+ + 2CN- Ag(CN)2-
d i f f 10 m V
-400
High copper concentrations
5
-600
Cyanide measurement The thermodynamic speciation of a solution containing 22 500 mg/L NaCN + 8000 mg/L Cu + is presented in Table 2. The titratable cyanide in this table is a calculated value which includes the free CN- and one CN- from Cu(CN)43-. The cyanide determination by titration with potentiometric end point for this solution is shown in Figure 5 to agree closely with this value. An added advantage of the potentiometric titration is that an estimate of the copper concentration can be made from the difference between the potentiometric differential peaks for the reaction of silver with Cu(CN)32- (Figure 6). The copper estimates shown in Figure 5 are slightly higher than the actual copper concentration, which appears to be associated with the slight underestimation of the titratable cyanide concentration. It has previously been reported that the amperometric technique can also provide an estimate of the copper concentration (Dai, Jeffrey and Breuer, 2005).
Ninth Mill Operators’ Conference
+
22500 mg/L NaCN + 8000 mg/L Cu
-800
0 0
1
2
3
4
5
6
7
8
9
10
11
mLs of 0.01M AgNO3
FIG 6 - Potentiometric silver nitrate titration of a solution containing + 22 500 mg/L NaCN + 8000 mg/L Cu .
The rhodanine titration on the other hand significantly overestimates the cyanide concentration (standard deviation of the repeat measurements was 200 mg/L). The cyanide concentration determined by rhodanine also increases significantly with increasing silver nitrate addition rate. It is suggested that the high copper concentration interferes with the rate of Ag+ association with the rhodanine affecting the end point determination. The mechanism for this is unclear at present.
Fremantle, WA, 19 - 21 March 2007
251
P L BREUER and J A RUMBALL
Decreasing the addition rate reduced the overestimation; however, the end point becomes very difficult to interpret below 2 ml/min due to the very slow colour change. A ten-fold dilution was found to exacerbate the overestimation with the apparent cyanide concentration increasing by more than 15 per cent. A possible explanation is that the silver complexes faster with cyanide from the Cu(CN)32- complex than with rhodanine and the equilibration (Equation 9) with the indicator complex (Rh-Ag+) is slow and also influenced by the concentration. 2−
−
−
Rh − Ag + + 2Cu(CN)3 ⇔ Rh + Ag(CN)2 + 2Cu(CN)2
(9)
Comparisons between the titration values and the thermodynamic titratable cyanide for two different cyanide concentrations with copper present are shown in Figure 7. Clearly, the rhodanine titration significantly overestimates the available cyanide for gold leaching when copper is present, the magnitude of which appears to be related to the copper concentration. The potentiometric and amperometric techniques on the other hand closely measure the available cyanide for gold leaching. 6000 ) 5000 L / g m 4000 ( ] N C 3000 a N [ d e 2000 t a r t i T
determination), and PbOH+ and Pb2+ become soluble, which interferes with the rhodanine indicator (gives the salmon pink end point colour). This can be avoided by maintaining the sample pH >11 or by the addition of a concentrated lead nitrate solution prepared in 1 M NaOH. Addition of solid PbO or PbCO3 could also be used. The results of measurements made using a concentrated lead nitrate solution prepared in 1 M NaOH are shown in Figure 8. The slightly lower cyanide titration values after lead addition could be attributed to the low solubility of lead cyanide or the oxidation of some sulfide to form thiocyanate. This is supported by the potentiometric titration value determined without lead addition. This determination is possible as silver sulfide was found to form preferentially to silver cyanide and thus it is titrated before the cyanide (Figure 9). Hence, the sulfide does not need to be removed for the potentiometric titration. This has the added benefit that the sulfide concentration can also be determined concurrently using this method. However, online potentiometric titration set-ups and the amperometric method are affected by sulfide ions; online potentiometric titrations generally only detect one end point and hence would include sulfide ions in the cyanide determination, and the build-up of silver sulfide precipitate effects subsequent measurements for both techniques unless removed. 4000 mg/L NaCN + 5 mM Na 2S
4000 3900 ) L / g 3800 m ( ] N C 3700 a N [
Rhodanine Potentiometric
1000
Rhodanine Potentiometric
3600
0 0
1000
2000
3000
4000
5000
3500
Thermodynamic titratable [NaCN] (mg/L)
0
FIG 7 - Comparison of thermodynamic and titration values for + cyanide with 8000 mg/L Cu present.
Gold leaching The leach rate of gold in cyanide solutions containing copper has been studied previously (Breuer, Jeffrey and Dai, 2005). This work showed that gold does leach in the presence of Cu(CN)32-; however, the leach rate is significantly slower than in the presence of CN- and Cu(CN)43-. Hence, the potentiometrically titratable cyanide measurement is the cyanide value of importance for gold leaching.
Sulfide ions
150
200
250
FIG 8 - Effect of lead nitrate (in 1 M NaOH) pretreatment on 2cyanide titration of solution containing 5 mM S + 4000 mg/L NaCN.
200
90
100 0
mV
80
diff mV
70
-100
60
-200 V -300 m Ag+ + 2CN-
-400
d i 50 f f m 40 V
Ag(CN)2-
30
2Ag+ + S 2 Ag 2S
-600
Cyanide measurement
100
PbNO3 (in 1 M NaOH) addition (% of req)
-500
20 10
-700
Direct rhodanine titration of a sample containing sulfide is not possible as silver is precipitated as silver sulfide, which masks the rhodanine indicator colour. The addition of lead ions and filtering before titration is a standard method for removing the interference of sulfide ions. Most importantly, it should be noted that the form in which the lead is added can affect the results. For example, if lead nitrate or a concentrated lead nitrate solution is added to remove the interference of sulfide ions before conducting a cyanide titration, the pH decreases due to the excess lead precipitating as PbO. This results in some HCN (aq) forming, which is not measured in the case of the potentiometric titration (low cyanide
252
50
-800
0 0
2
4
6
8
10
12
14
mLs of 0.01 M AgNO 3
FIG 9 - Potentiometric titration of solution containing 9 mM S 4000 mg/L NaCN.
2-
and
Gold leaching The leach rate of gold in cyanide solutions containing sulfide ions has been studied previously (Jeffrey and Breuer, 2000). This work showed that gold dissolution is very slow in the presence of
Fremantle, WA, 19 - 21 March 2007
Ninth Mill Operators’ Conference
CYANIDE MEASUREMENT AND CONTROL FOR COMPLEX ORES AND CONCENTRATES
sulfide ions and the presence of lead can assist in overcoming the effect of sulfide ions. Recent laboratory test work confirmed that gold dissolution does not occur to any appreciable extent when sulfide ions are present in the leach (Figure 10). Once sufficient oxygen was added (at the 24 hour mark) to oxidise the sulfide ions, improved gold recovery was observed. Sulfide ions are not typically found in gold leach solutions unless the ore or concentrate contains appreciable reactive sulfides. For the latter, being able to quantify sulfide ions is important for controlling reagent addition to optimise gold recovery.
using the potentiometric method is not possible due to the concurrent titration of the third cyanide associated with copper and thiosulfate. Thiosulfate does not interfere with the amperometric cyanide measurement when -50 mV is utilised. However, interference and contribution to silver oxidation by thiosulfate does occur at the higher potentials used to estimate the copper concentration.
CONCLUSIONS Potentiometric titrations are recommended in preference to rhodanine titrations when measuring the cyanide concentration in circuits treating sulfide or copper rich ores and concentrates. The potentiometric titration may also be tailored to yield sulfide and copper ion concentration as part of the cyanide measurement procedure. Using default set-up procedures, the online potentiometric titration measurement of cyanide will be affected by sulfide ions and a silver sulfide precipitate will eventually foul the electrode. The amperometric technique potentially offers comparable capabilities to the potentiometric titration, though careful set-up of the amperometric sensor is required for these complex leach solutions. Gold leaching is hindered by the presence of sulfide ions and hence sufficient air or oxygen addition is required in the leach to eliminate or minimise the presence of sulfide ions. The gold leach rate does not always follow the ionic cyanide or any of the cyanide measurements from the various techniques with pH. Above pH 9.2 the gold leach rate is constant, and only decreases with decreasing pH below 9.2 when cyanide is limited.
Thiocyanate and thiosulfate ions The interference of thiocyanate ions on the rhodanine and potentiometric titration cyanide measurements was investigated with a solution containing 4000 mg/L NaCN and 100 mM KSCN (5.8 g/L SCN). No interference of thiocyanate was identified in the determination of cyanide by either titration method. The potential for interference of thiocyanate on the concurrent cyanide and copper determinations using the potentiometric titration was investigated with solutions containing 22 500 mg/L NaCN, 2000 or 8000 mg/L Cu+ and 100 mM KSCN. In comparison to when no thiocyanate was present, a small increase was found in the cyanide determination which was reflected by a similar decrease in the copper determination. This is possibly due to a complexation equilibrium of thiocyanate with copper (cyanide complexes much stronger than thiocyanate), which displaces a small amount of CN-. Thus, the cyanide determination mo st likely reflects the ionic cyanide available for gold leaching. However, the copper estimation is slightly low and at high thiocyanate concentrations this can be as much as 15 per cent. Thiosulfate ions have also been found in cyanide leach solutions where reactive sulfides are present in the ore. Thiosulfate was found to interfere with the cyanide determination using the rhodanine titration method, resulting in an over-determination of the cyanide concentration. AgCN(s) was found to precipitate before the change in the rhodanine indicator colour was observed, which correlated with silver having formed AgCN(s) and Ag(S2O3)-. The potentiometric method was effective in distinguishing between the end points of the silver reactions with cyanide and thiosulfate, with accurate determination of the ionic cyanide concentration possible. However, in copper cyanide solutions containing thiosulfate an estimate of the copper concentration
ACKNOWLEDGEMENT The authors would like to thank Newcrest Mining Ltd for their financial support for a portion of the work presented in this paper.
REFERENCES Breuer, P L, Jeffrey, M I and Dai, X, 2005. Leaching and recovery of copper during the cyanidation of copper containing gold ores, in Treatment of Gold Ores (eds: G Deschenes, D Hodouin and L Lorenzen), pp 279-291 (The Canadian Institute of Mining, Metallurgy and Petroleum: Montreal). Oxygen addition started
9000
60
Cu
8000
50
Fe 7000
Sulfide ions
) L / g 6000 m (
A 40 u r e c o v e 30 y r ( % ) 20
Au recovery
-
2 5000 S , e F 4000 , u C 3000
2000 10 1000 0 0
5
10
15
20
25
30
35
40
45
0 50
Time (hr)
FIG 10 - Gold leaching from a concentrate containing reactive sulfides.
Ninth Mill Operators’ Conference
Fremantle, WA, 19 - 21 March 2007
253
P L BREUER and J A RUMBALL
Dai, X, Jeffrey, M I and Breuer, P L, 2005. The development of a flow injection analysis method for the quantification of free cyanide and copper cyanide complexes in gold leaching solutions, Hydrometallurgy, 76(1-2):87-96. Heath, A R, Rumball, J A and Bailey, S, 1999. An amperometric method for measuring cyanide in CIP/CIL circuits, Minerals Engineering, 12(11):1313-1326.
254
Jeffrey, M I, 1998. A kinetic and electrochemical study of the dissolution of gold in aerated cyanide solutions: The role of solid and solution phase purity, PhD thesis, Curtin University of Technology, Bentley, Werstern Australia. Jeffrey, M I and Breuer, P L, 2000. The cyanide leaching of gold in solutions containing sulfide, Minerals Engineering, 13(10-11): 1097-1106.
Fremantle, WA, 19 - 21 March 2007
Ninth Mill Operators’ Conference
