a kinetic study of the cementation of gold from cyanide solutions onto copper

hydrometallurgy

ELSEVIER Hydrometallurgy 46 (1997) 55-69 , ,

A kinetic study of the cementation of gold from cyanide solutions onto copper

H.H. Nguyen, T. Tran *, P.L.M. Wong Centre for Minerals Engineering, The University of New South Wales, Sydney 2052, Australia

Received 8 October 1996; accepted 9 December 1996

A b s t r a c t

The kinetics of cementation of gold onto copper was evaluated using a copper rotating disc and suspended particles systems. It was found that the cementation of gold onto copper is controlled by a kinetic step. For both rotating disc and suspended particles systems, the effects of temperature, cyanide and gold concentration on the rate of cementation are more significant than those of rotation speed and solution pH. The kinetic rate constant of cementation of gold onto copper is comparatively smaller than those found for the gold-zinc-cyanide or silver-copper- chloride systems. The activation energy was found to be 53.4 and 54.1 k J / tool for copper rotating disc and suspended particles, respectively, which values are close to the measured value of 56.9 kJ/mol found in the electrochemical study. The morphology of the deposits, determined by Field Emission Scanning Electron Microscope, confirmed observations from experimental measure- ments, showing the passivation or acceleration of cementation due to the different types of deposit formed.

1. I n t r o d u c t i o n

Coppe r -go ld ore deposits have been discovered frequently in Australia. The treatment of these types of ores by cyanidation, however, has been plagued by several problems. The copper minerals, either as oxides, sulphides or metall ic copper, exhibit

very high solubility in cyanide solution [1]. Among these, chalcopyrite (CuFeS 2) and chrysocolla (CuSiO 3) are the least soluble in cyanide, whereas other minerals such as azurite (2CuO. Cu(OH)2), malachite (CuCO 3 • Cu(OH)2), cuprite (Cu20) and chal- cocite (Cu2S), exhibit high solubility. The presence of native copper also causes high

* Corresponding author. E-mail: [email protected]

0304-386X/97/$17.00 © 1997 Elsevier Science B.V. All rights reserved. PII S0304-386X(96)00093-X

56 H.H. Nguyen et al. / Hydrometallurgy 46 (1997) 55-69

consumption of cyanide and significant loss of gold. According to La Brooy [2], the cut-off grade for direct cyanidation is 0.5% Cu for oxidised gold ores and 1% for sulphide ores, above which the consumption of cyanide by copper minerals becomes significant. Each 1% of soluble copper in an ore increases NaCN consumption by up to 23 kg / t (which goes to form copper cyanide complexes). The dissolution of copper minerals generally proceeds more rapidly (due to their higher concentration in the ores) than for gold, thus necessitating maintaining the free cyanide level high enough in the pulp or heap leach system for gold to be extracted from the ores.

Copper(I) cyanide complexes exist in various forms as Cu(CN)~, Cu(CN) 2- and Cu(CN) 3-. The Cu(CN)43- species do not readily adsorb onto activated carbon during gold processing and it would appear that these Cu(I) complexes also take part in the gold extraction process [3,4].

Apart from causing a high cyanide consumption, copper minerals, especially native (metallic) copper, also create problems during plant operations. In heap leaching operations, a lower overall gold recovery was experienced, which was initially thought to be due to incomplete gold extraction, because cyanide is depleted by its retention with residual copper minerals trapped in the ores [5]. It was found that, at ambient conditions and pH 11, gold concentration in a solution containing 1000 mg/1 NaCN and 0.5 g / l Cu ( - 53 + 45 Ixm) decreased dramatically from 20 mg/1 to almost zero in the first 2 h. However, in the presence of sufficient cyanide and oxygen, the cemented gold subse- quently redissolves back into the solution [6]. A better understanding of the copper interaction is essential before a method can be developed to improve the gold recovery during heap leaching of gold ores containing native copper.

Following the studies on various aspects of gold cyanide stability and electrochemistry of the cementation of gold onto copper [6,7], this study was carried out to elucidate the effect of several factors on the cementation kinetics and deposit morphology. The kinetics of cementation reaction can be conveniently evaluated by measuring the rate of gold disappearance from the test solution, caused by its cementation onto a rotating disc or suspended particles of known surface area. Due to its well defined hydrodynamic flow pattern, the rotating disc system has been successfully used to study the cementation kinetics of gold and copper onto zinc from gold-cyanide liquors or silver onto zinc and copper from gold-chloride liquors [8-10]. Cementation kinetics have also been successfully studied using suspended particles [11,12].

Most cementation reactions are found to obey the first-order kinetic law [13,14] and the cementation of gold onto copper can be evaluated by the following rate equation:

[Au]t 1 A - - - k - - t ( 1 )

Log [Au]o 2.303 V

Where: [Au]t---gold concentration at time t (mg/l) ; [Au] o = initial gold concentration (at t = 0) (mg/l); k = cementation rate constant (cm/s); A = surface area of copper disc or particles (cm2); V = volume of the test solution (cm 3) and t = reaction time (s).

The morphology of gold deposited onto copper could affect the cementation reactions by either accelerating its rate or passivating the copper surface. According to Miller [14], the deposit surface may be influenced by the solution hydrodynamics, concentration of

H.H. Nguyen et al. / Hydrometallurgy 46 (1997) 55-69 57

reactants, temperature, and addition of a ligand and an organic colloid. In general, the reaction rate is enhanced significantly if the deposit surface is either dendritic or botroiydal. However, under certain conditions which lead to a tight, smooth or coherent deposit, the cementation reaction may become inhibited. The cementation reaction may also be inhibited due to the high initial concentration of the noble metal ion and limited disc surface area, and the deposit on the disc therefore accumulates quickly and blocks the disc surface, as has been shown in several studies [8-10,14].

In this study, the kinetics of gold cementation onto copper were evaluated by using a copper rotating disc and suspended particles systems which have different flow (mixing) patterns. A morphological study on the precipitated gold was also conducted.

2. Experimental

2.1. Materials and equipment

The schematic diagram of the equipment set-up for the cementation kinetic study using copper rotating disc is represented in Fig. 1. It consists of a reaction cell and instrument for pH, temperature and Eh measurement. All chemicals and materials used in this study were of analytical grade. The copper disc had a diameter of 3 cm and a working surface area of 7.07 cm 2. An amount of 0.3 g/1 copper powder (size range - 45 + 38 I~m and specific surface area of 226.9 cm2/g) was used for each experiment, conducted with copper particles suspended in a stirred reactor.

2,2. Experimental procedures

For the cementation kinetic study using a copper rotating disc, 1 1 of gold cyanide solution was prepared at the desired initial gold and cyanide concentrations, pre-de- oxygenated by purging high purity nitrogen gas and adjusted to the test pH, then set in a water bath to equilibrate to the set temperature. The copper disc was thoroughly polished

1 DC Motor

2 DC Current Supplier

3 pH Meter

4 Multimeter

5 Thermometer

6 Reference Electrodc

7 pH Electrode

8 N2 Gas Inlet

9 Copper Disc

10 Reaction Cell with

Test Solution

I I Water Bath

Fig. 1. Schematic diagram of equipment set-up for the cementation kinetic study using a rotating disc system.

58 H.H. Nguyen et al. /Hydrometallurgy 46 (1997) 55-69

before immersing in the test solution at the start of each experiment. For the kinetic study using copper particles similar procedures were applied. A defined amount of copper powder ( - 4 5 + 38 ixm) was suspended in the test solution as the experiment started. Nitrogen gas was passed slowly over the test solution during the entire experiment to minimise the interference of oxygen from the atmosphere. At pre-determined time intervals 5 ml samples were withdrawn for gold and copper analysis using an atomic absorption spectrophotometer. The solution pH and reaction mixed potential were also monitored throughout each experiment, which was run for 180 rain or 60 min for the study on copper disc and particles, respectively. After each experiment, the copper discs and particles were washed thoroughly with distilled water and stored in a desiccator for the morphological study. Due to the very smooth, shiny and coherent deposit on the copper discs, the photographs of the morphology of the gold deposit on the disc showed no distinctive features between gold grains. However, the morphology of the gold deposit on copper particles (after 60 rain of reaction) studied by using a Field Emission Scanning Electron Microscope (FESEM) shows some differences, as typically represented in Figs. 14 and 15.

3. Results and discussion

3.1. Kinetic study

3.1.1. Effect of NaCN concentration The effect of cyanide concentration on the kinetics of cementation of gold onto the

copper rotating disc and suspended particles was investigated at different NaCN concentrations ranging from 100 to 1000 ppm while other variables were kept constant. The first-order kinetic plots of log{[Au]t/[Au] o} versus time are shown in Figs. 2 and 3 for rotating disc and suspended particles, respectively. It is clear from these figures that

"~ -20 ~' × <

~-~ -40

-60 "~ [] 200m~,'f. NaCN

\ A 500m,vL NaCN "-x..X

=80 X 1000mg/L NaCN

-100

0 30 60 90 120 150 180 Reaction time, (rains)

Fig. 2. Variation in Log{[Au] t / [Au] o} ratio with time at various NaCN concentrations. Conditions: 25°C, pH 11,500 rpm, and 20 m g / l Au(1), copper disc.


-50 <

% -I0O <~

-150 ,.d

% - -200

-250

A 1000rag/l_ NaCN

0 I0 20 30 40 50 60

Reaction time, (rains)

Fig. 3. Variation in Log{[Au] t / [Au] o} ratio with time at various NaCN concentrations. Conditions: 25°C, pH I1,300 rpm, and 20 m g / l Au(1), 0.3 g / l copper, powder size - 4 5 + 38 ~m.

the slopes of these plots increase after an initial period of reaction, indicating that the reaction was enhanced for the whole range of NaCN concentration studied (the initial period of reaction is called stage 1, and the following period is referred to as stage 2 from here onwards). The cementation rate constants obtained from the slopes of these first-order kinetic plots by using Eq. (1) for both rotating disc (kcd) and suspended particles (kco) therefore increased with an increase in cyanide concentration for both stage 1 and stage 2, as summarised in Tables 1 and 2, respectively.

It can be seen from Tables 1 and 2 that the values of the cementation rate constant determined for the suspended particle system (kcp) are generally higher than both those determined for the rotating disc system (kcd) and predicted values (kp) [7] for similar

Table 1 Summary of rate constants (kco) of cementation of gold onto copper rotating disc for different variables

[NaCN] Temp. Rotation speed Solution pH [Au(I)] kcdo) (stage 1) kcd~2 ) (stage 2) (mg/ l ) (°C) (rpm) (mg/ l ) (cm/s) ( cm/s )

100 25 500 l l 20 0.212)<10 -3 0.966×10 -3 200 25 500 11 20 0.342)< 10 -3 0.711 )< 10 -3 500 25 500 11 20 0.586 × 10- 3 1.11 × 10- 3

1000 25 500 11 20 1.21 X 10 -3 3.42 × 10- 3 500 10 500 11 20 0.190)< 10 -3 0.266× 10 -3 500 35 500 11 20 1.27 × 10- 3 0.380 X 10- 3 500 45 500 11 20 2.33 X 10 -3 0.277 )< 10- 3 500 55 500 l l 20 4.18)< 10 -3 0.163)< 10 -3

1000 25 500 11 10 0.825 X 10 -3 2.64× 10 -3 I000 25 500 11 40 2.54× 10 -3 1.23X 10 -3 500 25 250 11 20 0.521 X 10 -3 0.521 X 10- 3 500 25 750 11 20 0.771×10 -3 0.771X 10 -3 500 25 1000 11 20 0.858×10 -3 0.858×10 -3 500 25 500 10 20 0.722X 10 3 0.966X 10 -3 500 25 500 12 20 0.472X 10 -3 1.04X 10 -3


Table 2 Summary of rate constants (k,p) for cementation of gold onto copper suspended particles for different variables

[NaCN] Temp. Rotation speed Solution pH [Au(l)] kcp0) (stage 1) kcp(2 ) (stage 2)

(mg / I ) (°C) (rpm) (mg/1) ( cm/s ) ( cm/s )

100 25 300 11 20 0 .541×10 -3 1.20×10 -3

500 25 300 11 20 0 .866×10 3 1.22)<10-3

1000 25 300 11 20 0 .974×10 3 2.14× 10-3

1000 10 300 11 20 0.359X10 3 0.853)<10 3

1000 15 300 11 20 0.667× 10 3 1.675× 10 -3

1000 35 300 11 20 2.71 × 10 -3 7.55× 10 -3

1000 45 300 11 20 3.87 × 10- ~ 9.44× 10- 3

1000 55 300 11 20 5 .51×10 3 15.57X10 -3

1000 25 300 11 10 0.756X10 3 1.75×10 3

1000 25 300 11 30 1.27 × 10- 3 2.42 × 10- 3

1000 25 300 11 50 3.09X10 3 1.95×10 3

1000 25 100 11 20 0.451 × 10 -3 1.73× 10 -3

1000 25 200 11 20 0.825× 10 -3 1.87× 10 -3

1000 25 400 11 20 1.26X 10 3 2.47× 10 3

1000 25 300 9.5 20 1.20 X 10-3 2.63 × 10- 3

1000 25 300 10 20 1.13× 10 -3 2.39× 10 3

1000 25 300 12 20 0.773 X 10 -3 1.96X 10 -3

conditions. This is probably because the value of the specific surface area of the copper powder used in Eq. (1), determined by using a Malvern Mastersizer, was smaller than the actual value, therefore causing a general increase in the calculated rate constant values. For zinc powder of the same particle size, Armoo [17] reported the value of the specific surface area, as determined by the BET method, to be 906 + 25 cm2/g, which is much greater than the value for copper powder used in this study. It is worth noting that the specific gravity of zinc is 1.25 times smaller than that of copper and the shape of zinc and copper particles may be different, causing the discrepancies in the measurement of the specific surface area. In the same context, to avoid the undesired error in determining the specific surface area of fine particles, Anacleto and Carvalho [12] used the values of k . a e (where k is the cementation rate constant and a e is the specific surface area) as a kinetic parameter to evaluate the cementation kinetics.

3.1.2. Effect of temperature It had been found in the electrochemical studies reported previously [7] that the

cementation of gold onto copper is controlled by a kinetic step, and the effect of temperature on the kinetics of the process is significant. The first-order kinetic plots of log{[Au]t/[Au] o} against time showing the effect of temperature (ranging from 10 to 55°C) are presented in Figs. 4 and 5 for a rotating disc and suspended particles, respectively. From the slopes of these plots, rate constants kcd and kcp can be calculated and plotted against 1 /T , as shown in Fig. 6. It can be seen from these graphs that the cementation rate and rate constants kCd and kcp of stage 1 increased greatly with an increase in temperature from 10°C to 55°C for both cases. The dramatic decrease in the


<Z -20

%

~ - 4 0

~ - 6 0 ~

-80 , i , ~ , , , , ,

0 30 60 90 120 150 180

Reaction time, (mins)

Fig. 4. Variation in Log{[Au],/[Au] o} ratio with time at various temperatures. Conditions: 500 mg/ l NaCN, pH 11,500 rpm, and 20 mg/I Au(I), copper disc.

rate of gold cementation and, as a result, rate constants of stage 2 at high temperatures for the copper disc are probably due to the quick formation of a compact and shiny gold deposit, which leads to severe blockage of the disc surface. Von Hahn and Ingraham [15] found that the silver deposited onto copper from cyanide solution was very smooth, shiny and coherent; resulting in a decrease in rate constant with time. In the case of suspended particles, due to the very large surface area of the copper particles (68.1 cm 2 for the 0.3 g / l copper powder used in this study, compared with 7.07 cm 2 for the copper disc), the passivation effect after stage 1 at high temperatures (35-55°C) was not observed. From the slopes of the plots of log{rate constants} versus l / T , the activation energies of the reaction, E a, can be calculated according to the Arrhenius relationship (slope = -Ea /2 .303R, where R is the gas constant).

The activation energies of stage 1 in the temperature range 10-55°C were found to be 53.4 and 54.1 kJ /mol for rotating disc and suspended particles, respectively, which are close to the measured value of 56.9 kJ /mol found in a previous electrochemical study

_~ -20 W

-40

-60

- .1oo ,o,,oc :, \ -120 , ,

0 10 20 30 40 50 60


Fig. 5. Variation in Log{[Au] t/[AU]o} ratio with time at various temperatures. Conditions: 1000 mg/ l NaCN, pH 11,300 rpm, and 20 mg/ l Au(1), 0.3 g / l copper, powder size - 45 + 38 Ixm.


-1.5

-2.0

-2.5

-3.0

-3.5

-4.0

3.0

A [ ] S t a g e 2 , copper disc

A A tX S t a g e 2 , copper particles

o I S,age 1, copper dis~ I ~ '~ i i , i I i i i i ~ i

3.1 3.2 3.3 3.4 3.5

1000/T, (°K)

3.6

Fig. 6. Plot of Log k c vs. 1 / T showing the effect of temperature on the rate constant of cementation of gold onto copper rotating disc and suspended particles.

[7]. These high activation energies also confirmed that the cementation process is controlled by a kinetic step. Miller et al. [11] reported that most of cementation reactions at low temperatures are controlled by a surface reaction mechanism (kinetic step) due to the coherent nature of the deposit formed at these temperatures.

3.1.3. Effect of solution pH The effect of solution pH in the range pH 9 .5-12 on the kinetics of cementation of

gold onto copper is not significant for both cyanide concentrations tested (500 and 1000 mg/1 NaCN), as typically shown in Figs. 7 and 8. The rate of gold cementation increased slightly with a decrease in solution pH from 12 to 9.5. This result agrees with the observation reported by Nicol et al. [16], who reported that a variation in the solution pH in the range 9 - 1 2 had no noticeable effect on the rate of cementation of gold onto zinc from solutions containing either 5 or 0.05 ppm of gold. A similar observation was

,.,; -5

-10

-20

-25

0 30 60 90 120 150 180


Fig. 7. Variation in Log{[Au] t/[Au]o} ratio with time at various solution pH values. Conditions: 500 m g / l NaCN, 25°C, 500 rpm, and 20 m g / l Au(I), copper disc.


-50

-zoo

-150

-200 %

- -250

-300 0 10 20 30 40 50 60


Fig. 8. Variation in Log{[Au] t / [Au] o} ratio with time at various solution pH values. Conditions: 1000 rag/1 NaCN, 25°C, 300 rpm, and 20 mg/ l Au(1), 0.3 g / l copper, powder size - 4 5 + 3 8 Ixm.

reported by Oo [18] for the cementation of gold onto zinc discs. The cementation rate constants for the copper rotating disc system were found to be 0.722, 0.586 and 0.472 × 10 -3 cm/s , which are close to the measured values of 0.824, 0.731 and 0.509 x 10 -3 c m / s found in the electrochemical study [7] for solution pH values of 10, 11 and 12, respectively. A slightly higher value for the cementation rate constant for copper particles is probably due to the reasons explained previously in Section 3.1.1. Furthermore, it should be noted that the experiments on rotating discs were conducted at constant 500 mg / l NaCN and 500 rpm, while the experiments on suspended particles were conducted at constant 1000 mg/1 NaCN and 300 rpm. However, it is clear from the plots of Log[rate constant] versus solution pH shown in Fig. 9 that the slopes of rate constants (kcd, kcp and kp) versus solution pH are similar, indicating a good agreement in the effect of solution pH on the rate of cementation of gold onto copper observed by different techniques.

1.4

I .c°°.'~'~° I ] .2 ~ I • Copper powder I

1.o I

~ o.s

~ 0.6

0.4 9.5 10.0 10.5 I1.0 11.5 12.0

Solution pH

Fig. 9. Plots of rate constant vs. solution pH showing the effect of solution pH on the rate constant of cementation of gold onto copper.


"~ -50 <

~ -I00

~ - 1 5 0 X

~-- -200 O 400rpm N,x ~ I

-250 i

0 10 20 30 40 50 60

Reaction time, (rnins)

Fig. 10. Variation in Log{[Au] t / [Au] o} ratio with time at various stirring speeds. Conditions: 1000 mg/ l NaCN, 25°C, pH 11, and 20 m g / l Au(1), 0.3 g / l copper, powder size - 4 5 + 38 Ixm.

3.1.4. Effect of disc rotation (stirring) speed The effect of disc rotation speed on the rate of cementation of gold onto copper disc

and particles is presented in Figs. 10 and 11, respectively. Fig. 11 represents the plot of cementation rate constant versus to~/2 compared with the predicted values, which shows the Levich relationship: k = 0.62D2/3v- l/6tol/2 (where D is the diffusion coefficient of reactant species, cm2/s; v is kinematic viscosity, cm2/s and to is the disc angular velocity, rad/s). As can be seen from these figures, the rate of gold cementation increases with an increase in disc rotational speed.

A slight difference in the cementation rate constant values for the copper disc and suspended particles systems shown in Tables 1 and 2 is probably due to the difference in the flow patterns. It is clear from these tables that the effect of stirring speed on the suspended particle system is more significant than for the rotating disc system, obvi- ously because of the more intensive mixing pattern of the suspended particle system.

1.5

1.2 [ IIDi~:kcd(1)]

~ 0.6

~ 0.3

0 . 0 - 0 2 4 6 8 to 12

Square root of disc angular velocity, (tad/s)

Fig. 11. Plots of rate constant vs. square root of disc angular velocity showing the effect of stirring speed on the rate constant of cementation of gold onto copper.


-~ -20 g ~- -40

~ -60 20ppra Au ~ ~ ^

-80 o 4oppm Au

- 1 0 0 ~ l , J ~,, I J I , I ,

0 30 60 90 120 150 180


Fig. 12. Variation in Log{[Au] t / [Au] o} ratio with time at various gold concentrations. Conditions: 1000 m g / l NaCN, 25°C, pH 11, and 500 rpm, copper disc.

3.1.5. Effect of goM cyanide concentration The rate of gold cementation onto copper increased with an increase in gold cyanide

concentration of the test solution, as can be seen in Figs. 12 and 13. This observation agrees with the results obtained from electrochemical studies. The rate is slightly enhanced after the initial stage. However, at high gold cyanide concentrations (40-50 mg/1 Au(I)), the rate of gold cementation decreased during stage 2, probably due to passivation of the copper disc (particle) surface.

3.2. Morphological study

Figs. 14 and 15 show the effect of cyanide concentration and temperature on the morphology of the gold deposit on copper particles. It is clear from these micrographs that cyanide concentration and temperature have a significant effect on the cementation of gold onto copper. The micrographs did not show any significant effect of stirring

= -50

< -loo r-~

-150

-200 o 3omga.. Au "~,,,, " ~ "

-- -250 o ~Oms/L Au

-300 ' . . . . . 0 10 20 30 40 50 60


Fig. 13. Variation in Log{[Au] t / [Au] o} ratio with time at various gold concentrations. Conditions: 1000 m g / l NaCN, 25°C, pH 11, and 300 rpm, 0.3 g / l copper, powder size - 4 5 + 38 Ixm.


q

I D

(a) x 20,O00mag.

(b) x 20,O00mag. Fig. 14. FESEM photographs showing the effect of NaCN concentration on the morphology of the gold deposit on copper particles. Conditions: 25°C, pH 11,300 rpm, 20 rng/l Au(1) and (a) 100 mg/ l NaCN; (b) 1000 mg/ l NaCN.

speed on the morphology of the gold deposit on copper particles. This supports the results of experimental measurement shown in the electrochemical [7] and cementation kinetic study.

1t.1-1. Nguyen et al. / Hydrometallurgy 46 (1997) 55-69 67

(a) x 20,O00mag.

(b) x lO,O00mag. Fig. 15. FESEM photographs showing the effect of temperature on the morphology of the gold deposit on copper particles. Conditions: 1000 mg/l NaCN, pH 11,300 rpm, 20 mg/1 Au(1) and (a) 10°C and (b) 45°C.

It seems that, at high temperatures and concentrations of NaCN, the deposit structure is more open and dendritic: deposits tend to be smoother otherwise. High temperature and NaCN concentration should therefore lead to acceleration of the cementation process.

68

4. Conclusions

HH. Nguyen et al. / Hydrometallurgy 46 (1997) 55-69

The results from kinetic studies using a copper rotating disc and suspended particles show that the kinetics of cementation of gold onto copper is dependent on various factors such as cyanide concentration, temperature and solution pH. It was found that the kinetics of cementation of gold onto copper was greatly affected by the reaction temperature and the cyanide and gold concentrations. The solution pH and disc rotation speed (suspension stirring speed in the case of particles) only slightly affect the reaction kinetics. These results agree well with those measured from the previous electrochemical study. The activation energy was found to be 53.4 and 54.1 kJ/mol in the case of copper rotating disc and suspended particles, respectively, which values are close to the measured value of 56.9 kJ/mol found in the electrochemical study reported earlier.

References

[1] Hayes, G.A. and Corrans, l.J., Leaching of gold-copper ores using ammoniacal cyanide. In: Extractive Metallurgy of Gold and Base Metals (Kalgoorlie, 26-28 Oct., 1992), pp. 349-353.

[2] La Brooy, S.R., Copper-gold ore treatment options and status. Randol Gold Forum, Vancouver '92. Randol International, Golden, CO (1992), pp. 173-177.

[3] Parsons, G.J., Newcombe, L.A. and Derham, D.W., CIL gold leaching and adsorption with a deficiency in free cyanide. In: 18th Int. Mineral Processing Congr. (Sydney, 23-28 May, 1993), pp. 1205-1211.

[4] Zheng, J., Ritchie, I.M., La Brooy, S.R. and Singh, P., Study on gold dissolution in the copper-am- monia-cyanide system with a rotating electrochemical quartz crystal micrubalance. Int. Symp. on Leaching Principles and Practice, 25th CIM Annu. Hydrometallurgy Meet. (Winnipeg, Canada, Oct. 15-18, 1995).

[5] Red Dome Mines, Queensland, Australia, pers. commun. [6] Nguyen, H.H., Tran, T. and Wong, P.L.M., Copper interaction during processing of gold ores, Part 1:

Cementation of gold onto copper. Miner. Eng. (submitted). [7] Nguyen, H.H., Tran, T. and Wong, P.L.M., Copper interaction during processing of gold ores, Part 2:

Electrochemical study. Miner. Eng. (submitted). [8] Hsu, Y.J. and Tran, T., Selective removal of gold from copper-gold cyanide liquors by cementation

using zinc~ Miner. Eng., 9(1) (1996): 1-13. [9] Oo, M.T. and Tran, T., The effect of lead on the cementation of gold by zinc. Hydrometallurgy, 26

(1991): 61-74. [10] Puvvada, G., Cementation of silver ions (chloro-complexes) onto rotating copper and zinc discs from

chloride solutions. Ph.D. Thesis, Univ. New South Wales (1993). [11] Miller, J.D., Wan, R.Y. and Parga, J.R., Zinc dust cementation of precious metals from alkaline cyanide

solution. In: A.E. Torma and I.H. Gundler (Editors), Precious and Rare Metal Technologies. Elsevier, New York (1989), pp. 281-290.

[12] Anacleto, A.L. and Carvalho, J.R., Mercury cementation from chloride solutions using iron, zinc and aluminium. Miner. Eng., 9(4) (1996): 385-397.

[13] Miller, J.D., The significance of electrochemistry in the analysis of mineral processing phenomena. In: T. Tran and M. Skillas-Kazacos (Editors), Electrochemistry, Current and Potential Applications. Proc. 7th Aust. Electrochem. Conf. (1988), pp. 128-131.

[14] Miller, J.D., Cementation. In: H.Y. Sohn and Wadsworth (Editors), Rate Processes of Extractive Metallurgy. Plenum, London (1979), pp. 197-241.

[15] Von Hahn, E.A. and Ingraham, T.R., Kinetics of silver cementation on copper in alkaline cyanide solutions and perchloric acid solution. Trans. AIME, 239 (1967): 1895-1900.


[16] Nicol, M.J., Schalch, E., Balestra, P. and Hegedus, H., A modem study of the kinetics and mechanism of the cementation of gold. J. South Afr. Inst. Min. Met., (1979): 191-198.

[17] Armoo, K.B.M., Cementation of gold from bromide solutions. Ph.D. Thesis, Univ. New South Wales (1994).

[18] Oo, M.T., Study on the recovery of gold from cyanide solutions. M.Sc. Thesis, Univ. New South Wales (1990).

a kinetic study of the cementation of gold from cyanide solutions onto copper

Documents