Process for copper and/or precious metal recovery

Abstract

A process for recovery of metal comprising copper and/or a precious metal from a metal containing material, including the steps of: leaching the metal containing material with an alkaline lixiviant and an amino acid or derivative thereof in order to produce a metal containing leachate; and extracting the metal from the leachate.

Claims

1. A process for recovery of metal comprising copper and/or a precious metal from a metal containing material, including the steps of: leaching the metal containing material with an aqueous alkaline solution having a pH of at least 9 and containing a lixiviant comprising an amino acid or derivative thereof in order to produce a metal containing leachate; and extracting the metal from the leachate, wherein the amino acid comprises glycine.

2. The process of claim 1, wherein the metal comprises a precious metal and the leaching step comprises leaching a precious metal containing material with an alkaline solution containing an oxidant and the amino acid or derivative thereof at an elevated temperature in order to produce a precious metal containing leachate.

3. The process of claim 2, wherein the oxidant is a peroxide, manganese dioxide, or an oxygen containing gas.

4. The process of claim 3, wherein the oxidant is hydrogen peroxide and the amount of hydrogen peroxide in solution is at least 0.005 wt %, and is a maximum of 5 wt %.

5. The process of claim 3, wherein the leachant further includes a leaching catalyst comprising cupric (copper(II)) species, present in a concentration of at least 1mM and up to 10 mM.

6. The process of claim 2, wherein the elevated temperature is at least 30 C.

7. The process of claim 1, wherein the leaching is conducted at ambient temperature.

8. The process of claim 1, wherein the material comprises ores, concentrates or tailings.

9. The process of claim 1, wherein the process comprises heap leaching, in-situ leaching, in-place leaching, vat leaching or tank leaching.

10. The process of claim 1, wherein the amino acid derivative comprises a peptide.

11. The process of claim 1, wherein the concentration of amino acid in the leaching solution is at least 0.001 M and is a maximum of 2 M.

12. The process of claim 1, wherein the pH is within a range from 9 to 13.

13. The process of claim 1, wherein the pH is above 10.

14. A differential leaching process for recovery of copper and precious metal from a copper and precious metal containing material, including the steps of: leaching the copper and precious metal containing material with an alkaline solution containing a lixiviant comprising an amino acid or derivative thereof under first conditions comprising ambient temperature and/or the absence of an oxidant in order to produce a copper containing leachate and precious metal containing residue; leaching the precious metal containing residue with an alkaline solution containing a lixiviant comprising an amino acid or derivative thereof under second conditions comprising elevated temperature and/or the presence of an oxidant, in order to produce a precious metal containing leachate; extracting the copper from the copper containing leachate; and extracting the precious metal from the precious metal containing leachate.

15. A process for recovery of metal comprising copper and/or a precious metal from a metal containing material, including the steps of: leaching the metal containing material with an aqueous alkaline solution containing a lixiviant comprising an amino acid derivative in order to produce a metal containing leachate, wherein the amino acid derivative comprises a peptide; and extracting the metal from the leachate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Notwithstanding any other forms which may fall within the scope of the apparatus and method as set forth in the Summary, specific embodiments will now be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 is a graph showing the gold concentrations in leach solution at different leaching time (pH 10, Temperature 60 C., 1% peroxide and 1M Glycine).

(3) FIG. 2 is a graph showing gold dissolution in solutions containing different glycine concentrations and 1% hydrogen peroxide at pH 10 and temperature of 60 C.

(4) FIG. 3 is a Plot of Log ([Au]c/[Au]s) against Log t for pregnant solution after leaching for 15 days (Loading time 4 hours, Carbon 1.466 g/L).

(5) FIG. 4 is a graph showing the effect of amino acids type on gold dissolution: 0.05M amino acid, 1% H.sub.2O.sub.2, pH 11, at 60 C.

(6) FIG. 5 is a graph showing the effect of amino acids mix on gold dissolution: 0.1M amino acid, 1% H.sub.2O.sub.2, pH 11, at 60 C.

(7) FIG. 6 is a graph showing the plot of Log ([Au]c/[Au]s) against Log t for pregnant solution after leaching (Loading time 23 hours, Carbon 1.55 g/L).

(8) FIG. 7 is a graph showing the effect of silver on gold dissolution: 1M glycine, 1% H.sub.2O.sub.2, pH 10, 60 C.

(9) FIG. 8 is a graph showing the effect of temperature on gold dissolution: 1M glycine, 1% H.sub.2O.sub.2, pH 10, at different temperatures.

(10) FIG. 9 is a graph showing the effect of temperature on gold dissolution: 0.1M glycine, 1% H.sub.2O.sub.2, initial pH 11.5, at different temperatures.

(11) FIG. 10 is a graph showing effect of temperature on gold dissolution rate over leaching time: 0.1M glycine, 1% H.sub.2O.sub.2, initial pH 11.5, at different temperatures.

(12) FIG. 11 is a graph showing the effect of hydrogen peroxide concentration on the measured E.sub.h of the leach solution: 0.1 M glycine, different percentages of H.sub.2O.sub.2, pH 11.5, 60 C.

(13) FIG. 12 is a graph showing the effect of hydrogen peroxide concentration on gold dissolution: 0.1M glycine, different percentages of H.sub.2O.sub.2, pH 11.5, 60 C.

(14) FIG. 13 is a graph showing the effect of leaching solution pH on gold dissolution: 0.5M glycine, 1% H.sub.2O.sub.2, pH, at 60 C.

(15) FIG. 14 is a graph showing the effect of leaching solution pH on gold dissolution: 0.1M glycine, 1% H.sub.2O.sub.2, pH, at 60 C.

(16) FIG. 15 is a graph showing the effect of Cu.sup.2+ ions on gold dissolution: 0.1M glycine, 0.1% H.sub.2O.sub.2, pH 11, at 30 C.

(17) FIG. 16 is a graph showing the effect of Cu.sup.2+ ions on gold dissolution: 0.1M glycine, 0.3% H.sub.2O.sub.2, 4 mM Cu.sup.2+, pH 11.9 and 30 C.

(18) FIG. 17 is a graph showing the effect of pyrite on gold dissolution from glycine-peroxide solutions: 0.1M amino acid, 1% H.sub.2O.sub.2, pH 11, at 60 C.

(19) FIG. 18 is a graph showing gold dissolutions in recycled barren solutions containing initially 1M glycine and 1% peroxide at 60 C. and pH 10.

(20) FIG. 19 is a graph showing gold dissolutions in fresh and aged solutions containing initially 1M glycine and 1% peroxide at 60 C. and pH 10.

(21) FIG. 20 is a graph showing gold leaching rates in solutions containing initially 1M glycine and 1% peroxide at 60 C. and pH 10.

(22) FIG. 21 is a graph showing gold concentration in solution containing 1M glycine, 1% peroxide, 5 mM Cu(II) at 40 C. and pH 10.

(23) FIG. 22 is a graph showing gold leach rate in solution containing 1M glycine, 1% peroxide, 5 mM Cu(II) at 40 C. and pH 10.

(24) FIG. 23 is a graph showing Log ([Au]c/[Au]s) against Log t for pregnant solution after leaching for 15 days (Loading time 4 hours, Carbon 1.466 g/L).

(25) FIG. 24 is a graph showing mass % of Copper minerals in a copper concentrate before and after leaching in glycine solutions (Leaching conditions: two-stages, 0.3 M glycine, 1% peroxide, room temperature, pH 11, 48 hours).

(26) FIG. 25 is a schematic diagram for two-stage counter-current copper leach process.

(27) FIG. 26 is a graph showing copper extraction (%) against leaching time (hours) from CuAu concentrate after two-stages leaching.

(28) FIG. 27 is a graph showing mass % of copper minerals in a copper concentrate before and after leaching in glycine solutions (Leaching conditions: one-stage, 0.4 M glycine, 1% peroxide, room temperature, pH 11.5, 96 hours).

(29) FIG. 28 is a graph showing copper extraction (%) against leaching time (hours) at different solution pHs (0.3M glycine, 1% H.sub.2O.sub.2, room temperature).

(30) FIG. 29 is a graph showing copper extraction (%) against leaching time (hours) at different peroxide concentrations (0.3M glycine, pH 11, room temperature, 10% pulp density).

(31) FIG. 30 is a graph showing copper extraction (%) against leaching time (hours) at different pulp densities (0.3M glycine, 1% H.sub.2O.sub.2, pH 11, room temperature).

(32) FIG. 31 is a graph showing copper extraction (%) against leaching time (hours) at different glycine concentrations (1% H.sub.2O.sub.2, pH 11, room temperature, 10% pulp density).

EXAMPLES

(33) Non-limiting Examples of a process for recovery of copper or precious metal from a copper and/or precious metal containing material will now be described.

Examples 1 to 15

Recovery of Precious Metal

(34) All of Examples 1 to 15 were carried out using solutions prepared from either analytical grade or synthesized reagents and Millipore water. Unless specified, all Examples were conducted using magnetic stirrers and Teflon coated magnetic stirrer bars. The gold and/or silver was added to a solution of amino acid and peroxide in a beaker and heated to the required temperature while stirring. Gold and gold-silver sheets used in all the examples were made from 99.99% pure gold and silver. Before each experiment, the surface of the each sheet was polished with Struers waterproof silicon carbide paper (FEPA P#2400). Finally the gold sheet was washed with distilled water and allowed to dry.

(35) For testing the carbon activity to adsorb gold-glycine complex, unless specified, 1.5 g/L of fresh carbon (2.36+2 mm) was added into the pregnant solutions after leaching. The adsorption experiments have been conducted at room temperature at rotation speed of 150 rpm. In order to evaluate the gold adsorption on carbon, sub-samples were taken at different time intervals and then diluted with aqueous sodium cyanide before being analysed using ICP-OES.

Example 1

(36) In Example 1, a solution containing 1M of the amino acid: glycine, and 1% of the oxidant, hydrogen peroxide, was used to dissolve pure metallic gold (as gold wire and gold foils) at a temperature of 60 C. FIG. 1 shows the amount of gold dissolved in solution (400 mL) containing 1M of glycine and 1% of peroxide over leaching time. It can be seen that gold dissolves under these conditions in reasonable amounts of up to 18 mg/L in 280 hours. In this example, lower reagents concentrations (0.1-0.4 M glycine), lower temperature (i.e. 40 C.) and natural pH of the solution (about pH 6) were also shown to be effective.

Example 2

Effect of Glycine Concentration

(37) The kinetics of gold dissolution in solutions containing different glycine concentrations and 1% hydrogen peroxide at pH 10 and temperature of 60 C. was studied and the results are plotted in FIG. 2. It can be seen from the results shown in FIG. 2 that, under the conditions of this Example, gold dissolution increases by increasing the glycine concentration up to 1 M. Table 1 shows the gold leach rate at different glycine concentrations.

(38) TABLE-US-00002 TABLE 1 Gold leach rate at different glycine concentrations: Glycine, 1% H.sub.2O.sub.2, pH 10, 60 C. Glycine, M Au, 10.sup.3 mol/m.sup.2 .Math. s 0.30 11.3 0.50 16.9 1.00 31.3

(39) The gold leaching rate in glycine-peroxide system as shown in Table 1 can be significantly higher than the rates using thiosulfate-ferric oxalate and ferric EDTA systems in the absence of thiourea.

Example 3

Gold-Glycinate Complex Adsorption on Carbon

(40) One of the considerations for an alternative to cyanide-based leaching of gold is the strength of adsorption of the leached gold on activated carbon. Therefore, it is appropriate to examine the ability of activated carbon to adsorb gold-glycine complex from the leach solution particularly from an industrial application perspective.

(41) Following some of the kinetic leach experiments, different amounts of fresh carbon were added into the pregnant leach solutions. Sub-samples from different adsorption tests were taken at different intervals and analysed by ICP-OES. The kinetics of gold and silver adsorption onto activated carbon have been evaluated by the determination of the carbon activity constant using Equation (1):
log(delta[Au or Ag]c/[Au or Ag]s)=n log t+log k(1)
delta [Au or Ag]c=change in [Au or Ag] on carbon from t=0 to t=t hours; [Au or Ag]s=[Au or Ag] in solution at t=t hours; n=an experimentally derived constant for the slope of the above equation; and k=an empirical rate constant at t=1 hour;

(42) The adsorbed gold and silver on carbon and the amounts of metals in solutions have been calculated and presented in Tables 2, 3, and 4.

(43) FIG. 3 also shows the plot of Log ([Au]c/[Au]s) against (Log t) for the data shown in Table 3. The adsorption experiments showed that the gold-glycine complex using the process of the disclosure is adsorbed onto the activated carbon in a rate similar or even higher than gold-cyanide complex.

(44) It can also be seen from the data shown in Tables 3 and 4 that the silver-glycinate complex is less well adsorbed on the activated carbon and the presence of silver enhances gold loading on carbon.

(45) TABLE-US-00003 TABLE 2 Adsorption of gold on activated carbon from pregnant solution after leaching for 456 hours (Solution volume 350 mL). Time Time [Au] [Au]c/ log([Au]c/ (min) (hr) (mg/L) [Au]s [Au]c [Au]s Log t [Au]s) 0 0.00 15.5 30 0.50 11.6 3.882 2649 229 0.301 2.359 60 1.00 9.96 5.504 3701 372 0.000 2.570 120 2.00 8.14 7.321 4852 596 0.301 2.775 240 4.00 6.47 8.993 5872 908 0.602 2.958

(46) TABLE-US-00004 TABLE 3 Adsorption of gold on activated carbon from pregnant solution after leaching a gold/silver alloy for 168 hours (Solution volume 380 mL). Time Time [Au] [Au]c/ Log([Au]c/ (min) (hrs) mg/L [Au]s [Au]c [Au]s log t [Au]s) 0 0.00 38.70 30 0.50 24.60 14.097 6565 267 0.301 2.426 96 1.60 15.82 22.882 10656 674 0.204 2.828 180 3.00 12.08 26.616 12395 1026 0.477 3.011 240 4.00 10.26 28.435 13242 1290 0.602 3.111

(47) TABLE-US-00005 TABLE 4 Adsorption of silver on activated carbon from pregnant solution after leaching a gold/silver alloy for 168 hours (Solution volume 380 mL). Time Time [Ag] [Ag]c/ log([Ag]c/ (min) (hrs) mg/L [Ag]s [Ag]c [Au]s Log t [Au]s) 0 0.00 56.1 30 0.50 48.1 8.079 3683 77 0.301 1.884 96 1.60 42.7 13.412 6114 143 0.204 2.156 180 3.00 39.1 17.028 7763 198 0.477 2.298 240 4.00 37.0 19.108 8711 235 0.602 2.371

Example 4

Effect of Amino Acids Type

(48) Glycine, histidine and alanine amino acids have been used to test the effect of amino acid type on gold dissolutions. The experiments have been conducted at 0.05 M of amino acids at pH 11 and 60 C. temperature. FIG. 4 shows the gold dissolution in different amino acids system. It can be seen that the initial gold dissolution in histidine solution is faster than glycine and alanine solutions, however, by extending the leaching, it was found glycine dissolves gold faster and to a greater extent than histidine and alanine.

(49) To evaluate the effect of amino acid mixtures, a mixture of 0.05 M Glycine and 0.05 M histidine, 1% H.sub.2O.sub.2, at pH 11.5 and 60 C. was assessed. FIG. 5 shows the effects of using a combination of glycine-histidine solutions and glycine only on gold dissolution. It is clear that using a mix of glycine and histidine dissolves gold higher than using glycine only.

(50) The Kinetics of gold adsorption onto activated carbon from glycine-histidine solutions has been evaluated by the determination of the carbon activity constant using Equation (2). The adsorbed gold on carbon and the amounts of metals in solutions have been calculated and presented in Table 5.

(51) $\begin{array}{cc}\frac{\log \left({\left[\mathrm{Au}\mathrm{or}\mathrm{Ag}\right]}_c\right)}{{\left[\mathrm{Au}\mathrm{or}\mathrm{Ag}\right]}_s}=n\log t+\log k& \left(2\right)\end{array}$

(52) [Au or Ag].sub.c=change in Au or Ag on carbon from t=0 to t=t hours; [Au or Ag].sub.s=Au or Ag in solution at t=t hours; n=an experimentally derived constant for the slope of the above equation; and k=an empirical rate constant at t=1 hour.

(53) FIG. 6 also shows the plot of Log ([Au]c/[Au]s) against (Log t) for the data shown in Table 5. The adsorption experiment shows that gold from solution containing glycine-histidine is adsorbed onto the activated carbon. The calculated carbon activity constant was 188 and the gold loading was 5.5 kg Au/ton of carbon. From the data shown in Table 5 and FIG. 6, it can be noticed that gold can be loaded onto carbon from solutions containing a mix of glycine-histidine solution.

(54) TABLE-US-00006 TABLE 5 Adsorption of gold on activated carbon from glycine-histidine solutions. Time Time [Au] [Au]c/ Log([Au]c/ (min) (hr) (mg/L) [Au]s [Au]c [Au]s Log t [Au]s) 0 0 24.084 0.000 0 0 30 0.5 19.143 4.941 2471 129 0.301 2.111 80 1.33 16.656 7.428 3714 223 0.124 2.348 150 2.5 15.03 9.054 4527 301 0.398 2.479 270 4.5 13.173 10.911 5456 414 0.653 2.617 1380 23 8.34 15.744 7872 944 1.362 2.975

Example 5

Effect of Silver

(55) To study the effect of silver on gold dissolution, foils (surface area 20 cm.sup.2) of pure gold and 50% gold-50% silver have been leached in the solutions containing glycine and peroxide. Gold and silver dissolution from pure gold and gold-silver alloy are shown in FIG. 7. It can be seen that the presence of silver enhances gold dissolution and silver dissolves faster than gold in glycine solution.

(56) Table 6 show the gold and silver leach rate after 168 hours from pure gold and 50% gold-50% silver. It can be seen that gold leach rate from gold-silver alloy is about 6 times higher than rate from pure gold. Silver leach rate is higher than gold in glycine-peroxide solutions.

(57) TABLE-US-00007 TABLE 6 Gold and silver leach rates from pure gold and gold-silver alloy: Glycine, 1% H.sub.2O.sub.2, pH 10, 60 C. Au, Ag Source Au, 10.sup.3 mol/m.sup.2 .Math. s Gold from (pure gold sheet) 31.3 Gold (from 50% Au50% Ag) 185 Silver (from 50% Au50% Ag) 247

Example 6

Effect of Temperature

(58) The effect of temperature on gold dissolution is shown in FIGS. 8, 9 and 10.

(59) FIG. 8 shows the effect of temperature on the kinetics of gold leaching in a solution containing 1M glycine, 1% H.sub.2O.sub.2, at pH 10. It can be seen that gold dissolution increases dramatically as the temperature increases from 23 to 60 C.

(60) FIG. 9 shows the effect of temperature on the kinetics of gold leaching at 0.1M glycine concentration at temperatures of 23, 30, 40, 60 and 75 C. Clearly, it can be seen that gold dissolution increases dramatically as the temperature increases. However at high temperature (75 C.) it was found that the initial gold dissolution is faster but the gold leach rate decreases rapidly.

(61) Gold leaching is a chemically controlled process in which temperature mostly affects the reaction rate. The most interesting results shown in FIG. 9 that after 264 h of leaching at room temperature, gold dissolution rate increased dramatically once the temperature has been raised to 60 C.

(62) FIG. 10 illustrates the gold dissolution rates over leaching time at different temperatures. It can be seen that at elevated temperature gold leach rate initially increases then starts to decrease by extending the leaching time. The average rate of gold dissolution after six days of leaching at 75 C. was 3910.sup.3 mol/m.sup.2.Math.s, which is higher than the gold leach rate of 210.sup.3 mol/m.sup.2.Math.s from ferric-thiosulfate system in the absence of thiourea.

Example 7

Effect of Peroxide

(63) The solution's pH and E.sub.h over time has been monitored using 90-FLMV meter. FIG. 11 shows the E.sub.h profiles of the glycine-hydrogen peroxide solutions over time at different hydrogen peroxide concentrations. It is clear to see from the results shown in FIG. 12 that the hydrogen peroxide significantly enhanced the gold dissolution. A minimum of 0.1% peroxide resulted in gold dissolution and increasing the hydrogen peroxide concentration up to 2% peroxide significantly enhances the gold dissolution.

Example 8

Effect of pH

(64) The effect of pH (by adding hydroxide ions) on the gold dissolution is shown in FIGS. 13 and 14. It can be seen the glycine-peroxide system is very sensitive to the leaching pH and hydroxide ions and it can be seen that gold dissolution increases significantly by increasing the leaching pH to above pH=10.

(65) FIG. 13 shows the effect of pH on gold leaching rate in solutions containing 0.5 M glycine and 1% peroxide at leaching temperature of 60 C. After only 24 hours of leaching at pH 11, the gold leaching rate was 0.35 mol/m.sup.2.Math.s. This leaching rate is higher than the gold leaching rate (0.22-0.25 mol/m.sup.2.Math.s) from 100 mM thiosulfate solutions in the presence of ferric oxidant and thiourea. Table 7 shows the gold leaching rate after different leaching times at pH 5.8, 10 and 11. The data show that gold leach rate at pH 11 is 30 times higher than the rate at pH 10 after 48 hours. However, it was found that the leach rate decreases by increasing leaching time at pH 11. The initial gold leaching rate at natural pH of solution (pH 5.8) was faster than leaching at pH and decreased by extended the leaching time.

(66) TABLE-US-00008 TABLE 7 Gold leach rate at different leaching pH: 0.5M Glycine, 1% H.sub.2O.sub.2, pH, 60 C. Au, 10.sup.3 mol/m.sup.2 .Math. s Leaching time, hr pH 5.8 pH 10 pH 11 24 8.11 0.59 352 29 8.75 1.30 367 48 5.13 11.47 322 119 4.19 14.34 174 167 3.02 16.93 142

(67) The effect of adding hydroxide ions, hence, pH of solutions on the gold dissolution for a solution containing 0.1M glycine, 1% H.sub.2O.sub.2, at 60 C. is shown in FIG. 14. Again, it was found that gold dissolution in glycine-peroxide solutions is very sensitive to the leaching pH and hydroxide ions. Gold dissolution increases significantly by increasing the leaching pH to higher alkalinity.

(68) Gold leaching rate is enhanced at pH higher than 10, preferably higher than 11 in solutions containing 0.1 M glycine and 1% peroxide at leaching temperature of 60 C.

(69) From the results shown in FIG. 14, it can be seen that adding some more peroxide into the system enhances gold dissolution. Table 8 shows the required amounts of caustic in mM to reach the targeted pH.

(70) TABLE-US-00009 TABLE 8 Required NaOH to achieve the targeted pH of the leach solution. Required NaOH Leaching pH (mM) 6.10 0 10.10 47.5 11.50 125.0 12.00 175.0 12.80 293.0

Example 9

Effect of Cu2+

(71) It has been found that adding Cu.sup.2+ to glycine-peroxide system enhances gold dissolution. FIG. 15 shows how the presence of Cu.sup.2+ ions enhances gold dissolution in glycine-peroxide system, in a solution containing 0.1M glycine, 1% H.sub.2O.sub.2, pH 11 at 30 C.

(72) An additional test has been conducted to study the effect of Cu.sup.2+ ions on gold dissolution glycine-peroxide system by increasing the leaching pH to 11.9 and peroxide concentration to 0.3%. The amounts of dissolved gold from this system against leaching are shown in FIG. 16. A comparison between the results of FIG. 15 in the presence of Cu.sup.2+ and FIG. 16 indicates that increasing pH and peroxide enhances gold dissolution. The gold-glycine solution in the presence of Cu.sup.2+ ions has been successfully loaded onto activated carbon.

Example 10

Effect of Pyrite

(73) Gold ore bodies may contain different gangue minerals of different reactivity; one of the most reactive minerals associated with gold is pyrite. To study the effect of pyrite, different amounts of pyrite minerals were added to the leach solution prior to gold sheet addition. FIG. 17 shows the effect of pyrite on gold dissolution in solutions containing pyrite (FeS.sub.2). It is clear that gold dissolution in the presence of pyrite is lower than the measure in the absence of pyrite. The decrease in gold dissolution may be attributed to the consumption of peroxide to oxidise pyrite, or catalytic decomposition on the pyrite surface.

Example 11

Activity of Recycled Solution

(74) Leaching tests were conducted using a recycled barren solution after gold and silver adsorption. A once or twice recycled barren solution was used to leach pure gold sheet of 1 cm width and 10 cm length. The results of these tests are shown in FIG. 18. It can be seen that the recycled leach solution leaches gold very effectively over time. The results shown in FIG. 18 illustrate that the leachant and process are robust in terms of reagent stability over time.

Example 12

Effect of Solution Aging

(75) A solution of 1M of glycine and 1% of peroxide has been left 4 days at room temperature. After aging, gold was added into the aged solution and samples were taken frequently and analysed for gold using ICP-OES. The results of gold leaching in fresh and aged solutions are shown in FIG. 19.

(76) The results illustrate that gold dissolves faster with a higher leaching rate in the aged solution than the fresh solution. Gold leach rate in aged solution and fresh solutions after 215 hours was 0.045 and 0.032 mol/m.sup.2.Math.s respectively. FIG. 20 shows the gold leach rate during 264 hours leaching in a solution containing 1M of glycine and 1% of peroxide. It is interesting to see that gold leach rate increases over leaching time.

Example 13

pH and Eh Over Time

(77) The electrochemical potential (Eh) and pH of the leach solution were measured over 19 days of leaching. Table 9 shows the values of pH and Eh over time for 456 hours of leaching. It can be seen that pH and Eh are reasonably stable over this time, again indicating the reagent stability.

(78) TABLE-US-00010 TABLE 9 pH and Eh over leaching time in solutions containing 1M glycine and 1% peroxide at 60 C. Time, hr pH E.sub.h (mV) 3 9.3 128 23 9.3 117 48 9.25 112 167 9.21 117 215 9.24 118 287 9.19 115 384 9.18 121 456 9.21 115

Example 14

Extended Leaching Time at 40 C

(79) In this experiment, a solution containing 1M of glycine, 1% of hydrogen peroxide and 5 mM Cu(II) has been used at temperature of 40 C. Pure metallic gold as gold foil of 36 cm.sup.2 surface area has been used in this example. FIG. 21 shows the amount of dissolved gold in solution (400 mL) containing 1M of glycine, 1% of hydrogen peroxide and 5 mM Cu(II). It can be seen that gold also dissolves at this condition in reasonable amounts.

(80) The most interesting results from this example are that gold leach rate increases over time (most of the gold leaching alternatives processes showed decreasing gold leach rate over time). These results reflect the robust stability of the reagents in the leach solution. The experiment was left run for about 14 days (334 hours). FIG. 21 shows the amount of dissolved gold in leach solution over time and FIG. 22 shows gold leaching rate in g/cm.sup.2.Math.day over the whole period of leaching. In this robust system, solution pH did not change over 14 days leaching time and the Eh was fluctuating between 50 mV to 40 mV.

Example 15

Adsorption of Gold on Activated Carbon

(81) Different amounts of activated carbon were added into the leach pregnant solutions from Examples 12 and 13. Samples from different adsorption tests were taken at intervals and analysed by ICP-OES. The adsorbed gold on carbon and the amounts of gold in solutions have been calculated and presented in Tables 10, 11, and 12.

(82) The Kinetics of gold and silver adsorption onto activated carbon has also been evaluated by the determination of the carbon activity constant using the following equation (3):
log(delta[Au or Ag]c/[Au or Ag]s)=n log t+log k(3)

(83) Where: delta [Au or Ag]c=change in [Au or Ag] on carbon from t=0 to t=t hours [Au or Ag]s=[Au or Ag] in solution at t=t hours n=an experimentally derived constant for the slope of the above equation. k=an empirical rate constant at t=1 hour r2=the correlation coefficient of the above equation

(84) As an example to show the activity of gold adsorption onto carbon, FIG. 23 shows the plot of Log ([Au]c/[Au]s) against (Log t) for the data shown in Table 10.

(85) The different adsorption experiments indicate that the leached gold using the process of the disclosure could be adsorbed onto activated carbon at a similar rate as gold cyanide complexes.

(86) It can also be seen from the data shown in Tables 11 and 12 that silver is slightly adsorbed on the activated carbon and the presence of silver enhances gold loading on carbon.

(87) TABLE-US-00011 TABLE 10 Adsorption of gold on activated carbon from pregnant solu- tion after leaching for 456 hours (Solution volume 350 mL). Carbon dry weight 0.513 g Loading (4 hrs) = 6.2 Kg/t log Time Time [Au]c/ [Au]c/ min (hrs) [Au] mg/L [Au]s [Au]c [Au]s Log t [Au]s 0 0.0 15.5 0.000 0 0 30 0.5 11.6 3.882 2649 229 0.301 2.359 60 1.0 9.96 5.504 3701 372 0.000 2.570 120 2.0 8.14 7.321 4852 596 0.301 2.775 240 4.0 6.47 8.993 5872 908 0.602 2.958

(88) TABLE-US-00012 TABLE 11 Adsorption of gold on activated carbon from pregnant solution after leaching gold/silver al- loys for 168 hours (Solution volume 380 mL). Carbon dry weight 0.816 g Loading (4 hrs) = 10.5 Kg/t log Time Time [Au] [Au]c/ [Au]c/ (min) (hrs) mg/L [Au]s [Au]c [Au]s Log t [Au]s 0 0.00 32.54 0.000 0 0 30 0.50 24.33 8.210 3823 157 0.301 2.196 96 1.60 15.87 16.670 7763 489 0.204 2.689 180 3.00 11.55 20.990 9775 846 0.477 2.928 240 4.00 9.78 22.760 10599 1084 0.602 3.035

(89) TABLE-US-00013 TABLE 12 Adsorption of silver on activated carbon from pregnant solution after leaching gold/silver al- loys for 168 hours (Solution volume 380 mL). Carbon dry weight 0.816 g Loading (4 hrs) = 1.54 Kg/t Time Time [Ag] [Ag]c/ log[Ag]c/ (min) (hrs) mg/L [Ag]s [Ag]c [Ag]s Log t [Ag]s 0 0.00 59.51 0.000 0 0 30 0.50 56.32 3.190 1454 26 0.301 1.412 96 1.60 54.33 5.180 2361 43 0.204 1.638 180 3.00 52.43 7.080 3228 62 0.477 1.789 240 4.00 51.59 7.920 3611 70 0.602 1.845

Examples 16 to 21

Recovery of Copper

(90) The following Examples 16 to 21 detail the recovery of copper from a copper-gold gravity concentrate. However, it is to be understood that the process of the present disclosure is not limited to recovery of copper from copper-gold concentrates, and can be also applied to the recovery of copper from other copper containing materials, such as copper ore concentrates that do not contain gold.

(91) A copper-gold gravity concentrate was produced from the cyclone underflow feeding into a batch centrifugal gravity separator at a copper-gold plant in Western Australia. The gravity concentrate conveniently concentrated many non-sulphide minerals of copper, and native copper, as well as sulphide minerals, with gold to provide a wide distribution of copper mineralogy. The gravity concentrate sample was then ground using a disc mill and screened using 150 and 106 m screens. The +150 m was recycled back to the mill.

(92) The particle size of the ground sample used in the leaching experiments was 100% 150 m and 80% 106 m. The sample was sent for elemental analysis using acid digestion followed by solutions analysis for different metals using inductively coupled plasma optical emission spectrometry (ICP-OES). The mineralogical compositions of the gravity concentrate before and after leaching were analysed by an integrated automated mineralogy solution providing quantitative analysis of minerals using quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) technique.

(93) All Examples were carried out using solutions prepared from analytical grade reagents and Millipore water. Unless specified, all experiments are conducted using a bottle roller in accordance with conventional laboratory practice. The concentrate and glycine solution were placed in a 2.5 L Winchester bottle. The slurry was agitated by rolling the bottle on a bottle roll at 150 rpm. Bottles were vented to allow for oxygen transfer, ensuring that a lack of oxygen did not limit the reaction rate.

(94) At different times, samples of the leach solution were obtained using a syringe-membrane filter (pore size 0.45 m). The filtrates were analysed for copper and iron by using atomic adsorption spectroscopy. The trace elements were analysed using inductively coupled plasma optical emission spectrometry (ICP-OES). The elemental analysis of residue was conducted using acid digestion followed by ICP-OES analysis.

(95) From the data shown in Table 13, it can be seen that of the common copper minerals, chalcopyrite (CuFeS.sub.2) is the least soluble in cyanide and other copper oxides and native copper show high solubility in cyanide solutions.

(96) TABLE-US-00014 TABLE 13 Solubility of Cu Minerals in 1% NaCN Solution % Copper Mineral Formula dissolved Azurite 2Cu(CO).sub.3Cu(OH).sub.2 94.5 Malachite 2CuCO.sub.3(OH).sub.2 90.2 Chalcocite Cu.sub.2S 90.2 Covellite CuS 95.6 Chalcopyrite CuFeS.sub.2 5.60 Native Copper Cu 90.0 Cuprite Cu.sub.2O 85.5 Bornite FeS2Cu.sub.2S 70.0 Enargite Cu.sub.3AsS.sub.4 65.8 Tetrahedrite (CuFeAgZn)12Sb.sub.4S.sub.13 21.9 Chrysocolla CuSiO.sub.3(nH.sub.2O) 11.8

(97) Table 14 shows the elemental analysis of the copper-gold concentrate used in Examples 16 to 21. The copper-gold concentrate has 3.75% Cu distributed amongst a range of copper minerals, including native copper.

(98) TABLE-US-00015 TABLE 14 Elemental analysis of the copper-gold concentrate Concentration (%) Sample ID Au Ag Cu As Fe Si Ni Al K Co Pb S Conc. 0.213 0.03 3.75 0.76 11.6 27.0 0.06 2.0 0.69 0.34 0.12 11.4

Example 16

Two-Stage Leaching

(99) The experiments showed that 98% of Cu was extracted in 48 hours in a two stage leach under the following conditions: 0.3 M Glycine, 1% H.sub.2O.sub.2, pH 11.0, 23 C. and 16% (% w/v) pulp density. The mineralogical compositions of the copper-gold concentrate before and after leaching were analysed by QEMSCAN are shown in Table 15. FIG. 24 shows also the mass percentages for each copper mineral in the concentrate before and after leaching. The results presented in FIG. 24 show that 100% of the metallic copper and sulfide copper minerals, such as bornite and chalcocite/digenite, were dissolved. About 80% of chalcopyrite was dissolved. QEMScan analysis of the residue showed that the unleached chalcopyrite occurred as liberated particles in the largest size fraction.

(100) TABLE-US-00016 TABLE 15 The mineralogical analysis of copper and gangue minerals in the concentrate before and after leaching (Leaching conditions: 0.3M Glycine, 1% H.sub.2O.sub.2, pH 11, room temperature) Bulk Mineralogy, Mass % Mineral Before Leaching After leaching Chalcocite/digenite 1.46 0.01 Cu-metal 1.30 0.00 Cuprite 0.88 0.00 Chalcopyrite 0.71 0.15 Bornite 0.27 0.02 Covellite 0.18 0.12 Exotic complex Cu- 0.09 0.00 sulphides Cu boundaries 0.34 0.02 Pyrite 28.55 32.33 Pyrrhotite 0.35 0.20 Arsenopyrite 0.01 0.00 Quartz 48.49 51.28 Feldpars 5.32 5.59 Calcite 0.12 0.10 Dolomite 0.09 0.11 Ankerite/Dolomite 0.78 0.61 Rutile/Anatase/Ilmenite 0.52 0.75 Hematite 0.69 1.71 Goethite 2.72 2.21 Other 7.16 4.75

(101) Table 16 presents the percentage of each copper mineral dissolved after leaching in glycine solution. The presence of covellite (CuS) in the final residue may be attributed to the re-precipitation of copper during leaching according to Eq. (2). The formation of covellite (CuS) during the leaching of copper sulfide minerals, such as chalcopyrite, has been identified by some studies. It can be concluded that covellite dissolves in the leach solutions and re-precipitates by the reaction of copper with either sulfur or sulfide during the leaching.
Cu+S.sup.0.fwdarw.CuS or
Cu.sub.2S.fwdarw.CuS+Cu.sup.2+2e.sup.(4)

(102) TABLE-US-00017 TABLE 16 The observed dissolution of copper minerals in 0.3M glycine solution at room temperature, 1% H.sub.2O.sub.2, pH 11. Cu dissolution, Mineral % Chalcocite/digenite 100 Cu-metal 100 Cuprite 100 Chalcopyrite 80 Bornite 92 Covellite 19 Exotic complex Cu- 99 sulphides Cu boundaries 95

(103) FIG. 25 shows the schematic diagram of a conceptual two-stage counter-current copper leach circuit, indicated generally by reference numeral 10. In order to achieve a high copper dissolution, the leaching can be conducted in two stages 12, 14 (such as by using two leaching reactors) with identical leaching conditions in each stage. At the steady state, fresh CuAu concentrate 16 will feed the first stage 12 and fresh (make up) leaching solution 18 will feed the second stage 14. The leached slurry exiting stage 12 is subjected to a first solid/liquid separation, 20, to produce a first copper pregnant leach solution, 22, and solid leach residue, 24. The residue 24 is fed to the second leach stage 14. The leached slurry exiting the second leach stage 14 is subjected to a second solid/liquid separation, 32, to produce the gold concentrate, 34 and a second copper PLS, 36. The second PLS is recycled to the first leach stage 12 as leach solution. The copper containing pregnant leach solution, 22, is subjected to electrowinning, 26, and recovery of copper, 28. The barren solution 30 from the electrowinning step 26 is recycled as process solution for the second leach stage 14. Table 18 shows the copper and other impurities concentrations in the final leach solution from stages 1 and 2.

(104) TABLE-US-00018 TABLE 17 Copper and impurities concentrations in stage 1 and 2 final leach solutions Concentration (mg/L) Sample ID Cu Au As S Fe Si Ni Co Pb K Mg Ca STAGE1 4745 0.85 24.7 185 12.1 9.14 5.21 3.14 16.4 14.8 14.4 25.1 STAGE2 1069 1.28 29.4 146 6.69 6.45 4.34 2.27 10.2 9.2 2.99 14.1

(105) About 98% of copper was leached using 0.3 mol/L glycine at room temperature with only about 12 mg/L Fe, 16 mg/L Pb and low impurities concentration transferred into the pregnant solution. It appears that iron does not dissolve significantly in the alkaline glycine solutions.

(106) FIG. 26 shows the copper dissolution as a function of time after leaching in two stages. It can be seen that more than 98% of copper has been dissolved. It can also be observed that, after 5 hours leaching, copper extraction is about 66% of copper and this initial rapid dissolution of copper is due to the presence of the highly soluble cuprite and metallic copper in the concentrate.

Example 17

Single Stage Leaching

(107) In this section, leaching of a copper-gold concentrate is performed in a single stage by increasing glycine concentration from 0.3 M to 0.4 M and extending the leaching time to 96 hours. FIG. 27 shows the mass percent of the copper minerals analysed by QEMSCAN before and after leaching for a comparison. From the copper concentration in the final leach solution, and copper in the final residue, the copper extraction was 82%. From the results shown in FIG. 27, it is apparent that 100% of chalcocite, cuprite, metallic copper, and only 50% of chalcopyrite have been dissolved. It is interesting to observe that, as shown in FIG. 27, copper has been re-precipitated as a covellite (CuS) or as very fine copper either adsorbed on clays or incorporated in the silicates (Cu-boundaries).

Example 18

Effect of pH

(108) The effect of leaching solution pH on copper dissolution is shown in FIG. 28. It can be seen the initial copper dissolution at lower pH (pH 8.0) is higher than the dissolution at pH 10 and 11.5. However, by extending the leaching time it was found that the copper dissolution increases at more alkaline pH (eg, pH 11.5). From the results shown in FIG. 28, it can be observed that copper dissolution slightly increases by increasing the leaching pH from pH 10 to pH 11.5.

Example 19

Effect of Peroxide

(109) To study the effect of using peroxide as an oxidant on copper leaching in glycine solution, 0%, 1% and 2% of peroxide were added to 0.3M glycine solution at room temperature. The results shown in FIG. 29 show that peroxide slightly increases copper dissolution.

(110) The most interesting result here is that copper extraction reaches up to 75% in a solution containing only glycine (no peroxide) on a vented bottle roll that allows enough oxygen transfer from surrounding air.

Example 20

Effect of Pulp Density

(111) To study the effect of pulp density on copper leaching in glycine solution, 10, 16 and 20% pulp densities were used. The effect of pulp density on copper dissolution is shown in FIG. 30. Increasing the pulp density from 10% to 20% decreases the copper extraction by about 10%. It is believed that the decrease of copper extraction at a higher pulp density can be attributed principally to the efficiency of oxygen transfer to the leach solution.

Example 21

Effect of Glycine Concentration

(112) The effect of glycine concentration on the copper dissolution is shown in FIG. 31. It is clear that by increasing the glycine concentration, the copper extraction slightly increases. It can be generally reported that copper dissolution depends on the concentration of glycine in the glycine-peroxide solutions.

(113) In the claims which follow, and in the preceding description, except where the context requires otherwise due to express language or necessary implication, the word comprise and variations such as comprises or comprising are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the apparatus and method as disclosed herein.

(114) Further patent applications may be filed in Australia or overseas on the basis of, or claiming priority from, the present application. It is to be understood that the following provisional claims are provided by use of example only and are not intended to limit the scope of what may be claimed in any such future applications. Features may be added to or omitted from the provisional claims at a later date so is to further define or re-define the invention or inventions.