Application examples of thiosulfate gold extraction

When using gold cyanide solution treated ore containing copper, manganese or copper and manganese, because the presence of copper and manganese, severely reducing the precious metal recovery, and increase cyanide consumption, so that the economic indicators of gold in I am in trouble. The gold is also extracted from the ore containing carbon and organic compounds. The cyanide plant also has some problems, namely the presence of carbonaceous materials in the gold ore, which makes it difficult for gold to be released from the carbon matrix. This is due to the price of gold. The cyano complex is preemptively adsorbed by carbon and subsequently lost to the tailings. This section describes examples of treatment of the above ore with thiosulfate and treatment of tailings and low-grade ore.
1) Leaching gold from copper-bearing gold concentrate
A domestic gold concentrate, gold-bearing minerals are chalcopyrite, pyrite and bornite. The main chemical composition: Au 50g / t, Cu 3.19%, Fe ₂ 0 ₃ 28.9%, MnO 0. 048%, Co 0. 042%, Pb <0.03%, Zn 0.10%, S 20.59%, Si0 ₂ 37.75% , A1 ₂ 0 ₃ 5.75%, concentrate particle size 100% ~ 100 mesh, in the slurry solid ratio of 3:1 and 40 °C, with a concentration of 0.8 ~ 1.0 mol / L of Na ₂ S ₂ 0 ₃ , 1.8 ~2.2 mol/L NH ₄ OH, 0.015 mol/L Cu ²⁺ and 0.1 mol/L Na ₂ S0 ₃ mixed solution were immersed for 1.5 h under oxygen agitation, the gold leaching rate was about 95%, and the residual gold residue was stored. In iron minerals.
Leachate gold cementation with zinc powder, the leaching solution after the replacement cycle as gold, after 7 cycles, the rate of increase in the gold leaching, 96.8% of circulating ,, leaching process, thiosulfate substantially no loss. S ₂ O ₃ ^2- increased when zinc powder was replaced, and S ₂ O ₃ ^2- was lost during the standing process. The loss of S ₂ O ₃ ^2- was related to the solution composition and the container sealing condition. Carefully controlled to minimize oxidative decomposition losses of thiosulfate.
2) for extracting gold from Arizona Santa Cruz manganese OroBlanco the gold mine, the ore containing Au 3 g / t, Ag 113 g / t, Mn0 2 7 g / t. The gold in the ore is finely granulated in the breccia matrix of the rhyolite and andesite , and most of the silver is symbiotic with Mn0 ₂ . Ore grinding to -200 mesh accounted for 80%, with a liquid-solid ratio of 1.5:1 and 50 °C, with a concentration of 1.48 mol / L of (NH ₄ ) ₂ S ₂ 0 ₃ , 4.1 mol / L of NH ₃ and The 0.09 mol/L Cu ²⁺ solution was stirred and leached for 1 h, and the gold leaching rate was 90%; the leaching time was 3 h, and the silver leaching rate was 70%.
The main factors affecting gold and silver leaching are temperature, thiosulfate concentration, copper ion concentration and ammonia concentration. The effect of leaching temperature on gold leaching is greater than that of silver leaching, as shown in Figure 1, while the effect of copper concentration and ammonia concentration on silver leaching is greater than gold leaching, as shown in Figures 2 and 3. The leaching of silver is sensitive to the change of copper ion concentration, and the silver leaching rate increases first and then decreases with the increase of Cu ²⁺ concentration. Gold leaching is less affected by divalent copper ions, but without Cu ²⁺ participation, gold is difficult to leaching, gold leaching rate is only 14%, and gold and silver leaching increases with the increase of S ₂ O ₃ ^2- concentration. When there is no S ₂ O ₃ ^2- , gold and silver are rarely leached, as shown in Fig. 4. In the ammonia solution, the copper ions oxidize the thiosulfate ions to the tetrathionate ions, thereby consuming the thiosulfate. At room temperature and pH 9.5-10, leaching for 28 h, the consumption of thiosulfate is about half of the original concentration.

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3) Leaching gold from low-grade gold-bearing primary ore The Northwest Institute of Non-ferrous Geology of China conducted an ammonia-based thiosulfate leaching gold experiment on natural gold-pyrite-altered rock type gold-bearing ore. Gold in the ore is dominated by natural gold, and gold is mostly present in the state of gold, fracture gold and interstitial gold in sulfide minerals and gangue minerals. Natural gold has a fine particle size and is mainly distributed in minerals such as pyrite, limonite, quartz and feldspar .
The main metal minerals in the ore are pyrite and natural gold; non-metallic minerals mainly include potassium feldspar and quartz, followed by plagioclase, mica and clay . In addition, there is a small amount of hematite, magnetite, galena, chalcopyrite, barite, sphalerite and so on. The results of analysis of ore elements are shown in Table 1.

The sample contains gold 4.57g / t, grinding fineness -200 mesh accounted for 65%, stirring leaching temperature 50 ° C, leaching time 3h, leaching liquid solid ratio 3:1. Leaching agent (NH ₄ ) ₂ S ₂ 0 ₃ 0.51 mol /L, Na ₂ S0 ₃ 0.2 mol/L, NH ₃ 3.3 mol/L, CuSO ₄ 1.7 g/L. The leaching rate of gold is 92.40%. [next]
During the screening process of leaching agent dosage and leaching conditions, it was observed that: 1 As the strong oxidant, Na ₂ S0 _{3 has} little change with the increase of concentration, as long as it is greater than 0.1 mol/L. the enhancement of the stability of the leaching system; â‘¡ leaching rate of gold with _{(NH 4) 2 S 2 0} 3 concentration increased there was a substantial increase in the leaching solution _{(NH 4) 2 S 2 0} 3 concentration of at least Maintaining the concentration of NH _{3 in the} leaching solution at 0.5 mol/L is beneficial to the increase of gold leaching rate, preferably 3. 3 mol/L; the concentration of 4CuS0 ₄ is about 1.7 g/L.
The test was carried out with different leaching methods under the condition that the original ore grade, the fineness and the leaching solution have the same solid ratio. The test results are shown in Table 2.

It is not difficult to see from Table 2 that the low-grade gold-containing primary ore is leached by ammonia thiosulfate method, which has the characteristics of short leaching time, low leaching temperature, and high leaching rate of gold, which is replaced by cyanide-free leaching gold. One of the more promising methods of cyanide leaching gold.
4) Leaching gold from carbonaceous gold ore The use of cyanidation to treat carbonaceous gold ore (pink ore) in the Freeport-McMoran Jerrit Canyon gold mine in Nevada, USA is in trouble. This paper describes the results of experiments conducted in an autoclave using ammonium thiosulfate solution.
In order to carry out the autoclave leaching experiment, the ore was first crushed to less than 152.4 mm (6 inches) and then pulverized to -100 mesh to analyze the mineral composition, gold grade and carbon content of the ore sample. The mine consists of dark black fragments and impure quartzite with a small amount of fine pyrite and some white calcite veins. The analysis results show that the mine contains 2.5% organic carbon and 4.9% total carbon. The average grade of ore gold is 12.2 g/t.
1 autoclave leaching. The experiment was carried out in a 500 cm ³ stainless steel autoclave. It consists of a stirrer with a 3.18 cm diameter impeller, a cooling coil and a thermocouple. The agitator, cooling coil and thermocouple are bolted to the lid. When the autoclave is heated, its temperature is controlled by an electric heating jacket. The autoclave is preheated to a temperature close to the desired temperature, the prepared leaching agent and the well-known ore are added to the kettle, the kettle lid is pressed, and stirring is started; the autoclave is vented with nitrogen, and then oxygen is introduced. The operating temperature range is from 25 ° C to 85 ° C while the partial pressure of oxygen is typically maintained at 103 kPa and the pH of the solution is measured before and after leaching.
After the leaching is completed, the solution is filtered out. The thiosulfate concentration in the filtrate was analyzed by electrochemical detection flow injection (FIA). After the solid slag is dried, the gold content in the slag is analyzed by a combination of fire test and atomic absorption. The purity of the initial thiosulfate sample used was also determined by the FIA ​​method. The results of the experimentally obtained thiosulfate consumption and gold leaching rate are shown in Tables 3 and 4.

2 The choice of the best leaching conditions. Effect of pH: To observe the effect of pH, the NH ₃ concentration was changed from 0.03 mol/L to 4.5 mol/L, which corresponds to a pH range of 8.5 to 10.5. Since a buffer solution is formed, the maximum pH is limited to about 10.5. In this pH range, the consumption of thiosulfate is almost constant, averaging about 15%; while the leaching rate of gold increases with increasing pH. The optimum pH is 10.5.
Effect of temperature: The experimental results between 25 ° C and 85 ° C are shown in Figure 5. The leaching curve has a maximum at 35 ° C and 75 ° C, a very small value at 65 ° C, and an optimum temperature of about 35 ° C. The thiosulfate consumption from 25 ° C to 55 ° C is generally increased, 55 ° C to 65 ° C is reduced, and then increased from 65 ° C to 85 ° C, which is a complex equilibrium relationship involving thiosulfate with temperature The result of the change. Taking into account the gold leaching rate, thiosulfate consumption and investment energy, the optimum temperature is 35 °C.

Figure 5
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Effect of ammonium thiosulfate concentration: The experiment was carried out at 35 ° C, pH = 10.5, and the thiosulfate concentration was changed from 0.09 mol/L to 0.88 mol/L. The leaching rate of gold increases only slightly with increasing thiosulfate concentration because the actual consumption of thiosulfate increases. The thiosulfate consumption is 5.3 × 10 ^-2 mol/L (58.9%) at a concentration of 0.09 mol/L, and 9×10 ^-2 mol/L at a concentration of 0.88 mol/L (10.2%). ). Considering the gold leaching rate and the total amount of thiosulfate used, the optimum thiosulfate concentration selected is 0.71 mol/Lo.
Effect of sulfite concentration: Add ammonium sulfite to the leaching solution to stabilize the thiosulfate and prevent sulfide sedimentation (6H ⁺ +4S0 ₃ ^2- +2S ₂ ←→3S ₂ 0 ₃ ^2- +3H ₂ 0). At 35 ° C, 0.71 mol / LS ₂ 0 ₃ ^2- , pH = 10.5, 0.15 mol / L CuSO ₄ , the sulfite concentration changed from 0 to 0.6 mol / L, leaching for 2 h. It is clear that sulfite has little effect on the gold leaching rate. However, thiosulfate consumption gradually decreases with increasing sulfite concentration. Considering the amount of sulfite, it is considered that a sulfite concentration of between 0.1 mol/L and 0.22 mol/L is suitable.
Effect of copper concentration: The concentration of copper sulfate changed from 0.05 mol/L to 0.2 mol/L under the conditions of 35`C, 0.71 mol/LS ₂ 0 ₃ ^2- , 0.22 mol/LS ₂ 0 ₃ ^2- and pH=10.5. The gold leaching rate and thiosulfate consumption did not have a significant effect. For such a result, there are two possibilities: first, because copper acts as a redox catalyst during the leaching process, so when it is above a certain concentration value, its concentration change has no effect on the reaction. Second, perhaps the more important reason is the presence of copper in the ore, which is sufficient to act as a catalyst.
Effect of time: at a temperature of 35 ° C, the concentration of the substance is 0.71 mol / L (S ₂ 0 ₃ ^2- ), 0.22 mol / L (SO ₃ ² ), 0.15 mol / L (CuSO ₄ ) and pH of 10.5, The effect of time on gold leaching rate and thiosulfate consumption was investigated under conditions of leaching time varying between 0.5 and 4 h. The gold leaching rate was 69% at 0.5 h and the gold leaching rate was 71% after 4 h. Under these conditions, the leaching of gold is very fast. The consumption of thiosulfate has an appropriate increase with time. The thiosulfate consumption is 10% at 0.5 h, and the consumption is increased to 20% after 4 h. A reaction time of 0.5 h to 1 h is sufficient.
Effect of oxygen pressure: Change the oxygen pressure from atmospheric pressure to 206 kPa (gauge pressure). The change in oxygen pressure has no major effect on the gold leaching rate or the thiosulfate consumption. The consumption of thiosulfate decreased slightly when the oxygen pressure was increased to 206 kPa (gauge pressure), and decreased from 12% at atmospheric pressure to 206% at 206 kPa. Therefore, a higher oxygen pressure may be advantageous if the leachate is recyclable.
Leaching of other types of ore: In addition to studying the above-described carbonaceous ore, the leaching of gold from representative oxidized ore and sulphide ore by thiosulfate solution was also investigated. When studying these mines, it was not possible to find the best conditions, but the best conditions for carbonaceous ore were used except for a small set of conditions. As indicated by the results of Tables 5 and 6, the thiosulfate leaching of the oxidized ore gives a good or better gold leaching rate as the refractory carbonaceous ore. The leaching rate for sulfide minerals is poor. Compared with the cyanidation method, the thiosulfate method is superior to the cyanidation method in that gold is leached from carbonaceous ore. However, the thiosulfate method is not as good as the cyanidation method.

Note: p ( O ₂ ) is 103 kPa ( gauge pressure ) ; time is 1 h ; temperature is 35°C The stirring speed is 0.333m /s; When the pH is 10.5 , [NH ₃ ] is 3.0 mol/L; [S ₂ O ₃ ^2- ] is 0.18 mol/L ; [Cu ²⁺ ] is 0.10 mol/L ; [SO ₃ ^2- ] is 0.01 mol/L .

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Technical parameters