A gold mine in Xinjiang Ili region, belonging to the gold-bearing quartz veins. Gold in the free nature of gold-based, simple occurrence state, most with quartz and pyrite associated. Metallic minerals pyrite, followed by the yellow copper ore, gold and natural galena like. The chemical analysis contained Au13.4g/t, Ag 452.4g/t, Cu 0.11%, Fe 4.95%, and S.I.147%. It can be seen that the gold mine is a high- silver low-sulfur oxidized gold mine. The use of cyanide leaching will contaminate the Ili River, so a non-cyanide process is employed.
Both gold and silver form a relatively stable complex with chloride ions. When an oxidant is present in the chloride solution, the gold and silver leaching reactions can be simply expressed as:
Au+OX+4Cl - —→ AuC1 4 - +OX ′
Ag+OX+4C1 - —→ AuC1 4 3- +OX ′
Ag+Cl - —→ AgCl
AgCl+2NH 3 —→ [Ag(NH 3 ) 2 ] + +C1 -
Wherein OX is an oxidizing agent and OX ' is a reduced state of the oxidizing agent.
In view of the above reaction, the possibility of leaching gold and silver from the gold ore in the presence of a chlorine salt or (and) ammonia was explored, and the purpose of separately leaching gold and silver was achieved by controlling appropriate leaching conditions.
1) NH 4 H-NaCl system chlorination of gold and silver The experimental results show that in NH 3 7%, oxidant 5%, NaCl 20%, liquid-solid ratio = 10:1, leaching time 120min, temperature 80 ° C leaching conditions With oxychloride as the oxidant, it is possible to choose to leaching silver first, and the leaching rate of silver is 98%. Most of the gold remains in the leach residue for easy handling. The downside is that about 24% of the gold is leached into the solution along with the silver. In order to achieve the purpose of separately leaching gold and silver, it is necessary to further improve the selectivity of the leaching process.
2) Oxidative leaching of gold and silver by HCl-NaCl system In order to investigate the possibility of leaching gold and silver by adding different types of oxidants in the HCl-NaCl system, the leaching conditions were determined as follows: liquid-solid ratio = 10:1, leaching time At 120 min, the temperature of 80 °C increased the amount of oxidant but the increase of gold leaching rate was not obvious, while the effect of silver leaching rate was more complicated. When the amount of oxidant is 2% - 5%, the silver leaching rate is greater than 96%. Excessive addition of oxidant will result in a decrease in silver leaching rate and then increase. In order to achieve the simultaneous leaching of gold and silver in the system, experiments with different oxidants were explored. Typical experimental results are shown in the table below. The experimental results show that in a HCl-NaCl system, a metal ion and an oxychloride as an oxidant can simultaneously leaching gold and silver, the gold leaching rate is 96%, and the silver leaching rate is greater than 98%. The leaching system is simple in process and is suitable for oxidizing gold ore with high silver content.
Results of adding different oxidants while leaching gold and silver | ||||
Temperature / °C | Leaching system | Add oxidant | Gold leaching rate /% | Silver leaching rate /% |
80 | H4OH-NaCl | Oxychloride | 24.6 | 5.1 |
80 | HCl-NaCl | Metal ion | 85.3 | 99.8 |
90 | HCl-NaCl | Oxychloride | 91.7 | 99.7 |
90 | HCl-NaCl | Double oxidant | 92.5 | 99.8 |
90 | HCl-NaCl | Double oxidant | 96.1 | 99.9 |
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