| At present, there are several methods including cyanidation, thiosulfate process, thiocyanate process, thioureal leaching, polysulfide process, halide process, other solvent process and so on of leaching gold and silver. Cyanidation has been far riper, and it is a low cost technology which is effective and widely used in industry. However, the use of cyanide is dangerous and causing a lot of environmental pollution with the metal cyanides in refuse. So non-toxic reagents should be found to replace cyanide. Thiosulfate can form stable coordination compounds with gold and silver, and the leaching speed is much higher than other methods. It is also slightly poisonous, less pollution, easy to use and low cost. Therefore, it has great advantages in processing carbonaceous gold mine, copper gold, complex sulphur gold mine which cyanidation is hard to deal with. We propose to leach silver, gold and other valuable metal by thiosulfate from flotation concentrate in Xiangyun Feilong(XYFL).This paper research into flotation concentrate in XYFL, experimental core sample is flotation concentrate of zinc sulfide ore leaching residues. The main metal elements of it is zinc (37.95%), also contains copper, lead, silver, gold and other valuable metals. The grade of silver is 1405.3g/t and gold is 8.7g/t. Gold and silver have higher value in core sample which will be main recycled in this experimental investigation.The result of analysis by electron microscopy and screen analysis on core sample shows that it is fine-grained and can enter the leaching process without grinding.Viable research program was decided after cyanidation test, leaching test of gold and silver, multi-stage countercurrent leaching test, ammonia-thiosulfate leaching test and exchange experiment. Reasonable technical parameters were also fixed through comparison tests of various operating conditions(concentration of thiosulfate, liquid-solid ratio, leaching time and temperature). At last, the expected targets were achieve.Non-ammonia thiosulfate leaching process was used first to deal with core sample in order to achieve a higher leaching rate in lower cost. Concentration of thiosulfate was controlled of 0.08M, liquid-solid ratio of ore pulp is 4:1. Leaching was divided into three sections at normal temperature, each leaching time is 12h. In the three sections, the average leaching rate of gold is up to 54.79% while the the average leaching rate of silver is 91.66%. Ammonia-thiosulfate leaching test of Sec leaching residue in non-ammonia thiosulfate leaching process was done to improve the leaching rate of gold further. The leaching rate of gold finally reached 72.41% while the leaching rate of silver is 90.64% when concentration of thiosulfate is 0.08M, concentration of bluestone is 0.032M, copper-ammonia ratio is 1:8 and temperature is 60℃. Both leaching targets of gold and silver achieve the desired objectives.The coefficient of recovery of gold is 75% and silver is 98.52% after the exchange experiment between zinc and gold (silver) in solution when adding amount of zinc is 5 times of silver in solution and time of replacement is 20min.It should be studied and developed further that how to use thiosulfate process to recover gold and silver efficiently. It needs to think deeply that consumption of thiosulfate is comparatively large, cyclic utilization is not easy, the use of ammonia causes environmental pollution and how to put thiosulfate process into practical application of industry better. |
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