Biohydrometallurgical treatment of old flotation tailings of sulfide ores containing non-nonferrous metals and gold

Proposed in the work is mining waste treatment using a three-step biohydrometallurgical process. The process includes: (i) a step of acid leaching (with sulfuric acid solution) to remove highly soluble copper and zinc forms, (ii) a step of leaching with biogenic ferric iron for the oxidation of sulfide minerals containing copper and zinc, as well as for the partial oxidation of gold-bearing pyrite, and (iii) a biooxidation step for a more complete pyrite oxidation, providing the release of gold associated with it. The subject of the research was a sample of pyrite flotation tailings containing copper, 0.26%, zinc, 0.22%, and gold, 0.67 g/t. Investigated was an acid leaching of pyrite tailings under different conditions. The leaching allowed to recover up to 35-36% of copper and zinc after 10 min. Leaching of pyrite tailings with biogenic ferric iron was studied. The highest efficiency shown was for the process carried out at the temperature of 80 °C, the pulp density of 30%, the ferric iron concentration of 30 g/L in the leaching solution, and the process duration of 8 h. As a result, approximately 14% of the pyrite oxidized, and the total zinc and copper recovery increased up to 86% and 64%, respectively. The highest efficiency of tailings treatment was shown for the biooxidation during the 12-day three-step process, which allowed to oxidize 97% of pyrite and to recover 96% of gold by carbon-in-pulp cyanidation. The total copper and zinc recovery during the three-step process was 79% and 96%, respectively. A flowsheet was proposed for the three-step process.