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BIOOXIDATION OF REFRACTORY PYRITE-ARSENOPYRITE GOLD BEARING SULFIDE CONCENTRATE

А. Г. Булаев

Abstract

Biohydrometallurgical technologies are widely used for the extraction of non-ferrous and precious metals from sulfide ores and concentrates including gold-bearing refractory concentrates. Biohydrometallurgical treatment of gold-bearing sulfide concentrates is based on the oxidation of sulfide minerals by acidophilic microorganisms oxidizing ferrous iron and sulfur. This makes it possible to increase gold extraction by subsequent cyanidation as biooxidation results in disruption of crystal lattice of sulfide minerals and gold finely dispersed in these minerals becomes available for dissolving by cyanide. In the present study, the possibility of processing of gold-bearing pyrite-arsenopyrite concentrate containing of 56% of pyrite, 14% of arsenopyrite, and 45.5 g/t of gold by tank biooxidation was studied. Biooxidation in continuous mode was performed at 40°C in laboratory scale reactors using association of acidophilic microorganisms. Residence time was 6 days. Pulp densities (solid to liquid ratio, S : L) were 1.5 : 10 and 1: 10. At pulp density of 1.5 : 10, biooxidation was not stable, probably due to high sulfide minerals content in the concentrate, while oxidation at a pulp density of 1 : 10 was stable, which was indicated by liquid phase parameters (pH, Eh, ferric and ferrous iron concentrations). Thus, biooxidation to obtain solid residue, which was used for further gold extraction was performed at a pulp density of 1 : 10. Biooxidation made it possible to oxidize 63% of pyrite and 95% of arsenopyrite. Gold recovery by cyanidation increased from 57% (from unoxidized concentrate) to 83% (from solid residue of biooxidation). Liquid phase of the pulp containing high concentration of Fe3+ ions (up to 22 g/L) was used for oxidative leaching of substandard copper-zinc concentrates. Three samples of copper-zinc concentrates containing 17 and 2.9%, 16 and 5.3%, and 6.2 and 7.3% of Cu and Zn were studied. Leaching of these concentrate performed at 80°C, pulp density of 1 : 10 for 3 h made it possible partially leach both copper and zinc. Copper content in the solid residues increased or did not change significantly, while zinc content decreased in comparison with the concentrates, as copper sulfide minerals of the concentrates (chalcopyrite and tennantite) are more refractory to oxidative leaching than zinc sulfide (sphalerite). Copper and zinc content in the residues was 17 and 1.45%, 16.7 and 2.9%, and 6.15 and 3.95%. Decrease in zinc content in substandard concentrates, which cannot be successfully conditioned by flotation, using alternative approach including hydrometallurgical methods is promising for the production of high-grade copper concentrates. Thus, in the present study, it was demonstrated that biooxidation of sulfide gold-bearing concentrates may be used not only to increase gold extraction rate, but also to obtain solutions with high Fe3+ content, which can be used for oxidative leaching of other mineral raw materials.

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DOI resolver: doi.org/10.5593/sgem2019v/6.3/s08.009

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