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COPPER AND ZINC BIOLEACHING FROM ARSENIC-CONTAINING POLYMETALLIC CONCENTRATE

А. Г. Булаев

Abstract

Metallurgy is currently faced with difficulties due to the depletion of easily processed mineral raw materials. Thus, the development of new technologies for processing of low-grade sulfide ores and substandard concentrates is an urgent task. Biohydrometallurgical methods based on the activity of acidophilic microorganisms can be used to extract metals from different sulfide concentrates including arsenic-containing. The treatment of these products using pyrometallurgical technologies poses a problem due to the loss of valuable components and emission of toxic gases. In this case, application of biohydrometallurgical methods may be more efficient and environmentally friendly. The goal of the work was to study copper and zinc bioleaching from arsenic-containing polymetallic concentrate at different temperatures and at the presence of organic substances (yeast extract (YE)). The concentrate contained 6.2% of copper, 7.3% of zinc, and 1.7% of arsenic. Pyrite, chalcopyrite, tennantite, and sphalerite were the main minerals. Bioleaching was performed using mixed culture of acidophilic microorganisms oxidizing ferrous iron and sulfur compounds (Sulfobacillus thermosulfidooxidans SH-1, Acidithiobacillus caldus MBC-1, and Acidiplasma sp. MBA-1). S. thermosulfidooxidans SH-1 and A. caldus MBC-1 are able to fix CO2 as carbon source oxidizing inorganic substrates, while Acidiplasma sp. MBA-1 requires organic substances for constructive metabolism and able to consume yeast extract or metabolites of autotrophs in mixed microbial populations. The experiments were carried out in flasks with 100 mL of mineral nutrient medium containing salts of nitrogen and phosphorus and 2 g of the concentrate on a shaker at temperatures from 40 to 60°C for 30 days. In one of the variants, the medium was supplemented with 0.02% YE as additional carbon source (mixotrophic conditions) to increase the activity of microorganisms. In other variant, the medium did not contain organic nutrients (autotrophic conditions). It was shown that bioleaching of arsenic, copper, and zinc was affected by the temperature and YE presence. Under autotrophic conditions, copper and zinc extraction levels were maximum at 55 and 40°C and comprised about 71 and 100%. In the same time, under mixotrophic conditions, copper and zinc extraction levels were maximum at 55°C and comprised about 50 and 87%. Arsenic leaching was maximal at 45°C under autotrophic conditions and at 50°C under mixotrophic conditions, but was comparatively low and comprised about 32 and 35%. Thus, the results of the present work demonstrated that copper and zinc may be successfully extracted from the concentrate by bioleaching, while arsenic leaching rate was low, that suggested the tennantite is refractory to biooxidation and its treatment require the development of combined hydrometallurgical methods, for example, including stages of sulfide leaching to disrupt tennantite and bioleaching to extract the metals.

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DOI resolver: doi.org/10.5593/sgem2019v/6.3/s08.011

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