Biological and acid leaching of low-grade sulfide concentrate containing Cu and Ni at different temperatures

Abstract

In this study, the bioleaching of low-grade nickel-copper concentrate was carried out using the nutrient medium containing yeast extract (YE) at temperature range of from 40 to 60°C in order to study the dependence of biooxidation rate and Cu and Ni extraction levels on the temperature and the presence of organic compounds. Mixed culture of the strains Sulfobacillus thermosulfidooxidans, Acidithiobacillus caldus, and Acidiplasma sp., moderately-thermophilic acidophiles, which oxidize sulfide minerals, was used in the experiments. Temperature and organic carbon source were shown to affect bioleaching. At 40−50°C, the influence of YE addition was insignificant. At 55 and 60°C bioleaching depended on YE presence. Nevertheless, microbial activity affected mainly iron leaching and allowed maintaining comparatively low pH of medium. Both Cu and Ni extraction rates almost was not affected by biooxidation activity. Thus, the leaching of the base metals form the concentrate was mainly determined by abiotic factors (acidity and temperature). Regardless of this fact, bioleaching may play a significant role for processing of similar sulfide concentrates, since to maintain favourable pH, abiotic acid leaching could require a large amounts of H2SO4, while biooxidation provides sulfuric acid generation.