Bioleaching of Low-Grade Ni-Sulfide Samples with a Mesophilic Consortium of Iron- and Sulfur-Oxidizing Acidophiles

The bioleaching of nickel-containing sulfide minerals from five ophiolitic ore samples was investigated in this study, using a mesophilic, acidophilic consortium that included Acidithiobacillus thiooxidans, Acidithiobacillus ferrooxidans, and Leptospirillum ferrooxidans. The experiments were carried out in the presence and absence of ferrous iron and elemental sulfur as additional energy sources for the bacteria. After 30 days of contact at 5% pulp density, nickel dissolution was in the range of 15-29% in the chemical leaching and 58-83% in the bioleaching. Accessory forsterite (Mg2SiO4) in the ophiolitic ore samples increased the acid consumption, attributed to the protonation of Mg-silicate surfaces. The ore samples with low Cr2O3/MgO ratios had high acid consumption. Post-leaching examination of solid residues showed the presence of a jarosite and sulfur layers, indicating mineral surface passivation and diffusion limitation.