The removal of pyritic sulphur from coal by Leptospirillum-like bacteria

Summary The microbial oxidation of pyritic sulphur was studied in a 4.5-l airlift fermentor at pH 1.5 and 100 g/l pulp density. By microbial leaching with Leptospirillum-like bacteria 85% of the pyritic sulphur was removed within 40 days; 30% of the removed pyrite was oxidized to elemental sulphur, the rest being transformed to soluble sulphate. Accumulation of elemental sulphur could be avoided by using a mixed culture of Leptospirillum-like bacteria and Thiobacillus ferrooxidans. Apart from oxidation of elemental sulphur neither the pure nor the mixed culture showed a significant difference as to removal of pyrite.