An experimental study of pyrite bio-leaching as a way to control spontaneous combustion

Bio-leaching of pyrite by native strains of acidophilic bacteria was examined by laboratory scale tests. Three groups of batch trials in agitated flasks and three continuous column leaching tests were performed. The leaching ability and efficiency of native bacteria was greatly improved by adaptation of the bacteria to the test conditions. These cultivated bacteria were then used for the leaching process. The changes in solution pH, Eh, Fe²⁺ concentration, and sulfate ion concentration were monitored throughout the tests. A portion of the pyritic sulfur is transformed into soluble sulfate ion. The desulfurization ratio of 42.6% was obtained in a flask shaking test and a ratio of 39.4% was obtained during column leaching. A weight gain test was performed on leached and unleached samples by exposing the samples to humid air for several days. A smaller weight gain of the bio-leached samples indicates that removing sulfur from the sulphide ore helps reduce its oxidation rate and the potential for spontaneous combustion.