Removal of pyrite from coal by conditioning with Thiobacillus ferrooxidans followed by oil agglomeration

Abstract

A novel process that can reject as much as 90% of the pyrite from finely divided coal is described. Cells of Thiobacillus ferrooxidans are mixed with an aqueous slurry of the coal and the mixture is vigorously agitated for as little as 15 min. Pyrite is apparently rendered hydrophilic and is rejected with the tailings when the hydrophobic coal is recovered by oil agglomeration. The process is superior to bacteriological oxidation which requires several days to remove comparable amounts of pyrite from coal through conversion to sulphate. It is shown that the bacterial cells can be recovered after agglomeration and used to treat at least six successive batches of coal. The minimum contact time, the minimum inoculum size and the ultimate number of times that the bacteria can be recycled are related variables that could not be defined under the laboratory conditions used. It was found, however, that Thiobacillus ferrooxidans grown on rejected tailings supplemented with inexpensive mineral salts are at least as effective in the process as cells grown in synthetic medium.