REMOVAL OF INORGANIC SULFUR FROM COAL BY THIOBACILLUS-FERROOXIDANS

The kinetics of removal of inorganic sulfur (FeS2) in Coal by Thiobacillus ferrooxidans was studied in a well-mixed batch reactor. Experiments were made at 30-degrees-C and pH 2.0 on adsorption of the bacteria to coal particles and bacterial desulfurization. In the adsorption experiments, it was found that T. ferrooxidans was selectively adsorbed on inorganic sulfur in coal and that the equilibrium data obeyed the Langmuir isotherm. The coal desulfurization was found to occur by a direct bacterial oxidation of FeS2, the chemical oxidation via ferric iron being insignificant. The FeS2 in coal was completely oxidized to sulfate ion, and the maximum conversion of 82% was achieved within two weeks. The observed rates of coal desulfurization were consistent with a kinetic model previously proposed for the bacterial dissolution of pure pyrite (FeS2) mineral. The key parameters appearing in the model, the growth yield and specific growth rate of the adsorbed bacteria, were evaluated by curve fitting, using the experimental data. This kinetic approach allowed us to predict the removal rate of inorganic sulfur from coal during the bioprocess.