MICROBIAL DESULFURIZATION OF COAL WITH THIOBACILLUS-FERROOXIDANS BACTERIA

Microbial desulfurization of Polish flame coal, characterized by high total concentration of sulfur and a high concentration of pyrite sulfur, was studied. The optimum conditions of the process were established. When using Thiobacillus ferrooxidans bacteria, the best results were obtained with desulfurization carried out on coal samples making 2.4 wt% of the extraction mixture at the initial concentration of ferrous ions of 15 g dm(-3) and for a process duration of seven days. Since desulfurization of coal mainly involves oxidation of the pyrite, a kinetic model of Fe2+ oxidation by Thiobacillus ferrooxidans bacteria was proposed. The process was found to be described well by the equation derived for autocatalytic reaction of the first-order, both towards the inorganic substrate (Fe2+) and the biocatalyst (protein). The rate constants and induction times of Fe2+ oxidation and protein growth were determined for different temperatures, pH values and initial concentrations of Fe2+. The highest rate constant and the shortest induction time were obtained for 35 degrees C and the initial Fe2+ concentration of 3 g Fe2+ dm(-3). No effect of pH changes, in a range 2.0-3.0, on the kinetics of the process was noted.