Biodesulphurization of coal: mechanism and rate limiting factors

The pyrite sulphur removal from coal by Thiobacillus ferrooxidans was studied in batch reactor. A combination of SEM, IR and XRD was used to study the presence of superficial phases and the changes in solid surface during biodesulphurization. Biodesulphurization was found to be a three-step process. In the first step (0-4 days), direct oxidation of pyrite by bacteria brought about 28% pyritic sulphur removal. Both direct and indirect oxidation contributed to the second step (4-10 days) resulting in 51% pyrite removal. The deposition of elemental sulphur, jarosite and ferric sulphate precipitates in the third step reduced the pyrite availability and ferric iron concentration in the leachate and brought the process of biodesulphurization to an end.