Biodesulphurization of coal: Mechanism and rate limiting factors

The pyrite sulphur removal from coal by Thiobacillus ferrooxidans was studi ed 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 bio desulphurization. Biodesulphurization was found to be a three-step process. In the first step (0-4 days), direct oxidation of pyrite by bacteria broug ht about 28% pyritic sulphur removal. Both direct and indirect oxidation co ntributed to the second step (4-10 days) resulting in 51% pyrite removal. T he deposition of elemental sulphur, jarosite and ferric sulphate precipitat es in the third step reduced the pyrite availability and ferric iron concen tration in the leachate and brought the process of biodesulphurization to a n end.