BIODEPYRITISATION OF HIGH-SULPHUR LOW-RANK COAL FROM MARITZA EAST DEPOSIT, BULGARIA

Depyritisation by Acidothiobacillus ferrooxidans of high-sulphur low-rank coal from Maritza East basin, Bulgaria, was carried out. Biotreated sample demonstrated high pyrite (similar to 76%) and moderate total sulphur (41%) desulphurisation at low diminishing in calorific value (similar to 5%). Reasonable decrease in combustible sulphur (21%) was obtained as well. By XRD analysis the appearance of ammonium jarosite as a by-product of the treatment was confirmed. Considerable increase in the content of the polar fraction in bitumen of biotreated coal, an indication for oxidation reactions, was registered. It was GC/MS confirmed by increased contents of oxygen homologues of diterpenoids, i.e. their phenol, ketone, quinone and ketophenol derivatives. Acidothiobacillus ferrooxidans slightly oxidise coal organic matter probably by forming some metabolites in the proposed experimental conditions.