Three species of thermophilic archaebacteria of the genera Sulfolobus (Sulfolobus acidocaldarius and S. solfataricus) and Acidianus (Acidianus brierleyi) were tested for their ability to oxidize pyrite and to grow autotrophically on pyrite, to explore their potential for use in coal desulfurization. Only A. brierleyi was able to oxidize and grow autotrophically on pyrite. Jarosite was formed during the pyrite oxidation, resulting in the precipitation of sulfate and iron. The medium composition affected the extent of jarosite formation.

Experiments were done in order to study the thermophilic archaebacterium Acidianus brierkyi during oxidation of pyrite (FeS$. The microorganisms were grown both separated from the pyrite by a membrane and in close contact with the pyrite. From the results it can be concluded that direct contact is needed for good growth of the strain studied. The obtained results indicate that the direct contact mechanism may be applied to oxidation of sulfidic minerals by A. brierleyi. IntroductionThere is a large degree of interest in biohydrometallurgy in order to use bioleaching to recover metals from low-grade ores where conventional methods are not economical. For exampel, gold is often trapped in a matrix of pyrite and arsenopyrite. The pyrite and the arsenopyrite can be dissolved by microorganisms thereby releasing the gold under mild conditions. Copper mining is another example where biohydrometallurgy has become an important process. Microorganisms capable of oxidizing pyrite and other sulfidic minerals have a potential for desulfurization of coal. The major part of the inorganic sulfur in coal consists of pyrite. The mechanism of microbial oxidation of sulfide minerals has been studied for many years. Two types of mechanisms have been proposed for the oxidation of the mineral pyrite (FeS2), a direct mechanism and an indirect mechanism (Eligwe, 1988). In the direct mechanism the microorganisms oxidize the pyrite directly and physical contact between the pyrite and the microorganisms is thought to be essential for the reaction. In the indirect mechanism the pyrite is oxidized chemically by ferric iron and the ferric iron is then regenerated by the microorganisms. The two mechanisms can be described by the following reactions where reactions 1) and 3) are biological.

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Acidianus brierleyi was demonstrated to remove pyritic sulphur from coal. A. brierfeyi was also found capable of catalyzing the removal of what is normally reported as organic sulphur from coal 171US34. A kinetic analysis was performed by assuming a first order reaction. The first order kinetics allowed a comparison with literature data for Thiobacillus ferrooxidans. Also, formation of jarosite was taken into account in the analysis. The simple first order kinetics was observed to fit the data on removal of sulphur satisfactorily.

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