L-cysteine addition enhances microbial surface oxidation of coal inorganic sulfur: Complexation of cysteine and pyrite, inhibition of jarosite formation, environmental effects

Abstract

Indigenous microorganisms were used to remove inorganic sulfur from high sulfur fat coal, and effect of L-cysteine on coal surface and biodesulfurization was investigated. It was found that L-cysteine addition enhanced coal biodesulfurization, and the optimal L-cysteine dosage was 1.6 g/L. With the optimal L-cysteine dosage, the Sulfobacillus were the dominant pyrite-oxidizing bacteria. After biodesulfurization for 30 days, the inorganic sulfur in coal decreased from 3.038% to 0.437%. L-cysteine was adsorbed on the coal surface through amino, carboxyl and sulfhydryl groups, and cysteine-Fe complex was formed by the interaction between interfacial -SH group of L-cysteine and pyrite, which was beneficial to sulfur transfer. Meanwhile, L-cysteine addition improved the adsorption of microorganisms on coal surface though reducing the Zeta potential of coal particle. The structural change of coal during the biodesulfurization showed that the pyrite was solubilized by Sulfobacillus to realize the removal of inorganic sulfur from coal, and L-cysteine addition inhibited the jarosite formation through improvement of pyrite bio-oxidation and corresponding pH decrease, which avoided the dissolved sulfur returning back to coal again. Moreover, the coal biodesulfurization with L-cysteine addition also presented obvious environmental benefit.

Keywords: Biodesulfurization; High sulfur coal; Indigenous microorganisms; L-cysteine; Pyrite.