Coal Desulfurization with Acidithiobacillus ferrivorans, from Balya Acidic Mine Drainage

Abstract

The biodesulfurization capability of a strain having sulfur and iron metabolism isolated from acidic mine drainage of Balya (Balikesir, Turkey) was studied. Molecular identification of the 16S rRNA gene showed that this bacterium was a strain of Acidithiobacillus ferrivorans. Desulfurization optimization experiments were performed by Taguchi's method. Statistical experimental arrangement L-16 (4(5)) was prepared to determine optimum sulfur removal. The optimum conditions for these parameters were found to be pH of 2.5, inoculum amount of 2%, pulp density of 1%, particle size of -500 + 250 mu m, and incubation time of 14 days. A value of "Prob > F" less than 0.0500 indicates that model terms are significant. The obtained yields of total sulfur removal were approximately 33%. According to variance analysis, it was seen that all parameters were effective in removal of total sulfur. Scanning electron microscopy and Fourier transform infrared spectroscopy analyses also indicated a modification of the coal surface after biodesulfurization. The redox potential was measured as 818 mV (7 days) and 788 mV (14 days) during the biodesulfurization experiment by the Pt-Ag/AgCl system of cyclic voltammetry, which suggested that the Fe3+/Fe2+ redox pair could be thermodynamically competitive with the O-2/H2O couple as the electron acceptor during bacterial sulfur oxidation, demonstrating that S-0 oxidation was coupled with Fe3+ reduction. Thermogravimetry, differential thermal analysis, and differential thermogravimetry curves for untreated and biotreated coal showed the differences in combustion profiles, possibly relating to structural alterations derived from biotreatments.