DESULFURIZATION OF COAL BY MICROBIAL COLUMN FLOTATION

Twenty-three strains capable of oxidizing iron were isolated from coal and ore storage sites as well as coal and ore mines, volcanic areas, and hot spring. Four strains were found to have high iron-oxidizing ac tivity. One strain (T-4) was selected for this experiment since the st rain showed the fastest leaching rate of iron and sulfate from pyrite among the four strains. The T-4 strain was assigned for Thiobacillus f errooxidans from its cultural and morphological characteristics. Bacte rial treatment was applied to column flotation. An increase of cell de nsity in the microbial column flotation resulted in the increase of py rite removal from a coal-pyrite mixture (high sulfur imitated coal) wi th corresponding decrease of coal recovery. The addition of kerosene i nto the microbial column flotation increased the recovery of the imita ted coal from 55% (without kerosene) to 81% (with 50 mu L/L kerosene) with the reduction of pyrite sulfur content from 11% (feed coal) to 3. 9% (product coal). The kerosene addition could reduce the pyritic sulf ur content by collecting the coal in the recovery. However, the additi on could not enhance separation of pyrite from the coal-pyrite mixture , since pyrite rejection was not affected by the increase of the keros ene addition. An excellent separation was obtained by the microbial fl otation using a long column which had a length-diameter (LID) ratio of 12.7. The long column flotation reduced the pyritic sulfur content fr om 11% (feed coal) to 1.8% (product coal) when 80% of the feed coal wa s recovered without the kerosene addition. The long column flotation n ot only attained an excellent separation but also reduced the amount o f cells for desulfurization to as little as one-tenth of the reported amount. (C) 1994 John Wiley and Sons, Inc.