| The purpose of this work was to investigate the feasibility of recovery and reclamation of ultrafine coal particles generated during the processing of coal. 10-35% of the total annual tonnage of coal in a typical coal preparation plant is estimated to be lost in forms of ultrafine particles during the mining, shipping, handling, and preparation of the coal. The proposed system consisted of an integrated circuit of selective flocculation followed by microbial desulfurization. The results indicate that using selective flocculation/froth flotation circuit, coal recovery is 85% with 75% pyritic sulfur and 60% ash rejections. In order to enhance the selectivity of the flocculation/flotation process a new dispersant/depressant chemical was developed. This reagent is the sodium salt of polyacrylate-acrylodithiocarbonate which is essentially a partially xanthated hydrophilic short chain polymer molecule (M.W. ;The remaining pyritic sulfur in the coal slurry was treated by microbial desulfurization using Thiobacillus ferrooxidans microorganism in a draft-tube fluidized bed bioreactor. The effects of bacteria adaptation to pyrite nutrient, initial cell concentration and coal slurry loading were also investigated. Using this reactor scheme and the adapted culture considerable enhancement of the bioleaching rate was obtained. The results indicate that 90% rejection of pyritic sulfur can be achieved in less than 24 hrs. Note that the previously reported data for the bioleaching rate are from 4 to 12 days for the same amount of pyritic rejection. This considerable increase in bioleaching rate of pyrite is believed to be due to a more efficient oxygen delivery mechanism which essentially activates the direct oxidation mechanism of the pyrite by the microorganism. |
