THE EFFECT OF PARTICLE-SIZE AND PH ON THE REMOVAL OF PYRITE FROM COAL BY CONDITIONING WITH BACTERIA FOLLOWED BY OIL AGGLOMERATION

The removal of 90% of the pyrite from coal by bacterial conditioning followed by oil agglomeration is attainable in Minto coal only if it is ball milled in the laboratory to an average particle size of about mu m. In grinding to industrially practical sizes of about 8 to 10 mu m, the maximum amount of pyrite removed was about 50%. Bacterial conditioning was greatest at pH 2. At pH 10, the presence of bacteria was detrimental to desulfurization by oil agglomeration. Bacterial conditioning does not involve pyrite oxidation by Thiobacillus ferrooxidans because of the pH of a coal-water mixture was normally about pH 5 for best pyrite depression where these bacteria are physiologically inactive, and because conditioning was achieved equally well with Thiobacillus acidophilus and Escherichia coli.