A MODEL FOR COAL DEPYRITIZATION

A simplified geometric model for the coal/pyrite system is based on the assumption that pyritic inclusions are spherical with a log-normal size distribution. A computer program simulates grinding of a coal sample following rules that produce several types of particle including liberated inclusions (unbroken by grinding), cubes of coal containing inclusions either submerged or protruding from one or more faces, and cubes of coal with spherical segments missing. It then examines each particle and predicts as a function of particle size, the float/sink curve, the fraction of the pyrite liberated, the fraction that is exposed to bacterial attack and the exposed surface area of the pyrite. It is shown that a bacterial depyritization process should produce a given level of pyrite removal with a larger coal particle size and loss of heating value than a physical gravity separation. The coal "sample" size that can be examined is limited to that containing 1000 inclusions by computer time considerations.