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Experimental results are reported on the biological atmospheric oxidation of FeS{dollar}\\sb2{dollar} embedded within mine rocks in the presence of Thiobacillus ferrooxidans. Three different potentially acid-producing rock samples from different coal seams are used. The rate of FeS{dollar}\\sb2{dollar} conversion or production of acid is studied with respect to sterility and variations in temperature, and particle size. Pore size distributions as well as changes in porosity with conversion have been determined for both inoculated and sterilized samples. It is found, under the same experimental conditions, that the inoculated samples produce five times more acid than the sterilized ones. This is attributed to the catalytic role played by the bacteria which corroborates fully with prior findings reported in the literature. By interpretation of data on temperature and particle size effects, it is concluded that biological oxidation of {dollar}FeS\\sb2{dollar} is controlled solely by intraparticle diffusion of oxygen and other substrates rather than by chemical kinetics. A structural mathematical model is developed based on the premise that the process is diffusionally controlled. The model is derived in considerable detail with respect to reaction chemistry and the role of bacteria in catalyzing these reactions. Incorporated in the model are provisions for structural changes of the inert solid matrix. The model consists of a set of mass balance and mass action equations with two moving fronts. This set of non-linear partial differential equations is solved numerically by finite-difference techniques using existing computer packages. The agreement of the experimental data with simulation establishes the model validity. The mysteries of biotic pyrite oxidation in mine waste rocks has been unraveled.