A general mathematical model is presented for the noncatalytic reaction between a porous solid and a gas with solid product formation under conditions controlled by intraparticle diffusion. The model has been formulated in general terms so as to allow the incorporation of specific details pertaining to actual systems. The formulation assumes that the gaseous reactant diffuses through the pore space of the particle followed by diffusion through the product layer. The resulting equations are solved numerically.This model has been used to predict conversion-time curves for the atmospheric oxidation of iron disulfide contained in porous solids. The predicted curves are in excellent agreement with the experimental data. In particular, it produces accurate estimates for the conversion rates of iron disulfide at different temperatures.
A robustious structural model is developed to describe the role of bacteria in the leaching process of lo w-grade ores under conditions controlled by intraparticle d vfusion. The main impetus behind developing this model is to provide an insight into such systems, together with a suitable framework for interpreting experimental data. The model is derived in detail with respect to reaction chemistry and the role of bacteria in catalyzing these reactions, specifically the synergism of chemistry, physics and biology in determining the overall behavior of the system. The model is used to simulate the atmospheric oxidation of iron disurfde contained in porous solids in the presence of Thiobacillus ferrooxidans (T. ferrooxidans). The experimental data are predicted well by the model, which demonstrates its applicability and supports the view that the rate of intraparticle dvfusion is the controlling mechanism for this system.
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