Determination of diffusion coefficient for coal leaching process

Coal leaching process has tremendous applications in the field of thermal and metallurgical industries. Coal leaching with alkaline solution removes silica, alumina and other acidic, ash bearing minerals present in the coal. Leaching with caustic soda has a better effect on the leaching process. In order to improve the leaching kinetics, development of the reaction kinetics is required. Indian coals are of drift origin and the mineral matter present in the coal is embedded inside the organic matter and hence, leaching is reaction controlled followed by diffusion controlled process. For studying the kinetics of the process, shrinking core model was adopted. Coal leaching kinetics at different alkali concentration was studied and diffusion coefficient is determined at room temperature. By using parametric estimation method, diffusion coefficient value obtained (DAe) is 1.2 × 10–10 m2/min and the silica and alumina rate constants are 4 × 10–6 mol/m2.min and 8 × 10–6 mol/m2.min respectively for the leaching of coal with 10% (w/w) caustic solution.