The kinetics of chlorination of alumina and bauxite with CO/CI2 mixtures were studied in the range 300-1100C. The temperature of prior calcination is critical in determining the reaction rates. An optimum chlorination temperature in the range 600C-750C was demonstrated such that there is no increase in reaction rates with increasing temperature. This lack of rate sensitivity to rising temperature is largely a function of the influence of gaseous diffusion gradients in the porous alumina together with a progressive decrease in surface area.