The kinetics of the chlorination of pyrite in two Turkish lignites in water and water-carbon tetrachloride media at ambient pressure (congruent to 610 mm Hg) are investigated. The effects of speed of stirring (5-20 s(-1)), particle size (74-88, 150-180 and 250-425 mu m), temperature (13-70 degrees C) and reaction time (0-18 000 s) were studied, The experimental data were analyzed on the basis of the unreacted shrinking core model, The fine pyrite particles are assumed to be embedded inside the coal particles, The rate-controlling step was found to be diffusion of chlorine through the ash (the coal matrix), The activation energies were calculated as 25.1 kJ mol(-1) for Dadagi coal in water medium and 25.0 kJ mol(-1) for Mengen coal in water-carbon tetrachloride medium.