Kinetics of dissolution in H2SO4 of sulfated phosphate rock

Abstract

In this study, the effects of temperature and acid concentration on the dissolution of the sulfated phosphate samples obtained after flue gas desulfurization in sulfuric acid solution were investigated and compared with the dissolution of raw phosphate rock. The dissolution rate increased as the acid concentration and temperature increased during the dissolution of raw and sulfated samples. The dissolution reaction can be divided into two regions, with different rates of the controlling step. The controlling step was found to be a pseudo-first order reaction before the inflection points, whereas the diffusion through a product layer was found to be the rate-controlling step after the inflection points. The apparent activation energies at the pseudo-first order reaction of the raw and sulfated sample were found to be 38.2 and 25 kJ.mol−1, respectively, for the temperature range 298−363 K. The apparent activation energies for the ash diffusion model for the raw sample in the temperature range of 298–328 K and sulfated sample in the temperature range of 298−363 K were found to be 32.6 and 36.7 kJ·mol−1, respectively.