Dissolution kinetics of periclase in dilute hydrochloric acid

Kinetics of the reaction between particulate sintered polycrystalline MgO and dilute hydrochloric acid were studied. The effects of process parameters, i.e., concentrations of H+H+ and Mg2+Mg2+ ions, temperature and particle size were investigated. It was observed that the rate of chemical dissolution of MgO: (a) increased with increase in both HCl concentration (from 10-410-4 to 10-2M) and temperature (from 25 to 60∘C); (b) decreased with increase in particle size (from 63 to 355μm); (c) was not affected by Mg2+Mg2+ ion concentration. Thorough comparison of our results with those published by other authors revealed that the “initial” stage of MgO dissolution has never been observed under the conditions of the experiments in the present work. It was concluded that the initial stage of MgO dissolution was probably too short to be detected and just the “advanced” kinetic regime was investigated. Values of the kinetic parameters were calculated, and apparent activation energy between 93 and 101kJmol-1 and the reaction order for H+H+ ions from 0.41 to 0.76 were obtained. The presented values of the reaction order for H+H+ ions are consistent, allowing for experimental error, with current kinetic theories and most of other experiments. However, the rate-controlling step could not be assigned unambiguously, because the same value of the reaction order for H+H+ ions can be predicted by various theories for different rate-determining steps. The broad variety of likely rate-determining steps indicates some intrinsic diversity in current kinetic models.