Dissolution of periclase in excess of hydrochloric acid: Study of inhibiting effect of acid concentration on the dissolution rate

Kinetics of the dissolution of particulate polycrystalline MgO in excess of hydrochloric acid were investigated, with special regard to the effect of activity of H+ ions, temperature and particle size. The results are presented in terms of the shrinking particle model. The overall process is controlled by the chemical reaction of MgO with H+ ions at the liquid–solid interface. The apparent activation energy was 58 kJ mol−1. Acid concentration (from 0.5 M to 5.1 M) was surprisingly found to have a decelerating effect on the dissolution rate of MgO, resulting in negative values of reaction order for H+ ions (from −0.16 to −0.18). We conclude that the regime studied here, characterised by decrease in the dissolution rate of MgO with an increase in H+ activity, occurs under far from mass-transfer control conditions in the solutions with low Mg2+:H+ molar ratio.