Influence of surface orientation on the variability of olivine dissolution rates

Abstract

Alkaline solid wastes containing olivine minerals can be suitable for CO2 mineralization due to their relatively higher reactivity and intrinsic alkalinity. However, an activation process is required to improve cation dissolution rates. Four pristine facets in an olivine single crystal were used to study their dissolution kinetics at far from thermodynamic equilibrium conditions. Vertical scanning interferometry was employed to analyse the distribution of surface dissolution rate and the evolution of etch pits. The dissolution rate exhibited an anisotropic distribution, by up to two orders of magnitude among facets. The rate law differed for each plane, with (010) face following zero-order, (120) plane exhibiting first-order, and (110) and (111) planes showing second-order reactions. Etch pits also displayed significant anisotropy, with spindle-shaped on (010) plane, droplet-shaped on (110) plane, and funnel-shaped on (111) plane. Strip-like etch pits only formed along certain scratches on (120) plane. Initially, the etch pits deepened, but after 200 h of reaction time, they grew in size. Raman and TEM analysis confirmed atomic-scale rearrangement of the dissolved surface, providing insights into etch pit morphology evolution. This work unveiled the anisotropic dissolution mechanism of olivine surfaces, enabling predictions of long-term reaction rates under diverse geochemical conditions.