Dissolution Kinetics and Mechanisms at Dolomite-Water Interfaces: Effects of Electrolyte Specific Ionic Strength

Elucidating dissolution kinetics and mechanisms at carbonate mineral-water interfaces is essential to many environmental and geochemical processes, including geologic CO2 sequestration in deep aquifers. In the present work, effects of background electrolytes on dolomite (CaMg(CO3)(2)) reactivity were investigated by measuring step dissolution rates using in situ hydrothermal atomic force microscopy (HAFM) at 90 degrees C. Cleaved surfaces of dolomite were exposed to sodium chloride and tetramethylammonium chloride (TMACl) aqueous solutions with ionic strengths (I) ranging from 0 to 0.77 m at pH 4 and pH 9. HAFM results demonstrated that dolomite step retreat rates increased with increasing solution ionic strength and decreasing pH. Comparison of [48 (1) over bar] and [(4) over bar 41] steps revealed that the anisotropy of [48 (1) over bar] and [(4) over bar 41] step speeds became significant as solution ionic strength increased, with NaCl exerting more pronounced effects than TMACl for the same I. To interpret the different trends observed for NaCl and TMACl, a dissolution mechanism involving orientation-dependent ion adsorption and consequent edge free energy changes is proposed.