Modeling the effect of dissolved hydrogen sulfide on Mg²⁺-water complex on dolomite {104} surfaces

The key kinetic barrier to dolomite formation is related to the surface Mg²⁺-H₂O complex, which hinders binding of surface Mg ²⁺ ions to the CO₃^2- ions in solution. It has been proposed that this reaction can be catalyzed by dissolved hydrogen sulfide. To characterize the role of dissolved hydrogen sulfide in the dehydration of surface Mg²⁺ ions, ab initio simulations based on density functional theory (DFT) were carried out to study the thermodynamics of competitive adsorption of hydrogen sulfide and water on dolomite (104) surfaces from solution. We find that water is thermodynamically more stable on the surface with the difference in adsorption energy of -13.6 kJ/mol (in vacuum) and -12.8 kJ/mol (in aqueous solution). However, aqueous hydrogen sulfide adsorbed on the surface increases the Mg²⁺-H₂O distances on the surrounding surface sites. Two possible mechanisms were proposed for the catalytic effects of adsorbed hydrogen sulfide on the anhydrous Ca-Mg carbonate crystallization at low temperature.