Modeling the Effect of Dissolved Hydrogen Sulfide on Mg2+-water Complex on Dolomite {104} Surfaces

TL;DR

This study uses density functional theory simulations to investigate how dissolved hydrogen sulfide influences the surface chemistry of dolomite, potentially catalyzing its formation by altering Mg2+-water interactions.

Contribution

It provides the first detailed thermodynamic analysis of hydrogen sulfide's role in modifying surface Mg2+-water complexes on dolomite (104) surfaces.

Findings

Water is more thermodynamically stable than hydrogen sulfide on the surface.

Adsorbed hydrogen sulfide increases Mg2+-H2O distances, suggesting a catalytic mechanism.

Two potential catalytic pathways for dolomite formation are proposed.

Abstract

The key kinetic barrier to dolomite formation is related to the surface Mg2+-H2O complex, which hinders binding of surface Mg2+ 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 Mg 2+ 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 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.