New Insights into Calcite Dissolution Mechanisms under Water, Proton, or Carbonic Acid-Dominated Conditions

Area of Science:

• Geochemistry
• Mineralogy
• Environmental Science

Background:

• Carbonate mineral dissolution is crucial for geological carbon sequestration, ocean acidification, and permafrost carbon cycling.
• Understanding calcite dissolution mechanisms is key to predicting these environmental processes.

Purpose of the Study:

• To elucidate the atomic-level mechanisms of calcite dissolution.
• To investigate the influence of water, H+, and carbonic acid on calcite dissolution kinetics.
• To determine the role of an anionic surfactant in inhibiting calcite dissolution.

Main Methods:

• High-pressure and temperature batch experiments were conducted on calcite.
• Laser profilometry was used to measure etch-pit geometries.
• Density functional theory calculations investigated species adsorption energies.

Main Results:

• Calcite dissolution is primarily governed by water adsorption to surface calcium (Ca) atoms.
• Adsorbed H+ enhances dissolution by weakening surface Ca-O bonds.
• Dissociative adsorption of carbonic acid (H2CO3) leads to adsorbed bicarbonate (HCO3-) and H+, with a net enhancement of dissolution.

Conclusions:

• Calcite dissolution is fundamentally controlled by water's interaction with surface Ca atoms.
• The presence of H+ and the dissociative adsorption of H2CO3 significantly influence dissolution rates.
• These findings improve models predicting solute impacts on carbonate mineral dissolution in complex aqueous systems.