Ion attachment and detachment reactions at mineral surfaces are often conceptualized with an emphasis on the solvation dynamics of the interface and its constituent ions. Certainly, experimental and theoretical evidence suggests that the kinetics of water exchange on metal ions, both in solution and at mineral surfaces, scale with the kinetics of dissolution and growth. However, little is known directly concerning the mechanisms of ion attachment and detachment, or the role of mineral surface ligands in these processes. In this study, we investigate the mechanisms of calcium and carbonate ion attachment and detachment from the calcite (104) surface using classical molecular dynamics simulations. The well-tempered metadynamics approach is used to obtain the energy landscapes for these reactions with respect to a reaction coordinate that describes the collective behavior of both the mineral surface and the interfacial solvent molecules. Our preliminary results suggest that in contrast to the water exchange reaction on Ca<sup>2+</sup>, which our simulations indicate occurs via an associative mechanism in solution and on the calcite surface (kink sites), the detachment reaction requires the simultaneous over-coordination of the ion by oxygen ligands from both the solvent and the mineral surface.

Metadynamics simulations of ion detachment from calcite (104)

ACS Spring Meeting 2021

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