(289f) A Molecular Dynamics Investigation of the Relative Stability of Alkaline Earth Metal-Chloride Complexes in Aqueous Solutions and on Gibbsite Surfaces

The adsorption of contaminants onto mineral surfaces is a critical process that ultimately affects the extent of contaminant migration in ground water. However, to this point, metal speciation at the mineral surface is not well understood through experiments. Furthermore, evidence suggests that metal speciation at the mineral surface differs from that in aqueous solution. Therefore, the prediction of contaminant adsorption through molecular simulations could potentially be an invaluable design tool for the remediation of hazardous and radioactive waste.

In this study, molecular dynamics simulations are conducted to investigate the stability of metal (M = Mg2+, Ca2+, Sr2+, Ba2+) and metal-cloride species in solution and at the gibbsite (001) surface. The intermolecular interactions are described through the CLAYFF forcefield and flexible SPC water model. Potential of mean force calculations are conducted to provide insight into the observed structural trends. For metals in solution, the calculated coordination numbers and M-H2O distances increase with increasing ionic radii, which are consistent with experimental observations. Simulations of the gibbsite-water interface suggest that these metals adsorb preferentially as inner-sphere complexes without associated chloride ligands. Overall, reasonable structures for the metal-chloride and metal-surface complexes are computed.