Natural waters typically contain a mixture of solutes, known to enhance the dissolution rate of silica. Different mechanisms for silica dissolution have been proposed, relating to the nature of species engaged in surface proton transfer, and how these mechanisms are affected by the presence of surface-sorbed ions, at varying pH. Several studies have examined the effects of cations near the negatively-charged quartz/silica surface present at neutral to basic pH. However different mechanisms are expected to predominate at acidic pH where silica surface charge is positive. Second harmonic generation spectroscopy reveals halides are capable of stabilizing protons present at the silica surface. Here we investigate the ability of Cl<sup>-</sup> in solution to stabilize protonated bridging oxygens at low pH using molecular modeling techniques. Both planewave DFT and forcefield (Garofalini and coworkers) models are employed. Effects are studied on both quartz surfaces and amorphous silica with varying silanol densities. Results are then related to potential dissolution reaction mechanisms of silica.

Modeled anionic stabilization of silica surface charge at low pH

251st National Meeting (2016)

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