A novel mechanism for protonating bridging O atoms (Obr) and dissolving quartz is proposed that is consistent with experimental data and quantum mechanical simulations of the a-quartz (101)/water interface. The new hypothesis is that H+-transfer occurs through internal surface H-bonds (i.e., SiOH�Obr) rather than surface-water H-bonds and that increasing ionic strength, I, favors formation of these internal H-bonds leading to a larger pre-exponential factor, A, in the Arrhenius equation and higher rates of dissolution.Projector-augmented planewave density functional theory (DFT) and classical molecular dynamics (MD) simulations and static energy minimizations were performed on the a-quartz (101) surface and with water, HCl, Na+ and Mg2+. The nature of the H-bonding of the surface silanol (SiOH) groups with the solution and with other surface atoms is examined as a test of the above hypothesis. Simulation results are used in surface complexation modeling to compare against experimental titration data. Statistically significant increases in the percentages of internal SiOH�Obr H-bonds, as well as the possibility of Obr protonation with H-bond linkage to silanol group, are predicted by these simulations consistent with the new hypothesis. This new hypothesis is discussed in relation to recent experimental data on silicate dissolution, and these results have been used to parameterize ReaxFF for silica-water to study silica dissolution.

Silicate dissolution: A mechanism based on simulations of the α-quartz (101)-water interface

243rd National Meeting (2012)

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