Calcite surface structure and reactivity: molecular dynamics simulations and macroscopic surface modelling of the calcite-water interfaceElectronic supplementary information (ESI) available: Potential energy and volume of a box of 2028 water molecules (Fig. S1); potential energy of the calcite slab plus water over the course of a production (Fig. S2); potential parameters used in this work (Table S1); distribution of HBs around surface calcium (Table S2) and carbonate (Table S3) sites for three

• Main Authors: Wolthers, M, Di Tommaso, D, Du, Z, de Leeuw, N. H
• Format: Article
• Language: English
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c2cp42290e

Calcite-water interactions are important not only in carbon sequestration and the global carbon cycle, but also in contaminant behaviour in calcite-bearing host rock and in many industrial applications. Here we quantify the effect of variations in surface structure on calcite surface reactivity. Firstly, we employ classical Molecular Dynamics simulations of calcite surfaces containing an etch pit and a growth terrace, to show that the local environment in water around structurally different surface sites is distinct. In addition to observing the expected formation of more calcium-water interactions and hydrogen-bonds at lower-coordinated sites, we also observed subtle differences in hydrogen bonding around acute versus obtuse edges and corners. We subsequently used this information to refine the protonation constants for the calcite surface sites, according to the Charge Distribution MUltiSite Ion Complexation (CD-MUSIC) approach. The subtle differences in hydrogen bonding translate into markedly different charging behaviour versus pH, in particular for acute versus obtuse corner sites. The results show quantitatively that calcite surface reactivity is directly related to surface topography. The information obtained in this study is not only crucial for the improvement of existing macroscopic surface models of the reactivity of calcite towards contaminants, but also improves our atomic-level understanding of mineral-water interactions. Calcite surface reactivity changes with surface topography: quantification from the atomic to the macroscopic scale.