In this study, we examined the effect of magnesium ions on calcite growth in aqueous solutions by monitoring the surface growth morphologies and step velocities in situ under varied experimental conditions in terms of Mg2+ concentrations, Mg/Ca ratios, and mineral saturation states (i.e., calcite). Depending on the calcite saturation indices (Wcalcite) and Mg/Ca ratios in the solution, the presence of Mg2+ can lead to (a) step rounding of both sides of the spiral hillock during the calcite growth at relatively low Wcalcite and low Mg/Ca ratios, or (b) preferential step bunching along the negative side of the hillock at relatively low Wcalcite and high Mg/Ca ratios. We interpret the biased effect of Mg incorporation (on the negative versus positive sides of the hillock) as a result of diffusional anisotropy due to differences in the terrace geometry (i.e., width) and Schwoebel barriers along the two directions. We also note that the preferential step bunching is more likely to occur at near-equilibrium conditions, where the driving force for step growth is rather low. Surface compositional analysis was further employed to explore the [Mg2+] distribution on the reacted substrates. Based on this study, incorporation of Mg does not show a strong inhibitory effect on calcite growth unless the [Mg2+] is increased to above a critical level.

Relationship between calcite growth morphology and surface diffusion behavior of magnesium

244th National Meeting (2012)

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