(703g) Study of Carbon Mineralization at the Surface of Mg- and Ca-Based Oxides

Decarbonization is necessary for us to mitigate the worst effects of climate change. Capture and sequestration of CO₂ will be one part of this multifaceted strategy. One promising route for CO₂ capture uses mine waste rocks containing alkaline Mg and Ca cations to passively capture CO₂ directly from the air and convert it to carbonates. This process is inherently cost effective as the capture does not require blowers or expensive adsorbent materials [1]; however, most widely available waste minerals are kinetically limited in terms of carbonation efficiency. To gain a fundamental understanding of the surface phenomena necessary for improving the kinetics of this carbonation process we use density functional theory (DFT) and ab initio steered molecular dynamics (AISMD). We progress from calculations of bulk mineral oxide thermodynamic properties to calculations of thermodynamics and dynamics in the presence of explicit water on low Miller index surfaces of MgO, CaO, brucite (Mg(OH)₂), and more complex silicate minerals. We show that differences in CO₂ adsorption energy under different water surface coverages can be used to explain experimental carbonation activity trends across different materials. Furthermore, AISMD simulations combined with umbrella sampling techniques provide us with results to explain and predict the rates of dissolution processes occurring at these surface-water interfaces. These surface-mediated dissolution processes are a necessary step for carbonation to proceed beyond the surface and into the mineral bulk; therefore, these results are critical for unveiling the chemical fingerprints of reactive mineral surfaces. We demonstrate agreement between calculation and literature experimental material trends and illustrate the difficulties inherent to using bulk descriptors for the prediction of material activity. Furthermore, strong dissolution facet dependence is shown for more complex silicate minerals, suggesting that the mechanisms of carbonation on these silicate minerals are hindered by low reactivity facets being preferentially exposed to air. Methods for improving the reactivity of these more widespread (but less reactive) minerals are proposed based on these mechanistic findings.

References:

1. Hasan, S. N. M. S. & Kusin, F. M. Potential of Mining Waste from Metallic Mineral Industry for Carbon Sequestration. IOP Conf. Ser. Mater. Sci. Eng. 458, (2018).