Formation and Dissolution of Surface Metal Carbonate Complexes: Implications for Interfacial Carbon Mineralization in Metal Silicates

S Zare and A Funk and MJA Qomi, JOURNAL OF PHYSICAL CHEMISTRY C, 126, 11574-11584 (2022).

DOI: 10.1021/acs.jpcc.2c02981

Rapid CO2 mineralization in natural and synthetic metal silicates provides a potentially scalable solution to address the untethered global carbon emissions. When metal silicates react with humidified CO2-rich fluids, a nanometer-thick water film adsorbs on mineral surfaces. Experiments show that such nanoscale reactive environments demonstrate an enhanced level of carbonic acid formation, metal-(bi)carbonate surface complexation, and fast carbon mineralization. Hindered by the spatiotemporal complexities of in situ measurements at the solid-liquid interface, the mechanistic picture of carbon mineralization mechanisms in water films remain obscure. Here, we leverage reactive and nonreactive molecular simulations to probe the elementary reaction steps involved in the interaction of bicarbonate with metal silicate surfaces. We observe that a reverse proton transport between the bicarbonate and surface hydroxides drives carbonate production and surface metal carbonate complexation in agreement with in situ spectroscopy measurements. The resultant carbonate can also contribute to the ligand-enhanced dissolution that appears to be slightly favorable over carbonate-unassisted dissolution. We also discuss the potential implications of metal carbonate complex formation and dissolution on lowering the growth's configurational entropy penalty and the rise of interfacial carbon mineralization pathways.

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