CO2 geological storage (GCS) is a promising approach to mitigate atmospheric CO2 by sequestrating CO2 deep underground. Among GCS trapping mechanisms, mineral entrapment, in which CO2 forms eventually solid mineral carbonates, is attractive and preferred because of its long-time safety and stability. The understanding of early stage of mineral carbonate nucleation under GCS conditions is essential for controlling the process of CO2 mineralization and precipitation. Here we investigate the mechanism of mineral clusters formation under GCS condition by conducting molecular dynamics simulations for systems composed of Mg2+, CO32- and water. Contrary to classical nucleation models, the results show a dynamics ionic polymer of Mg2+-CO32- appears at the early stage, which is strongly hydrated by water. Then, an amorphous structure of MgCO3 forms from the disordered and unstable ionic polymer, serving as a precursor of stable and highly ordered mineral carbonate crystals. Besides, the impacts from temperature, pH, brine components and mineral substrates on growth of MgCO3 are indispensable, based on analysis of thermodynamics and transport properties, e.g. solvation free energy, potential of mean force, radial distribution function and diffusion coefficient of Mg2+ and CO32-. Moreover, the concentration of Mg2+, CO32- and ratio of Mg2+/CO32- can significantly influence the topology and morphology of magnesium carbonate at the early stage. This research provides some fundamental understanding of CO2 mineralization in GCS.

Early stage of prenucleation of magnesium carbonate in CO2 geological storage

ACS Fall 2021

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