Exploring Mechanisms of Hydration and Carbonation of MgO and Mg(OH) 2 in Reactive Magnesium Oxide-Based Cements

[EN] Reactive magnesium oxide (MgO)-based cement (RMC) can play a key role in carbon capture processes. However, knowledge on the driving forces that control the degree of carbonation and hydration and rate of reactions in this system remains limited. In this work, density functional theory-based simulations are used to investigate the physical nature of the reactions taking place during the fabrication of RMCs under ambient conditions. Parametric indicators such as adsorption energies, charge transfer, electron localization function, adsorption/dissociation energy barriers, and the mechanisms of interaction of H2O and CO2 molecules with MgO and brucite (Mg(OH)2) clusters are considered. The following hydration and carbonation interactions relevant to RMCs are evaluated: (i) carbonation of MgO, (ii) hydration of MgO, carbonation of hydrated MgO, (iii) carbonation of Mg(OH)2, (iv) hydration of Mg(OH)2, and (v) hydration of carbonated Mg(OH)2. A comparison of the energy barriers and reaction pathways of these mechanisms shows that the carbonation of MgO is hindered by the presence of H2O molecules, while the carbonation of Mg(OH)2 is hindered by the formation of initial carbonate and hydrate layers as well as presence of excessed H2O molecules. To compare these finding to bulk mineral surfaces, the interactions of the CO2 and H2O molecules with the MgO(001) and Mg(OH)2 (001) surfaces are studied. Therefore, this work presents deep insights into the physical nature of the reactions and the mechanisms involved in hydrated magnesium carbonates production that can be beneficial for its development.M.G.G., H.N., and P.K. are grateful for the support of the Academy of Finland grant CCC (329477) and the University of Oulu and the Academy of Finland Profi5 funding (326291). K.A.A. and W.C acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 101002219). H.M. acknowledges funding from “Departamento de Educación, Política Lingüística y Cultura del Gobierno Vasco” (Grant No. IT1358-22). The authors acknowledge the CSC-IT Center for Science, Finland, for providing computational resources