  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 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.
