Interatomic potentials of Mg ions in aqueous solutions: structure and dehydration kinetics

Mineral carbonation (MC) of carbon dioxide (CO₂) represents a very promising and long-term solution for the use of captured and stored anthropogenic CO₂. One of the potential product of mineral carbonation is magnesite (MgCO₃), which is used in a wide range of impacting industrial applications spanning from agriculture to manufacturing. Formed via aqueous carbonation of Mg²⁺ ions, industrial production is limited by the slow precipitation rates of magnesite; high temperatures and CO₂ pressures being a requisite to expedite direct precipitation of anhydrous MgCO₃. Research has therefore focused on characterizing and optimizing the fundamental aspects of this slow precipitation under ambient conditions, in order to increase the efficacy and profitability of the process. The principal difficulty arises from the very strong Mg²⁺–H₂O interaction, which raises the barrier for dehydration while hindering nucleation and subsequent growth of Mg-carbonates. Computational modelling, using quantum chemical and molecular dynamic methods, has been used to characterize the structure, energetics, dynamics and kinetics of the Mg²⁺ (de)hydration process, from the atomic- to meso-scopic scales, employing differing interatomic potentials. Herein, we employ ab initio methods to quantitatively assess several of the currently available Mg²⁺-ion models. Of these, the Dubouè-Dijon parameterised Lennard-Jones models employing Electronic Continuum Correction provide the best agreements with quantum-chemical results, due to models using a +1.5 charge for Mg in lieu of its classically assigned +2.