Mechanistic aspects of the water-mediated CO2 mineralization

One of the pathways to CO2 mitigation consists in accelerating the natural process of its mineralization. In this reaction, Mg- and Ca-bearing minerals (oxides, hydroxides and silicates) combine with CO2 to form carbonates, which are very stable solids with the ability of permanently storing CO2. This reaction, though thermodynamically spontaneous, occurs in nature with a very low rate, requiring millions of years to reach completion. One accelerating factor of this reaction is represented by the presence of water, assisting the release of metal ions and their precipitation as carbonates through processes occurring at the solid/liquid interface. The water-mediated mineralization opens some opportunities to enhance the reaction through physical-chemical methods. In a recent approach, the strong coupling of water and electrolytes with microwave radiation is exploited to efficiently heat the system to temperatures at which the reaction proceeds through the direct precipitation of anhydrous phases (magnesite and calcite). Additionally, the presence of proper electrolytes subjected to the energization of microwaves makes it possible to attain a catalysing effect, allowing for a strong reduction of the temperature at which precipitation of anhydrous phases occurs. In this contribution, the results obtained in the field of the water-mediated mineral carbonation reaction, with particular emphasis on the prerogatives related to the use of microwave irradiation, will be illustrated. As reaction systems, mineral water slurries with defined concentration subjected to slight overpressures of carbon dioxide under mild hydrothermal conditions will be considered. To get insights into the microscopic mechanism of the reaction, scanning probe microscopy monitoring of the mineral surface subjected to carbonation treatments at the solid/vapour interface will be presented.