2023

Hellen Silva Santos; Hoang Nguyen; Fabricio Venancio; Durgaprasad Ramteke; Cornelis A P Zevenhoven; Päivö Kinnunen

The mechanisms involved in the natural formations of dolomite (CaMg(CO3)2) and magnesite (MgCO 3) have endured as challenging research questions over centuries, being yet a matter under investigation in multiple fields. From a geochemical perspective, it is still unknown why there are recent natural for-<br/>mations of dolomite and magnesite at ambient conditions, and yet most available synthetic routes for precipitating these minerals require high temperatures and/or pressures. The core scientific gap is that<br/>even though dolomite and magnesite are the most thermodynamically stable phases among the respective polymorphs/intermediates, their formation is controlled by slow kinetics and their syntheses at ambient conditions remain a challenge. Research findings lead to possible explanations based on the<br/>chemical and thermodynamical properties of the system: (i) the high energy barrier for dehydrating the Mg2+·6H2O cations hinders the carbonation of Mg precursors, inducing a preferential formation of the hydrated magnesium carbonates polymorphs, (ii) the intrinsic structural/spatial barrier of the CO 32−<br/>groups in the rhombohedral arrangement of dolomite and magnesite shifts the system towards the formation of the respective polymorphs. However, further studies are still needed to enable a clearer under standing of the phenomenon. Recently, the research question at hand gained broader significance due to<br/>the relevance of Mg carbonates for routes of carbon capture and utilization/storage, which has been seen as one of the most promising solutions for such processes. The main socio-economic motivations behind such interest on these carbon mineralization methods are the high availability of Mg precursors (from natural sources to industrial waste-streams), the long-term geological storage of CO 2 as magnesite, the possibility of utilizing the carbonate products in construction materials applications, and the relevance<br/>of the routes for climate mitigation actions. Therefore, understanding the mechanisms and kinetics of Mg carbonates precipitation is of fundamental importance for many fields, ranging from geology to necessary<br/>environmental actions. This review focuses on gathering the main information concerning the geochemical and chemical advances on the dynamics and mechanisms of Mg carbonates precipitation. It aims at providing a comprehensive summary of the developments from the fundamental sciences to the applications of Mg carbonates.