Effect of Ammonium Sulfate on the Precipitation Mechanism of Mg Carbonates

The carbonation of Magnesium feedstocks is a promising route for carbon capture and utilization since it has the potential to minimize carbon footprints in the construction sector while addressing the criticality of Mg raw materials in the EU. However, the high energy requirements involved in the extraction and carbonation of Mg from Mg-rich feedstocks hinder commercial carbon mineralization. Long-lasting knowledge gaps remain regarding Mg-carbonates precipitation mechanisms and kinetics, known as the geochemical problems related to magnesite and dolomite formation. Despite centuries of research on the topic, it is unknown why these anhydrous Mg carbonates are found in modern geological formations but cannot be synthesized under ambient conditions. This study investigates one of the topics related to this geochemical dilemma, namely, the effect of sulfate ions on Mg-carbonate precipitation, which has contradictory findings in the literature. Recent studies involving molecular dynamics simulations have predicted an acceleratory role of sulfate additives on the precipitation of Mg carbonates, while experimental and geochemical investigations show evidence of inhibitory as well as acceleratory roles. This study explores the effect of solution concentrations on the catalytic role of ammonium sulfate in the precipitation system. The findings demonstrate that ammonium sulfate additives hinder the precipitation of crystalline Mg carbonates under the investigated conditions, shifting the reaction toward the formation of amorphous Mg carbonates at high sulfate concentrations via a nonclassical crystallization pathway.