Effect of Ammonium Sulfate on the Precipitation Mechanism\nof Mg Carbonates

The carbonation of\nMagnesium feedstocks is a promising route for\ncarbon capture and utilization since it has the potential to minimize\ncarbon footprints in the construction sector while addressing the\ncriticality of Mg raw materials in the EU. However, the high energy\nrequirements involved in the extraction and carbonation of Mg from\nMg-rich feedstocks hinder commercial carbon mineralization. Long-lasting\nknowledge gaps remain regarding Mg-carbonates precipitation mechanisms\nand kinetics, known as the geochemical problems related to magnesite\nand dolomite formation. Despite centuries of research on the topic,\nit is unknown why these anhydrous Mg carbonates are found in modern\ngeological formations but cannot be synthesized under ambient conditions.\nThis study investigates one of the topics related to this geochemical\ndilemma, namely, the effect of sulfate ions on Mg-carbonate precipitation,\nwhich has contradictory findings in the literature. Recent studies\ninvolving molecular dynamics simulations have predicted an acceleratory\nrole of sulfate additives on the precipitation of Mg carbonates, while\nexperimental and geochemical investigations show evidence of inhibitory\nas well as acceleratory roles. This study explores the effect of solution\nconcentrations on the catalytic role of ammonium sulfate in the precipitation\nsystem. The findings demonstrate that ammonium sulfate additives hinder\nthe precipitation of crystalline Mg carbonates under the investigated\nconditions, shifting the reaction toward the formation of amorphous\nMg carbonates at high sulfate concentrations via a nonclassical crystallization\npathway.