Catalytic Activity of Solution Additive Anions for Magnesite and Calcite Precipitation in Microwave-Assisted Mineral Carbonation Experiments

Identifying catalytic routes for magnesite and calcite precipitation from Mg- and Ca-bearing minerals is key to developing carbon-neutral or negative industrial processes. This study experimentally evaluates the catalytic activity of over 20 environmentally friendly additive anions—including carboxylates, inorganics, and ammonium salts—for promoting magnesite and calcite formation during the carbonation of brucite [Mg(OH)₂] and portlandite [Ca(OH)₂] in aqueous slurries. Carbonation is driven by microwave (MW)-assisted heating at 100–200 °C under hydrothermal conditions, with CO₂ partial pressures below 8 bar. Results reveal a significant enhancement in magnesite precipitation when additives are combined with MW energy, enabling crystallization at much lower temperatures. For calcite, MWs alone nearly double the precipitation yield, with further improvements in the presence of additives. Among promising catalyzers, chelating agents like citrate and tartrate increase induction times and reduce overall yield at higher concentrations. In contrast, additives forming simple ion pairs—such as acetate and sulfate—show improved performance with increased concentration. These findings highlight the importance of additive selection and MW energy in optimizing mineral carbonation for sustainable applications.