Highly efficient CO2 mineralization: Mechanisms and feasibility of utilizing electrolytic manganese residue as a feedstock and implementing ammonia recycling

Electrolytic manganese residue (EMR) and CO2 emissions from the electrolytic manganese metal (EMM) production process present significant challenges to achieving cleaner production within the industry. Given the high capacity for CO2 sequestration and the stability of the sequestered forms, CO2 mineralization methods utilizing minerals or industrial residues have garnered considerable research interest. The efficacy of such methods is fundamentally dependent on the properties of the materials employed. EMR, due to its calcium sulfate dihydrate (CaSO4·2H2O) content, possesses an intrinsic potential for CO2 solidification. In this study, we propose a novel method for CO2 mineralization utilizing EMR, coupled with NH3·H2O recycling. Experimental results indicated that under conditions of a reaction temperature of 55 °C and a pH of approximately 8, each ton of EMR can sequester 0.16 t of CO2, with equilibrium achieved within 10 min. The mineralization mechanism was elucidated using SEM, TG curves, and XRD analyses, which revealed that Ca2+ ions are initially leached from CaSO4·2H2O in the EMR, subsequently precipitating with CO32− ions to form CaCO3. This CaCO3 layer effectively covers the surface of CaSO4·2H2O, inhibiting further Ca2+ release and stabilizing the reaction equilibrium. Furthermore, the ammonia in the solution is regenerated into NH3·H2O, facilitating its reuse and preventing secondary pollution. The utilization of EMR for CO2 mineralization not only mitigates carbon emissions in the EMM production process but also promotes environmentally sustainable practices in the industry. This study highlights a promising pathway towards achieving carbon neutrality and cleaner production in electrolytic manganese production. [Display omitted] •CO2 and EMR were synergistically treated with a mass ratio of 0.16:1.•CaSO4·2H2O dissolves first, and the resulting Ca2+ reacts with CO32− to form CaCO3.•Carbonation products of EMR are a mixture of CaCO3, CaSO4·2H2O, and SiO2.•The ammonia in the solution can be regenerated into NH3·H2O for recycling.