Highly efficient CO₂ mineralization: Mechanisms and feasibility of utilizing electrolytic manganese residue as a...

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 CO₃^2- 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.