High-efficiency CO2 sequestration through direct aqueous carbonation of carbide slag: determination of carbonation reaction and optimization of operation parameters.

Under the dual-carbon target, CO₂ mineralization through solid wastes presents a mutually beneficial approach for permanent carbon emission reduction at a low material cost, while also enabling the resource utilization of these wastes. However, despite its potential, a comprehensive understanding about the effect of industrial solid waste properties and operating parameters on the carbonation process, and the mechanism of direct aqueous carbonation is still lacking. A series of experiments were conducted to compare the carbonation performance of fly ash, steel slag, and carbide slag. Subsequently, CO₂ mineralization by carbide slag was systematically studied under various operating parameters due to its high CO₂ sequestration capacity. Results showed the reactivity of CaO and Ca(OH)₂ was higher than that of CaO·SiO₂ and 2CaO·SiO₂. Carbide slag demonstrated a sequestration capacity of 610.8 g CO₂/kg and carbonation efficiency ζ_Ca of 62.04% under the conditions of 65 °C, 1.5 MPa initial CO₂ pressure, 15 mL/g liquid-to-solid ratio, and 200 r/min stirring speed. Moreover, the formation of carbonates was confirmed through XRD, SEM-EDS, TG, and FTIR. A mechanism analysis revealed that initially, the rate of the carbonation process was primarily controlled by the mass transfer of CO₂ in the gas–liquid interface. However, the rate-determining step gradually shifted to the mass transfer of Ca²⁺ in the solid–liquid interface as the reaction time increased. This study lays the foundation for the large-scale implementation of CO₂ sequestration through carbide slag carbonation. [ABSTRACT FROM AUTHOR]