Direct CO₂ Capture by Carbide Slag: Moisture Regulation, Uptake Performance, and Reaction Kinetics

Abstract

To evaluate the feasibility of carbide slag as a low-cost calcium-based solid waste for CO₂ mineral capture, direct carbonation experiments were carried out under different moisture contents. The effects of moisture content on CO₂ uptake, carbonation efficiency, phase composition, and morphology were investigated. Five moisture contents of 0%, 5%, 10%, 20%, and 30% were selected, and CO₂ was introduced at ambient temperature and pressure. The results show that the abundant Ca(OH)₂ in carbide slag can react with CO₂ to form CaCO₃, indicating that carbide slag has potential for direct mineral carbonation of CO₂. As the moisture content increased from 0% to 20%, the CO₂ uptake of carbide slag gradually increased. The best carbonation performance was obtained at 20% moisture content, where the CO₂ uptake reached 4.60 mol/kg after 120 min, corresponding to a CO₂ fixation amount of 0.2024 g/g and a carbonation efficiency of 36.8%. When the moisture content increased further to 30%, the CO₂ uptake decreased to 3.20 mol/kg. TG/DTG, XRD, and FTIR results indicate that Ca(OH)₂ was gradually converted into CaCO₃ during carbonation. An appropriate amount of moisture promoted CaCO₃ formation and deposition, whereas excessive moisture hindered CO₂ diffusion and reduced the carbonation efficiency. These results demonstrate that moisture regulation is an important factor for improving the efficiency of direct CO₂ capture by carbide slag and provide a reference for low-cost CO₂ mineralization using alkaline industrial solid wastes.