Direct mineral carbonation of carbide slag waste in fixed bed reactor: comparison of dry and wet route

Global climate change due to heavy industrial carbon dioxide (CO₂) emissions has become one of the most significant environmental concerns. Mineral carbonation of alkaline wastes into valuable products is a promising CO₂ capture, storage, and utilization technique. This study investigated the direct mineral carbonation of carbide slag, a byproduct of acetylene production, in both dry and wet phases under moderate conditions (≤ 120 °C, ≤ 1 MPa) in a fixed bed reactor. Mineral carbonation of carbide slag was validated by online gas chromatography, thermogravimetric analysis, and microstructure characterization of the carbonated products. Moreover, the effects of operational parameters such as temperature, pressure, gas–solid ratio, superficial gas velocity, particle size, and initial gas concentration on the carbonation reaction were studied. The results show that wet-phase carbonation at a liquid‒solid ratio of 0.2 achieves a maximum carbonation efficiency of 37% and a CO₂ capture capacity of 4.6 mol CO₂ kg⁻¹, outperforming the dry phase under ambient conditions. Humidity in the inlet gas stream and a higher reaction pressure improved carbonation in both phases. A maximum carbonation efficiency of 97% was observed, with a CO₂ capture capacity of 12.2 mol CO₂ kg⁻¹ in the wet phase of mineral carbonation at 1 MPa pressure. Microstructural analyses revealed a significant formation of calcium carbonate in the carbonated samples. This study highlights the potential of carbide slag for effective CO₂ capture through mineral carbonation, offering an environmentally friendly and scalable solution for reducing greenhouse gas emissions.