Direct aqueous mineralization of CO2 with carbide slag in a bubble column reactor: the role of liquid recycling

This study presents an experimental investigation on the direct aqueous carbonation of carbide slag with a focus on implementing a liquid-phase recycling strategy. The effects and underlying mechanisms of key operational parameters, including the liquid-phase recycling ratio, the number of recycling cycles, and reactor preparation method (cleaning method), are systematically compared and analyzed. The research confirms the technical feasibility of the liquid-phase recycling process. The results demonstrate that carbonation efficiency improves and stabilizes with successive recycling cycles. A higher liquid recycling ratio significantly enhances the overall carbonation efficiency and solid-phase CO 2 sequestration, primarily attributed to an increased concentration of HCO 3 − ions in the recycled aqueous phase, which promotes CaCO 3 precipitation and creates a synergistic cycle that improves reaction kinetics. A critical finding is the substantial impact of reactor preparation. Thorough cleaning of the reactor utilizing acetic acid solution between cycles leads to a stable and significant boost in carbonation efficiency. In contrast, merely rinsing with water, which leaves residual solid deposits, causes an initial efficiency increase followed by a continuous decline in subsequent cycles. This decline is linked to increased mass transfer resistance, reduced effective interfacial area, and impaired reaction kinetics due to particle accumulation. Consequently, the study recommends liquid-phase recycling operation with complete slurry drainage between experiments to mitigate these negative effects. This work provides fundamental data and theoretical insights into the flow, mass transfer, and reaction characteristics of the process, offering valuable guidance for the development of efficient liquid-phase recycling methods in direct aqueous mineral carbonation.