Synergistic CO2 mineralization using coal fly ash and red mud as a composite system

CO₂ mineralization plays a critical role in the storage and utilization of CO₂. Coal fly ash (CFA) and red mud (RM) are widely utilized as CO₂ mineralizers. However, the inert calcium species in CFA limit its carbonation capacity, meanwhile the substantial Ca²⁺ releasing of RM is hindered by a covering layer of calcium carbonate. In this study, CO₂ mineralization in a composite system of CFA and RM was investigated to enhance the carbonation capacity. Multiple analyzers were employed to characterize the raw materials and resulting mineralization products. The results demonstrated that a synergistic effect existed in the composite system of CFA and RM, resulting in improving CO₂ mineralization rate and efficiency. The produced calcium carbonate was ectopically attached the surface of CFA in the composite system, thus slowing down its coverage on the surface of RM. This phenomenon facilitated further releasing Ca²⁺ from the internal RM, thereby enhancing CO₂ mineralization efficiency. Meanwhile, the inclusion of RM significantly improved the alkalinity of the composite system, which not only promoted the dissolution of Ca²⁺ of the inert CaSO₄(H₂O)₂ in CFA, but also accelerated CO₂ mineralization rate. The investigation would be beneficial to CO₂ mineralization using industrial solid wastes.