Dual benefits of manganese recovery and carbon mineralization via pH swing-assisted carbonation process in iron and steelmaking by-products

Ex-situ carbon mineralization utilizing iron and steelmaking by-products are a promising approach for the circular economy by enabling by-product recycling, resource recovery, substantial CO₂ sequestration, and the production of value-added solid carbonates (e.g., CaCO₃, MgCO₃). However, the variability in the physicochemical properties of these by-products poses challenges in predicting leaching, precipitation, and carbonation behavior, which is generally influenced by their generation processes. In this context, this study focuses on the recovery of manganese (Mn) and CO₂ sequestration utilizing blast furnace slags (air-cooled, IS-A; water-cooled, IS-W), and electric arc furnace slag (EAF) and its dust (EAF-D) via a pH swing-assisted carbonation process. Leaching behavior for magnesium (Mg), aluminum (Al), silicon (Si), calcium (Ca), iron (Fe), and manganese (Mn) in IS-A and IS-W was identical, though differences emerged in the precipitation behavior of major elements due to co-precipitation. The IS-A and IS-W included higher Ca content (IS-A, 21.4 wt%; IS-W, 24.3 wt%) compared to EAF and EAF-D, resulting in impressive CO₂ storage capacities (IS-A, 93 kg CO₂/ton slag; IS-W, 128 kg CO₂/ton slag). In contrast, EAF and EAF-D had higher Mn content (EAF, 19.4 wt%; EAF-D, 34.7 wt%), with concentrations achieving up to 27.4 wt% for EAF and 46.7 wt% for EAF-D, alongside notable recovery efficiencies (EAF, 29 %; EAF-D, 68 %). The carbonation process produced high purity CaCO₃ (92–98 %). These findings underscore the potential of iron and steelmaking by-products as feedstock for carbon mineralization and resource recovery, thereby contributing to a more sustainable society.