Integrating reductants and organic ligands for improved Mn recovery and CO₂ sequestration from electric arc furnace slag

Electric arc furnace (EAF) slag exhibits great potential in carbon mineralization and resource recovery due to its high calcium (Ca) and manganese (Mn) content. In particular, a pH swing-assisted carbonation process has been recognized as a plausible option to simultaneously recover valuable resource (Mn) and sequester CO₂ via reactions with Ca forming calcium carbonate (CaCO₃). However, the presence of insoluble Mn^3 + often poses a significant challenge, leading to a low leaching efficiency for Mn. This study investigates the effects of reductants, including hydrogen peroxide (H₂O₂), ascorbic acid (C₆H₈O₆), and sodium sulfite (Na₂SO₃), in enhancing Mn leaching efficiency by effectively converting Mn³⁺ into its more leachable Mn²⁺ form. Additionally, the ligand effects of biogenic volatile organic acids, including acetic acid (C₂H₄O₂), propionic acid (C₃H₆O₂), butyric acid (C₄H₈O₂), and valeric acid (C₅H₁₀O₂), were evaluated to improve the overall leaching efficiency of Ca and other major elements, as well as Mn. The synergistic effect of reductants and organic acids resulted in superior leaching efficiencies (∼100 %) for magnesium (Mg), aluminum (Al), Mn, and Ca. The pH swing process utilizing this synergistic effect achieved great Mn recovery and obtained solid residue included an Mn concentration of up to 43.2 wt% at pH 9. Following Mn recovery, carbonation was conducted using the residual leachate, resulting in the formation of high-purity CaCO₃ (93 %), with a CO₂ storage capacity of 118 kg/ton slag. These findings highlight the potential of EAF slag as a sustainable Mn source while simultaneously contributing to CO₂ storage.