Investigation of pH swing carbon mineralization for valuable element recovery and CO₂ sequestration using steelmaking slag

Carbon capture, utilization, and storage (CCUS) technology is a key approach to mitigate climate change and achieve net-zero emissions. Among CCUS technologies, ex-situ carbon mineralization via pH swing processes using steelmaking slag presents dual benefits: resource recovery and CO₂ reduction through CaCO₃ production. However, challenges like co-precipitation and solubility issues require further investigation. Here, we explore the in-depth elemental precipitation behavior using basic oxygen furnace (BOF) and kanbara reactor (KR) slags. Elements were extracted using 2 M HCl solution and sequentially precipitated by adjusting the pH from 5 to 10 with 2 M NaOH solution. CO₂ gas was then bubbled to generate CaCO₃. Major elements (Ca, Mg, Fe, Mn, Si, Al) and minor elements (Ti, Cr, Cu) were identified. Al, Si, Ti, and Cr precipitated at pH 3.5–5, Fe and Cu at pH 7–8, Mn at pH 8–9, Mg at pH 10, while Ca remained in solution for carbonation at pH 10. The precipitation behavior was dependent on the solubility of each element (K_sp) and affinity for hydroxide ions (OH⁻). The purities of CaCO₃ from BOF and KR slags were 98.4 % and 97.4 %, with CO₂ storage capacities of 93 kg/t slag and 131 kg/t slag, respectively.