Mechanistic study on the promotion of Ca²⁺ leaching in steel slag through high-temperature solid waste modification

Indirect carbonation of steel slag is an effective method for CO₂ storage, reducing emissions, and promoting cleaner production in the steel industry. However, challenges remain, such as low Ca²⁺ leaching rates and slag management complexities arising from variations in mineral compositions. To address this, a high-temperature modification process is proposed to alter the mineral composition and facilitate the synergistic utilization of calcium and iron. This study delves into the effects of various solid waste modifications on the leaching of Ca²⁺ and the total iron content within steel slag. Results show that high-basicity modified slag forms Ca₂(Al, Fe)₂O₅, reducing calcium leaching. Low-alkalinity modified slag produces calcium-rich aluminum minerals and also reduces the leaching of Ca²⁺ ions. At a basicity of 2.5, coal gangue, fly ash, and blast slag achieve maximum Ca²⁺ leaching rates of 88.93%, 89.46%, and 90.17%, respectively, with corresponding total iron contents of 41.46%, 37.72%, and 35.29%. Upgraded coal gangue exhibits a 50.02% increase in calcium leaching and a 15.58% increase in total iron content compared to the original slag. This enhances CO₂ fixation and iron resource utilization. Overall, the proposed indirect carbonation and iron enrichment modification offer a novel approach for the resource utilization and environmental stability of steel slag.