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Leaching of Metal Ions from Blast Furnace Slag by Using Aqua Regia for CO2 Mineralization

Blast furnace slag (BFS) was selected as the source of Ca for CO 2 mineralization purposes to store CO 2 as CaCO 3 . BFS was dissolved using aqua regia (AR) for leaching metal ions for CO 2 mineralization and rejecting metal ions that were not useful to obtain pure CaCO 3 (as confirmed by XRD analysis). The AR concentration, as well as the weight of BFS in an AR solution, was varied. Increasing the AR concentration resulted in increased metal ion leaching efficiencies. An optimum concentration of 20% AR was required for completely leaching Ca and Mg for a chemical reaction with CO 2 and for suppressing the leaching of impurities for the production of high-purity carbonate minerals. Increasing the liquid-to-solid ratio (L/S) resulted in the increased leaching of all metal ions. An optimum L/S of 0.3/0.03 (=10) was required for completely leaching alkaline-earth metal ions for CO 2 mineralization and for retaining other metal ions in the filtered residue. Moreover, the filtrate obtained using 20% AR and an L/S of 0.3/0.03 was utilized as Ca sources for forming carbonate minerals by CO 2 mineralization, affording CaCO 3 . The results obtained herein demonstrated the feasibility of the use of AR, as well as increasing pH, for the storage of CO 2 as high-purity CaCO 3 .