Carbon mineralization technology involves reactions between carbon dioxide (CO2) and alkali earth metals such as calcium and/or magnesium to form thermodynamically stable solid carbonates (i.e., CaCO3, and MgCO3), and is currently being recognized as a promising method of both storing and utilizing CO2. In particular, industrial solid wastes such as steelmaking slags (steel and iron slags) are considered to be suitable alkaline feedstock for carbon mineralization. The aqueous carbon mineralization process of steelmaking slags generally includes the extraction of alkali earth metals in a low pH condition, followed by carbonation with CO2 at a high pH. However, since steelmaking slags often exhibit limited leachability depending on their physicochemical properties, it often has an important role in the design of the carbon mineralization process. Here, the leachability of the steel slag was examined in both acidic and basic conditions. The extraction kinetics as well as the various operating factors, such as temperature, and particle size distribution, under an acidic condition were also examined for the potential carbon sequestration using the alkaline wastes.