Experimental Investigation and Mechanism Analysis of Direct Aqueous Mineral Carbonation Using Steel Slag

The carbonation of industrial calcium-rich byproducts such as steel slag demonstrates significant potential for CO 2 sequestration. This technique aids in reducing carbon emissions while also promoting waste recycling. Despite its advantages, gaps remain in the understanding of how steel slag characteristics and operational parameters influence the carbonation process, as well as the underlying mechanism of direct aqueous carbonation. We evaluated the carbonation performance of three types of steel slag at temperatures below 100 °C. The slag with the highest CO 2 sequestration capacity was chosen for a systematic evaluation of the effects of operating conditions on carbonation efficiency. Thermodynamic analysis indicated that the reactivity of CaO and Ca(OH) 2 with CO 2 exceeded that of CaO·SiO 2 and 2CaO·SiO 2 . Under conditions of 85 °C, a particle size less than 75 μm, an initial CO 2 pressure of 0.5 MPa, a liquid-to-solid ratio of 5 mL/g, and a stirring speed of 200 rpm, the steel slag achieved a sequestration capacity ( K ) of 283.5 g(CO 2 )/kg and a carbonation efficiency (ζ Ca ) of 51.61%. Characterization of the slag before and after carbonation using X-ray diffraction, SEM-EDS, thermogravimetric analysis, and Fourier transform infrared spectrometry confirmed the formation of new carbonates. Mechanistic analysis revealed that the rate-limiting step initially involved the mass transfer of CO 2 , transitioning to Ca 2+ mass transfer as time progressed. Our research provides a viable technique for CO 2 capture and a beneficial approach for reutilizing waste steel slag. Furthermore, solid residues after capturing CO 2 have the potential for conversion into carbon-negative building materials, offering a sustainable strategy for steel companies and other enterprises with high carbon emissions.