Pressurized in situ X-ray diffraction insights into super/subcritical carbonation reaction pathways of steelmaking slags and constituent silicate minerals

Abstract This study explores mineral carbonation of industrial stainless steelmaking slags and relevant synthetic constituent minerals via in situ pressurized X-ray diffraction, to clarify carbonation reaction pathways and efficiency for carbon storage and waste valorization. The primary mineral phases of Argon Oxygen Decarburization (AOD) and Continuous Casting (CC) slags, namely, akermanite, bredigite, cuspidine, merwinite, and β- and γ-C2S, were reacted in a custom-built beryllium-capped XRD reactor filled with either water-saturated (wet) subcritical CO2(g), or wet supercritical CO2(SC), in a series of carbonation experiments. Formation of calcite and aragonite was observed for most Ca-bearing minerals, transient precipitation of metastable vaterite was observed, while carbonation of AOD and CC slags in CO2(SC) resulted in hydrated crystalline calcium carbonates and indirect evidence of amorphous carbonate. Results obtained suggest that low-pressure subcritical carbonation routes are attractive for standalone slag carbonation processes, while high-pressure supercritical carbonation routes are amiable to symbiotic integration with CO2(SC)-generating green technologies.