Experimental investigation of hot steam temperature effects on physicochemical properties and mineralization efficiency in steel Slag-CO2 systems.

In the face of intensifying global warming, carbon capture, utilization, and storage (CCUS) technologies are increasingly recognized as critical pathways toward achieving carbon neutrality. Although alkaline steel slag exhibits significant carbon sequestration potential, traditional mineralization methods are limited by low mass transfer efficiency and rapid efficiency decay caused by pore blockage and active surface coverage. To address these limitations, this study proposed an innovative approach leveraging steam-mediated activation to restructure the physicochemical properties of steel slag, thereby overcoming conventional barriers. Using a custom-designed hot steam-CO2 mineralization reactor, we systematically investigated the advantages of hot steam activation over conventional wet mineralization. Furthermore, we elucidated the effects of HS temperature on steel slag-CO2 mineralization efficiency and its underlying mechanisms. Results showed that the hydrated steel slag treated with hot steam exhibits a 2.4-fold increase in specific surface area and a 1.8-fold enhancement in porosity compared to conventional wet processing. This significant optimization of the mineralization conditions leads to an improvement in mineralization efficiency, reaching 22.48 %, which is four times higher than that achieved by conventional wet methods. With increasing hot steam temperature, mineralization efficiency showed significant enhancement, rising from 9.2 % at 100 °C to a peak of 35.14 % at 220 °C. The mineralization product CaCO3 exhibited a dual effect: filling micropores to reduce porosity for pores <3.5 nm, while forming new nanopores through stacking to increase porosity for pores >3.5 nm. The rapid generation of mesopores and macropores further drove the overall porosity increase. As HS temperature rose, the surface content of CaCO3 and C-S-H in MSS increased significantly. The pore-forming effect of CaCO3 stacking resulted in higher porosity, reaching 9.2 and 6.5 times the porosity and specific surface area of RSS at 220 °C, respectively.