Promotion effects of gypsum on carbonation of aluminates in medium Al ladle furnace refining slag

Medium Al ladle furnace refining slag (MAS) can potentially absorb CO2 owing to its high percentages of active Ca, Mg and Al. However, it was hardly focused on. Here, the effects of gypsum on the compressive strength and CO2 uptake of carbonation-cured MAS blocks were evaluated. Carbonation curing improved the strength of MAS–gypsum samples by 1.57–3.64 times. Moreover, 8.33% gypsum promoted the strength and CO2 uptake of 24-h carbonation curing MAS samples by 97.82% and 24.69%, respectively. Microanalysis indicates that Gypsum stimulates reactivity of aluminates and shifts the hydration products of aluminates from C4AHx to ettringite and hemicarboaluminate. They were then carbonated into calcite and monocarboaluminate in CO2-rich environments. Adding gypsum contributes to an increase in carbonation products amount. The carbonation products filled the pores and bound the MAS particles, thereby enhancing the strength of MAS. This study preliminarily proves the feasibility of CO2 mineralization of MAS–gypsum for building materials.