Valorizing Carbide Slag as Cement-Compatible CaCO3 Suspension via Pretreatment-Controlled Carbonation

Calcium carbonate (CaCO3) suspensions derived from industrial calcium sources offer a viable route for low-carbon cement systems, yet their effectiveness is frequently constrained by limited interfacial compatibility with hydration products. In this study, carbide slag was carbonated to prepare CaCO3 suspensions, and an integrated pretreatment–carbonation route combining acid washing, wet milling, and triethanolamine-assisted crystallization regulation was employed to modify the carbonation products. Following the integrated treatment, the MgO and SO3 contents decreased from 0.93% and 1.52% in CS-CaCS to 0.33% and 0.51% in MCS-CaCS, respectively, accompanied by reduced coarse agglomeration and improved apparent wetting behavior. At a carbonate dosage of 15%, the 28-day compressive strength increased from 55.7 MPa for CS-CaCS to 76.8 MPa for MCS-CaCS, corresponding to an improvement of 37.9%. Nanoindentation further showed that the mean hardness and reduced modulus increased from 1.81 to 6.18 GPa and from 50.0 to 74.7 GPa, respectively. The performance recovery is attributed to the concurrent effects of suppressed impurity inheritance, reduced agglomeration, enhanced carbonate participation in hydration, and improved local particle–hydrate organization. These findings demonstrate the potential of the integrated route for converting carbide slag into a more cement-compatible CaCO3 suspension.