Calcium recovery from waste carbide slag via ammonium sulfate leaching system

Waste carbide slag (WCS) is a typical industrial solid waste with high calcium content, which shows highly potential in preparation of CaCO3 by CO2 mineralization technology. This study demonstrated the feasibility of efficient calcium leaching from WCS using ammonium sulfate ((NH4)2SO4) under mild conditions (≤40 °C，0.1 MPa). Nearly 90% calcium was converted into calcium sulfate dihydrate (CaSO4·2H2O) in about 15 min, and after impurity separation the CaSO4·2H2O with about 90% whiteness and 94% purity was effectively collected. In addition, a surface coverage kinetics model suitable for this leaching system was proposed. It was found that, kinetics behavior followed the chemical reaction control mechanism within the first minutes and then switched to the product islands diffusion-control along with CaSO4·2H2O crystallization. Accordingly, calcium leaching in (NH4)2SO4 system could be reinforced by readjusting S/L after reaching equilibrium. This process provides a potential path for the resource treatment of industrial solid wastes such as calcium carbide slag and desulfurization gypsum.