Enhanced dealkalization of bauxite residue through calcium-activated desulfurization gypsum

A novel integrated approach to remove the free alkalis and stabilize solid-phase alkalinity by controlling the release of Ca from desulfurization gypsum was developed. The combination of recycled FeCl₃ solution and EDTA activated desulfurization gypsum lowered the bauxite residue pH to 7.20. Moreover, it also improved the residual Ca state, with its contribution to the total exchangeable cations increased (68%−92%). Notably, the slow release of exchangeable Ca introduced through modified desulfurization gypsum induced a phase transition of the alkaline minerals. This treatment stabilized the dealkalization effect of bauxite residue via reducing its overall acid neutralization capacity in abating pH rebound. Hence, this approach can provide guidance for effectively utilizing desulfurization gypsum to achieve stable regulation of alkalinity in bauxite residue.