Deep dewatering of bauxite residue via the synergy of surfactant, coagulant, and flocculant: Effect of surfactants on dewatering and settling properties

Abstract

Complex surface properties and high fineness of bauxite residue (BR) make it hard to compact and settle, which reduces the solid content of the BR cake and solid–liquid separation efficiency. The proposed three-step procedure involving surface wettability adjustment, charge neutralization, and flocculation through the synergy of surfactants, lime, and polyacrylamide (PAM) was carried out. Polycarboxylate superplasticizer (PCE) significantly improved BR dewaterability and decreased the water content from 45.85% to 36.71% (2%) compared with the original BR cake. But the solid recovery also reduced from 93.29% to 89.28% (2%), and the BR slurry was still a stable suspension. The synergy of PCE (0.5%), lime, and PAM effectively coagulated and flocculated the BR particles, and improved BR dewaterability. The average BR particle sizes enlarged from about 10 µm to 22 µm, and the solid recovery and settling rate elevated to 99.35% and 1.596 m/h. The water content of the BR cake reduced from 52.33% to 47.18% compared without PCE addition. The surface behavior and adsorption behavior analysis showed that PCE neutralized the surface charge and decreased the surface tension of BR particles with the adsorption of PCE on its surface. The study gave a feasible suggestion for the efficient dewatering and fast settling of BR.