Enhanced Solid-Liquid Separation of As(Ⅲ) Sulfide from Copper Smelting Waste Acid: Synergistic Effect and Mechanism of As2S3 Seed and PAM Flocculant

Sulfidation is recognized as a competitive method to remove arsenic from copper smelting waste acid. However, despite its ability to shed As(Ⅲ) efficiently, the sulfidation driven by S(-Ⅱ) supersaturation levels generates fine particles that severely hamper subsequent solid-liquid separation. In this study, the results manifest that expanding S(-Ⅱ) dosage and downgrading acidity (i.e., H 2 SO 4 concentration) can foster As(Ⅲ) removal, but diminish the particle size distribution of As(Ⅲ) sulfides. Based on the diffusion-growth model, except for in-situ CuS and CdS, concomitant anions and cations decelerate As(Ⅲ) sulfide settling. This is attributed to enhanced negative charges on the particle surface. In pursuit of better settling performance of As(Ⅲ) precipitate, a strengthening strategy of As 2 S 3 crystal seed and polyacrylamide(PAM) flocculant is proposed, where the preparation of As 2 S 3 crystal seed from arsenic waste complies with the green recycling-production standards. By involving 10   g/L As 2 S 3 crystal seed as heterogeneous nucleation and 5   ml/L PAM flocculant as framework support, the settling velocity of As(Ⅲ) sulfide is boosted by approximately 170%, delivering valuable guidance for reinforcing gravity settling performance in thickener processes.