Abstract:To address difficulties in separating arsenic (As) from antimony (Sb) and tin (Sn) in arsenic-antimony-tin residue, a thermodynamic analysis of Sb(Ⅲ)-Sn(Ⅳ)-H2O system was conducted, and pH control window for phase separation was determined to be 9.0~10.3. Accordingly, a two-stage alkaline leaching process consisting of first-stage soda leaching and second-stage alkaline oxidative leaching was proposed for arsenic removal, supplemented by oxidative precipitation of antimony for its recovery. Effects of key parameters on As removal and Sb/Sn separation were systematically investigated, and the optimal conditions for each stage were determined. Under the optimized conditions, As content in the residue decreased from 17.52% to 1.81%, achieving an overall As removal rate of 92.14%, while direct recovery rates of Sb and Sn reached 97.74% and 95.44%, respectively. Mechanistic analysis revealed that during the first-stage leaching, arsenate decomposed to release AsO43?, while simultaneous hydrolysis of Sb3+ and Sn4+ generated colloidal Sb2O3·xH2O and Sn(OH)4, which adsorbed and encapsulated arsenic. In the second-stage leaching, H2O2 oxidized the colloidal Sb2O3·xH2O to crystalline NaSb(OH)6 precipitate, disrupting encapsulation structure and enabling further release of arsenic. Phase and valence transformations were verified by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope with energy dispersive spectroscopy (SEM-EDS) characterizations. This process enabled selective removal of As and simultaneous enrichment of Sb and Sn.