Antimony(III/V) removal from industrial wastewaters: treatment of spent catalysts formally used in the SOHIO acrylonitrile process

A treatment and volume reduction process for a spent uranium–antimony catalyst has been developed. Targeted removal, immobilization and disposal of the uranium component has been confirmed, thus eliminating the radiological hazard. However, significant concentrations of antimony ([Sb] ≥ 25–50 mg L⁻¹) remain in effluent from the process, which require removal in compliance with Korean wastewater regulations. Antimony(III/V) removal via co-precipitation with iron has been considered with optimal pH, dose and kinetics being determined. The effect of selected anions – Cl⁻, SO₄²⁻ and PO₄³⁻ – have also been considered, the latter present due to a prior uranium removal step. Removal of Sb(III) from both Cl⁻ and SO₄²⁻ media and Sb(V) removal from Cl⁻ media to below release limits were found to be effective within 5 minutes at an iron dose of 8 mM (molar ratio, [Fe^III]/[Sb] = 20) and a target pH of 5.0. However, Sb(V) removal from SO₄²⁻ was significantly hampered requiring significantly higher iron dosages for the same removal performance. Phosphate poses significant challenges for the removal of Sb(V) due to competition between PO₄³⁻ and Sb(OH)₆⁻ species for surface binding sites, attributed to similarities in chemistries and a shared preference for an inner vs outer binding mechanism.