Selective Removal of U(Ⅵ) by Immobilized Sulfate-reducing Bacteria

The sulfate-reducing bacteria immobilized in polyvinyl alcohol-sodium alginate beads were prepared. The impacts of Zn²⁺, Cu²⁺, acetate, oxalate and citrate on the reduction of U(Ⅵ) were investigated. Furthermore, selective removal of U(Ⅵ) or heavy metals was assessed. The results indicate that the existing of Zn²⁺ or Cu²⁺ doesn’t affect U(Ⅵ) removal appreciably when their concentrations are less than 100 mg/L, but they can inhibit U(Ⅵ) removal completely while their concentrations reach 150 mg/L. In the presence of monodentate ligand (acetate), U(Ⅵ) can be removed readily, whereas HQKmultidentate ligands (oxalate and citrate) impose an inhibition on U(Ⅵ) removal. In organic-free wastewater, direct selective removal of U(Ⅵ) can be achieved based on thermodynamic considerations and optimized by appropriately lowering COD/SO^2-₄. In wastewater containing multidentate organics, U(Ⅵ) can be firstly complexed during precipitation of Zn²⁺ and Cu²⁺, and then removed directively after degradation of organic ligands.