Preparation Of Sulfate-reducing Bacteria Immobilized Microspheres And Properties U (Ⅵ) Removal

Uranium mining and milling production technologies, such as in-situ leaching,heap leaching and stope leaching, has been generally used in China, accompanyingwith the release, dissolution, migration of uranium, causing long-lasting radioactivecontamination and resource loss. Investigation shows that U（Ⅵ） could be removedthrough enzymatic reduction/precipitation in the presence of electron donor, eg. H2orlactate. For the industrial application of this bioprocess, immobilization techonologycould be an vital strategy. In this study, polyvinyl alcohol （PVA） and sodiumalginate（SA） were used as entrapment agents, and the optimal conditions weredetermined by the orthogonal experiment. The reduction properties, effects of heavymetals and organics on U（Ⅵ） removal were investigated. Finally, selective removal ofU（Ⅵ） was assessed and optimized. The main results of this work are as follow：（1） The optimum conditions for the preparation of immobilized sulfate-reducingbacteria beads were determined by the orthogonal experiment in terms of themechanical stability, mass transfer, difficulty of forming beads and biological activityof SRB cells （W/V）: PVA8%, SA0.5%, CaCl₂3%（1.5h） and0.5M Na₂SO₄（2.5h）.（2） SRB immobilized in PVA/SA beads could alleviate harsh conditions such aspH, heavy metals and organics. In a wide range weak acidic environment（3.0⁶.0）,U（Ⅵ） could be removed efficiently and steadily. With the condition of U（Ⅵ）concentration of15mg/L, beads volume6.0g/L and pH6.0, U（Ⅵ） removal ratereached94.67%.（3） The presence of Zn²⁺or Cu²⁺did not affect U（Ⅵ） removal appreciably whenits concentration less than100mg/L, but they could inhibit U（Ⅵ） removal completelywhile its concentration reached150mg/L.（4） In the existing of monodentate ligand （acetate）, U（Ⅵ） could be removedreadily, whereas multidentate ligands （oxalate and citrate） imposed an inhibition onU（Ⅵ） removal.（5） In organic-free wastewater, direct selective removal of U（Ⅵ） could beachieved based on thermodynamic considerations and optimized by appropriatelylowering COD/SO₄^2-； and in wastewater containing multidentate organics, as U（Ⅵ）was firstly complexed during precipitation of Zn²⁺and Cu²⁺, and then removeddirectively after degradation of organic ligands.