Nickel accumulation by immobilized biofilm of Cirobacter sp. containing cell-bound polycrystalline hydrogen uranyl phosphate

Hydrogen uranyl phosphate (HUO2PO4: HUP), deposited enzymatically on Citrobacter N14 cells immobilized as biofilm on ceramic Raschig rings in a flow-through column, removed nickel quantitatively from dilute aqueous solution in the form of nickel uranyl phosphate, via intercalative ion exchange. Nickel-loaded columns were regenerated by washing either with citrate buffer or with buffer containing UO22 and phosphate donor (glycerol 2-phosphate), this giving additional crystalline HUP deposit for subsequent improvement of nickel removal. No uranium release occurred during selective desorption of Ni, proving the integrity of the biofilm within the column. The use of ceramic supports to manufacture an artificial, bioinorganic, ion exchanger is novel and the use of solid matrices overcomes the problems of mechanical stability which limit the applications of gel-immobilized cells for large-scale processes. © Rapid Science Ltd. 1998