Zirconium in aqueous flows was moderately biomineralized by immobilized Citrobacter N14 cells, in the form of gel-like deposits, probably comprising a mixture of zirconium hydrogen phosphate (Zr(HPO4)(2)) and hydrated zirconia (ZrO2). The simultaneous presence of uranyl ion (UO22+) did not facilitate zirconium deposition and the biomineralization of uranium itself as HUO2PO4 was repressed by zirconium in the presence of excess inorganic phosphate, Liberated enzymatically. Nickel (Ni2+) was not significantly removed from aqueous flows by sorption into cell-bound zirconium deposits, although cell-bound hydrogen uranyl phosphate (HUP) facilitated nickel removal via intercalative ion exchange into its polycrystalline lattice. A preformed layer of HUP also promoted zirconium removal, at 100% efficiency at pH 2.6, maintained over 38 column fluid-volumes before saturation.