BIOACCUMULATION OF NICKEL BY INTERCALATION INTO POLYCRYSTALLINE HYDROGEN URANYL PHOSPHATE DEPOSITED VIA AN ENZYMATIC MECHANISM

A Citrobacter sp. accumulates uranyl ion (UO22+) as crystalline HUO2PO 4 . 4H(2)O (HUP), using enzymatically generated inorganic phosphate. N i was not removed by this mechanism, but cells already loaded with HUP removed Ni2+ by intercalative ion-exchange, forming Ni(UO2PO4)(2) . 7 H(2)O, as concluded by x-ray diffraction (XRD) and proton induced x-ra y emission (PIXE) analyses. The loaded biomass became saturated with N i rapidly, with a molar ratio of Ni:U in the cellbound deposit of appr ox. 1:6; Ni penetration was probably surface-localized. Cochallenge of the cells with Ni2+ and UO22+, and glycerol 2-phosphate (phosphate do nor for phosphate release and metal bioprecipitation) gave sustained r emoval of both metals in a flow through bioreactor, with more extensiv ely accumulated Ni. We propose 'Microbially Enhanced Chemisorption of Heavy Metals' (MECHM) to describe this hybrid mechanism of metal bioac cumulation via intercalation into preformed, biogenic crystals, and no te also that MECHM can promote the removal of the transuranic radionuc lide neptunium, which is difficult to achieve by conventional methods.