BIOSORPTION AND RETENTION OF SEVERAL ACTINIDE AND FISSION-PRODUCT ELEMENTS BY BIOMASS FROM MYCOBACTERIUM-PHLEI

The properties of mobile, 5% w/w cell suspensions of Mycobacterium phl ei have been examined for their capacity to adsorb and retain uranyl(V I) and neptunyl(V) cations from nitrate-buffered solutions at pH 1. Eq uilibrium conditions of sorption were attained after 3 hours for conce ntrations (C) in the range 0.015-18 mM cation and indicated a maximum specific adsorption capacity (Qe(max)) of 182 mu mol/g dry biomass for C greater than or equal to 10 mM. NpO2+ generally showed higher Qe va lues than UO22+ at corresponding concentrations. Lixiviation tests wit h cation-loaded biomass in neutral and acidic media indicated that the extent of desorption did not vary extensively between pH 7 and pH 1 a nd did not exceed 3% for U and 1% for Np ions at pH 7 during 7-day per iods of treatment. Analogous experiments with U-loaded biomass subject ed to neutron activation prior to lixiviation enabled retention measur ements for various fission-product isotopes produced in situ and showe d that retention of Np-239 formed within the cellular matrix was > 99% at pH 7 and greater than or equal to 94% at pH 1.