Colloidal Regularities of the Interaction between Uranium(VI) and the Cells of Metal-Resistant Bacillus cereus AUMC 4368 Bacterial Culture

Abstract

Sorption of uranium(VI) by the cells of metal-resistant Bacillus cereus AUMC 4368 bacterium was studied in aqueous solutions as a function of pH, equilibrium concentration of metal, and the presence of co-ions with account of the changes in phase state of metals and biocolloids. Experimental data indicate that the sorption of uranium(VI) by negatively charged biocolloids is maximal at pH 4.2–4.5 (1.2 mM per 1g of dry biomass), when metal is present in the form of positively charged hydroxocomplexes. At pH ≥ 8, the interaction between uranium(VI) and the cells is inhibited due to the formation of negatively charged water-soluble hydroxocarbonate complexes and uranate ions. Co, Sr, Cu, Ca, Mg, and Zn ions do not influence the efficiency of sorption of uranium(VI) in a weakly acidic medium, but can cause inhibiting effect in neutral pH region. The most pronounced effect expressed in broadening of sorption range and in the heterocoagulation of uranyl is observed in the presence of Fe3+ ions. It was established that the binding of uranium(VI) occurs by the carboxyl surface groups of Bacillus cereuscell surface. Uranium(VI) is irreversibly bound by the carboxyl groups of cell surface and its efficient desorption is possible only during the interaction with citric acid or sodium hydrocarbonate with the formation of water-soluble complexes transferred to aqueous phase. It was shown that uranyl in the form of organocomplexes (citric, humatic, and fulvatic) is not sorbed by biocolloids.