Reversible accumulation of uranium by bacteria-based sol-gel ceramics

Bacillus sphaericus JG-A12 was isolated from the uranium mining waste pile "Haberland" near the town of Johanngeorgenstadt, Saxony, Germany. The drain water and the soil at this site are highly contaminated with heavy metals and radionuclides. Sorption experiments with vegetative cells and spores of B. sphaericus JG-A12 demonstrate specific and reversible accumulation of U, Cu, Pb, Al and Cd from the drain water of the waste. The latter makes this bacteria an interesting candidate for the development of in situ bioremediation processes based on biological ceramics (biocers). In addition, B. sphaericus JG-A12 possesses a surface layer (S-layer) which differs at its N-terminal domain (220 amino acid residues) significantly from all other S-layers studied up to date. In this study vegetative cells, spores and stabilized S-layer sheets were immobilized in the SiO2 matrix by dispersing in aqueous silica nanosols, gelling and drying. Variations in the porosity and structure of the biocers were achieved by different drying methods or adding water soluble compounds as sorbitol. The time dependence of the uranium sorption and desorption by the free biocomponents and biocomposites was investigated. Localization of the bound metals and a characterization of the metal complexes formed at the biocer were carried out using scanning electron microscopy and EDX.