Biosorption of uranium and copper by biocers

dBiological ceramic composites (biocers) made according to aqueous sol-gel protocol were used as selective metal binding filters. The biological component of the biocers Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile. Vegetative cells and spores of this strain are known to bind selectively U, Cu, Al, Cd, and Pb in large amounts. Sol-gel ceramics were prepared by dispersing vegetative cells, spores, and stabilized surface-layer proteins (S-layer) in aqueous silica nanosols, gelling, and drying. The biosorption of uranium and copper by the three kinds of biocers and by their single components was investigated with dependence on time, concentration, and preparation conditions. Biocers with cells possess the highest binding capacity compared to matrixes with spores and an S-layer. Freeze-drying of prepared biocers or adding water-soluble compounds as sorbitol lead to higher porosity and faster metal binding. Uranium was bound mainly to the biological component but also to the SiO2 network. In contrast, copper was only bound by the cells, spores, or S-layer. Bound uranium and copper were completely removed by washing with aqueous citric acid.