Biosorption of Uranium and Copper by Biocers

Biological ceramic composites (biocers) made according to an 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 in dependence on time, concentration and preparing conditions. Biocers with cells possess the highest binding capacity compared to matrices with spores and S-layer. Freeze drying of prepared biocers or adding water soluble additives 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.