Removal and recovery of uranium by waste digested activated sludge in fed-batch stirred tank reactor

This study demonstrated the removal and recovery of uranium(VI) in a fed-batch stirred tank reactor (STR) using waste digested activated sludge (WDAS). The batch adsorption experiments showed that WDAS can adsorb 200 (± 9.0) mg of uranium per g of WDAS. The maximum adsorption of uranium was achieved even at an acidic initial pH of 2.7 which increased to pH of 4.0 in the equilibrium state. Desorption of uranium from WDAS was successfully demonstrated by releasing more than 95% uranium using both acidic (0.5 M HCl) and alkaline (1.0 M Na2CO3) eluents. Due to the fast kinetics of uranium adsorption onto WDAS, the fed-batch STR was successfully operated at hydraulic retention time of 15 minutes. Twelve consecutive uranium adsorption steps with average uranium adsorption efficiency of 91.5% required only two desorption steps to elute more than 95% of uranium from WDAS. Uranium was shown to interact predominantly with the phosphoryl and carboxyl groups of the WDAS, as revealed by in situ infrared spectroscopy and time-resolved laser-induced fluorescence spectroscopy. This study provided a proof-of-concept of the use of fed-batch STR process based on WDAS for the removal and recovery of uranium.