Magnetic modification of used tea leaves for uranium adsorption

Used tea leaves, or tea waste (TW), were crushed into powder and mixed with graphene oxide (GO) in water, followed by adjusting the pH value of the resulting suspension with ammonia to 11, adding FeCl2·4H2O under magnetic stirring, filtration and drying to prepare a rGO/Fe3O4/TW (with mass ratios of 1:2:1) hybrid material. The structure and crystalline phases of the material were characterized by FTIR and XRD. Isotherms for uranium adsorption were obtained and its kinetics were measured in a conical bottle that was placed in a shaker. The effects of the pH value of the uranium solution, adsorption time and initial concentration on the uranium adsorption were investigated. Results indicate that the hybrid has a much faster adsorption rate than TW with a uranium removal rate up to nearly 100% in 20 min for an initial uranium concentration of 10 mg L−1. The maximum adsorption capacity of the hybrid is 103.84 mg g−1 while that of TW is 97.70 mg g−1. The hybrid with adsorbed uranium can be easily separated from the solution by applying a magnetic field. The isotherms and kinetics of uranium adsorption on the hybrid are best fitted by the Langmuir isotherm model and the pseudo-second-order model, respectively. The hybrid has good reusability with an uranium removal rate of about 85% after 5 cycles.