Removal of uranium from acidic aqueous solution by natural fluorapatite

Removal of uranium(VI) from uranium(VI) containing waste water is urgently needed with the global nuclear energy exploitation. The present work have successfully completed removal of uranium(VI) by natural fluorapatite. The natural fluorapatite before and after adsorption of uranium(VI) was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The experimental results are as follows: (1) At 308 K and pH3, solid-liquid ratio is 0.12 g/L, equilibrium time is 180 min and initial uranyl ion concentration is 100 mg/L, the adsorption capacity of uranium(VI) by natural fluorapatite reaches 620.08 mg/g and the concentration of uranyl ion after adsorption is 25.59 mg/L; (2) The adsorption process of uranium(VI) by natural fluorapatite is in accordance with the pseudo-second-order kinetics and Langmuir isotherm adsorption model; (3) The adsorption of uranium(VI) by natural fluorapatite is a spontaneous and endothermic reaction. The results show that the removal mechanism of uranium(VI) by natural fluorapatite is surface mineralization. After adsorption of uranium(VI) is conducted, two new phases of meta-autunite (Ca(UO2)2(PO4)2.2H2O, Ca(UO2)2(PO4)2.6H2O) are generated on the surface of natural fluorapatite. The meta-autunite can maintain high stability in pH ≥ 3 aqueous solution. Consequently, natural fluorapatite can be used as the promising mineralizer for the purification and solidification treatment of uranium(VI) containing waste water.