Removal Characteristics Of U(VI) In Wastewater By NZVI/EG

Nuclear energy applied widely results in the sustaining development of the uranium mining and metallurgy industry, which produce a large number of uranium containing radioactive wastewater and potentially threats to the natural environment seriously. So the treatments of this wastewater become a research hotspot.This research synthetizes NZVI/EG composite by dipping-reduction–calcination method, in which EG is the carrier and Fe(NO3) 3 is the precursor. The best ratio of raw materials is found according to the U(VI) removal efficiency. Then, EG and NZVI/EG as adsorbent are used to remove U(VI) ions from aqueous solution respectively. The effects of p H, adsorbent dosage, initial U(VI) ions concentration, temperature and equilibrium time on adsorption of U(VI) is investigated by static adsorption experiments. Thermodynamic model and kinetic model are used to fit removal process and study the removal characteristics. Removal mechanism is studied by these characterization methods, such as BET, SEM, EDS, XRD, FITR, etc.The experiment results of removal U(VI) by EG show that the maximum adsorption occurs at p H of 6.5 and the adsorption reaches equilibrium within 4h. Meanwhile the removal rate is up to 98.08% for initial U(VI) concentration of 10 mg/L and adsorbent dosage of 2.0g/L at 30℃. The adsorption process fits well with the Langmuir isotherm model and pseudo-second-order kinetic model, and the maximum adsorption capacity for U(VI) ions is 27.03mg/g. Thermodynamic study reveals that adsorption of U(VI) on EG is primarily due to spontaneous exothermic reaction. BET surface area test, SEM-EDS and FTIR spectroscopy verify that physical adsorption is the main adsorption mechanism and surface functional groups play a supplementary role. Desorption experiments show that EG is a reusable adsorbent.The experiment results of removal U(VI) by NZVI/EG show that the best ratio of raw materials is Fe:C=1:0.75. It has high Removal efficiency at p H between 4 to 7, and the 4 is the best. And the adsorption reaches equilibrium within 4h. Meanwhile the removal rate is up to 98.87% for initial U(VI) concentration of 10 mg/L and adsorbent dosage of 1.0g/L at 30℃. The adsorption process fits well with the Langmuir isotherm model and pseudo-second-order kinetic model, and the maximum adsorption capacity for U(VI) ions is 67.11mg/g. Thermodynamic study reveals that removal of U(VI) on NZVI/EG is primarily due to endothermic reaction. BET, SEM-EDS and XRD verify that NZVI successfully load in expanded graphite surface. Crystal form of NZVI is stable, and uranium is adsorbed in material surface. Removal mechanisms are physical adsorption, Reduction of precipitation and coprecipitation with iron corrosion products.