Preparation Of Amidoximated Polyacrylonitrile/ Exfoliated Na-Montmorillonite Composite And The Adsorption Performance For Uranium

The removal/recovery of uranyl from radioactive wastewater or seawater gained more attention in the recent years, and fell into deep demands in the development of nuclear power plant. A novel compsite of amidoximated polyacrylonitrile/exfoliated Na-montmorillonite(Na-Mont-APAN) was prepared using in-situ emulsion polymerization technology. The adsorption performance and mechanism of uranyl onto the adsorbent were also discussed.XRD, FT-IR, TEM, EDX, BET, potentiometric titration, element analyzer were used to characterize the prepared material. The results show that montmorillonite is exfoliated and the amidoxime group is formed. The material is nonporous and amorphous, with a small specific area of 4.8cm2/g, and the elemental composition is determined to be C, N, H, O, Na, Al and Si.Batch adsorption experiment results show that Na-Mont-APAN has high adsorption capacity and selectivity for uranyl, however, exhibits strong dependence on pH and ionc strength. At low pH, the functional group may be partly destroyed, leading to a lower adsorption capacity. With pH increasing, the adsorption amount gradually increases to the maximum amount at pH 5.5, and then decreases until pH 9. The complicated trend may result from the influence of uranyl speciation, protonation of AO, and the precipitation of hydrolytic uranyl. The increase of ionc strength facilitates the adsorption, especially in the cases of hydrochlorate, perchlorate and nitrate. The affinity of Na-Mont-APAN with metal ions is found to be in the order of U>>b>Cd>Cu>Ni>>Zn>Fe, Ca, Na. Kinetic experiment results show that the adsorption can attain equilibrium in 30 min at pH 4-6, and the adsorption rate gets slower at pH 6～7. Pseudo-second-order model can describe the adsorption process well with R2 values close to 1.The adsorption isotherm experiment was performed at 298K,308K and 318K. It is found that the adsorption isotherm curve matches well to Langmuir model, and the adsorption of uranyl onto Na-Mont-APAN may be a spontaneous, endothermic and chemical process.The adsorption mechanism was also discussed with the aid of FT-IR, XPS and Ruranyl/AO. The maximum adsorption capacity is determined to be identical to the active sites density, and about half of the AO group density, indicating that the reactive stoichiometry may be 1:1 or 1:2. FT-IR spectra shows that O in oxime participates in the coordination but N in amine may not. XPS spectra further confirm the results, and shows N in oxime also participates in the coordination. There is no sufficient evidence which can demonstrate the interaction of N in amine and uranyl. Based on the above analysis, a η2 coordination mode was proposed and used to describe the adsorption of uranyl on Na-Mont-APAN.Due to high adsorption capacity, good selectivity, high salt-tolerance and well reusability, the new prepared Na-Mont-APAN gives a promising candidate for the recovery/removal of uranyl from seawater, radioactive waste water or nuclear industry effluent.