Research On Cesium Removal By A Novel Synthesized Zirconium Phosphate-based Hybrid Nanomaterial

With the extensive application of radioisotope technology, the treatment of radioactive waste streams is of considerable concerned by the public. 137 Cs is a typical highly toxic radionuclide in radioactive wastewater, and it must be effectively separated to ensure environmental safety. Ion exchange resin is a common material to remove 137 Cs from wastewater, but it has a poor selectively sorption property to 137 Cs since the process is vulnerable effected by competing ions. In this study, to improve the selectively sorption property to 137 Cs, a novel zirconium phosphate-based hybrid nanomaterial was synthesized: nanoscale Zr P beads as inorganic ion exchanger was loaded on macroporous cation exchange resin D001, and used to remove Cs(I) from simulated wastewater. This study provide theoretical basis and technical support to the highly effectively separation of 137 Cs in practical application.Firstly, zirconium phosphate beads were prepared by direct precipitation method with particle dimension of 0.2 μm~1 μm, and nanoscale Zr P existed in the beads with particle dimension of about 50 nm. Zr P beads were mainly amorphous with the structural characteristics of α-Zr P. Zr P has got a strong selectively sorption property to Cs(I), when the Ca/Cs(mol/mol)≤128 in simulated wastewater, the removal efficiency of Cs(I) is over 70%, while the removal efficiency of Cs(I) on D001 is 0. In the initial 10 min, the removal capacity of Cs(I) on Zr P has reached 53.8% of the maximum removal capacity. The adsorption process is best described by pseudo-second order kinetics model(R2=0.9343). The decrease of temperature was beneficial to the removal of Cs(I), and the adsorption process can be described by Langmuir isotherm model.Based on the highly efficient removal property to Cs(I) on Zr P, using in-situ precipitation method to synthesize a novel zirconium phosphate-based hybrid nanomaterial Zr P-D001. D001 was chosen as supporter to resolve the solid-liquid separation difficulty of Zr P beads in practical application. With the increasing of Zr P beads, the load process of Zr P onto D001 began from the outer surface of the resin spheres, and then Zr P diffused evenly to the inner porous surface of the resins until the inner space was fully loaded by Zr P beads. Compared to D001, Zr P-D001 performed a stronger selectively sorption property to Cs(I); when the Ca/Cs(mol/mol) came to 32, the removal efficiency of Cs(I) on D001 decreased to 0, whereas the removal efficiency of Cs(I) on Zr P-D001 was 23.45%. XRD and FTIR spectra showed that existed a strong specific binding effect between Cs(I) and Zr P on Zr P-D001, and Cs2Zr(PO4) and Cs Zr(PO4)2?x H2 O were generated during the adsorption process. XPS spectra indicated that the removal of Cs(I) on Zr P-D001 was contributed by both Zr P and D001; when the Ca/Cs(mol/mol) increased from 0 to 0.3, the peak area of Zr P-Cs : D001-Cs increased from 1:3 to 4:1, this phenomenon showed that in the absence of competing ions, the D001 in the hybrid nanomaterial played the main role to the removal of Cs(I), whereas when Cs(I) and Ca(II) co-existed in the simulated wastewater, Zr P ingredient became the main ion exchanger.The results of kinetics experiments indicated that in the initial 30 min, the removal rate of Cs(I) on Zr P-D001 was significantly higher than that on D001, the adsorption process achieved equilibrium at 90 min, the removal efficiency could reach 81%; the adsorption process is best described by pseudo-first order kinetics model(R2=0.9901). Meanwhile, the sulfonyl on D001 showed pre-concentration effect to Cs(I) in the microenvironment, the removal efficiency of Cs(I) on Zr P-D001 at kinetics equilibrium reached 81%, it was 2.45 times higher than the maximum removal efficiency of Cs(I) on Zr P. When the p H in solution was from 4 to 10, the removal efficiency of Cs(I) on Zr P-D001 were above 95%, indicating Zr P-D001 could be adapted to a very wide range of p H to remove Cs(I). Low temperature is beneficial to the removal of Cs(I) on Zr P-D001. The results of fixed-bed tests showed that compared to D001, the treated effluent of the adsorption column filled with Zr P-D001 was 10 times than D001 before reaching the breakthrough point, indicating that the zirconium phosphate-based hybrid nanomaterial has got the potential to be applied in practical wastewater treatment.