Abstract:
There are a large amount of uranium, niobium, and niobium elements in the unqualified products generated during the production and manufacturing process of U-Nb-Zr alloy materials, as well as in the wastewater generated during the analysis and characterization process. In order to achieve the recovery and reuse of uranium and reduce the discharge of radioactive waste, this work adopted a membrane separation technology based on graphene oxide membranes(GOMs). By utilizing the size difference between uranyl ions and niobium and zirconium hydrate ions, the separation of uranyl ions from uranium, niobium and zirconium ion solutions under strong nitric acid system was explored. Six groups of GOMs with different graphite particle sizes and oxidation degrees were prepared. The effects of membrane oxidation degree, membrane thickness, solution acidity, and ion concentration on screening and separation efficiency was evaluated. SEM show that the thickness of 1.2 mg GOMs is about 1 μm, and there are obvious wrinkles on the surface of GOMs, provided a channel for the passage of small molecules and ions. XPS and FTIR show that the order of oxidation degree of the six groups of GOMs is 325S2>200S2>200S1>325S1>100S1>100S2. The experimental results show that the GOMs products(200S1) with 200 mesh(particle size is 75 μm) graphite as the raw material and oxidized at 35 ℃ for 2 h have smaller interlayer spacing in 3 mol/L HNO
3 solution, and this material can most effectively achieve the separation of uranium from niobium and zirconium. Under the screening separation conditions of 200S1 membrane mass of 1.2 mg, solution acidity of 3 mol/L HNO
3, \mathrmUO_2^2+ initial concentration of 3.7 mmol/L, and Nb
5+ and Zr
4+ initial concentrations of 1.1 mmol/L, the Nb
5+ concentration(0.40 mmol/L) and Zr
4+ concentration(0.38 mmol/L) measured in infiltration side at 48 h are approximately twice the concentration of \mathrmUO_2^2+ (0.21 mmol/L). The permeability of \mathrmUO_2^2+ at 48 h is only 5.32%, while the ion permeability of Nb
5+ and Zr
4+ are 36.39% and 34.30%, respectively, approaching osmotic equilibrium. The pseudo-first order separation rate constant of Nb
5+(
0.0087 h
−1) is approximately 8 times that of \mathrmUO_2^2+ (
0.0011 h
−1), while Zr
4+(
0.0080 h
−1) is approximately 7 times that of \mathrmUO_2^2+ (
0.0011 h
−1). The separation factors of
α(Nb/U) and
α(Zr/U) reach 10.2 and 9.3, respectively. In addition, cyclic experiments show that the 200S1 membrane still has screening and separation ability after being reused 5 times. This work provides a new method for the recovery of uranium in U-Nb-Zr materials, and can also provide technical reference for the separation of uranium in high-level radioactive waste.