氧化石墨烯膜筛分分离强硝酸体系下铀铌锆中铀的性能

    Performance of Graphene Oxide Membrane for Separating U From U-Nb-Zr Alloys Under Strong Nitric Acid System

    • 摘要: 以铀、铌和锆元素为主要成分的废物产生于核燃料元件生产制备过程中,为实现铀的回收再利用,减少放射性废物的排放,采用基于氧化石墨烯膜(GOMs)的膜分离技术,探究强硝酸体系下铀铌锆中铀的分离。制备了六组石墨原材料粒径不同和氧化程度不同的GOMs并评价了其筛分分离性能。结果表明:以200目(粒径为75 μm)石墨为原材料,于35 ℃氧化2 h的GOMs产品(200S1)在3 mol/L HNO3溶液中具有较小的层间距,且最能有效实现铀与铌和锆的分离。在200S1膜质量为1.2 mg,溶液酸度为3 mol/L HNO3, \mathrmUO_2^2+ 、Nb5+和Zr4+的初始浓度分别为3.7、1.1、1.1 mmol/L的筛分分离条件下,48 h时渗透侧Nb5+浓度(0.40 mmol/L)和Zr4+浓度(0.38 mmol/L)约为 \mathrmUO_2^2+ 浓度(0.21 mmol/L)的2倍。Nb5+的渗透速率常数(0.0087 h−1)约为 \mathrmUO_2^2+ (0.0011 h−1)的8倍,Zr4+的渗透速率常数(0.0080 h−1)约为 \mathrmUO_2^2+ 的7倍。 \mathrmUO_2^2+ 、Nb5+和Zr4+的48 h离子渗透率分别为5.32%、36.39%和34.30%。铌与铀的分离因子α(Nb/U)和锆与铀的分离因子α(Zr/U)可分别达到10.2和9.3。此外,循环实验表明,可通过重复利用200S1膜降低分离成本。本工作为铀铌锆材料中铀的回收提供了全新方法,也可为高放废液中铀的分离提供技术参考。

       

      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 HNO3 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 HNO3, \mathrmUO_2^2+ initial concentration of 3.7 mmol/L, and Nb5+ and Zr4+ initial concentrations of 1.1 mmol/L, the Nb5+ concentration(0.40 mmol/L) and Zr4+ 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 Nb5+ and Zr4+ are 36.39% and 34.30%, respectively, approaching osmotic equilibrium. The pseudo-first order separation rate constant of Nb5+(0.0087 h−1) is approximately 8 times that of \mathrmUO_2^2+ (0.0011 h−1), while Zr4+(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.

       

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