铌钽掺杂六方相氧化钨对锶铯的吸附性能研究

The fission products 90Sr and 137Cs are very important in addressing waste disposal issues because they generate large amounts of heat for the first several hundredyears. Heat generation in the repository is an issue because heat combined with slight moisture from the surrounding rock could accelerate corrosion of the waste canisters if it comes into contact with them. To avoid this, 90Sr and 137Cs must be separated from other radioactive fission products. Tungsten oxide with hexagonal tungsten bronze structure (hex-WO3) has attracted much attention owing to its well known tunnel structure. Guest ions in the “hexagonal window” tunnels of the hex-WO3 can be exchanged by Cs+, Sr2+ and other ions. We have found that adsorption amount of Sr2+ and Cs+ onto hex-WO3 can be improved by isomorphous incorporation of Tantalun or Niobium ions. The Tantalun or Niobium doped hex-WO3 is very robust in acidic solution and may be used as adsorbents to separate 90Sr and 137Cs from fission waste. The bulk of radioactive effluent can be disposed as low-level waste with concomitant cost savings if the strategy that to pretreat 90Sr and 137Cs by a small volume of sorbent is achieved. The aim of the proposal is to study chemical and charge imbalance of hex-WO3 induced by isomorphic substitution of Tantalum or Niobium ions if there is any local change and to elucidate the nature of the Cs+ and Sr2+ siting in the Tantalum or Niobium doped hex-WO3 when Cs+ and Sr2+ ions are captured and immobilised in hexagonal tunnels after adsorption process is carried out. To understand the adsorption behavior as a function of Tantalum or Niobium doped hex-WO3, particularly how framework composition may be tailed for optimum ion adsorption behavior, the host-gust chemistry interaction between Tantalum or Niobium doped hex-WO3 noumenal framework and extraframework Sr2+ and Cs+ cations also will be detailed performed. The results of this project will reveal the structural basis of selectivity for Cs+ and Sr2+ of Tantalum or Niobium doped hex-WO3 and could avail to design and develop new efficient and selective sorbents for the treatment of 90Sr and 137Cs waste effluents.

六方钨青铜结构的氧化钨沿着c 轴方向存在六元环孔道，孔道中容纳的客体离子能被其它离子交换，可以用作吸附剂处理酸性放射性废液。前期研究中发现铌或钽掺杂能明显提高六方氧化钨对Sr2+和Cs+的离子吸附能力，采用该材料能同时将90Sr 和137Cs 从强酸性放射性废液中分离出来，简化放射性废液的后续处理流程，降低二次废液的产生量。拟继续开展材料的合成方法研究,通过结构解析研究铌、钽掺杂对六方氧化钨微观结构的影响。采用离子吸附实验、滴定实验研究离子吸附过程。采用谱学测试分析考察Sr2+和Cs+进入氧化钨骨架孔道后发生的主客体作用。通过以上实验与理论数值模拟相结合的方法，分析材料本体结构与不同客体离子之间固相键合能力的差异，阐明铌、钽掺杂对材料吸附Sr2+和Cs+性能的影响机理。研究结果可望为放射性废液中90Sr 和137Cs 吸附材料的结构设计与材料合成提供理论

核武器研制、核能开发及裂变同位素生产过程中产生的高放废液的处理处置一直是具有挑战性的工作。90Sr和137Cs是高放废液放射性强度的主要贡献者，因而从高放废液中分离提取90Sr、137Cs是高放废液降级处理的关键。无机离子交换材料因能耐高温、抗辐射，可以流态化色谱操作，且利于后期水泥（或陶瓷）固化处理，一直是90Sr和137Cs分离材料的研究热点。六方相氧化钨（hex-WO3）具有典型的八面体晶体结构，沿着c轴方向存在一维孔道，其孔道中可以容纳客体分子如结晶水、Na+离子等，因为孔径大，客体离子半径相对小，很容易被交换，表现良好出离子交换性能，有望用于从放射性废液中分离137Cs、90Sr。氧化钨存在多种晶相，相互掺杂会堵塞孔道，影响离子吸附性能。因此，需要可控合成获得道畅通、空隙率高的hex-WO3，从而实现客体离子在足够大的孔道空间中自由交换，解决现有材料因孔径较小，客体分子运输转移不畅，甚至堵塞孔道，进而影响材料中客体离子与目标核素离子的自由交换过程，导致材料对客体离子的吸附容量相对低的问题。本项目中通过结构微调和表面修饰两种方式对hex-WO3实现可控合成，显著提高其对Sr2+、Cs+离子的吸附容量。在pH>4的硝酸溶液中，当Sr2+、Cs+离子初始浓度为都为200mg·L-1，溶液100mL，吸附剂量200mg条件下，hex-WO3对Sr2+的吸附容量为~35mg·g-1，Nb掺杂后提高到约45mg·g-1（提高28%），Ta掺杂后提高到约50mg·g-1（提高42%），hex-WO3对Cs+的吸附容量为约45mg·g-1，Nb掺杂后提高到约60mg·g-1（提高33%），Ta掺杂后提高到约65mg·g-1（提高44%）。结果表明Nb、Ta掺杂能明显提高材料对Sr2+、Cs+的吸附容量（总吸附能力>0.3mmol·g-1，远高于钛硅酸、沸石等0.1mmol·g-1的吸附）。获得的材料即使在酸性溶液中（约1 mol·L-1 HNO3）对Sr2+和Cs+离子仍有很高的吸附能力，而公开报道的其他材料如钛硅酸、沸石等材料在该酸度下已溶解，失去吸附能力。该项目的研究为后期高放废液的处理及关键裂变核素的分离提取奠定了良好的技术基础。