Study on treatment and disposal form for used uranium catalyst for organic synthesis

几十年来，含有贫化U和Sb作为复合氧化物的催化剂用于丙烯腈的有机合成，并且在日本将废催化剂作为铀废物安全地储存。今后应进行安全和经济的处置。然而，不幸的是，铀同位素的半衰期很长，不易衰变，而且几种子核素的化学和放射性太强，不能直接在浅水区处置。锑的化学毒性也要考虑。然后，我们提出了一种净化铀和锑的方法，并通过利用催化剂的SiO2载体将废催化剂玻璃化成玻璃基质。我们的研究目标是从SiO_2催化剂载体的亚微米级微孔中高收率地回收铀和锑，并将其调理成合适的废物形式以进行浅层土地处置。为了实现这些目标，提出了利用硼硅酸盐玻璃的相分离现象处理催化剂，并使用催化剂的真实的试样在实验室规模下进行了实验测试。通过实验实现的回收率对于铀大于99.3%，对于锑大于97.0%，并且对于最终的玻璃化固体，用去离子水浸出的铀和锑的浓度低于电感耦合等离子体光谱仪的检测限，0.1 mg dm3<-3>。

For several decades, catalysts containing depleted U and Sb as a composite oxide were used for organic synthesis of acrylonitrile, and the spent catalysts are stored securely as uranium waste in Japan. A safe and economical disposal should be performed in the future. Unfortunately, however, uranium isotopes have long half lives to decay, and chemical and radioactive toxities of several daughter nuclides are too significant to dispose directly in a shallow land. We should take account of chemical toxity of antimony, too. Then we are proposing a method of decontaminating uranium and antimony and vitrifying the spent catalysts into a glass matrix by making use of the SiO2 supports of the catalyst. The goals of our study are recoveries of uranium and antimony with high yields from the tiny pores in sub-microns in diameter of SiO2 supports of the catalysts, and conditioning into a proper waste form for the shallow land disposal. In order to achieve these goals, treatment of the catalysts utilizing phase segregation phenomena of borosilicate glass was proposed and experimentally tested in a laboratory scale using a real specimen of the catalyst. The recovery yields achieved by the experiments were greater than 99.3% for uranium and 97.0% for antimony, and concentrations of uranium and antimony leached with de-ionized water for the final vitrified solids were below the detection limits by inductively coupled plasma spectrometer, 0.1 mg dm^<-3>.