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

几十年来，含贫铀和Sb的催化剂作为复合氧化物被用于丙烯腈的有机合成，废催化剂作为铀废物安全地储存在日本。今后应进行安全、经济的处置。然而，不幸的是，铀同位素的半衰期很长，几个子核素的化学和放射性毒性太大，不能直接在浅滩上处理。我们还应该考虑到锑的化学毒性。然后，我们提出了一种利用催化剂的SiO2载体净化铀和锑并将废催化剂玻璃化成玻璃基体的方法。我们的研究目标是从催化剂的直径为亚微米的SiO2载体的微小孔隙中高收率地回收铀和锑，并将其处理成适当的废物形式用于浅层土地处理。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来处理催化剂，并在实验室规模上使用催化剂的真实样品进行了实验测试。实验获得的铀和锑的回收率分别大于99.3%和97.0%，且去离子水浸出的最终玻璃化固体中铀和锑的浓度均低于电感耦合等离子体谱仪的检测限（0.1 mg dm^<-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>.