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

几十年来，以贫铀和锑为复合氧化物的催化剂被用于丙烯腈的有机合成，在日本，废催化剂被安全地作为铀废料储存。今后应进行安全、经济的处置。然而，不幸的是，铀同位素有很长的半衰期可以衰变，而且几种子核素的化学和放射性毒性太大，不能直接处置在浅海土地上。我们也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二氧化硅载体来净化铀和锑，并将废催化剂玻璃化成玻璃基质的方法。我们研究的目标是从催化剂的SiO_2载体直径为亚微米的微孔中高产率地回收铀和锑，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对催化剂进行处理，并在实验室规模上使用真实的催化剂样品进行了实验测试。实验中铀的回收率大于99.3%，锑的回收率大于97.0%，用去离子水浸出的最终玻璃化固体中铀和锑的浓度低于电感耦合等离子体光谱仪的检出限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>.