Separation of cesium from nitric acid media with mixed oxides of tantalum, titanium and silicon

Yamagishi, Isao ; Morita, Yasuji  

Binary hydrous oxides of Si, Ti, Zr, Nb and Ta were synthesized under the hydrothermal condition to separate Cs from nuclear waste. Their selectivity toward Cs and chemical stability were examined in nitric acid media. Tantalates containing Si or Ti as well as titanosilicate showed high distribution coefficients above 100 ml/g in 3 M nitric acid. Perovskite phase (NaTaO) in the tantalate disappeared with increasing Si or Ti content, and pyrochlore phase formed. Exchange capacity for Cs in 3 M nitric acid increased with content of Si or Ti in the tantalates up to specific molar ratios of Si/Ta = 0.5 or Ti/Ta = 0.26. The Cs capacity of these tantalates unaltered even after contact with nitric acid at 90 C but that of titanosilicate decreased to 1/20 of its initial capacity due to destruction of the structure. The tantalate of Si showed rapid adsorption kinetics and higher capacity for Cs than that of Ti.