Fundamental Study on the Solidification of Cs + and Sr 2+ with Hydrous Ti IV Oxide Modified with Si and Zr
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FUNDAMENTAL STUDY ON THE SOLIDIFICATION OF Cs+ AND Sr2+ WITH HYDROUS Ti1 v OXIDE MODIFIED WITH Si AND Zr
Y. Inoue, H. Yamazaki, and R. Erza Department of Nuclear Engineering, Faculty of Engineering, Tohoku University, Aramaki, Aoba-ku, Sendai, 980 Japan ABSTRACT
Fundamental data are provided for the potential use of hydrous TilV-si oxide (TS) and hydrous TiIv-Zr oxide (TZ) as the solidification media of radioactive Cs' and Srj2 . The sorption capacity for Cs' and Sr2 +, at various conditions, and the structure and the composition of the exchangers in these ionic forms, at high temperature, were investigated, followed by measuring the leaching rate from the calcined exchangers into water at room temperature. TS uptakes more Cs+ and Sr2 ' than TZ does. The leaching rate from calcined TS is much lower than that from calcined TZ, due to the formation of titanium silicates of Cs+ or Sr2 ÷. Based on these results, TS is considered2 to be superior to TZ, in sorption capacity, and the fixation capability of Cs+ and Sr ÷, on the exchanger matrix. INTRODUCTION The solidification of radionuclides with zeolites and sodium titanate has been studied as an alternative process of radioactive waste management, since these materials have 1 relatively high sorption capacity and fixation capability for various radionuclides. ,2 However, it is necessary to survey the performance of various inorganic ion exchangers in order to select the most promising solidification medium for radioactive liquid wastes of different compositions. Hydrous Tihv oxides, modified 3with either Si or Zr, have larger ion-exchange capacity than simple hydrous metal oxides. ,4 They are promising for use as solidification materials of radionuclides in a huge volume of liquid wastes, since they have a large sorption capacity for cations and can be transformed into stable solid forms by heat treatment. In this paper, we report fundamental data for the potential use of hydrous Til'-Si oxide (TS) and hydrous TilV-Zr oxide (TZ) as the solidification media of radioactive Cs÷ and SrS+. EXPERIMENTAL
The exchangers studied have molar ratios of Ti to metallic elements constituting the matrices (Ti/(Ti + Si or Zr)) of 0.52 in TS, and 0.50 or 0.70 in TZ; TS was precipitated at pH 7.6 by adding a 0.5M Na 2SiO 3-1M NaOH solution to a 0.5M TiC14 solution, and TZ was precipitated at pH 13 by pouring a mixture of IM TiC14 and IM ZrOCI2 solutions into a IM NaOH solution. For comparison, simple hydrous Si and Ti1v oxides were prepared by the methods described previously.3 The exchangers with a desired particle size (63-210,pm) were converted to the H' form by treating them with HCI solution (0.05-0.5 M) and stored in a desiccator containing a saturated NH 4 CI solution (relative humidity: 79% at 25 QC). The compositions of the exchangers in the H+ form were Ti0 .52Si0 .48 0 2. 2.09H 2 0 (TS52), Tio.50Zr 0 .5002'2.39H 20 (TZ50), Ti 0 .70Zr 0 .30 02o 1.96H 20 (TZ70), TiO2 '1.39H 20 (Hyd. TiO2 ), and SiO 2 , l.27H 20 (Hyd. SiO 2). The sorption capacity of the exchangers for Cs÷ and
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