Adsorption Behavior of I - Ions on Minerals for Geologic Disposal of 129 I Wastes
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ADSORPTION BEHAVIOR OF I' IONS ON MINERALS FOR GEOLOGIC DISPOSAL OF 1291 WASTES
M. SAZARASHI, Y IKEDA, R. SEKI*, H. YOSHIKAWA**, and Y TAKASHIMA Institute of Research and Innovation, 1201, Takada, Kashiwa-shi, Chiba 277 *Department of Chemistry, University of Tsukuba, 1- I-1, Tennodai, lbaraki 305 **Tokai Works, Power Reactor and Nuclear Fuel Development Corporation, 4-33, Muramatsu, Tokai-mura, Naka-gun, Ibaraki 319-11, Japan.
ABSTRACT The F adsorption on a modified mineral, which is prepared by impregnating Ag(l) nitrate complex with thiourea(tu) into montmorillonites, have been studied by batch method. The modified mineral was found to adsorb I- ions selectively even under the coexistence of CI- ions. The distribution ratio(Kd) is 5000 ml/g under the conditions of initial (I-1 = 1.0 x 10-5 M(M = mol/dm 3 ), pH = 6.4, and solution/modified mineral = 100 ml/g. It was found that the [Ag(tu)]I precipitates are formed by mixing NaI solution with Ag(l)-tu complex solution, while any precipitates are not formed in addition of NaCI solution, and that anion exchange property of the modified mineral is low. Furthermore, it was confirmed that the [Ag(tu)]I complexes are present in the modified minerals after adsorbing F ions. From these results, the I- selective adsorptivity of the modified mineral was considered to be due to the formation of [Ag(tu)]I precipitates within the interlayer region of montmorillonite.
INTRODUCTION In the geologic disposal of radioactive wastes, 12 9 1 is one of significant nuclides, because 7 its half-life is long(tl/ 2 =1.7X 10 years) and its most likely species, i.e., I- ion, is poorly sorbed on most geologic media. Therefore, it is required to develop the methods for immobilizing the radioiodine for a long period. As one of the immobilizing methods, application of materials capable of adsorbing F ions to barriers around 1291 wastes has been proposed[ 1-6]. In order to identify the materials capable of adsorbing F ions, we have examined the adsorptivities of various minerals (cinnabar, alophane, attapulgite, chalcopyrite, and montomorillonite) to I- ions. As a result, the cinnabar was found to have fairly high adsorptivity to I- ions[7], which was considered to be due to the reaction between I- ions and thermally unstable components in the cinnabar[8]. However, it is supposed to be difficult to use the natural minerals as the adsorbents of F ions in the geologic disposal, because of their low adsorptivities to F ion and toxicity. Hence, we have tried to prepare modified minerals for adsorbing I- ions, which are the montmorillonite intercalating Ag(I)-tu complexes within interlayer regions[9]. In the present paper, we deal with the adsorptivities of the modified mineral to F ions and its adsorption mechanism.
Mat. Res. Soc. Symp. Proc. Vol. 353 0 1995 Materials Research Society
1038
EXPERIMENTAL Synthesis of Ag(l) complex with thiourea(tu) The complex was synthesized by adding the silver nitrate solution(O.2 M, 50 ml) to the thiourea solution(2.0 M, 50 ml). The solution was cooled and t
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