[en] The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. ? Elucidate the controls on the rate and extent of contaminant reactivity. (2) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions

[en] The proposed research will elucidate the principal biogeochemical reactions that govern the concentration, chemical speciation, and reactivity of the redox-sensitive contaminant uranium. The results will provide an improved understanding and predictive capability of the mechanisms that govern the biogeochemical reduction of uranium in subsurface environments. In addition, the work plan is designed to: (1) Generate fundamental scientific understanding on the relationship between U(VI) chemical speciation and its susceptibility to biogeochemical reduction reactions. (2) Elucidate the controls on the rate and extent of contaminant reactivity. (3) Provide new insights into the aqueous and solid speciation of U(VI)/U(IV) under representative groundwater conditions

[en] The effect of different solid components of calcareous soil on the retention of I was investigated by a batch technique and selective extraction method, and the effect of γ-irradiation was also investigated. The sorption and desorption isotherms of I on the one untreated, three treated soils and the calcareous soil irradiated with γ-rays were determined at 30 deg C, pH 8.1±0.2 and in the presence of 1.0x10^-4M or 0.67x10^-5M CaCl₂. It was found that the sorption-desorption hysteresis on the calcareous soil actually occurs on the same time scale, that iodine can be easily transported in the calcareous soil and that the exceptionally high contribution of organic matter to the iodine sorption is demonstrated. (author). 6 refs., 6 figs., 1 tab

[en] The effect of different solid soil components of calcareous soils on the retention of SeO₃ has been investigated by a batch technique and selective extraction method. The sorption and desorption isotherms of SeO₃ on the untreated calcareous soil and the three treated soils were determined at 20 deg C, pH 7.8 ± 0.2 and it the presence of 0.001M CaCl₂. It was found that all isotherms are linear, the sorption-desorption hysteresis for untreated soil and treated soils is obvious and the retention of SeO₃ in calcareous soil is mainly attributed to the oxides. (author). 12 refs., 5 figs., 1 tab

[en] The effect of various solid soil components on the retention of Cs was investigated by using batch technique and selective extraction method. The sorption and desorption isotherms of Cs on the untreated, calcareous soil and the three treated soils were determined at 20 deg C, pH 7.8 ± 0.2 and in the presence of 0.001 M CaCl₂. It was found that all isotherms are nonlinear, and that the sorption-desorption hysteresis on the calcareous soil actually occurs on the same time scale. (author)

[en] Previous authors reported that for some sorption systems the overall distribution coefficient (K_d) for a radionuclide or trace element on a mixture of minerals could be predicted from the additivity rule, the distribution coefficients on individual minerals and their mass fractions and that for some sorption systems, deviations from the additivity rule were found. In this paper, the additivity rule and its applicability to soils were analyzed from the theoretical considerations and the nature of soils. It was found that under the simplifying assumptions: 1) reversible and independent sorption reactions, 2) an equilibria of sorption reactions, 3) homogeneous surfaces, 4) insolubility of ion exchangers or sorbents, 5) no new phase formation, and 6) no interactions between individual minerals of the mixture, the additivity rule is formally valid. In practice, because of these crucial assumptions, the nature of soils and the difference in the experimental conditions for the sorption on mixtures and for the sorption on individual minerals, in general, the additivity rule is not applicable to the sorption systems of soils. (orig.)

[en] The adsorption-exchange equilibrium time and the adsorption isotherms of UO₂²⁺, ¹³⁷Cs, ¹⁶⁹Yb and HPO₄^2- on modified peat have been investigated by batch experiments. The effect of pH on the adsorption-exchange percentage (E) and the distribution coefficients (K_d) was also examined. It was found that the adsorption-exchange of UO₂²⁺ and ¹⁶⁹Yb on the modified peat was described well by Freundlich isotherm, whereas the adsorption-exchange of ¹³⁷Cs and HPO₄^2- on modified peat corresponded to a Langmuir isotherm and the maximum adsorption capacities of the modified peat for ¹³⁷Cs and HPO₄^2- ions were 4.4 and 4.1 μg/g, respectively. The optimum pH for the adsorption-exchange of UO₂²⁺, ¹³⁷Cs, ¹⁶⁹Yb and HPO₄^2- on the modified peat was 7.0 at 25 deg C. (author)

[en] The effects of pH, ionic strength and FA (fulvic acid) on the sorption and desorption of Eu(III) and Yb(III) on alumina were respectively investigated by using batch technique and radiotracers ^152+154Eu and ¹⁶⁹Yb. The distribution coefficients for sorption and desorption of Eu on alumina at pH 4.4, 4.6 and 5.7 in 1 mol/l NaCl solutions as a function of solid phase concentration were determined in the presence or absence of FA. The effects of pH, FA and ionic strength on the distribution coefficients for sorption and desorption of Yb on alumina were determined in 0.01–2.0 mol/l NaNO₃. It was found that pH and FA influenced the sorption of Eu(III) and Yb(III) on alumina greatly. A surface hydrolysis model can satisfactorily and qualitatively explain the observations on bare alumina. The competition among the complexations of surface free hydroxyl groups, soluble and sorbed fulvic acids can satisfactorily and qualitatively explain the observations on the coated alumina.