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Abstract  

With the low permeability and high swelling property, Gaomiaozi (GMZ) bentonite is regarded as the favorable candidate backfilling material for a potential repository. The diffusion behaviors of HTO in GMZ bentonite were studied to obtain effective diffusion coefficient (D e) and accessible porosity (ε) by through- and out-diffusion experiments. A computer code named Fitting for diffusion coefficient (FDP) was used for the experimental data processing and theoretical modeling. The D e and ε values were (5.2–11.2) × 10−11 m2/s and 0.35–0.50 at dry density from 1,800 to 2,000 kg/m3, respectively. The D e values at 1,800 kg/m3 was a little higher than that of at 2,000 kg/m3, whereas the D e value at 1,600 kg/m3 was significantly higher (approximately twice) than that of at 1,800 and 2,000 kg/m3. It may be explained that the diffusion of HTO mainly occurred in the interlayer space for the highly compacted clay (dry density exceeding 1,300 kg/m3). 1,800 and 2,000 kg/m3 probably had similar interlayer space, whereas 1,600 kg/m3 had more. Both D e and ε values decreased with increasing dry density. For compacted bentonite, the relationship of D e and ε could be described by Archie’s law with exponent n = 4.5 ± 1.0.

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Abstract  

The transport processes of Na+, K+, Cs+, Ca2+, Zn2+, Mn2+, Fe3+ and HPO 4 2− ions were studied in soils by radioabsorption method. The effective diffusion coefficients varied in the interval of 10−16–10−10 m2s−1. The effective diffusion coefficient of Ca2+, Co2+, Zn2+ and Fe3+ ions increased by several orders of magnitude as a result of the addition of a complex forming agent.

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This paper reports a radiochemical study of the kinetics of ion exchange of Na+ and Cs+ with H+ on hydrous titanium dioxide. The experimental conditions are set to favor the particle diffusion mechanism only, and this is confirmed by the Bt versus t plots. On the basis of these studies the various physical parameters such as the effective diffusion coefficients, activation energies and entropies of activation have been evaluated. Tentative explanations are given for these results, from which some conclusions are drawn.

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Abstract  

The effect of pH and concentration on the diffusion of 137Cs in the compacted bentonite is studied with capillary method at the ionic strength of 0.1M NaClO4. The apparent diffusion coefficient increases with increasing concentrations if the sorption of radionuclides is largely dependent on the radionuclide concentrations. The apparent diffusion coefficient decreases with increasing pH because most of the radionuclide sorption on the bentonite increases with increasing pH. The interlaminary space contributes significantly to the radionuclide diffusion and sorption in compacted bentonite. The relationship of the apparent diffusion coefficient and the effective diffusion coefficient of 137Cs is also discussed.

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Abstract  

We have examined the working diameter of capillary columns with diameter of 5, 7, 10 and 20 mm. These modified capillary columns were carefully filled with local Taiwan laterite (LTL). The porosity and density of these packed columns was 0.51±0.02 g/g and 1.27±0.05 g/cm3, respectively. The diffusion experiments were then carried out in synthetic groundwater with Cs loading of 0.1mM at room temperature. Experimental results have shown that the diffusion profiles of modified capillary columns fit Fick’s second law very well. This result revealed that the working diameter of a capillary column can be expanded to at least to 20 mm without affecting the validity of the derived diffusion coefficients. Among these columns, the ones with 5 mm diameter show the most consistent results of the derived K d, apparent and effective diffusion coefficients. Although the derived distribution and effective diffusion coefficients slightly decrease as the diameter of these columns increases due to the increase of the solid/liquid ratio. These values are still informative of the Cs diffusion in local Taiwan laterite. Moreover, our results clearly demonstrate the potential of using “modified capillary method” to study the diffusion behaviors of concerned radionuclide because columns with large diameter enable the filling with more versatile geological substances.

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Abstract  

The efficiency of nutrients, microelements and plant protective agents and additives applied on foliar and various aeriel parts of plants depends on the adsorption of their spray drops and the penetration of agents into tissues, cells and inner caves. The permcability of tha cuticular membrane and the mode of entry of above substances through the cuticle and their mobility in other tissues are poorly understood but have been the subject of intensive research. The traditional methods in biological systems are the automicroradiography and sample taking methods. The radioactive tracer method developed by us is suitable for determining the effective diffusion coefficients characterizing the migration processes and concentration distributions of these materials in plants by consumption of minimal amount of -labelled radioactive isotopes in very short time.

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Abstract  

The membrane extraction of Y, Ce, Eu, Tm and their binary mixtures Ce–Y, Ce–Eu, Ce–Tm with supported liquid membranes containing TBP and HDEHP as carriers in decanedodecane hydrocarbon solvent, has been studied. Upon extraction with TBP aqueous nitrate solutions of rare earth elements (REE) were used as feed phase. In some cases they also contained EDTA or DCTA. In most cases, the receiving phase was an aqueous solution of EDTA. Extraction with HDEHP was performed from nitrate and chloride solutions and the receiving phase was the corresponding dilute acid. Pertraction of an element through a membrane was studied as a function of time and of initial composition of phases. The results are presented in the following forms: flux of metal through membrane, coefficients of permeability, separation factors and effective diffusion coefficients.

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Abstract  

Methodology for diffusion coefficient determination was applied on sandstone samples, using conservative non sorbing tracer. The results proved that methodology, through-diffusion cell design and GoldSim diffusion module can be used for sandstone samples in order to determine important migration parameters, necessary for transport model input. However, rock heterogeneity factor has to be taken into account in any case as it can potentially change rock properties, even within centimeter scale. Effective diffusion coefficient D e for rock samples was determined. The values fell into the range of 1.0–6.17 × 10−10 m2 s−1. Discrepancies in measured and simulated porosity were observed. Statistical analyses revealed that values of diffusion coefficient D e were in close interrelation to primary mineral (quartz) and cement forming minerals (kaolinite and organic matter).

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Summary  

This paper reports the radiochemical study of the ion-exchange of Cs+, Na+, Sr2+ and Eu3+ ions with H+ by chromium hexacyanoferrate(II) which was prepared in a granular form using a gel method. The slow steps which determine the rate of exchange of these ions are directly proportional to the particle diameter and this is confirmed from the linearity test of Bt vs. t plots at different particle diameters. Boyed’s equation and Reichenberg’s tables were used for evaluating all the kinetic parameters. The results reveal that the effective particle radii are unchanged for both chromium hexacyanoferrate(II) dried at 60 and 120 °C. The obtained data were analyzed using McKay plots and Arrhenius equation and the kinetic and thermodynamic parameters, e.g., effective diffusion coefficient, activation energies and entropies of activation have been evaluated. The mobility of these ions inside the particles of chromium hexacyanoferrate(II) decrease in the order of Eu3+>Sr2+>Na+⊃Cs+.

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Summary  

The effects of bentonite density and fulvic acid on the sorption and diffusion of 90Sr2+in compacted bentonite were investigated by using a capillary method. The experiments were carried out at pH 7.0±0.1 in the presence of 0.01M NaClO4. The results suggest that the sorption and diffusion of 90Sr2+in compacted bentonite decreases with increasing the density of compacted bentonite. The presence of FA enhances the sorption of Sr2+, but reduces the diffusion of Sr2+in compacted bentonite. The porosity of the compacted bentonite plays an important role in the sorption and diffusion behavior of 90Sr2+. Using the calculated effective diffusion coefficients the long-term relative concentration distribution of strontium was evaluated in compacted bentonite.

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