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Abstract

This paper is about comparing the effectiveness of the sorbent materials of granulated activated carbon in removing of bromates from drinking water. The limit value (10 µgl−1) of bromates in the drinking water was stated by World Health Organization. In order to insure the reduced concentration of bromates in the drinking water, an experiment was performed using the batch test. In this experiment different types of sorbent materials with different properties were testing. Based on batch test were measured the parameters like the immediate adsorption capacity, the adsorption efficiency, and the concentration of bromates after the adsorption were measured at the evaluated time.

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Investigations are currently carried out in Saxony to study environmental impacts due to uranium-mining activities. Radioactive and other inorganic species were determined in both mining waters of different origin and leachates from mediumscale column experiments and batch-tests. Uranium concentrations were measured using -spectrometry, absorption spectrophotometry, square-wave polarography and inductively coupled mass spectrometry. For mining waters the concentration range was less than 1 to ca 4 mg·dm–3, in one case up to 7 mg·dm–3.

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An application of distribution coefficients in transport models must take into account, among others, influences of solution-to-solid (V/M) ratios. Therefore, with batch tests the dependence of sorption and desorption coefficients on V/M in rock-groundwater systems of the Gorleben site was investigated. Experiments show that sorption (RS) and desorption (RD) coefficients of Ra, U, Pa and Ac decrease with decreasing liquid/solid ratios. In order to understand the V/M-effect sorption isotherms for different V/M ratios and, moreover, quantities for characterizing specific sorption of nuclides have been measured. The results allow the postulation of a model for describing approximately RS-V/M-relationships of different nuclide/rock/groundwater system with specific parameters.

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The reactive mechanism of cesium in crushed granite was demonstrated in this study through a numerical analysis or a model of the results of sorption/desorption kinetic tests. To employ such numerical analysis, this study applied batch kinetic tests with different solid to liquid ratios (1: 20 and 1: 30) for the characterization of sorption/desorption reaction of Cs and the calibration/validation of hypothesized reactive models. Based on the least square errors (LSE) between numerical analysis and results of batch tests, the two-site sorption models, which are corresponding to two decay constants (λ 1 and λ 2), might be more adequate than one-site sorption models in characterizing Cs sorption/desorption. Moreover, a two-site Langmuir kinetic model has been found to be capable of appropriately describing Cs sorption/desorption under test conditions.

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In order to assess radionuclide diffusion and transport properties in compacted bentonite, the “in-diffusion” method based on bentonite filled capillaries is used. The effect of 99TcO4 - concentration and pH value of the solution, the contact time and the dry density of compacted bentonite on the apparent diffusion coefficient (D a) and on the distribution coefficient (K d) values obtained from the capillary test was studied. The D a and K d values decrease with increasing of the bulk dry density of compacted bentonite. Ion exclusion influences the diffusion of 99TcO4 - in the same substance. As compared to literature data, the K d values obtained from capillary tests are in most cases lower than those from batch tests, the difference between the two K d values is a strong function of dry density of the compacted bentonite.

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In this study, the diffusion behavior of cesium and selenium with 10−4M concentration in mudrock was studied by trough-diffusion tests and summarized in order to provide confidence on long-term performance assessment of nuclear waste repositories. The diffusion process of Cs and Se reached equilibrium after 60 and 500 days, respectively. Besides, it also displays that the distribution coefficients (K d) of Se in through-diffusion tests is higher than that of Cs in agreement with that obtained from the batch method. The K d value (15.14±1.99 mL/g) of Cs by diffusion techniques is equivalent to that of batch method (15.10±0.40 mL/g) because sorption of Cs was assumed to fast sorption step. However, the K d value of Se (137.58±12.20 mL/g) derived from the diffusion technique is higher than that from batch tests (76.72±2.96) and showed an obvious variation with K d of Cs. The difference of K d between diffusion and batch methods resulted from the fact that 14 days were not long enough to reach equilibrium or stable state in the batch method.

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Study of fine-particle media, because of their high sorption capacities, is of particular importance for the use as backfill materials in waste repository design, and because argillaceous formations are particularly suitable as host rock formations. In this study, sorption and retardation characteristics of strontium in fine-particle media were studied to evaluate the distribution coefficient (K d) and retardation factor (R d) of this radioactive element in fine-particle media, which was comprised of selected particles with a diameter less than 1 mm from a candidate site to dispose very low level waste (VLLW). The results indicated that K d values of strontium under different initial concentrations ranged between 20 and 110. Values of strontium R d measured from column experiments ranged between 36 and 102, with the corresponding K d values, determined from solving the inverse problem of R d calculating formula, ranging between 5 and 20. In conclusion, the K d value of Sr from the batch tests was found to be higher than these from the column experiments.

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Abstract  

Instead of radioactive 90Sr, common strontium chloride was used to simulate the migration of radioactive strontium chloride in surface hydroxylated, silanized, and common quartz sand. The sorption and retardation characteristics of strontium (Sr2+) in these surface modified quartz sands were studied by batch tests and column experiments. The equilibrium sorption data for Sr2+ on different wettability sands were described by the Langmuir and Freundlich isotherm models, and the Langmuir model has been found to provide better correlation for hydrophilic sand. The breakthrough curves (BTCs) of Sr2+ in these media were analyzed with the equilibrium convection–dispersion equation (CDE) and a non-equilibrium two-region mobile–immobile model (TRM) using a nonlinear least square curve-fitting program CXTFIT. The TRM model showed better fit to the measured BTCs of Sr2+, and the parameters of the fraction of mobile water indicated that significant preferential flow effected the non-equilibrium transport of Sr2+. Although TRM model could not fit the Sr2+ BTCs very well, the parameter estimated by TRM model may be more reliable than those obtained from batch experiments because the transport of Sr2+ in these kind of sand is non-equilibrium processes.

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Distribution coefficients (K d), apparent diffusion coefficients (D a) and retardation factor (Rf) in this work obtained by batch and through-diffusion experiments have been performed, respectively. The accumulative concentration method developed by Crank (The mathematics of diffusion, <cite>12</cite>) was applied to realize apparent and effective diffusion coefficient (D a and D e) of Se. Besides, a non-reactive radionuclide, HTO, was initially conducted in through-diffusion experiment for assessing the ability of radionuclide retardation. The distribution coefficients (K d) obtained by batch tests in 14 days under aerobic and anaerobic systems were 6.98 ± 0.35 and 5.21 ± 0.25 mL/g. Moreover, Rfcal and K d cal of Se obtained from accumulative concentration’s method in through-diffusion test showed an obvious discrepancy with the increase of length/diameter (L/D) ratio. However, it presented an agreement of RfH/Se and K d H/Se in a various L/D ratio by comparison of apparent diffusion coefficient’s (D a) between HTO and Se. It appears that the RfH/Se and K d H/Se obtained from the through-diffusion experiments are lower than those derived from the batch experiments. Therefore, it demonstrates that reliable Rf and K d of Se by through-diffusion experiments could be achieved at a non-reactive radiotracer (HTO) prior to tests and will be more confident in long-term performance assessment of disposal repository.

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Aiming the selective recovery of palladium from high level radioactive liquid waste (HLW), a chelating thiamide type sorbent, CWP–TU, was prepared by the modification of Japanese cedar wood powder (CWP). Convection oven and microwave heating were separately used for modification purpose and found that microwave heating is more effective over oven heating. CWP–TU was extensively studied for the adsorption of Pd(II) from nitric acid medium. The batch test showed that nitric acid concentration of 3 M or higher is favorable for Pd(II) loading. Consistent adsorption of Pd(II) under gamma irradiation condition demonstrated the feasibility of using CWP–TU in real HLW. Also, Pd(II) only adsorption from simulated HLW solution verified the palladium only selectivity of the sorbent as well as the lack of influence of coexisting metal ions on its affinity toward Pd(II). CWP–TU holds maximum Pd(II) loading capacities of 0.98 mol/kg at 30 °C and 1.04 mol/kg under gamma irradiation. A comparative study using some ion exchange resins revealed that the resins are either ineffective in nitrate medium or lack stability under irradiation.

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