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  • Author or Editor: Tao Wang x
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Abstract  

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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Abstract

The deactivation of alkali solid catalysts for the synthesis of glycerol carbonate from glycerol and dimethyl carbonate was investigated. Calcium oxide, calcium hydroxide and calcium methoxide were chosen as the representatives of the alkali solid catalysts. When the catalysts were recycled, the yield of glycerol carbonate decreased dramatically. The alkali solid catalyst was converted to the basic calcium carbonate Cax(OH)y(CO3)z, which was the cause of the decrease of glycerol carbonate yield. It was found that the chemical interactions of the alkali solid catalyst with glycerol and glycerol carbonate led to the formation of the basic calcium carbonate Cax(OH)y(CO3)z, for which the mechanism was proposed. Based on the deactivation mechanism, calcium diglyceroxide was adopted as a new catalyst for the transesterification of glycerol and dimethyl carbonate. Compared to calcium oxide, calcium hydroxide and calcium methoxide, calcium diglyceroxide showed excellent reusability for the transesterification of glycerol and dimethyl carbonate. For calcium oxide, calcium methoxide and calcium diglyceroxide, there were dissolution losses of the catalysts in the reaction medium. For calcium hydroxide, the catalyst dissolution loss in the reaction medium was nearly negligible. For calcium diglyceroxide, the dissolution of the catalyst in the reaction medium did not influence the yield of glycerol carbonate significantly.

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Abstract  

Oxidized multiwalled carbon nanotubes (MWCNTs) were characterized by SEM and FTIR. The sorption of Th(IV) on MWCNTs was studied as a function of contact time, pH, ionic strength, Th(IV) concentration and temperature. The results indicate that the sorption of Th(IV) on MWCNTs is strongly dependent on pH and weakly dependent on ionic strength. The sorption thermodynamics of Th(IV) on MWCNTs was carried out at 293.15, 313.15 and 333.15 K, respectively, and the thermodynamic parameters (standard free energy changes (ΔG 0), standard enthalpy change (ΔH 0) and standard entropy change (ΔS 0)) were calculated from the temperature dependent sorption isotherms. The sorption of Th(IV) on MWCNTs is a spontaneous and endothermic process. The oxidized MWCNTs may be a promising candidate for the preconcentration and solidification of Th(IV), or its analogue actinides from large volumes of aqueous solutions.

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Abstract  

The effect of organic matter and iron oxides as solid components of the red earth 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 red earth and the three treated soils were determined at 20°C, pH 6.8 or 7.2 and in the presence of 0.01M CaCl2. It was found that the sorption-desorption hysteresis for untreated an treated soils is obvious and the clays play an important role in the sorption-desorption hysteresis, and that the retention of SeO3 on red earth is attributed to the iron oxides to a great extent.

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Abstract  

The factors affecting the sorption of radioeuropium(III) by bentonite and kaolinite were studied with the aim to assess the important factors which should be included in modeling of radioeuropium(III) migration in soils and sediments. Europium(III) is an analogue of trivalent actinides. The distribution coefficients of radioeuropium for sorption on bentonite and kaolinite from aqueous solutions were determined by using the batch method, and it was found that they were sensitive to the loading, the pH, the humic substance and the sorption direction. Thus, these sorption characteristics of radioeuropium on bentonite and kaolinite were found to be different from those of radiocobalt1, and the mathematical modeling of trivalent lanthanides and actinides migration will be more complicated than that of radiocobalt. It is improbable that the migration modeling with a constant distribution coefficient will be successful in the case of trivalent lanthanides and actinides.

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Abstract  

The sorption and desorption of radiocesium on a calcareous soil from Jiuqian County of Gansu Province (China) were studied by using batch and column experiments. The sorption-desorption isotherms and the breakthrough curves, displacement curves on the whole soil and two treated soils were determined. Based on these results, it was found that the sorption and retention of cesium are mainly determined by the clay minerals, that the sorption-desorption hysteresis of cesium on the calcareous soil is obvious and that the organic matter has a little positive contribution and the calcium carbonate has a little negative contribution to the sorption of cesium on the whole soil. The results from batch experiments were consistent with the results from column experiments.

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Abstract  

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°C, pH 7.8±0.2 and in the presence of 0.001M 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.

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Abstract  

The effect of different solid components of calcareous soil on the retention of Sr was investigated by using batch technique and selective extraction method. The sorption and desorption isotherms of Sr on the untreated calcareous soil and the three treated soils were determined at 20°C, pH 7.8±0.2 and in the presence of 0.001 M CaCl2. It was found that all isotherms are linear and that the sorption of Sr on the calcareous soil can be described by a reversible sorption process and the sorption mechanism is mainly ion exchange.

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Abstract  

The distribution coefficients of 47 elements from Na to Bi on untreated calcareous soil, treated soil to remove CaCO3 and treated soil to remove both CaCO3 and organic matter, respectively, were determined by using a multitracer technique. The variation of the distribution coefficients of 47 elements was explained in terms of chemical bond formation and hydration. The effect of different solid components of the calcareous soil on the adsorption was investigated.

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