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  • Author or Editor: Tao Wang x
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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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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  

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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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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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 factors affecting the sorption of radiocobalt by bentonite and kaolinite were studied with the aim to assess important factors which should be included in modelling radiocobalt migration in soils and waters. The distribution coefficients of radiocobalt sorption on bentonite and kaolinite from aqueous solutions were determined by using the batch method, and it was found that they were insensitive to the loading, the initial pH, the ionic strength, the humic substance and the sorption direction. Thus, the sorption characteristics of radiocobalt on bentonite and kaolinite facilitated the mathematical modelling of radiocobalt migration. In addition, the sorption kinetics and the sorption mechanism of radiocobalt on bentonite and kaolinite were also examined.

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Abstract  

This paper is an extension of previous papers1–3. The breakthrough curves and the displacement curves of125I and75SeO3 on the calcareous soil, the treated soil to remove CaCO3 and the treated soil to remove organic matter were determined at pH 7.8, at 20°C and in the presence of 1·10−3 or 1·10−4 mol/l CaCl2. These results from column experiments and from batch experiments in the previous papers1,2 were mutually complementary. It can be definitely concluded that iodide is retained to a very small degree and tetravalent-selenium is retained to a small degree by calcareous soil and that organic matter in calcareous soil acts as a significant trap of iodide and CaCO3 acts as a trap of tetravalent selenium. Iodide and tetravalent-selenium would be expected to have relatively high dissemination in calcareous soil.

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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  

Th(NO3)4 was irradiated with 25 MeV/nucleon 40Ar ion beam. The target material irradiated was dissolved in 12 mol/l HCl and the Th in the HCl solution was extracted with 20% (V/V) TBP solution in CCl4 successively, then the TBP solution remaining in the aqueous phase after 4 successive extractions was stripped with benzene. A carrier-free and salt-free multitracer solution containing 38 elements from Be to Bi and 67 radionuclides was prepared. The convenient extraction method was developed for the separation between the target material Th(NO3)4 and the large number of fission products.

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