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Summary  

To provide comprehensive information for assessing the safety of geological disposal of radioactive waste, the additivity of sorption properties during different reaction times for various bentonite/quartz sand mixtures was investigated. Se and Cs were the nuclides of interest. Synthetic seawater (SW) was employed as the liquid phase tosimulate the possible groundwater conditions while the disposal site is an island area. Batch sorption experiments were conducted to measure the distribution ratio, R d. Regardless of whether Cs and Se were used, the additivityat the reaction time of 7 and 14 days was better than that of 28 and 56 days.Interactions between bentonite and quartz sand might occur in synthesized seawater in reactions beyond 14 days. Under the experimental conditions,the additivity equation could be corrected by the composition ratio and reaction time. Long-term prediction of the R dby short term batch sorption experiments would be helpful while assessing buffer materials mixed by bentonite and quartz sand.

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Abstract  

The separation of the trivalent metal ions Am(III) and Eu(III) by extraction chromatography employing TBP impregnated macroporous XAD-4 resin as the stationary phase was examined; some parameters affecting the distribution ratio (Kd) and the column resolution (Rs) of Am(III) and Eu(III) were investigated. These parameters are the effect of TBP loading, aqueous nitrate concentrations, and flow rate. Both Kd andRs increase with the TBP loading.

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Abstract  

The diamide N,N,N,N′-tetraoctyldiglycolamide (TODGA) was synthesized and characterized. The prepared TODGA was applied for extraction of Ce(III) from nitric acid solutions. The equilibrium studies included the dependencies of cerium distribution ratio on nitric acid, TODGA, nitrate ion, hydrogen ion and cerous ion concentrations. Analysis of the results indicates that the main extracted species is Ce(TODGA)2(NO3)3HNO3. The capacity of Ce loading is approximately 45 mmol/L for 0.1 M solution of TODGA in n-hexane. Finally, the thermodynamic parameters were calculated: K (25 °C) = 3.8 × 103, ΔH = −36.7 ± 1.0 kJ/mol, ΔS = −54.6 ± 3.0 J/K mol, and ΔG = −20.4 ± 0.1 kJ/mol.

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Abstract  

Extraction of europium(III) from nitric acid medium by a solution of tri-n-butylphosphate (TBP) and n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in the room temperature ionic liquid, 1-alkyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (amimNTf2 where a = butyl or hexyl or octyl), was studied. The distribution ratio of (152+154)Eu(III) in TBP-CMPO/bmimNTf2 was measured as a function of various parameters such as the concentrations of nitric acid, CMPO and NaNO3. Remarkably large distribution ratios were observed for the extraction of europium(III) when bmimNTf2 acted as diluent. The stoichiometry of metal-solvate in organic phase was determined by the slope analysis of extraction data.

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Abstract  

The solvent extraction of technetium from urine with TBP has been investigated. The distribution ratio of technetium was determined as a function of HCl concentration and reaction time. The distribution ratio in the HCl-TBP system containing urine is consistently lower than that without urine. The chemical forms of technetium in urine, analyzed by paper chromatography, indicated that pertechnetate was reduced in the presence of HCl and that the reduction of pertechnetate was enhanced by urine. The observed decrease in the distribution ratio was attributed to the enhanced reduction of pertechnetate by urine.

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Abstract  

The influence of the concentration of nitric, hydrochloric and phosphoric acids, petroleum sulfoxides (PSO), salting-out agent, kind of diluent and temperature on the distribution ratio of U(VI) and Th(IV) has been systematically studied. It is found that the extraction regularity of PSO is similar to that of TBP. The distribution ratio in phosphoric acid is lower, but it increases with the increase of hydrochloric acid concentration and reaches a high value. The U(VI) exhibits the maximum distribution ratio at 3–4 mol/l HNO3. The distribution ratio of U(VI) and Th(IV) increases rapidly in the presence of a salting out agent. The extracted compounds are determined to be UO2(NO3)22PSO and Th(NO3)42PSO. The extraction enthalpies of U(VI) and Th(IV) with PSO were also calculated.

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Abstract  

The thermodynamic extraction of uranium(VI) with hexyloctylsulfoxide (HxOSO) has been studied. It was found that the distribution ratio increases with increasing nitric acid concentration up to 2.3 mol/l and then decreases. The distribution ratio also increases with increasing extractant concentration. The extracted species appears to be UO2(NO3)2 .2HxOSO. The influences of temperature, sodium nitrate and oxalate concentrations on the extraction were also investigated, and the thermodynamic functions of the extraction reaction were obtained.

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Abstract  

The extraction of Am(III) and Eu(III) using a γ-pre-irradiated N,N′-dimethyl-N,N′-dibutyltetradecyl malonamide (DMDBTDMA) modified with N,N′-dihexyloctanamide (DHOA) in n-dodecane (NDD) at 4.5M HNO3 has been studied as a function of the absorbed dose up to 2×106 Gray. The distribution ratios of Am(III) and Eu(III) were almost constant until a dose of 1×105 Gray and then they decreased gradually up to a dose of 2×106 Gray. The decrease of the distribution ratios of Am(III) and Eu(III) are due to the decreasing concentration of the DMDBTDMA by a γ-pre-irradiation and these results were supported by a determination of the DMDBTDMA concentration with a gas chromatography method. The distribution ratios of Am(III), Eu(III), Ce, Nd and Y with γ-pre-irradiated (DMDBTDMA-DHOA)/NDD have also been studied as a function of the nitric acid concentration and the extraction temperature.

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Abstract  

Batch method was used to investigate the sorption behavior of radioiodine on organic rich soil, alumina, chlorite-illite clay mixture and bentonite.131I was used as tracer. The grain sizes of the samples used were all below 38 m. A rather slow kinetics was observed for the adsorption of radioiodine on organic rich soil. The distribution ratio increased with increasing solution/solid (V/m) ratio, and the contact time. The pH of the synthetic groundwater did not change the distribution ratio appreciably. The soil biomass however, showed a striking effect on the adsorption of radioiodine. Among the clay minerals, the highest distribution ratio value was found for chlorite-illite clay mixture. All the values were however well below those of the organic rich soil. The sorption data were fitted to Freundlich and Dubinin-Radushkevich types isotherms. Means energies of adsorption, as well as the affinity ratios of the sorption sites to iodine and chlorine were calculated.

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Abstract  

The solvent extraction of U(VI) by p-tert-butylcalix[n]-arene acetate (HnL) (n=4, 6, 8) has been studied. The effects of acidity in aqueous phase and concentration of extractant in organic phase on the distribution ratio were examined. It has been found that the distribution ratio is proportional to [H+]−2 and [HnL](O) and the extracted complex species is UO2Hn −2L. The equilibrium constants of the extraction reactions have been determined. The reaction mechanism is discussed.

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