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  • Author or Editor: Š. Palágyi x
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Abstract  

The separation of radioiodine from water by multistage isotope exchange between iodide and molecular iodine in a heterogeneous liquid system under both static and dynamic conditions has been studied in two model arrangements. Equations were derived which enable the calculation of the theoretical separation efficiency in dependence on both the volume concentration and concentration of the carrier of radioiodide in water. It was found that under the same conditions, the calculated values are in a satisfactory agreement with experimentally determined values of the separation efficiency.

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Abstract  

A rapid and specific method for the determination of131I in environmental water samples in the presence of some of the most important fission products is described. Radioiodine is separated from acidified water using tri-n-octylamine solution in toluene with dissolved iodine by one-stage static procedure with about 90% separation efficiency and 200-fold volume concentration. After the decolorization of the organic phase with NaOH in methanol, radioactivity of131I is counted by a toluene base liquid scintillator with a counting efficiency of 70%. The method is simple and enables to determine low radioactivity131I with a detection limit less than 5 pCi/1 in about 1.5 hrs.

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Abstract  

Possibilities of the preconcentration of solutes in liquid-liquid extraction have been investigated from the point of view of transport processes in two models. It was found that the multistage dynamic (flow) column operation with a stationary extracting phase containing solutes to be separated enables to obtain higher preconcentrations than the one-stage static (batch) process with a factor available to reach its maximum value of 2 for separations approaching 100 percent extraction. The theoretical considerations were confirmed in the separation of131I from aqueous solutions.

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Abstract  

Theoretical possibilities of the application of isotopic exchange in a heterogeneous liquid system to the separation of radionuclides have been investigated. With certain simplifying assumptions, equations were derived which enable the calculation of both the separation efficiency and volume concentration for a one-stage separation process under static or dynamic conditions. The relations obtained can be used in the choice of an appropriate method for the separation and simultaneous enrichment of trace amounts of radionuclides from large-volume liquid samples by equilibrium isotopic exchange.

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Abstract  

The application of isotope exchange in a liquid-liquid system for the separation and preconcentration of131I and131IO3/– from water is described. For this purpose a solution of elemental iodine in tri-n-butyl phosphate diluted with toluene was used. The influence of various factors on the separation efficiency of131I was investigated. These are: time of the exchange, concentration of a carrier in the aqueous phase, concentration of I2 in the organic phase, volume ratio of the phases, pH, foreign ions, storage of the organic phase, etc. The method is quite rapid and the selective preconcentration of these chemical forms of radioiodine from water can be accomplished even in the presence of the most important fission products. This method makes also possible to separate these chemical forms from each other under controlled pH conditions. The activity of the separated radioiodine can be measured advantageously, e.g., by homogeneous liquid scintillation counting after decolourization of the organic phase.

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Abstract  

A study is presented on the use of isotopic and non-isotopic ion exchange in a heterogeneous liquid-liquid system for the separation of131I from water. The method is based on the reaction between radioiodide in the aqueous phase and trioctylmethylammonium iodide or chloride in the organic phase. The effect of some important experimental parameters on the separation efficiency is discussed. It has been found that under optimum conditions the method of isotopic ion exchange can be used for the radiochemical determination of iodine in water.

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Abstract  

Theoretical possibilities of the preconcentration of solutes in multistage static liquid-liquid extraction have been investigated. It was found that the preconcentration increases with increasing distribution ratio of the solutes between two phases as well as with the number of stages (n) and reaches its maximum value for n approaching infinity, i.e., in dynamic extraction. Comparison of the preconcentration in multistage (Pns) and one-stage (p1s) static operations shows that the relative preconcentration (qns=pns/p1s) increases to infinity as the separation efficiency approaches 100%. Some of these theoretical considerations have been confirmed in extraction of radioiodine from aqueous solutions.

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Abstract  

Transport of 125I, 137Cs+ and 85Sr2+ radionuclides in crushed granitoidic rocks and homogenized soils was studied. Two simple methods for calculation of breakthrough curves in flow column experiments with groundwater as transport medium have been described. The first method, so called non-linear approach, is derived on the assumption of a reversible non-linear sorption isotherm described with Freundlich equation, i.e., with non-constant distribution and retardation coefficients. The second method, so-called linear approach, is applied for reference only, and is based on the assumption of a reversible sorption characterized with linear sorption isotherm, i.e., with constant distribution and retardation coefficients. Both methods model the experimental breakthrough curves with the integrated form of the simple 1-D advection–dispersion equation (ADE) expressed analytically for pulse application of radiotracer to the liquid phase before entering the columns. The integrated form of the ADE equation was modified by the so-called peak position and peak height correction coefficients the advantage of which consists among others in the elimination of the influence of starting concentration. The comparison of both approaches has shown that fitting by means of non-linear approach has given rather reliable values of the transport parameters and calculated dependences, especially in a case of 137Cs system characterized evidently with non-linear type of sorption isotherms. As for 125I, the sorption capacity of all solid samples studied is nearly on the zero level and 125I is practically not retarded, and from this point of view it behaves as non-interacting component. In addition, it was found that the modified ADE gives rather better results than the classical one.

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Abstract  

In this work, the sorption of 137Cs+ dissolved as 137CsNO3 in the solution of 10−6 M CsNO3 in SWG, and its desorption by solution mentioned, were investigated under dynamic conditions in columns with crushed granitic materials of various grain sizes, namely, of pure granite and, of corresponding filling materials. It aims at the quantification of the influence of grain size on the retardation and distribution coefficients of 137Cs, as well as on the other transport parameters (Peclet numbers and dispersion coefficients). For their determination, model based on erfc-function was used, assuming reversible equilibrium linear or non-linear sorption/desorption isotherms. By means of both model approaches, the experimental BTC S were fitted using non-linear regression procedure, in the course of which the parameters mentioned were sought. The obtained results also validated the applicability of the linear equilibrium isotherms of the 137Cs+ sorption/desorption in the studied transport processes and systems. Depending on the grain size, the retardation coefficients were between 40–93 in pure granite and 140–200 in filling materials. These values correspond to distribution coefficients of 11–34 cm3/g and 40–69 cm3/g, respectively. It was found that both retardation and distribution coefficients increase with decreasing grain size.

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