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Abstract  

A radiotracer method was used for investigation of the adsorption and desorption of radium on stream sediments under conditions similar to those prevailing in waste and surface waters. The effects of pH, ionic strength and Ca2+ or SO 4 2– ions were studied. The results were compared with analogous data characterizing radium interaction with model solids representing components of the sediments. It has been found that the adsorption affinity of the sediments for radium cannot be easily derived from their composition or other properties. No simple correlation with specific surface area, organic matter, oxidic coatings or other components of the sediments was observed. However, an exceptional role of barite (barium sulfate) in the sediments was noted. In the presence of sulfate ions (60 mg/l) this component was responsible for the uptake of predominant or at least significant part of radium, depending on the barite content of sediments. In the absence of added sulfate ions, the adsorption of radium at ph 5–9 on sediments containing barite was lower than on similar sediments without this component, indicating that other components may be more efficient in radium adsorption.

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Abstract  

Uptake of radiostrontium by sediments from two small streams was studied as a function of pH and composition of aqueous phase, of the concentration of strontium, of contact time, temperature and liquid-to-solid ratio (V/m), using laboratory model experiments. Between pH 5 and 12 the uptake increased with pH and shifted to higher pH values with increasing V/m ratio. Addition of cations suppressed the uptake in the order Na+<K+<Ca2+. Increase in strontium concentration had negligible effect up to 10–5–10–4 mol·dm–3 concentration due to high concentrations of dissolved and exchangeable strontium present in the systems. The V/m ratio had no influence on Kd in the range of V/m=20–446 cm3 · g–1 but Kd value for V/m=0.79 cm3 · g–1 was significantly lower. Two-step kinetics of the uptake was observed in most cases with a rapid first step (<100 min) followed by a slow increase. No difference was found between the uptake at 10°C and 22°C. Adsorbed radiostrontium could be easily desorbed with river water. The easiness of desorption decreased with repeated desorption. Drying of sediment did not affect the first desorption, repeated desorptions slightly decreased. Conclusions were drawn on the mechanism of radiostrontium uptake and on the importance of the factors studied for modelling of radiostrontium migration in rivers.

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Abstract  

The suitability of zone electrophoresis and of free-liquid electrophoresis for investigation of the physico-chemical forms of trace elements in aqueous solutions has been examined. Comparison of the electrophoretic mobilities of tervalent cerium determined by these two methods has demonstrated that adsorption of trace elements on the supporting medium renders zone electrophoresis unsuitable for investigation of hydrolytic and other reversible reactions of trace elements accompanied or preceded by significant adsorption. Free-liquid electrophoresis should be preferably used for this purpose as it is much less complicated by adsorption effects.

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Abstract  

The effect of variable composition of water and suspended solids in a small river on the kinetics of uptake of58Co and137Cs by the solids has been analyzed using two kinetic models describing the uptake by two consecutive or parallel reactions. At first, experimental data on the kinetics were obtained by laboratory batch experiments with 6 samples of unfiltered water taken under different flow conditions. Then, parameters of the kinetic models were determined by computer fitting of the experimental data. After subtracting the effect of the concentration of the solids, the variability of the parameters due to the variable composition was determined. The results proved that despite the variability, the description of the kinetics by the two-step kinetic models is more accurate than that using a one-step kinetic model. Approximately equal accuracy of the description with both two-step kinetic models was ascertained. It is recommended that kinetic and equilibrium parameters of radionuclide uptake by suspended solids should always be determined by experiments with repeatedly sampled unfiltered water.

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Abstract  

The effects of concentration of the solid phase and of temperature on the kinetics of interaction of radionuclides with the solid phase suspended in river water were analyzed using two kinetic models describing the interaction by two parallel or consecutive reactions. At first the effect of concentration of the solid phase was theoretically described using four parameters and simple relations. Then kinetic curves were determined by laboratory experiments for the uptake of carrier-free58Co from river water on bottom sediment and on suspended solids of a small river. The curves were analyzed using the kinetic models by calculating the parameters through computer fitting to the experimental data. The parameters thus obtained depend on the concentration of solid phase in the predicted way. Some deviations from theory were due either to agglomeration of sediment particles at higher sediment concentratins or to experimental erros. Equal accuracy of description of the curves with both kinetic models was ascertained. Apart from the concentration of solid phase, the following factors are found to significantly affect the parameters: temperature (13 or 23 °C), properties of solid phase (sediment or suspended solids), sediment age and/or water composition. It is recommended that kinetic parameters suitable for modeling the migration of radionuclides in rivers be obtained by experiments on repeatedly taken samples of unfiltered river water.

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Abstract  

Theoretical and experimental analysis of the open-ended capillary diffusion method for study of the state of trace elements in aqueous solutions is presented. It is shown by theoretical considerations that the use of the discontinuous capillary method of diffusion and the evaluation of single measurements using the classical Anderson-Saddington equation yields incorrect diffusion coefficients if two or more forms of the trace element with significantly different diffusion characteristics are simultaneously present in the solution. A new method for the evaluation of diffusion is suggested, which enables calculation of the abundance of two different forms of a trace element. The method employs a continuous measurement of diffusion combined with computer analysis of the data obtained. Verification of the method is carried out for a particular case using trace radiocerium. The effect of adsorption on the diffusion measurement and interpretation is discussed.

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Abstract  

Theoretical and experimental analysis of the diaphragm diffusion method for study of the state of trace elements in aqueous solutions is presented. It is shown that the method has substantial advantages over other diffusion methods and over conventional use of dialysis, particularly when nucleopore or other membranes with small internal surface area are employed. These advantages include rather short experimental time, not exceeding tens of minutes, lower adsorption losses and lower shift of equilibria among various forms of the trace element studied. A new method for the continuous measurement of and for the evaluation of diffusion is suggested, which enables calculation of the abundance of colloidal forms of the element. Verification of the method is carried out for a particular case using trace radiocerium.

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Abstract  

The paper aims at the analysis of principal factors affecting the interaction of radiocesium with freshwater solids, important for the migration of radiocesium in rivers. Uptake of radiocesium by bottom sediments and suspended solids from small streams was studied as a function of pH and composition of aqueous phase, of the concentration of cesium in water and of the composition of freshwater solids, using laboratory model experiments. pH had negligible effect on the uptake in the pH range 5–9, the uptake decreased at pH values less than 3–5 depending on the nature and concentration of the solids. Addition of cations suppressed the uptake in the order K+>Na+>Ca2+, the suppression began at 0.001, 0.01 and 0.1 mol.dm–3 concentration, respectively. Increase in cesium concentration in water caused a decrease of radiocesium uptake, but at very low concentrations of cesium combined with higher concentration of sediment (2g·dm–3) the uptake was independent of cesium concentration. Removal of carbonates, oxidic coatings and organic matter from a sediment did not affect the sorption properties of the sediment. The nature of the effects found confirms that cesium is sorbed mainly by clay components of freshwater solids. Results obtained are compared with literature data and conclusions are drawn on the importance of the factors studied for modelling of radiocesium migration in rivers.

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Factors affecting interaction of radiocesium with freshwater solids

II. Contact time, concentration of the solid and temperature

Journal of Radioanalytical and Nuclear Chemistry
Authors: P. Beneš, M. Černík, and P. Lam Ramos

Abstract  

The paper aims at the analysis of principal factors affecting the interaction of radiocesium with freshwater solids, important for the migration of radiocesium in rivers. Uptake and release of radiocesium by bottom sediment and suspended solids from a small stream were studied as a function of contact time during the uptake and releases, of concentration of the solid phases and of temperature, using laboratory model experiments. Kinetics of the uptake were found to be singificantly affected by temperature and concentration of the solid phase. The kinetics and the concentration effect can be quantitatively described using kinetic model of two parallel or consecutive reactions. Kinetic parameters for the model were determined. Distribution coefficient Kd is independent of sediment concentration in the range of 20–70 mg·dm–3 but passes through a maximum at higher concentration values. Release of radiocesium adsorbed on the freshwater solids was found to be quite rapid and a simple kinetics of the release from freshwater solids was observed. The amount released decreased with increasing contact time of radiocesium with solid phase. Quantitative evaluation of the release revealed partial irreversibility of radiocesium uptake on the solids studied. Results obtained are compared with literature data and conclusions are drawn on the importance of the factors studied for modeling of radiocesium migration in rivers.

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Abstract  

The radiotracer method has been used for investigation of the adsorption and desorption of traces of radium on ferric hydroxide and quartz under conditions similar to those prevailing in waste and surface waters. The effects of pH, liquid to solid ratio, ionic strength and presence of Ca2+ or SO 4 2- ions have been studied. It has been concluded that at pH less than 7 and at concentration of suspended sediments (of common composition) less than 100 mg·1–1 ferric hydroxide and quartz have negligible effect on the state and migration of radium in surface waters. Radium adsorbed on quartz can be easily desorbed with dilute solutions of hydrochloric acid or sodium chloride.

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