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Kinetics of radionuclide interaction with suspended solids in modeling the migration of radionuclides in rivers
III. Variability of kinetic parameters
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.
Kinetics of radionuclide interaction with suspended solids in modeling the migration of radionuclides in rivers
II. Effect of concentration of the solids and temperature
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.
Factors affecting interaction of radiocobalt with river sediments
I. pH and composition of water, and contact time
Abstract
The paper aims at the analysis of principal factors affecting interaction of radiocobalt with freshwater solids, important for migration of radiocobalt in surface streams. Uptake and release of radiocobalt by sediment from a small river have been studied as a function of pH and composition of aqueous phase, the cobalt concentration and contact time, using laboratory model experiments. A factor of primary importance is the contact time due to slow and two-step kinetics of radiocobalt uptake, which also strongly depends on the concentration of sediment in suspension. pH exerts the most significant effect on the interaction in the pH region of 5–7.5, where the uptake increases with pH. Ionic strength of water phase (I) and concentration of cobalt in water (c) affect the interaction only at rather high values of I or c and their variation can be neglected in the modelling of radiocobalt transport in streams under ordinary conditions. Desorption by river water of radiocobalt pre-adsorbed on the sediment passes through a maximum with desorption time, decreases with increasing adsorption time and increases upon drying of the sediment prior to desorption. Results obtained are compared with literature data and conclusions are drawn concerning the mechanism of radiocobalt uptake by the sediment.
Factors affecting interaction of radiocobalt with river sediments
II. Composition and concentration of sediment, temperature
Abstract
The paper aims at the analysis of principal factors affecting the interaction of radiocobalt with freshwater solids, important for migration of radiocobalt in surface streams. Uptake of radiocobalt by sediment from a small river have been studied as a function of composition of the sediment, of liquid-to-solid ratio (V/m) and of temperature, using laboratory model experiments. The study of the effect of sediment composition was based on selective extraction of the sediment prior to the uptake and indicated that radiocobalt was sorbed on several components of the sediment simultaneously, probably on clay minerals, organic matter and oxidic coatings. Relative importance of these components depends on the pH and composition of the aqueous phase and on the concentration of radiocobalt. Distribution coefficient Kd characterizing the uptake of radiocobalt is nearly independent of the V/m ratio in V/m range typical for rivers, but decreased at V/m<1.7 dm3·g–1. Increase in temperature from 13°C to 23°C accelerate radiocobalt uptake but did not affect the 
equilibrium
value of the uptake. Results obtained are compared with literature data and conclusions are drawn concerning the importance of the factors studied for modelling of radiocobalt migration in rivers.
Abstract
Adsorption of radium was studied on glass and polyethylene from aqueous solutions containing 8–40 pg·dm–3 224Ra and on membrane filters, glass and polyethylene bottles from waste and river waters containing 2–170 pg·dm–3 226Ra. The adsorption from aqueous solutions was determined as a function of pH and composition of the solutions and interpreted as due to ion exchange of Ra2+ ions for counter ions in the electric double layer on glass and polyethylene or due to chemisorption of RaSO4 (RaCO3) ion pairs on glass. Borosilicate glass adsorbed radium substantially more than polyethylene. The adsorption of dissolved forms of radium from the waste and river waters during storage and membrane filtration of the waters was negligible, but a significant loss of particulate forms of radium was sometimes observed during the storage. It has been recommended to separate dissolved and particulate forms of radium soon after the sampling and to prefer polyethylene to glass as container material for storage of dissolved forms of radium.
Blue sticky traps on 3.0 m high poles were used to determine the characteristics of Thrips tabaci and Frankliniella occidentalis migratory flight in Israel from 2003 to 2007. In an open area, both thrips species were caught from March to November. The dominant species was T. tabaci except during the spring. About 70% of the thrips were caught below 1.0 m above ground. Trapping height appears to reflect thrips’ concentration gradient in the air because it was not affected by setting up the poles over a sticky surface. From April to September the westerly sea breezes usually exceed 10 km/h from late morning to twilight time. As a result, about 85% and 10% of the thrips were caught in the morning and at dusk, respectively. When we used similar traps mounted on wind vanes, at 1.0 m above ground 70% of the thrips were caught on the leeward side. Thus, it appears that thrips fly mainly upwind during their migration. Indeed, while most prevailing winds are from the west, most thrips were caught on the eastern side of the poles (40–50%) and the fewest on the western side (10–20%). This information may be used to focus monitoring and control of these thrips in time and space.
Abstract
The AgPO3−Pr(PO3)3 system has been studied for the first time by differential thermal analysis, X-ray diffraction and IR spectroscopy. The system shows one compound AgPr(PO3)4 which melts in a peritectic decomposition at 1069 K. An eutectic appears at 761 K. AgPr(PO3)4 belongs to the monoclinic system with space group P2t/c,Z=4. The parameters of the unit cell are:a=12.000(9),b=13.177(4),c=7.046(5) Å and β=123o,81(6),Z=4. Its IR absorption spectrum is typical of chain phosphates.
Abstract
Large samples of papers published in theJournal of Biological Chemistry in all decades and in some mid-decades werechecked in order to study the referencing pattern, throughout the period 1910–1985, in an internationally leading journal, with especially high 
citation impact
. All measures show that there has been a significant growth in the number of references per paper, during most of the period, but mainly from the 1950's on, refuting Meadows' upper limit. A detailed comparison to a wide range of fields shows theJBC rates to be among the highest. Eight factors affecting the number of references are discussed, and some projections for the future are made.
Abstract
The physico-chemical state of trace lead in aqueous nitrate solutions (I=0.01) was studied using equilibrium calculation, free-liquid electrophoresis, dialysis and centrifugation methods and210, 212Pb. It has been found that lead is present exclusively as nonhydrolyzed cations in solutions of pH 2–3.5. Colloidal or larger particulate forms of lead exist in solutions of lower acidity (pH>4). They are of pseudocolloidal nature, i.e. they are formed by adsorption of lead on solid impurities in the studied solutions. The pseudocolloids are negatively charged at pH>5 and reversible at pH 4–7. Reversibility of the adsorption of lead on impurities decreases at pH>7. Experiments have indicated that a significant hydrolysis of bivalent lead takes place already at pH>4. Anionic hydroxo-complexes of lead predominate in alkaline solutions of pH>12.
