Europium distribution coefficients

Therefore, the preliminary investigation described herein examined several aspects of the behavior of the equilibrium distribution coefficients for the sorption of rubidium, cesium, strontium, barium, silver, cadmium, cerium, promethium, europium, and gadolinium from aqueous sodium chloride solutions. These solutions initially contained one and only one of the nuclides of interest. For the nuclides selected, values of Kp were then... 

The distribution coefficients for europium also appear to be strongly influenced by low values of the solution pH. Such behavior is similar to that of barium and silver and again suggests that the sorption of the lanthanides may be due to at least two separate mechanisms, which are also probably essentially the same as those discussed for barium. 

For the nuclides studied (rubidium, cesium, strontium, bariun silver, cadmium, cerium, promethium, europium, and gadolinium) the distribution coefficients generally vary from about 10 ml/gm at solution-phase concentrations on the order of 10 mg-atom/ml to 10 and greater at concentrations on the order of 10 and less. These results are encouraging with regard to the sediment being able to provide a barrier to migration of nuclides away from a waste form and also appear to be reasonably consistent with related data for similar oceanic sediments and related clay minerals found within the continental United States. 

The degree of the metal extractions depends on its concentration. Por example, with increasing europium concentration the distribution coefficients in the alkali-DOBTA system decrease, while in the alkali-tartaric acid system a maximum at 7x10 4 M Eu concentration is observed. As we suggested the enhancement in the metal distribution coefficient is evidently due to the metal polymerization in the organic phase, and the decrease is caused by polymerization in the aqueous phase, which eventually results in low extractable polymer form. The latter assumption is supported by the fact that as the alkali concentration increases the maximum on extraction curves undergoes a shift towards lower concentration of the metal. 

The second point of interest is the relationship between ionic radius and distribution coefficients (Onuma et al. 1968, Jensen 1973, Philpotts 1978). This is demonstrated in fig. 22 for plagioclase which shows the regular variation in with ionic radius, and the dramatic effect due to the presence of europium as the divalent ion. 

McKay. G. A., J. Wagstaff, and L. Le, REE distribution coefficients for pigeonite constraints on the origin of the mare basalt europium anomaly (abstract), in Lunar and Planet. Sci. XXI, pp. 173-114, Lunar and Planetary Bistitute. Houston. 1990. 

On the other hand, Dyrssen and Liem (1960) report (table 7) greater variation in both distribution ratios [for americium and europium extraction by dibutyl phosphoric acid (HDBP)] and in separation factors as a function of diluent. The separation factors and distribution coefficients are correlated (more or less consistently) inversely with the distribution ratio of the extractant between the phases. In this system, the largest separation factors are observed in n-hexane, chloroform, and carbon tetrachloride. Diluents capable of direct coordination (i.e., those possessing potential oxygen-donor atoms) are correlated with reduced distribution ratios and separation factors. The observations of greater separation factors in non-complexing diluents suggest that more effective separation is observed when the inner-coordination sphere of the hydrophobic complex is not disturbed. 

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