Rubidium 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 principal rubidium salts which would probably have been present in the sediment (chloride, sulfate, bicarbonate, etc.) are all soluble in water. As discussed later, the red clay was thoroughly dialyzed prior to use (including prior to analysis by emission spectroscopy). Any rubidium salts initially present in the clay samples would, therefore, have been removed by the dialyzing solution. Hence, it was assumed that the rubidium concentration given in Table I represented sorbed rubidium which had been in equilibrium with the rubidium in the original interstitial seawater. Then when calculating distribution coefficients from experimental data, the concentration given in Table I was used as the initial clay-phase rubidium concentration, rather than zero as used with most of the other species studied. 

Distribution Coefficients. The distribution coefficients determined for rubidium (at ll C) and for cesium (at ll C for -log Ci less than 5 and at for -log greater than 5) are summarized in Figure 1. Over the range of solution-phase concentrations in which both rubidium and cesium were studied, the rubidium coefficients appear to behave very similarly to those for cesium. For solution-phase concentrations on the order of 10 3 mg-atom/ml, the coefficients are on the order of 100 ml/gm, as was expected. Furthermore, the distribution coefficients obtained for cesium generally appear consistent with the corresponding coefficients obtained for similar oceanic sediments and related clay minerals found within the continental United States (6,7,8,9510,12,13). In the pH range of 6.3 to 8.0, the cesium coefficients appear to... 

The distribution coefficients evaluated for silver (at C) are also given in Figure 3 The silver coefficients determined in 0.68 N NaCl solutions are somewhat less than the corresponding coefficients for cesium and rubidium, and also for strontium and barium. Such results are probably due to either anionic complex formation (22) and/or a less favorable sorption equilibrium. (FurthermoreJ the experiments done using silver in sodium chloride solutions required equilibration times on the order of 90 days, as opposed to two to four days for most other experiments, and it appears that processes, which may or may not be important, are involved which are not understood.)... 

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. 

For each nuclide studied, the sorption distribution coefficients appeared to result from a minimum of two separate mechanisms. In all cases, one mechanism appears to be an ion-exchange phenomena associated with the silicate phases and appears to have a relatively much larger sorption capacity than the other mechanism. In the case of cesium (and probably rubidium) the second mechanism appears to also be related to the silicate phases and may or may not be an ion-exchange phenomena. However, for the other elements studied, the second mechanism appears to be related to the hydrous iron and manganese oxides and again may or may not be an ion-exchange process. 

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