Cs-Na selectivity

Extraction of Cesium and Sodium Cs/Na Selectivity and Competitive Extraction of Cesium in the Presence of an Excess of Sodium... 

Calix-crowns extract cesium from acidic and alkaline solutions with extremely high Cs/Na selectivity.66 71 Because their selectivity is higher, it seems promising to use the calix-crown instead of DB21C7 for extraction of cesium in mixtures with the... 

Lamare, V., Bressot, C., Dozol, J. F., Vicens, J., Asfari, Z., Ungaro, R., and Casnati, A. Selective Extraction of Cesium at Tracer Level Concentration from a Sodium Nitrate Solution With Calixcrowns. Molecular Modeling Study of the Cs+/Na+ Selectivity, Sep. Sci. Technol. 32 (1997), 175-191. 

The Cs /Na selectivity from 3 mol/L aqueous [51] NaNOs solution was about 90%. With the two-stage process 99% removal of trace quantities of caesium was achieved and sodium retention not higher than 10%. 

The sequence of the selectivities towards cations is also solvent dependent for dibenzo-18-crown-6 [11] the sequence is K+ > Na+ > Rb+ > Cs+ in water, methanol, dimethylformamide and dimethyl sulfoxide (Dechter and Zink, 1976 Srivanavit et al., 1977), whereas it is Na+ > K+ > Rb+ > Cs+ in acetonitrile (Hofmanova et al., 1978). A reversal of the K+/Na+ selectivity on going to apolar aprotic solvents was also observed for fluorenyl salts (Wong et al., 1970). Whereas for alkali cations the sequence of binding constants and enthalpies are the same in water (Izatt et al., 1976a), they differ considerably in methanol/water mixtures (Izatt et al., 1976b), dimethyl sulfoxide and acetone (Arnett and Moriarity, 1971). 

The flexible macrobicyclie ligands 31—33 display high K+/Na+ selectivity (300—600), but weak K+/Rb+, Cs+ selectivities. On the other hand, the more rigid ligand 30 shows a K+/Na+ selectivity similar to those of the flexible ligands 19 and 31—33, but it also has appreciable K+/Rb+, Cs+ selectivity. 

Frensdorff (3) has determined log K values for the reaction in methanol of several cyclic polyethers of varying ring size and numbers of donor atoms with Na+, K+, and Cs+ (all chlorides). The log K values are plotted in Fig. 2 where several trends are evident. The relationship between ring size and cation size which has been referred to as the selectivity order changes from Na+>K+ for dicyclohexyl-14-crown-4 to Na+ K+>Cs+ for cyclohexyl-15-crown-5, to K+ >Cs+ Na+ for dibenzo-... 

Both Table II and (8) show clearly that membrane selectivities may depend highly on the concentration cs of the carrier within the membrane phase. Although the ligands 1023 and 1149 induce Ca2+- and Na+-selectivities, respectively, in bilayer membranes,50,51 the correlation of these selectivities with those of bulk membranes is not as pronounced as indicated in Fig. 2.50 In bulk membrane experiments Ca2+ and Na+ are found to be preferred by 10 and 11, respectively.23,49 52 For a more careful comparison of the selectivities, the concentration cs of the ligand in the membrane phase should be adjusted. 

The equilibrium constant is called the selectivity coefficient, because it describes the relative selectivity of the resin for Li+ and Na+. Selectivities of polystyrene resins in Table 26-3 tend to increase with the extent of cross-linking, because the pore size of the resin shrinks as cross-linking increases. Ions such as Li+, with a large hydrated radius (Chapter 8 opener), do not have as much access to the resin as smaller ions, such as Cs+, do. 

Crown ethers continue to be one of the most useful parts of supramolecular chemistry/91 From the beginning computations of metal ions complexes with synthetic ionophores/101 which have been aptly reviewed/111 emphasized the importance of including explicitly solvation in free energy calculations, also with ab initio calculations on calixarene complexes/121 Molecular dynamics simulations of 18-crown-6 ether complexes in aqueous solutions predict too low affinities, but at least correctly reproduce the sequence trend K+ > Rb+ > Cs+ > Na+. However, only the selection of K+ over Rb+ and Cs+ is ascribed to the cation size relative to that of the crown cavity, whereas K+ appears in these calculations to be selected over Na+ as consequence of the greater free energy penalty involved in displacing water molecules ftomNa/1131... 

Wipff, G., Lauterbach, M. (1995), Complexation of Alkali Cations by Calix[4]crown Ionophores Conformation and Solvent Dependent Na+ / Cs+ Binding Selectivity A MD FEP study, Supramol. Chem. 6, 187-207. 

Catalytic Reactions. As the techniques for solid-state n.m.r. continue to improve with the simultaneous improvement in sensitivity and hence speed, there will be a growing trend to look at chemical reactions occurring on or in catalysts. There have already been a number of instances where catalytically stimulated reactions have been studied by 13C n.m.r. - the alkylation of toluene by methanol on X zeolite, for example,138 in which the influence of the cation, Na+ or Cs+, on selectivity was deduced. The adsorption binding and decomposition of various metal carbonyls on A1203 or in zeolites has been studied,139 likewise, the nature and sites of interaction of CO and C02 on X and Y zeolites.140... 

A particular aspect of water treatment is the rehabilitation of accidentally contaminated soils by radionuclides. This is well illustrated by the works carried out after the Cernobyl catastrophe. The incorporation of clinoptilolite into contaminated soils reduced the transport of heavy metals and radionuclides from soils into ground water and biomass (7). Union Carbide s IONSIV EE-95 (CHA) and A-51 zeolites (LTA) with excellent Cs+/Na+ and Sr2+/Na+ selectivities, respectively, have also been employed for decontamination of high activity level water in the reactor containment building from Cs+ and Sr2+ after the accident at Three Miles Island (5). The radioisotope loaded zeolites were then transformed into glasses for ultimate disposal. 

The application of a two-temperature scheme for separating Li -NH4 and Cs -Na mixtures in a fixed bed of sulfonate cation exchanger is described in the literature [28,29]. However, such an approach has not been developed further because of the complexity of moving temperature zones and the need to shift points of solution input and output. Besides temperature change in simple cases of ion exchange with sulfonated cation exchanger does not influence changes in selectivity sufficiently. 

The affinity series of the inorganic exchangers for alkali metal ions vary depending on both the crystalline form of the exchanger and the nature of the sorption media. Most of the hydrous oxides can be obtained as amorphous structures. At low loading the amorphous hydrous oxides of Al, Si, Ti, Zr, Ce(IV) and Sb(V) exhibit the usual selectivity sequence Li+ < Na < K < Rb < Cs+. This selectivity sequence is observed with the... 

The three aplasmomycins (12-14) were compared in terms of antibacterial activity (Table 6), alkali metal ion selectivity (Table 7) and transport ability. The results summarized below show that the antibacterial activity of aplasmomycin B (13) was nearly equal to that of aplasmomycin, while aplasmomycin C (14) showed a weaker activity. It was also noted that the ability to form complexes with other metals does not directly correspond with antibacterial activity. Cation selectivity decreased in the order Rb > K > Cs = Na > Li. The three aplasmomycins did not show any affinity towards divalent cations. 

A series of chromatographic silicas, radiotracer Cs > Na the selectivity increases when a pore diameter decreases [3179]. This result suggests a size-exclusion effect, which may also be responsible for the cation selectivity in other silicas. 

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