Ion-exchange behavior

A tremendous variety of structures is known, and some of the three-dimensional network ones are porous enough to show the same type of swelling phenomena as the layer structures—and also ion exchange behavior. The zeolites fall in this last category and have been studied extensively, both as ion exchangers and as gas adsorbents (e.g.. Refs. 185 and 186). As an example, Goulding and Talibudeen have reported on isotherms and calorimetric heats of Ca -K exchange for several aluminosilicates [187]. 

Ion exchange (qv see also Chromatography) is an important procedure for the separation and chemical identification of curium and higher elements. This technique is selective and rapid and has been the key to the discovery of the transcurium elements, in that the elution order and approximate peak position for the undiscovered elements were predicted with considerable confidence (9). Thus the first experimental observation of the chemical behavior of a new actinide element has often been its ion-exchange behavior—an observation coincident with its identification. Further exploration of the chemistry of the element often depended on the production of larger amounts by this method. Solvent extraction is another useful method for separating and purifying actinide elements. 

Figure 4. The ion-exchange behavior of cationic radon on a column packed with K PF. ...

Fuger, J. (1958). Ion exchange behavior and dissociation constants of americium, curium and californium complexes with ethylenediaminetetraacetic acid, J. Inorg. Nucl. Chem. 5, 332. 

Convergence or divergence in the linearity of the plots of retention time versus the logarithm of the number of residues, i.e. /c iex i versus In d, can be employed to characterize the regular ion-exchange behavior of polypeptides in terms of the role of polypeptide chain length... 

The structure of and possible cation location in these materials is fairly well known (2, 8, 4, )> and their ion-exchange behavior toward a multitude of pairs of ions, mostly including sodium, has been measured and interpreted in terms of basic properties of ions, crystal structures, and pore dimensions. The major part of these studies is with alkali- and alkaline-earth cations, alkylammonium ions, rare-earth cations, and silver and thallium ions (1). In contrast, the ion adsorption of transition metals in faujasite has received little attention. 

This paper presents some data relating to these aspects which have been obtained in the course of an extensive experimental study of the ion-exchange behavior of transition-metal ions in X and Y zeolites. 

The temperature-dependent irreversibility demonstrates that the ion-exchange behavior of NaX towards bivalent cations depends strongly upon the thermal history of the sample. The rather pronounced differences in behavior of transition-metal ions, also observed in synthetic zeolite 4 A (9) is in very sharp contrast with the nearly identical, either hydrated or crystallographic, dimensions of these ions (10). Obviously, this observation raises important questions as to the value of the current interpretation (nearly) exclusively in terms of physical dimensions of ions and pore width. In contrast, the similarity of behavior in mont-morillonite is remarkably close the AG0 value for the replacement of Na by either Ni, Co, Cu, or Zn is —175 cal ( ll)/equivalent, irrespective of the nature of the cation (11). Therefore, the understanding of their difference in behavior in zeolites must take other effects into consideration. 

Selectivity of adsorption and the relative tendency toward adsorption may be inferred from ion exchange behavior (6, 30, 80, 81, 84). 

Examples of Ni2+, Co + and Zn2+ ion exchange for Na+ in zeolites include exchange of Na-A (1), Na-X (2,3). The work cited above provides a sampling of the variety of ion exchange behavior exhibited in these systems. 

In deriving the shapes of these isotherms, we first must define isotherms for ideal clays and ideal oxides. We then combine these ideal functions into overall isotherms and compare the derived functions to experimental isotherms determined for various adsorbents. We will show that observations which have been said to preclude ion exchange are, in fact, quite consistent with ion-exchange behavior. We will not attempt to derive actual values of equilibrium distribution coefficients, but rather we seek only to define the shapes of the isotherms. 

Among these titanates, ion-exchange behavior has been demonstrated in K2Ti205, Na2Ti307, and Na2Ti409. 

Ion-Exchange Behavior of Sodium Titanate. The ion-exchange characteristics of sodium titanate supports are summarized in Fig. 1 (2). In the figure, proton consumption is plotted by the solid line as the Nao.sTi is titrated from a basic pH ( 12) with HC1. Na+ (+) loss from and Cl" (-) adsorption onto the support are followed by... 

Escherichia coli B was incubated with 2,6-diaminopurine (XXIV), and 6-amino-2-(methylamino)-9-(5-0-phospho-D-ribosyl)purine (XXV) was isolated from the acid-soluble extract of the cells. 5-Nucleotidase liberated a nucleoside containing D-ribose. Hydrolysis of the nucleoside (or nucleotide) with N hydrochloric acid liberated 6-amino-2-(methylamino)purine, which was identified by paper chromatography and by its ultraviolet absorption spectrum. The chromatographic and ion-exchange behavior of the extract also suggested the presence of either a pyrophosphate or a triphosphate of the 6-amino-2-methylamino-(D-ribosyl)purine. In a similar manner, 2,6-diamino-9-(5-0-phospho-D-ribosyl)purine (XXVI) was isolated and identified, together with its possible pyrophosphate or triphosphate. 2,6-... 

Since the amino acids are the chemical units from which proteins are formed, the ion-exchange equilibria of amino acids will help provide insight with respect to the ion-exchange behavior of proteins [2,3]. 

When measurements are made to investigate the ion exchange behavior of a cation or anion it is common practice to determine the distribution coefficient, D,, where... 

The oxides of metals, such as Ti, Zr, Ce(IV) and Th exhibit amphoteric ion-exchange behavior (Fig. 3). The decrease in acid strength of their oxides, Ti > Zr > Ce > Th, is paralleled by the decrease in the effective crystal ionic radii of these metals. The pH, of the oxides follows the opposite pattern, Ti < Zr < Ce < Th. It has been believed until recently that silica gel shows no anion-exchange character, even in acid solution, but anion... 

Each curve can be classified into the following five types of ion-exchange behavior ... 

Four types of hydrous antimony oxide (antimonic acid), the amorphous (A-SbA), the glassy (G-SbA), the cubic (C-SbA), and the monoclinic (M-SbA) are known so far [138]. Both the A-SbA and G-SbA affect the selectivity sequence Li" < Na" < K" " < Rb+ < Cs", while the selectivity sequence of C-SbA is unusual with Li" " K+ < Cs < Rb" Na" " for micro amounts in acid media (Fig. 19). The degree of crystallinity of a-ZrP strongly influences its ion-exchange behavior as mentioned earlier. The pH versus base added plots for a-ZrP with different crystallinity are shown in Fig. 13. It is seen that each increase in acid concentration at a fixed reflux time is reflected in the shape of the curves. The titration curves with the most well-defined plateaus were obtained with the most highly crystalline samples [126]. 

In Chapter 8, Zuyi Tao, in order to provide a better understanding of the ion-exchange behavior of amino acids, has compiled their particular acid-base properties, their solubility in water, their partial molal volumes, and their molal activity coefficients in water at 25 C. This information has been used in Gibbs-Donnan-based equations to facilitate a better understanding of the mechanism of amino acid uptake by ion exchangers at low and high solution concentration levels. Measurement of distribution coefficients and separation factors are also described. The eventual resolution of thermodynamic ion-exchange functions (AG, AH, and AS) is provided for the reader. 

Crystalline alumina may exist in various forms the T-form is generally used in chromatography. Alumina strongly adsorbs water molecules, as depicted in Fig. 1. The two different hydroxyl groups show acidic or alkaline properties, resulting in amphoteric characteristics and ion exchange behavior of the alumina surface, as demonstrated in Fig. It has been further shown that the... 

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