Ion-exchange theory

In this chapter, we consider several simple models of ion sorption and exchange that can be applied within the context of a geochemical model. These models include distribution coefficients, Freundlich and Langmuir isotherms, and ion exchange theory. In the following chapter (Chapter 10), we consider surface com-plexation theory, which is more complicated but in some ways more robust than the models presented here. 

As the figure shows the exchange of Sr2+ on Na+-montmorillonite fits the ion exchange theory very well. But the adsorption of heavy metals cannot be accounted for by this theory. Co(II) behaves as if it were monovalent Kd for americium is independent of [Na+] (americium occurs at pH = 6.5 as a hydroxo complex). 

A stoichiometric model can conveniently be invoked to explain the ion-exchange retention process [43 6]. As discussed in detail in these cited papers on ion-exchange theory, useful information about the involved ion-exchange process can be deduced from plots of log k vs. the log of the counterion concentration [X], which commonly show linear dependencies according to the stoichiometric displacement model (Equation 1.1)... 

C. E. Harland, Ion Exchange Theory and Practice. Cambridge, U.K. The Royal Society of Chemistry, 1994. 

For equilibrium conditions, Donnan ion exchange theory (6) may be used to describe quantitatively equilibria for trace quantities of chemical elements in the presence of high homologous salt concentrations. The radionuclides 90Sr and 137Cs constitute a very small fraction of the mass of the chemical constituents in rainfall thus the equilibrium distribution of these nuclides between solid and liquid phases may be estimated as... 

In contrast to the ion exchange theory, much evidence indicates that cells have an active ion pump that removes Na+ from cells and introduces K+. For example, the cytoplasm of the giant axons of nerves of squid can be squeezed out and replaced by ionic solutions. Erythrocyte ghosts can be allowed to reseal with various materials inside. Ion transport into or out of cells has been demonstrated with such preparations and also with intact cells of many types. Such transport is blocked by such inhibitors as cyanide ion, which prevents nearly all oxidative metabolism. However, the cyanide block can be relieved by introduction into the cells of ATP and other phosphate compounds of high group-transfer potential. 

Maroudas, A. (1968) Physicochemical properties of cartilage in the light of ion exchange theory. Biophysical Journal 8, 575-595... 

Step 3. Read about the radiochemistry of iodine to improve your understanding of the radioanalytical chemistry of iodine. An old but helpful monograph is Radio chemistry of Iodine, NAS-NS-3062, by Milton Kahn and Jacob Kleinberg, Office of Scientific and Technical Information, US DOE, 103 pp (1977). A copy may be obtained from the instructor, the library, or internet search. Also read about ion-exchange theory and practice, and in particular, the relative affinity of anions for strong-base ion-exchange material. 

Walton, H. F. 1949. Ion exchange equilibria. In F. C. Nackod, Ed. Ion Exchange Theory and Practice. Academic, New York. 

Extraction chromatography (reversed phase partition chromatography) has been used in analytical and biochemistry to effect chemical separations. It is a method which combines the simplicity of ion exchange and the selectivity of solvent extraction. Ion exchange theory may be used to calculate the number of theoretical plates in the column and the enrichment coefficient. Extraction chromatography as a separation method has been recently reviewed by Cerrai (J) and Katykhin (7). 

Ion-exchange models are commonly used to describe radionuclide sorption onto the fixed-charged sites of materials like clays. Ion exchange will be strongly affected by competition with monovalent and divalent ions such as Na" " and Ca, whereas it will be less dependent on pH over the compositional ranges common for natural waters. Many studies of strontium and caesium sorption by aluminosilicates (e.g., Wahlberg and Fishman, 1962 Tamura, 1972) have been carried out within the framework of ion-exchange theory. Early mechanistic smdies... 

These three-layer silicates are characterized by permanent surface charges (due to isomorphic substitutions). Therefore the binding of cations is assumed to be caused by stoichiometric ion exchange of interlayer ions. These concepts hold well for alkaline and earth-alkaline cations their adsorption and their ionic strength dependence can be characterized by distribution coefficients derived from ion exchange theory. It has been known for some time, however, that... 

In recent years, a number of electrolytic processes have utilized membranes in producing both anodic and cathodic products. By far, however, the most important application of this technology has been in the chlor-alkali industry. Intense commercial and academic interest has been focused into this field during the past decade so that ion exchange theory as applied to membranes is in a more advanced state than any of the other ion exchange systems. The primary examples of industrial chlor-alkali electrochemistry are found in the production of chlorine, caustic soda and potash, hydrogen and hypochlorite (1) (4). 

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