Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.751590
Title: Ion exchange of some oxyacids
Author: Harvey, James Frederick
Awarding Body: University of Surrey
Current Institution: University of Surrey
Date of Award: 1963
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Abstract:
The validity of the concept of R value or ratio x : z for ions of the type H[w]X[x]O[y][z-] has been investigated through examination of seven model acid systems. The R value is found to be an accurate reflection of a single ionic species present in solution, and to indicate changes from one species to another as the predominant one in solution. In the regions of pH where two or more ionic species are in equilibrium, differences are found between the ratio of species in the resin and in solution. Such differences are usually marginal and in no way invalidate the R value technique. However, they impose a limitation on the technique in that the pH - R value curve is not the same as the one calculated from the species present in solution at a given pH value, but is displaced somewhat, usually towards a lower pH. This discrepancy at the point where the value of R changes is due mainly to the selectivity of the resin, which usually shows a preference for the ionic species of higher charge. Barrer's statistical thermodynamic approach to selectivity is extended to accommodate divalent species. The data relating R value to pH are expressed as ion-exchange isotherms, and the theoretical equation expressing selectivity is then 'fitted' to the experimental isotherms. The theoretical equation is based on the premise that the relative interaction energies of pairs of neighbouring ion types within the resin is the major operative factor in anion selectivity. Because of the approximate nature of the model used it cannot be expected to provide a complete explanation of the phenomenon of selectivity, but the correlation between theoretical and practical curves is remarkably good. It is also found that the capacity and concentration of the external solution of the resin produces changes in the selectivity in accordance with the predicted trend. Although not included in the theoretical treatment, the effect of variation of water-regain is also examined. The iodic acid system, originally included for study as a model of a simple condensation process,was found to contain only monomeric species at the concentrations studied. Several techniques other than ion exchange were used in confirmation of this observation. This work is described separately in Appendix 2.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.751590  DOI: Not available
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