City Research Online

Abstract

To provide an effective method for the removal of trimethyllead ions from effluents, a detailed examination of both the kinetics and equilibrium thermodynamics of ion exchange of trimethyllead into a variety of zeolites of varying ion exchange capacities was required.

As a base upon which the research programme could be built, a study of the kinetics and equilibrium properties of the exchange of lead ions in a range of zeolites, having varying framework silica to alumina ratios, were examined at 25°C and at total solution normalities of 0.05 and 0.lg equiv. dm-­³. Ion exchange isotherms were constructed for all systems, but non-stoichiometric behaviour was observed in all cases. Selectivity sequences for the lead exchanges could nevertheless be deduced, and as a general rule it was found that the more siliceous the zeolite, the lower the preference for lead. Ion exchange behaviour can be rationalized in terms of ion hydration and electrostatic ion binding energies. The selectivity sequences are discussed in terms of simple dielectric theory, which is shown to have serious limitations in predicting affinity trends in zeolites of different framework charge.

The kinetics and equilibrium selectivity characteristics of the trimethyllead/sodium binary system in NaX and NaY were initially examined to clarify both the influences of silica to alumina ratio, and the ion size and shape, on the exchange properties of these zeolites. The effects of changes in sodium chloride content on the selectivity of the zeolites for the trimethyllead ion was of particular interest because of the nature of effluents currently obtained. Exchange limits suggested a possible dissociation within the zeolite. The high degree of selectivity exhibited by these zeolites for the inorganic lead ion did not extend to this organolead ion, and subsequently a study of the selectivity for the trimethyllead ion by acid treated clinoptilolite samples was carried out to note the effect, if any, that higher silica contents may have on the preferential sorption of organics from water.

An initial examination of hydronium ion exchange as a function of pH is also reported. The importance of hydronium exhange has frequently been underestimated in past studies and it is felt that it should be taken into account not only during preparation, but also in ion exchange of zeolites.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science Q Science > QD Chemistry
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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