Ion Exchange: Theory and Practice (Royal Society of Chemistry Paperbacks) - Softcover

Harland, C. E.

Softcover

ISBN 10: 0851864848 ISBN 13: 9780851864846

Verlag: Royal Society of Chemistry, 1994

Inhaltsangabe

Extensively revised and updated from the popular 1975 guide for college teachers. Explains the theory, history, methods, and industrial applications of ion-exchange materials. Includes 22 experiments that require inexpensive equipment and demonstrate the principles being described. Annotation copyright Book News, Inc. Portland, Or.

Über diesen Titel

Auszug. © Genehmigter Nachdruck. Alle Rechte vorbehalten.

Ion Exchange

Theory and Practice

By C. E. Harland

The Royal Society of Chemistry

Copyright © 1994 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-0-85186-484-6

Contents

Preface, v, 
Boxes, xiii, 
Acknowledgements, xv, 
Chapter 1 Discovery and Structure of Solid Inorganic Ion Exchange Materials, 1, 
Chapter 2 The Development of Organic Ion Exchange Resins, 21, 
Chapter 3 Structure of Ion Exchange Resins, 39, 
Chapter 4 Properties and Characterization of Ion Exchange Resins, 49, 
Chapter 5 Ion Exchange Equilibria, 90, 
Chapter 6 The Kinetics and Mechanism of Ion Exchange, 134, 
Chapter 7 Some Basic Principles of Industrial Practice, 166, 
Chapter 8 Water Treatment, 179, 
Chapter 9 Non-water Treatment Practices, 238, 
Chapter 10 Some Engineering Notes, 261, 
Appendix, 277, 
Subject Index, 280, 

CHAPTER 1

Discovery and Structure of Solid Inorganic Ion Exchange Materials

THE PHENOMENON

An ion exchange reaction may be defined as the reversible interchange of ions between a solid phase (the ion exchanger) and a solution phase, the ion exchanger being insoluble in the medium in which the exchange is carried out. If an ion exchanger M-A+, carrying cations A+ as the exchanger ions, is placed in an aqueous solution phase containing B+ cations, an ion exchange reaction takes place which may be represented by the following equation:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1.1)

For reasons which will be considered later, the anion in solution does not necessarily take part in the exchange to any appreciable extent. The equilibrium represented by the above equation is an example of cation exchange, where M- is the insoluble fixed anionic complement of the ion exchanger M-A+, often called simply the fixed anion. The cations A+ and B+ are referred to as counter-ions, whilst ions in the solution which bear the same charge as the fixed anion of the exchanger are called co-ions. In much the same way, anions can be exchanged provided that an anion-receptive medium is employed. An analogous representation of an anion exchange reaction may be written:

[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1.2)

Further development of a physical model for the exchanger phase is best left until Chapter 2 when synthetic ion exchangers will be considered in more detail, but the previous equations illustrate the essential difference between ion exchange and other sorption phenomena. The main fact is that electroneutrality is preserved at all times in both the exchanger and solution phases, and this in turn requires that counter-ions are exchanged in equivalent amounts. The most important features characterizing an ideal exchanger are:

1. A hydrophilic structure of regular and reproducible form.

2. Controlled and effective ion exchange capacity.

3. Rapid rate of exchange.

4. Chemical stability.

5. Physical stability in terms of mechanical strength and resistance to attrition.

6. Consistent particle size and effective surface area compatible with the hydraulic design requirements for large scale plant.

Manufacturers of modern ion exchange materials have progressed a long way towards meeting all these requirements when compared with the prototype materials described below. The cost to industry of modern ion exchange resins is high, varying typically from £1000 to £4000 per m3. Therefore exchanger properties which minimize the volumes required (e.g. high exchange capacity), or which prolong resin life (e.g. physical and chemical stability), are important considerations. It therefore follows that continued efforts to improve the exchanger characteristics listed above play an important part in the activities of resin manufacturing companies.

INORGANIC MATERIALS

References to ion exchange phenomena have been attributed to Old Testament scribes, and later to Aristotle, but the first descriptions in modern scientific terminology have been credited to two English soil chemists, H. S. Thompson and J. T. Way in the mid-nineteenth century. They observed 'base' or cation exchange between calcium and ammonium ions on some types of soil. Upon treating a column of soil with a solution of ammonium sulfate it was found that most of the ammonia was absorbed, whilst the calcium contained originally in the soil was released and passed out of the column. Further studies furnished many sound conclusions as to the nature of ion exchange reactions, some of the more important ones being:

1. Exchange involved equivalent quantities of ions.

2. Certain ions were more easily exchanged than others.

3. The temperature coefficient for the rate of exchange was small.

4. The aluminosilicate fractions of soils were responsible in the main for the exchange although these components rarely took part in the exchange itself.

5. Materials possessing exchange properties could be synthesized from soluble silicates and aluminium sulfate.

The equivalence law governing the phenomenon was established in the early scientific history of the subject, as also was the fact that some ions were more easily exchanged than others; in other words ion exchangers showed greater selectivity or affinity for different ions. That an exchanger could be chemically synthesized proved to be of the utmost importance; it is for this reason that ion exchange studies and applications have reached such an advanced state today.

The ion exchange capacity of an exchanger is a measure of its total content of exchangeable ions, and is conventionally expressed in terms of the total number of equivalents of ion per kilogram (milli-equivalents per gram) of the exchanger in its dry state and in a given univalent ionic form. As will become evident when describing practical applications, the operating exchange capacity of an exchanger is invariably less than its total capacity. Also because of the presence of 'colloidal humus' in natural soils, exchange capacity data was difficult to systematize and to reproduce in relation to the inorganic minerals which were present. Consequently further studies were carried out utilizing the separated microcrystalline aluminosilicates, or 'clay fractions' of the soil which were obtainable in quite a pure form. These experiments proved that the main exchange agents were indeed contained in the finest or clay-like fractions of soils. Our knowledge of the structure and classification of such materials has shown that some of the inherently finely divided clay materials are directly responsible for the exchange characteristics observed; however, the phenomenon is not purely a property of particle size.

Why the clay minerals should possess an appreciable exchange capacity became more fully understood with the establishment of the crystal structures of the various types, for which most of the early credit is due to W. L. Bragg, L. Pauling, and others. Therefore before the ion exchange relationships of such materials can be fully understood a general appreciation of their structures is essential.

Geologically and genetically, clay minerals are difficult to define simply and adequately, but broadly they are layer lattice silicates of secondary origin. In the same classification are the micas, talc, chlorites, and serpentines which are not strictly clay minerals. In this context, secondary origin means that mineral formation has arisen from the weathering of primary or igneous rock, e.g....

Details zur Ausgabe

• Verlag: Royal Society of Chemistry
• Erscheinungsdatum: 1994
• Sprache: Englisch
• ISBN 10: 0851864848
• ISBN 13: 9780851864846
• Einband: Taschenbuch
• Anzahl der Seiten: 302
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: Nicht verfügbar