One model system for the investigation of selectivity in inorganic ion exchangers is a group of synthetic analogues of the mineral umbite. Hydrothermally synthesized trisilicates with the general form A2BSi3O9.H2O, where A is a monovalent cation, and B = Ti4+, Zr4+, and Sn4+ have been shown to have ion exchange properties. The extended three dimensional framework structure offers the ability to tune the selectivity based on the size of the cavities and channels. The unit cell volume, and therefore the pore size, can be altered by changing the size of the octahedral metal. The substitution of Ge for Si can also increase the pore size. A variety of cations have been exchanged into the trisilicates including alkali and alkaline earths, lanthanides, and actinides. The reason for the selectivity rests in the pocket of framework oxygens which make up the exchange sites. Close examination of the cation environments shows that the ions with the greatest affinity are those that have the closest contacts to the framework oxygens. For example, among alkali cations, zirconium trisilicate demonstrates the greatest affinity for Rb+ and has the most A-O contact distances approaching the sum of their ionic radii. The origins of selectivity also rely upon the valence of the incoming cation. When cations are of similar ionic radius, a cation of higher charge is always preferred over the lower valence. Ion exchange studies in binary solutions of cations of different valence, but similar size (1.0Å ) have proven the selectivity series to be Th4+ > Gd3+ > Ca2+ > Na+. Through structural characterization, kinetic studies, and use of in situ x-ray diffraction techniques the origins of selectivity in these inorganic ion exchangers has been further elucidated. The principles gleaned from these studies can be applied to other inorganic framework materials. The umbite system has the potential to be altered and tailored for specific separation needs. The trisilicate materials presented in this work are representative of the types of advances in inorganic materials research and prove their potential as applicable compounds useful for solving real world problems.

Thesis (M.Phil.)--City University of Hong Kong, 2009. / "Submitted to Department of Economics and Finance in partial fulfillment of the requirements for the degree of Master of Philosophy." Includes bibliographical references (leaves 63-73)

Inaug.-diss.--Halle-Wittenberg. / Lebenslauf. "Literaturverzeichnis": p. [186]-193.

Proefschrift.--Nederlandsche Handels-Hoogeschool, Rotterdam. / Includes bibliographical references.

Inaug.-diss.--Freiburg. / Lebenslauf. "Literatur-verzeichnis": p. 69-71.

Thesis ( M.S. ) -- University of Texas at Arlington, 2008.

Thesis (Ph.D.)--Virginia Commonwealth University, 2009. / Prepared for: Dept. of Psychology. Title from title-page of electronic thesis. Bibliography: leaves 99-106.

The aim of this thesis is to compile a glossary of technical terms relevant to stock exchange mergers and alliances. Since technical communication can only be described meaningfully in the context of technical information, technical knowledge, and terminology, judgmental analysis will be applied to the literature on stock exchange mergers and alliances to identify management theories that are able to explain stock exchange mergers and alliances. One aim is to find out which general theories on mergers and alliances have a high explanatory value for stock exchange cooperation. In the first part of the thesis, the stock exchange world is examined. First a general overview of the theory of corporate growth is given next the changes in the environment of stock exchanges are examined. In the analytical part, fourteen general management theories are applied to stock exchange cooperation. The criteria used to identify the explanatory value of the different theories are the critical success factors of stock exchanges identified in the first part of the thesis. A point system is introduced in order to make the results of the analysis of the different theories more comparable. The final part of the paper consists of an English-German glossary containing the relevant technical terms of stock exchange mergers and alliances. (author's abstract)

The aim of this research was to provide a comprehensive evaluation of the heavy metal removal performance of two synthetic zeolites, Zeocros CA150 and Zeocros CG180. Detailed laboratory investigations of the key parameters known to affect zeolitic ion exchange were performed with respect to lead, zinc, copper, cadmium and nickel by means of batch equilibrium tests. The study into the effect of contact time suggests that a near equilibrium state was reached within two hours. As metal hydroxide precipitation was minimal at pH 6.0 and the structural integrity of the zeolite was maintained, metal removal at this pH is predominantly by ion exchange rather than chemical precipitation. Fluctuations in both silicon and aluminium release from the zeolites suggest that partial dissolution may occur under mildly acidic conditions, an observation discussed elsewhere in the literature. Heavy metal removal decreased with increasing metal loading, with the zeolites exhibiting Significantly lower operating exchange capacities compared to the theoretical ones. Exchange capacities varied between 1.3-4.9 meq/g and 0.5-4.6 meq/g for CA 150 and CG180 respectively for the five metals studied. Throughout all of the experimental investigations, lead was removed preferentially (>99%) and nickel removal effiCiencies were the lowest «20%). The results from the mixed metal studies demonstrated that lead removal was the least affected by the presence of other heavy metals whereas cadmium, copper and zinc removal was suppressed in comparison to that from Single metal solutions. The presence of competing ions was not found to adversely affect lead removal by CA 150 and CG180, with copper and cadmium removal showing the most suppression in the presence of calcium, magnesium, potassium and sodium. Zinc uptake by both zeolites proved the most sensitive to the addition of hardness ions even under soft water conditions. The zeolites were also demonstrated to achieve up to 100% removal from real effluents, outperforming a natural zeolite, clinoptilolite. Overall, this research has demonstrated the considerable potential of these synthetic zeolites to selectively remove heavy metals from complex contaminated effluents, indicating their possible application as a tertiary technology for effluent treatment.

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