Browsing by Author "Maes, Andre"

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    Charge Density Effects in Ion Exchange Pari 1.—Heterovalcnt Exchange Equilibria
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1977, 73 (11), 1977) Maes, Andre; Cremers, Adrien
    A thermodynamic study is made of the Na–Ca heterovalent exchange reaction in 4 montmorillonite clay minerals with complete octahedral isomorphic layer charge but varying in charge density (Otay, three Camp Berteau samples which are 0, 25 and 40 % reduced in charge by the Hofmann–Klemen effect). The free energy of exchange decreases linearly with the logarithm of the charge density, as predicted from double layer calculations. The endothermicity of the reaction almost balances the entropy, both of them decreasing in magnitude as the charge density decreases. Interlamellar hydration changes, correlated with d001 spacing measurements, can explain the observed effects.
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    Charge density effects in ion exchange. Part 2.—Homovalent exchange equilibria
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (05), 1978) Maes, Andre; Cremers, Adrien
    A thermodynamic study is made on the effect of surface charge density on the sodium–cesium equilibrium in three clay minerals, Otay montmorillonite, hectorite and a series of Camp Berteau montmorillonite samples with reduced layer charge. It is shown that the standard free energy, enthalpy and entropy changes for the reversible displacement of sodium by cesium ions increase linearly with surface charge density. The opposite effect of charge density on cesium selectivity in zeolites and clay minerals is discussed in terms of electrostatic and hydration effects and the swelling properties of clays.
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    Site Group Interaction Effects in Zeolite-Y: Part 1 .—Structural Examination of the First Stages of the Ag Ion Exchange
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (1), 1978) Costenoble, Martin; Maes, Andre
    The localization of Na+ and Ag+ ions in hydrated zeolites NaAg-Y containing 2, 7.25 and 14 Ag+ ions/u.c. is studied by X-ray diffraction. A high preference of Ag for site I is observed. On increasing the silver content the Ag occupancy of site I reaches a maximum value of ~4 Ag/u.c. at the expense of Na+ ions in site I'. The Ag to Na preference pattern derived is; site I > site II > site 1' ~ unlocalized.
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    Site Group Interaction Effects in Zeolite-Y: Part 2.—Na-Ag Selectivity in Different Site Groups
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (1), 1978) Maes, Andre; Cremers, Adrien
    The influence of the nature of the ion neutralizing a certain site group on the selectivity in another group is studied in zeolite-Y. The high Ag to Na preference in the small cages in the binary system is reduced by filling the large cavities with Cs+ or NH.J ions. The selectivity data are fitted in terms of the occupancy and selectivity coefficient of 4 (binary system) and 2 (ternary system) types of sites. The calculated occupancies in each site agree with the observed ones, which are obtained from X-ray studies. The thermodynamic ion exchange formalism for the case of several groups of sites is discussed.
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    Stability of Metal Uncharged Ligand Complexes in Ion Exchangers: Part 2.—The Copper + Ethylenediamine Complex in Montmorillonite and Sulphonic Acid Resin
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1978, 74 (1), 1978) Maes, Andre; Peigneur, Paul; Cremers, Adrien
    The thermodynamic stability of the copper+ethylenediamine complex is determined in montmorillonite and a macroreticular sulphonic acid resin using ion exchange data and the complex formation function. Both methods are in excellent agreement and correspond to an increase in the overall stability constant of 103 for montmorillonite and 101·3 for the resin. The stepwise formation constants K1K2 of the ion exchanged complex are 1011·6 and 1011·5 for montmorillonite and 1011·65 and 109·7 for the resin, as compared with values of 1010·7 and 109·3 for the bulk solution. Some tentative interpretation is offered in terms of a decreased ligand solvation in the ion exchanger.