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Journal ArticleDOI

Polybasic Acid Character of Hydrogen Clay Minerals: Multiple Dissociation Constants and Free Energy Changes in Neutralisation Reaction

01 Jan 1973-Transactions of The Indian Ceramic Society (Taylor & Francis)-Vol. 32, Iss: 6, pp 129-134
TL;DR: In this paper, the titration behavior, the dissociation constants (pK values) of clay acidoids and the free energy changes in neutralisation reactions are dependent on the chemical composition and charge on unit structural layers.
Abstract: Potentiometric titration of clay poly acidoids prepared by the action of dilute acids on clay fractions isolated from kaolin, aquagel, sedimentary rock, soil, vermiculites and chlorite schist showed two inflections (except in acid montmorillonoid) due to reaction of H+ and Al3+ and polymeric hydroxy Al and Fe with bases. Attempt has been made to show how the titration behaviour, the dissociation constants (pK values) of clay acidoids and the free energy changes in neutralisation reactions are dependent on the chemical composition and charge on unit structural layers.
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Journal ArticleDOI
TL;DR: In this paper, it is suggested that the apparent pH-dependent exchange capacity of some soils may be due to the presence of clay-sesquioxide complexes, through the interaction of positively charged metal ion-hydroxy complexes with exchange sites, with the progressive conversion of these to the corresponding hydroxides upon the addition of base.
Abstract: Buffer curves of Al- or Fe-montmorillonites and hectorite in 1.0N KCl had appreciably smaller slopes between pH 5 and 8.5 than did curves for corresponding H-clays. Aluminum or ferric hydrous oxide-clay complexes gave buffer curves indicative of almost no exchangeable Al, Fe, or H on permanent-charge sites, but rather showed a regular increase in pH with additions of NaOH. The behavior of the clay-sesquioxide complexes is thought due to the existence, at pH below about 5, of hydroxy-Al or Fe-ions on exchange sites, with the progressive conversion of these to the corresponding hydroxides upon the addition of base. That such a reaction can result in apparent pH-dependent cation-exchange capacity (CEC) was shown by the reasonably good correspondence between CEC's measured at various pH values and the amounts of base necessary to titrate the complexes to those pH's. It is suggested that the pH-dependent CEC's of some soils may be due to the presence of clay-sesquioxide complexes. In other cases, apparent pH-dependent exchange capacity can be “created” during the neutralization of Al- or Fe-clay, through the interaction of positively charged metal ion-hydroxy complexes with exchange sites. Aluminum- or Fe-hydroxy complexes with montmorillonite were not stable upon digestion in dilute salt solutions, but underwent dismutation to produce the corresponding metal ion and hydroxide. While sesquioxide-montmorillonite complexes resembled many acid soils so far as titration behavior and pH-dependent CEC are concerned, the chlorite-like complexes were far less stable than those found in soils.

56 citations

Journal ArticleDOI
15 Mar 1963-Science
TL;DR: Wyoming montmorillonite treated with hydrogen-ionsaturated resin shows, on titration in 1N KNO3 with NaOH by a continuously recording instrument, a third buffer range between pH 5.5 and 7.6, comparable to "third range" buffering noted in aged, partially neutralized aluminum chloride solutions.
Abstract: Wyoming montmorillonite (bentonite, particles 2 to 0.2 µ in diameter) treated with hydrogen-ionsaturated resin shows, on titration in 1N KNO 3 with NaOH by a continuously recording instrument, a third buffer range between p H 5.5 and 7.6 in addition to the first range where exchangeable hydronium is neutralized and the second range where a reaction with exchangeable aluminohexahydronium, Al(OH 2 ) 6 3+ , occurs. The third range increases considerably when the hydrogen-ion-saturated clay is aged, and is attributed to basic aluminum compounds formed in the presence of negative charges of montmorillonite, comparable to "third range" buffering noted in aged, partially neutralized aluminum chloride solutions.

32 citations