Hydrogen-Aluminum Clays: A Third Buffer Range Appearing in Potentiometric Titration

See allHide authors and affiliations

Science  15 Mar 1963:
Vol. 139, Issue 3559, pp. 1052-1054
DOI: 10.1126/science.139.3559.1052


Wyoming montmorillonite (bentonite, particles 2 to 0.2 µ in diameter) 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 in addition to the first range where exchangeable hydronium is neutralized and the second range where a reaction with exchangeable aluminohexahydronium, Al(OH2)63+, 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.