Ageing characteristics related to cation exchange and interlayer spacing of some Brazilian bentonites

This study investigated the influence of cation type on the sodium deactivation of Brazilian bentonite varieties. Four bentonite clays were studied, including three mixed-cationic and one magnesium. Swelling and the main exchangeable cations (Na(+), K(+), Mg(2+) and Ca(2+)) were the main evaluation parameters in this study. Periodic washes of the sodium-activated bentonites were performed based on the hypothesis that a possible desorption of the cations (primarily Na(+)) could cause the deactivation. Sodium activation was monitored using XRD measurements and an increase in swelling. Sodium deactivation was observed and monitored via a decrease in swelling. Positive and negative effects, caused by the proportions of the cations and the dominance of Mg(2+), were emphasized by the set of cationically different samples applied in this study, which helped to answer the influence of main exchangeable cations, specially Mg(2+), on the deactivation process.