Interactions between hydroxy-aluminium species and homoionic Na- and Ca-montmorillonite particles, as manifested by ζ potential, suspension stability and X-ray diffraction

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Abstract
The interactions between and higher molecular weight hydroxy-Al species with homoionic Na- and Ca-montmorillonite have been studied by measuring adsorption of the hydroxy-Al on to the clay, turbidity of the resulting suspensions, electrokinetic potential, and d(001) basal spacing. The isolated “Al13” ions are adsorbed according to a cation-exchange process which causes flocculation of the tactoids at low concentrations. At higher concentrations, the adsorption of either isolated “Al13” or/and higher molecular weight species is mainly responsible for the dispersion of clay particles with a net positive surface charge (ζ ∼ + 50 mV). Consequently, the tactoids are destroyed.