Colloidal magnesium aluminum hydroxide and heterocoagulation with a clay mineral. II. Heterocoagulation with sodium montmorillonite

Montmorillonite dispersions were completely coagulated by magnesium aluminum hydroxide when the hydroxide mass fraction, chi, was 0.2 or greater. The hydroxide dispersion required only a montmorillonite mass fraction of 0.06 for total coagulation. Thus, heterocoagulates were formed for 0.2 < chi < 0.94. At an excess of montmorillonite, network formation between the oppositely charged particles led to maxima of the yield value and the storage modulus at 0.4 < chi < 0.5. At higher hydroxide contents, chi > 0.5, both properties decreased steeply, indicating the reduced mechanical stability of the network. Divalent anions at concentrations above 1 mmol/l acted as liquefying agents for the dispersed heterocoagulates. The specific surface area of the freeze-dried dispersions increased to a maximum value at chi = 0.65. The pore size distributions revealed that montmorillonite lamellae and hydroxide particles were not homogeneously distributed.