Interfacial chemistry and particle interactions of polydispersed chlorite clay mineral dispersions as a function of pH, solid content and ageing time have been investigated in the pH range 2-9 at 25 degrees C. Particle zeta potential, reflecting interfacial chemistry indicates a strong pH history and solid loading dependency. Zeta potential trends observed from high to low pH sweep show that an isoelectric points of pH approximate to 2.5 and 5, respectively for dilute (0.05 wt.%) and both 8 and 57 wt.% suspension. An electrokinetic potential bifurcation is observed upon reverse pH from low (e.g. 2) to high value (e.g. 9), indicative of pH-mediated interfacial chemistry modification. Particle interactions measured through dispersion shear yield stress show a similar pH-history dependency and compliance with DLVO theory. Supernatant analysis suggests that the suspension pH dependent behaviour may be attributed to the leach of Mg(II), Fe(II/III), Al(III) and Si(IV) ions from the chlorite particles at lower pH. Formation and specific adsorption of hydrolysed metal complexes onto particles which occurs at higher pH values manifest in the observed interfacial chemistry and particle interactions. The findings enable us to accurately rationalise the nature of the inter-particle forces underpinning particle network structure and strength as a function of dispersion conditions during aqueous processing of clay-based minerals. (C) 2012 Published by Elsevier B.V. on behalf of The Institution of Chemical Engineers.