pH-mediated interfacial chemistry and particle interactions in aqueous muscovite dispersions

Interfacial chemistry and particle interactions of aqueous muscovite dispersions have been investigated in the pH range 2–9. Particle zeta potential, reflecting interfacial chemistry, indicated a strong pH-history and solid loading dependency. Pristine particles’ zeta potentials measured from high to low pH indicated an isoelectric point (iep) at ∼pH 4.5. Subsequent measurements from low to high pH showed differing electrokinetic potentials with iep shift to higher pH values, the extent of which depended upon particle volume fraction and aging time. Dispersion shear yield stress analysis revealed similar pH-history and solid loading dependency. Incongruent leaching was observed to be responsible for the interfacial chemistry change and rheological behaviour. Upon decreasing pH from 9 to 2, considerable leaching of the key elements in muscovite, Al(III), Si(IV), K+ and Fe(III), occurred. The species concentrations decreased dramatically upon subsequent pH increase to higher values due to their hydrolysis and specific adsorption. Dispersion shear yield stresses recorded from high to low pH sweep were pH-independent. Similar measurements from low to high pH values, however, showed a strong pH-dependency, with maximum yield values at the ieps. The interfacial chemistry and particle interactions, both displaying bifurcation behaviour, showed good compliance with DLVO theory.