LYOTROPIC EFFECT IN SURFACE-CHARGE, ELECTROKINETICS, AND COAGULATION OF A HEMATITE DISPERSION

Surface charge, electrokinetic, and coagulation kinetics measurements were carried out with an aqueous dispersion of positively charged hematite in order to evaluate the lyotropic effect of different anions. The interpretation of the surface charge and electrokinetic data yielded the intrinsic equilibrium constant for counterion association with the surface charged groups (K(ass)0) and the inner layer capacitance (C). It was established that the effectively "smaller" ions have higher values of both parameters, indicating stronger affinity towards association in the interfacial layer. The critical coagulation concentrations for different counterions were calculated by considering their association with surface charged groups and the Gouy-Chapman model for the diffuse part of the interfacial layer. The agreement with the experimental values supports the conclusion that the lyotropic series can be quantitatively characterized by the parameters K(ass)0 and C.