Critical Coagulation Concentration of Allophane

Abstract

The critical coagulation concentration (CCC) of pure allophane, an amphoteric colloid, was measured for different electrolytes and pHs. The CCC of monovalent electrolytes under alkaline conditions was Na⁺ > K⁺>NH₄⁺ for cations corresponding to the hydrated radii of cations in water. The sante relationship was noted for anions under alkaline conditions in which NO₃^- > Cl^-. Allophane coagulated under divalent counter-ions, i.e., Ca²⁺, Mg ²⁺ at a higher pH, and SO₄^2- at a lower pH. The CCC was essentially the same regardless of the species or the valence of the co-ions. The CCC of non-deferrated allophane was higher under acidic conditions and lower under alkaline conditions compared to that of deferrated allophane according to the difference in the point of zero net charge of each allophane. The CCC estimated by the DLVO theory, assuming the domain size of dispersed allophane to be 100-500 nm, showed good agreement with that measured for NaCl.