動電音響法による粘土鉱物のゼータ電位に吸着イオン種が及ぼす影響

抄録

Zeta (ζ) potentials of the clays saturated with various ion species estimated by electrokinetic sonic amplitude (ESA) method reflected the corresponding mean particle or aggregate size which showed the dispersibility, as generally mentioned.
In kaolin minerals such as kaolinite and halloysite, the value of ζ-potential and the dispersibility were affected with the difference of cationic valence, but they were not concerned with the cationic or hydrated ionic radius. The neutralization of surface charges on clay particles by monovalent cations was hardly perfect in kaolin minerals. On the other hand, divalent cations were perfectly neutralized the surface charge, and ζ-potentials of kaolin minerals saturated with them showed about zero.
In montmorillonite, Li⁺ and Na⁺ were adsorbed in its interlayer poison as hydrated ion, its surface charges on particles did not neutralize perfectly, and made the ζ-potential relatively high. The dispersibilities of Li⁺-and Nat⁺-saturated montmorillonite were extremely high, in consequence. Rb⁺ and Cs⁺ were, however, adsorbed strongly in the interlayer position of montmorillonite as nonhydrated ion, and they negated perfectly its surface charges. On the other hand, divalent cations neutralized perfectly the surface charges of montmorillonite although they were adsorbed as the hydrated form in its interlayer position. The ζ-potentials of Rb⁺-, Cs⁺-, Ca²⁺-, Sr²⁺-and Ba²⁺-montmorillonite were nearly zero, and their dispersibilities were also low.
In allophane, the value of ζ-potential and the dispersibility were affected with the difference of cationic valence, but they were not concerned with the cationic or hydrated ionic radius. The negative charge of allophane was not perfectly neutralized by monovalent cations, but it was perfectly done by divalent cations, in higher pH region than its isoelectric point. The neutralization of positive charge of allophane by monovalent anions was hardly perfect in the pH region below its isoelectric point. On the other hand, divalent anion was perfectly neutralized the positive charge of allophane, and its ζ-potential saturated with SO₄^2- was shown zero, and its dispersibility also relatively decreased.
It is concluded that the estimation of ζ-potential by ESA method in clay minerals saturated with various ion species was effective, and gave a similar result of the previous studies by applying other methods such as electrophoresis and ultrasonic vibration potential.