Charge Reversal of Kaolinite by Hydrolyzable Metal Ions: An Electroacoustic Study

Abstract

Abstraet--Electroacoustic measurements at 1 MHz, using the Electro-Sonic Amplitude (ESA), on a kaolinite suspension provide a ready method for following the adsorption of hydrolyzable metal ions onto the clay surface. Co 2 § Cd 2 § and Cu 2 § ions show similar behavior: The initially negative surface becomes less negative, approaches zero, and may become positive at pH values around neutral, depending on the initial metal concentration. At higher pH, electrokinetic potential goes through a maximum. If the surface has become positive, it becomes less so; and at still higher pH values it may become negative again, depending on the metal ion concentration. The behavior can be interpreted using the model proposed by James and Healy.

The titration of clay minerals

“…According to these authors, this result agrees with electroacoustic measurements performed on kaolinite, indicating that most of the surface charge is balanced by monovalent ions [26]. Hence, the surface complexes contribute nothing to the electrokinetic charge.…”

Cd(II) binding by particulate low-rank coals in aqueous media: sorption characteristics and NICA–Donnan models

“…3a and 3b. The zeta potential profile of Collie coal in the presence of cadmium is consistent with many similar studies of metal ion adsorption onto both inorganic [42][43][44] and organic substrates [45]. Above p[H + ] 5, a significant increase in zeta potential occurs (i.e., the zeta potential becomes less negative), usually ascribed to adsorption of cationic species onto the surface of a negatively charged substrate.…”

Effect of humic substances on Cu(II) solubility in kaolin-sand soil

“…This shows that kaolinite can compete strongly with humic substances for Cu(II) in neutral pH conditions, possibly because copper can form particularly stable partially hydrolyzed surface coatings on kaolinite in this pH range (Hunter and James, 1992).…”