Equilibrium and kinetics of sorption of ions of lantan on natural zeolites

Abstract

       The purpose of this work was to study the equilibrium and kinetics of sorption of lanthanum ions on natural monomineral zeolites - analcime, stilbite, mesolite, scolecite, chabazite. The isotherms and kinetic curves of sorption of lanthanum ions on zeolite minerals contain clearly pronounced fractures. Similar isotherms containing extreme values of capacitance with its sharp drop were obtained by us in previous studies
of the sorption of lanthanum ions on zeolite-containing tuffs. The rate of sorption of lanthanum ions on zeolites is controlled by diffusion in the grain. The obtained data indicate that the appearance of kinks on isotherms and kinetic curves of sorption of lanthanum ions on zeolite minerals is a regularity reflecting the nature of the sorbent and depends on structural factors. Structural factors include: the presence of 8-membered
silicon-oxygen rings in the structur, the type of channels, the nature of the exchange cation and its localization, and the concentration of oxygen ions that ensure the electrostatic attraction of lanthanum ions to the zeolite framework. We assume that the appearance of kinks on sorption isotherms of lanthanum ions on zeolites can also be due to the fact that the sorbed high-charge lanthanum ions undergo hydrolysis in the zeolite
phase, as a result of which the formed hydroxo compounds lead to a narrowing of the micropores, which limits ion exchange and determines a sharp drop in the capacity. Thus, the sorption capacity of zeolite minerals with respect to lanthanum ions depends significantly on the nature and structure of the zeolite.