Abstract
The results of studies of the adsorption of lanthanum ions from aqueous solutions of kaolin are presented. It has been shown that kaolin is a fairly effective adsorbent of lanthanum ions from aqueous solutions with different pH values. The kinetics of the adsorption of lanthanum ions by kaolin was studied. It was shown that the rate of adsorption of lanthanum ions on the surface of kaolin particles at pH 6 is higher than at pH 3. The adsorption process is described by an equation similar to the first-order equation. The found graphically values of the adsorption rate constants increase when they are going from pH 3 (0.01 min-1) to pH 6 (0.12 min-1). The isotherms of adsorption of lanthanum ions by kaolin have a complex form and, according to Giles’s classification, belong to L-type isotherms. The description of the adsorption process was carried out by models of Freundlich, Langmuir, Hill – de Bura. The values of the correlation coefficients (R2) in the linearization of the isotherm of the monomolecular adsorption of lanthanum ions by kaolin particles show that the adsorption with the maximum probability is described by the Langmuir equation. The effect of pH and temperature in the range of 293-313 К on the process of lanthanum adsorption by kaolin particles was studied. It is shown that the value of adsorption increases with increasing temperature, which indicates the chemical nature of adsorption. Adsorption proceeds most efficiently in media with a pH of 8. Using the Dubinin-Radushkevich model, which indicates the nature of the adsorbate adsorbate on the adsorbent, the average free adsorption energy was calculated. The calculations showed that the values of the free adsorption energy E are in the range from 8 to 11 kJ/mol, which indicates the chemical nature of the interaction of the adsorbate with the adsorbent. Thus, the process of adsorption of lanthanum ions on the surface of kaolin proceeds by the ion-exchange mechanism, and the fixation of lanthanum ions has a chemical nature.
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