Rezumat
A comparative study of the applicability of adsorption models of Langmuir, Freundlich, BET, and Redlich- Peterson to describe the experimental adsorption isotherms of fluoride on two samples of aluminum oxyhydroxides, (A100)-hydroxide and (A600)–alumina has been carried out. The constants and parameters of these equations have been defined. Comparison of the regression coefficients R2 shows that the Freundlich model best describes the experimental data on the adsorption of fluoride with studied samples. This indicates that the adsorption of fluoride occurs on a heterogeneous surface and that the majority of active sites have different quantities of energy. The Dubinin-Radushkevich isotherm model has been applied to determine the constants of the equation later used to calculate the free energy of adsorption of fluoride on the studied samples. The energy is equal to 14.6 and 7.7 kJ/mol for samples A100 and A600, respectively. On this basis it is concluded that the sorption process proceeds through the fluoride ion-exchange, and binding of fluoride ions on the surface of the sorbent has a chemical nature.