Adsorption of malachite green from aqueous solutions using carob and eucalyptus twigs: a kinetic and isotherm study

الملخص

This study aimed to investigate the adsorption behavior of malachite green (MG) dye on the surfaces of the twigs of carob and eucalyptus plants in aqueous solutions. Carob and eucalyptus twigs were collected from two trees in the city of Gharyan, Libya. Then, the kinetics and adsorption isotherms of the adsorption of MG on both adsorbents were evaluated. The results showed that the surfaces of the twigs of carob and eucalyptus plants adsorbed the dye with almost the same efficiency. The kinetic experiments of the adsorption of MG on both adsorbents were well described by a pseudo-first- order model. And the pseudo-second-order model, the kinetic Elovich model, and the intra-particle diffusion model, where the values of the correlation coefficient (R²) indicated that the adsorption data agree well with the four kinetic models. It has been found that the mechanism of MG adsorption process on carob and eucalyptus follows a chemical adsorption process according to the parameters obtained in the study. The experimental data were analyzed by the Langmuir, Freundlich, Timken, and Dubinin Radushkevich adsorption isotherm models of adsorption. The characteristic parameters for each isotherm and related coefficients of determination were determined. It was found that the adsorption of dye on the surface of carob and eucalyptus is more consistent with the Freundlich model, which proves the non-homogeneity of the surface of the twigs of the two plants. The value of the Tamkin constant B_t, which represents the adsorption capacity, agreed closely with the adsorption capacity obtained practically, and the energy of adsorption (E) obtained from D-R isotherm suggests chemical adsorption.