Trichlorophenol removal from aqueous solutions by modified halloysite: kinetic and equilibrium studies

Abstract

To obtain new materials, we modified Algerian halloysite by thermal activation (HalC), acid activation (HalA), combined thermal-acid activation (HalCA) and acid-thermal activation. X-ray diffraction, Fourier Transform infrared and BET textural analysis were used to characterize changes. After the HalC of halloysite at 600°C, no XRD peaks were shown and a total disappearance of the absorption bands ranging from 3,700 to 3,600 cm−1. The treatment of halloysite by sulphuric acid increases the surface area from 185.4 to 321.0 m2/g. Halloysite is first calcined and then activated by acid, its surface area increases from 74.3 to 538.6 m2/g. The effect of initial pH, adsorbent dose, contact time and temperature on the removal of 2,4,5-trichlorophenol (TCP) by modified halloysite samples was investigated. Equilibrium data were fitted to the Langmuir, Freundlich and Toth models. The best fit of the cited models was the Freundlich model, which suggested infinite adsorption onto heterogeneous surface. The pseudo-first-order, pseudo-second-order and intraparticle diffusion models were applied to the experimental kinetic data. The results showed that the pseudo-second-order is the best model to describe the process. The study of thermodynamic parameters shows that the process of adsorption of TCP onto the prepared samples was spontaneous, endothermic and physical in nature.