ADSORPTION OF TOLUENE ON BENTONITES MODIFIED BY DODECYLTRIMETHYLAMMONIUM BROMIDE

The adsorption of toluene was studied by using various types of adsorbents (Na⁺- and Al³⁺-bentonite) modified by dodecyltrimethylammonium bromide (DTAB). The characterization of these new sorbing matrices by XRD and IR indicates that DTAB tallow interacted with bentonite and increased the interlayer spacing of the clay with double-layered formation. Adsorption of toluene on modified bentonites was characterized by linear isotherms with no limitation of adsorption within the concentration range studied, thus indicating a mechanism of adsorption due to partition. Adsorption was fast and favored by a slightly acid medium. Pseudo-first-order, pseudo-second-order, the Elovich equation, and intra-particle diffusion models were used to fit the experimental data. The adsorption kinetic of toluene was described by the pseudo-first order onto DTAB-Na-bent, and pseudo-second order onto DTAB-Al-bent. The intra-particle diffusion process was identified as the main mechanism controlling the rate of toluene adsorption. Thermodynamic parameters such as standard free energy change (ΔG ⁰), the standard enthalpy change (ΔH ⁰), and the standard entropy (ΔS ⁰) were also evaluated. The variation of adsorption energy versus the types of adsorbent suggested a physical adsorption mechanism.