Adsorption characteristics and the kinetics of the Cr(VI) on the Thuja oriantalis

The cone biomass of Thuja oriantalis is a waste itself and a readily available adsorbent in nature. The kinetics of adsorption of Cr(VI) by the Thuja oriantalis was found fast, and reached equilibrium in 20 min and followed pseudo second order rate equation. The adsorption behavior of Cr(VI) on the Thuja oriantalis has been studied as a function of the solution agitation rate, pH and temperature. Results have been analyzed by Langmuir Freundlich, Radke-Prausnitz, Brunauer, Emet and Teller (BET) and Dubinin–Radushkevich (D–R) adsorption isotherms. The mean energy of adsorption was calculated as 38.3 kJ mol−1 from the D–R adsorption isotherm. The rate constants have been calculated for 289, 315 and 333 K, and the activation energy (Ea) was derived using the Arhenius equation. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° were calculated from the slope and intercept of linear plot of ln KD against 1/T. The ΔH° and ΔG° values of Cr(VI) adsorption on the Thuja oriantalis show endothermic heat of adsorption. But negative free energy value, indicating that the process of Cr(VI) adsorption is favored at high temperatures.