Study of the Kinetics and Thermodynamics of Adsorption of Hexavalent Chromium on the Luffa Cylindrica Cords

Abstract

In the present work, the objective is to determine the potential use of natural materials, Luffa cylindrica cords for the removal of Chrome (VI) through the adsorption batch process under different experimental conditions. The determination of the concentrations of Chrome (VI) has been performed using a UV - visible spectrophotometer. Adsorption studies were carried out under various parameters such as contact time, pH, initial concentration, and temperature. The results obtained show that Luffa cylindrica cords/Chrome (VI) have an adsorption capacity of 29.98 mg/g. The adsorption process was rapid and reached equilibrium in 60 min of contact at 343K and pH 7.7. The different adsorption models Langmuir, Freundlich, Temkin, and Elovich were used for the mathematical description of the adsorption equilibrium, and it was found that the very well - equipped experimental data for the Langmuir model (R2=0.9700), the pseudo-first-order and pseudo-second-order kinetic models were applied to the experimental data. The experimental data fitted very well the pseudo-second-order kinetic model (R2= 0.982) and also followed the model of intraparticle diffusion (Kdif vary from 0.687 to 4.040 mg/(g min1/2) for concentrations between 25 and 150 mg/L), whereas diffusion is not the only rate - control step. The thermodynamic parameters study shows that the negative value of ΔH° (-11.49 kJ/mol) indicated that the adsorption of Chrome (VI) on Luffa Cylindrica cords was exothermic, the reaction was accompanied by a decrease in entropy (- 0.033 kJ/K. mol). The Gibbs free energy increased from -0.171 to -1.722 kJ/mol, respectively for Chrome (VI) when the temperature was increased from 296 to 343 K. The studied system shows that the adsorption process is spontaneous. The physical properties of the biosorbent were determined by FT-IR analysis and X-RD.