Equilibrium, Kinetic and Thermodynamic Study on Chromium(VI) Removal from Aqueous Solution Using Pistia Stratiotes Biomass

Abstract

A basic investigation on the adsorption Cr(VI) ions from aqueous solution by Pistia stratiotes biomass was investigated under batch mode. The influence of solution pH, sorbent dose, initial chromium(VI) concentration, contact time, stirring rate and temperature on the removal process were investigated. A biosorbent dosage of 5 g L -1 showed maximum metal uptake capacity (qe) of 7.24 mg g -1 for an initial metal ion concentration of 10 ppm. Sorption equilibrium time was observed in 15 min. The equilibrium adsorption data were analyzed by the Freundlich, Langmuir, Dubinin-Radushkevich and Temkin adsorption isotherm models. The kinetics of chromium(VI) ion was discussed by pseudo-first-order, pseudo-second-order and intra-particle diffusion models. It was shown that the adsorption of chromium(VI) ions could be described by the pseudo-second order kinetic model. Thermodynamic parameters such as Gibbs free energy (G o ), the enthalpy (H o ) and the entropy change of sorption (S o ) have also been evaluated and it has been found that the adsorption process was spontaneous, feasible and endothermic in nature. Desorption experiments with 2 M NaOH inferred the reusability of the adsorbent. The results indicated that Pistia stratiotes biomass can be used as an effective and low-cost adsorbent to remove Cr(VI) ions from aqueous solutions.