Adsorption of Valeric Acid from Aqueous Solution Onto the Activated Carbon

In this research, adsorption of valeric acid from aqueous solution was investigated at different temperatures (25, 35 and 45°C) by using activated carbon in a batch system. In order to determine the functional groups in structure of adsorbent and surface characteristics of adsorbent, FTIR and SEM analysis were used, respectively. In the adsorption experiments, the effect of important parameters such as effect of contact time, the amount of adsorbent, temperature and initial acid concentration were investigated. Equilibrium time was determined 120 min. The optimum amount of adsorbent was determined 1.0g (for 40ml of solution). Investigation of the temperature effect demonstrated that the percentage of removed valeric acid increased by increasing the temperature. Different types of adsorption isotherms models such as Langmuir, Freundlich, and Temkin models were applied to analyze the equilibrium data at different temperatures and Langmuir isotherm had the most agreement with experimental data at different temperatures (with maximum R2 values). The maximum adsorption capacity by using Langmuir isotherm model was determined 196.078 mg/g. Different kinetic models such as pseudo- first order, pseudo-second order, Elovich and intraparticle diffusion model were chosen to describe the kinetic of adsorption, and pseudo-second order model had the best agreement with experimental data for each adsorbents. Thermodynamic parameters like standard Gibbs free energy changes of adsorption ( Gads  ) , standard enthalpy changes of adsorption ( Gads  ) and standard entropy changes of adsorption ( Gads  ) were calculated by using equilibrium constant values at different temperatures. Negative value of (Gads) demonstrated that adsorption of valeric acid was spontaneity and positive values of ( Gads  ) showed that adsorption of valeric acid on adsorbent was endothermic.