Kinetics and Thermodynamics of Adsorption Methylene Blue by Groundnut Shell

Abstract

The groundnut shell treated by nitric acid was used as a adsorbent for removal of methylene bluefrom aqueous solution in batch adsorption system. The effects of amount of adsorbent, initial methyleneblue concentration, pH of solution and temperature were throughly investigated. The results revealed thatan increase in initial concentration and temperature boosted adsorption capacity of methylene blue. Thevarious pHs of solution did not show difference in adsorption capacity. The pseudo-first order and pseudosecondorder were employed to evaluate the kinetic model. It was found that the pseudo-second ordermodel was fit for describing the adsorption behavior. The initial rate of adsorption increased from 6.25 to7.53 mg/g-min when initial concentration of methylene blue was increased from 10 to 50 mg/l, respectively.The Langmuir isotherm was suitable in describing the adsorption process. The thermodynamicsstudy revealed that changes in enthalpy, enthropy and Gibbs free energy were 90.70 kJ/mol, 321.79J/mol-K and -8.47 kJ/mol, respectively. The Gibbs free energy was nagative value, suggesting spontaneousof adsorption process. The activation energy was 27.80 kJ/mol.

Keywords : Adsorption / Methylene Blue / Groundnut Shell / Kinetics / Thermodynamics