Removal of Cu(II) from aqueous solution by agricultural by-product: peanut hull

Peanut hull, an agricultural by-product abundant in China, was used as adsorbent for the removal of Cu(II) from aqueous solutions. The extent of adsorption was investigated as a function of pH, contact time, adsorbate concentration and reaction temperature. The Cu(II) removal was pH-dependent, reaching a maximum at pH 5.5. The biosorption process followed pseudo-second-order kinetics and equilibrium was attained at 2h. The rate constant increased with the increase of temperature indicates endothermic nature of biosorption. The activation energy (E(a)) of Cu(II) biosorption was determined at 17.02kJ/mol according to Arrhenius equation which shows that biosorption may be an activated chemical biosorption. Other activation parameters such as DeltaH(#), DeltaS(#), and DeltaG(#) were also determined from Eyring equation. The equilibrium data were analyzed using the Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models depending on temperature. The equilibrium biosorption capacity of Cu(II) determined from the Langmuir equation was 21.25mg/g at 30 degrees C. The mean free energy E (kJ/mol) got from the D-R isotherm also indicated a chemical ion-exchange mechanism. The thermodynamic parameters such as changes in Gibbs free energy (DeltaG(0)), enthalpy (DeltaH(0)) and entropy (DeltaS(0)) were used to predict the nature of biosorption process. The negative DeltaG(0) values at various temperatures confirm the biosorption processes are spontaneous.