Equilibrium and thermodynamic analysis of zinc ions adsorption by olive oil mill solid residues

Abstract

This work investigated the equilibrium batch dynamics of using olive oil mill solid residues as an adsorbent for zinc removal from aqueous solutions. It was found that a sorbent concentration of 4 g L −1 achieved the best removal percentage and the best sorbent capacity. Adsorption equilibrium was reached in 60 min for an initial zinc concentration of 0.25 mmol/L and 180 min for an initial zinc concentration of 1–3 mmol/L. A particle size of olive mill residue ranging from 0.85 to 1.18 mm was used in the study. It was found that the maximum adsorption capacity of zinc was at a pH value of 5.0. It was found that q max for zinc ions, was 5.63, 6.46, and 7.11 mg g −1 at temperature values of 298, 308, and 328 K, respectively. The data pertaining to the sorption dependence upon metal ion concentration could be fitted to a Langmuir isotherm model. The second-order kinetic model provided the best correlation of the data. The change in entropy (Δ S°) and heat of adsorption (Δ H°) for zinc ions adsorption on olive mill solid residues were estimated as −1419 kJ kg −1 K −1 and 4.7 kJ kg −1, respectively. The examined low-cost adsorbent could offer an effective way to decrease zinc ions concentration in wastewater.