Sorption of copper(II) from aqueous solutions by cedar sawdust and crushed brick

Abstract

In the present study, the aptitudes of cedar ( Cedrus atlantica Manatti) sawdust and crushed brick to remove copper(II) ions from aqueous solutions were investigated. Kinetic results and equilibrium removal isotherms were determined. The influence of pH and ionic strength on the sorption of copper was also studied. The removal of copper by both sorbents increased with an increase in contact time and pH (from 1 to 6) and decreased with an increase in ionic strength. Various kinetic models such as the pseudo-first and pseudo-second order rate equations, Boyd model, and external mass-transfer expression were tested. It was concluded that, for both sorbents, copper sorption occurs through a film diffusion mechanism and the kinetic results were best described by the pseudo-second order kinetic model. The equilibrium data has been correlated with both Langmuir and Freundlich isotherms. The results indicate that the Langmuir model fits the data better. The Freundlich model does not lead to a correct determination of the maximum sorption capacity. Thermodynamic parameters such as the changes in free energy, enthalpy, and entropy of sorption of the copper-sorbent systems were also evaluated. The negative values of the change in free energy indicate the feasibility and spontaneous nature of the process, and the negative heats of the change in enthalpy suggest the exothermic nature of the process. Additionally, different types of chemical treatments were applied: alkaline treatments (NaOH, KOH), acidic treatments (H 2SO 4, H 3PO 4, CH 3COOH), treatments with mineral salts (NaCl, KCl, Na 2HPO 4, NaHCO 3), treatment with urea, and phosphorylation treatment (urea + H 3PO 4) in order to enhance the sorption aptitudes of the both sorbents. Among the studied chemical treatments applied, treatments with mineral salts (Na 2HPO 4, KCl, NaCl, and NaHCO 3) for crushed brick and alkaline treatments by NaOH and KOH for cedar sawdust were the most effective.