Application of chemically modified orange peels for removal of copper(II) from aqueous solutions

The present study concerns the process of chemical activation of agricultural waste, namely orange peels, to remove copper ions from aqueous solutions. In fact the use of orange peels without any pretreatment leads at the most a copper retention percentage of the order of 75%, whereas percentages over 99% could be achieved by means of chemical activations with sulphuric acid, caustic soda, methanol and acetic anhydride. A parametric study was also included, investigating the influence of the pH, initial concentrations of metal and the type of activation on the copper retention onto the orange peels. The results showed that saturation was reached after 10 and 5 min, for the cases of no pretreatment and the chemical activation of the orange peels, respectively. The pH study indicated that a value between 4 and 6 seemed to be the most adequate. The results did also show that the copper initial concentration value did have an influence on the retention capacity for the natural solid support. The sorption kinetic study showed that the process could be considered of a pseudo-second order, whereas the obtained equilibrium data were best fitted to the Freundlich model.