Removal of copper in aqueous solution by apple wastes

Removal of copper from a solution was investigated to evaluate the cation-exchange capacities of apple residues from agricultural wastes. The effects of solution pH, ionic strength, co-ion, ligands, initial metal concentrations, and particle size of apple residues were studied. The optimal pH range for copper removal by apple residues was shown to be from pH 5.5 to 7.0, and the maximum percentage of copper removal was 91.2%. Increasing ionic strength, up to 0.1 N, has little effect on metal uptake. The presence of co-ions such as lead decreases the removal capacity of copper as expected. The presence of ligands, such as EDTA and ammonia, also reduces metal removal efficiency due to the formation of a metal-ligand complexation in solution. Equilibrium of copper sorption was established very rapidly initially and decreased markedly after 1 hour. Equilibrium isotherms of copper fit the Langmuir equation adequately. Column experiments showed that the dynamic capacity of chemically modified apple residues was four to five times higher than that of raw residues which contained acidic groups such as carboxylic and phenolic functional groups. The adsorbed copper ions were completely recovered with three bed volumes of 0.5 N HCl. Thus, modified apple residues could be applied successfully for metal removal from wastewater.