Water purification using different waste fruit cortexes for the removal of heavy metals

The use of different cortex fruit wastes, including banana, kiwi and tangerine peels, for removing toxic and heavy element Cd+2, Cr+3 and Zn+2 ions from aqueous solutions has been previously investigated. The ground material was powdered in a mortar and passed through a screen to obtain two different particle sizes, 1 and 2 mm, for all of the powders. In preliminary experiments using kiwi cortex, material with a 1-mm particle size showed a higher retention capability (up to 10–16% of Cd+2, Zn+2 and Cr+3) than material with 2-mm particles. Considering these results, material with a 1-mm particle size was used in further experiments with the other waste materials. For Cd+2, Zn+2 and Cr+3 removal, it was determined that kiwi and tangerine cortex showed better biosorption capability when compared with banana cortex (up to 35% more for Cd, 25% more for Zn and 35% more for Cr). The effects of the initial concentration (10–100 mg/l), pH (2–10), adsorbent dosage (0.1–2.0 g) and contact time (5–120 min) were studied at room temperature. A strong dependence of the adsorption capacity on the initial metal concentration was observed. The capacity increased as the initial concentrations decreased. A maximum removal was observed at an adsorbent dosage of 2.0 g and an initial concentration of 10 mg/l. The adsorption isotherms of the different cortex fruit wastes were determined. The equilibrium data were tested using a Langmuir isotherm model, and the kinetics conformed to the pseudo-second equation. The order of the maximum adsorption capacity of these metal ions on banana was Cr+3 < Cd+2 < Zn+2, whereas it was Cd+2 < Cr+3 < Zn+2 for kiwi and tangerine. Complexation is proposed as the adsorption mechanism. The experimental results show that the natural biosorbent was effective for the removal of pollutants from an aqueous solution.