Abstract
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 2mm, 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 (10–100mg/l), pH (2–10), adsorbent dosage (0.1–2.0g) and contact time (5–120min) 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 2.0g and an initial concentration of 10mg/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.