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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.

Environmentally friendly copper oxide nanoparticles (CuO NPs) were prepared with a green synthesis route without using hazardous chemicals. Hence, the extracts of mint leaves and orange peels were utilized as reducing agents to synthesize CuO NPs-1 and CuO NPs-2, respectively. The synthesized CuO NPs nanoparticles were characterized using scanning electron microscopy (SEM), Energy Dispersive X-ray Analysis (EDX), BET surface area, Ultraviolet–Visible spectroscopy (UV–Vis), and Fourier Transform Infrared Spectroscopy (FT-IR). Various parameters of batch experiments were considered for the removal of Pb(II), Ni(II), and Cd(II) using the CuO NPs such as nanosorbent dose, contact time, pH, and initial metal concentration. The maximum uptake capacity (qm) of both CuO NPs-1 and CuO NPs-2 followed the order of Pb(II) > Ni(II) > Cd(II). The optimum qm of CuO NPs were 88.80, 54.90, and 15.60 mg g−1 for Pb(II), Ni(II), and Cd(II), respectively and occurred at sorbent dose of 0.33 g L−1 and pH of 6. Furthermore, isotherm and kinetic models were applied to fit the experimental data. Freundlich models (R2 > 0.97) and pseudo-second-order model (R2 > 0.96) were fitted well to the experimental data and the equilibrium of metal adsorption occurred within 60 min.

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The effective removal of heavy metals from aqueous wastes is among the most important issues for many industrialized countries. Removal of arsenic (As) from aqueous solutions was studied using Rhazia stricta biomass. The batch experiments are carried out to investigate the effect of the significant process parameters such as pH, contact time, solute concentration and adsorbent dose. The optimum pH required for maximum adsorption was found to be 5. The equilibrium data for the adsorption of As(V) on R. stricta are tested with various adsorption isotherm models such as Langmuir, Freundlich, Tempkin and Generalized equation. Results indicate the following order to fit the isotherm: Langmuir (1 and 2) > Tempkin > Generalized form > Freundlich. A comparison of two kinetic models showed that our data fitted well to the Elovich model.