Studying the Removal Process of Heavy Metals (Ni and Zn) from Aqueous Solution Using Orange Peel

The removal of toxic metals from wastewater is of great interest in the field of water pollution, which is a serious cause of water degradation. Numerous metals such as chromium, mercury, lead, copper, cadmium, manganese, etc. are known to be significantly toxic. The purpose of this study is to investigate the Ni2 and Zn2 adsorption by using orange peel as a cheap adsorbent.
The orange peel was pretreated separately with 0.4 mol/L NaOH, 0.4 mol/L HNO3 and distilled water and the obtained adsorption abilities were compared. Adsorption experiments were performed at different initial concentrations of adsorbent, Ni2 and Zn2 ions and different pHs. Adsorption isotherms of metal ions on adsorbents were correlated with common isotherm equations such as Longmuir and Freundlich models.
The maximum adsorption capacities were achieved for Ni2 (34 mg/g) by alkali modified orange peel and for Zn2 (47 mg/g) by acid modified orange peel. The experiments showed that optimum pH was 6 and the adsorption value was reduced with decrease of pH. Morover, adsorption was decreased with rise of primary concentration of metal ions.
Results showed that isotherm models were best fit to Longmuir model for the modified orange peel. Comparison of the parameters of models revealed that the capacity of orange peel for adsorption of cooper was higher than for adsorption of lead.