Orange peel derived natural and modified pectin for the removal of heavy metals from aqueous solution

Abstract

Heavy metal contamination in wastewater from different industries and agricultural sources pose a serious threat to the environment. Therefore, there is urgency to explore a viable and cost effective method to resolve this problem. In this direction, pectin, a complex polysaccharide, has been extracted from orange peel (6.23 % yield) by acid extraction protocol to investigate it’s potential as a biosorbent for two heavy metal ions including Cu2+ and Pb2+. To obtain enhanced adsorption capacity, functional group modification of pectin (from methyl ester to carboxylic acid) was performed via. saponification reaction. Modified pectin was achieved in 64.01 % yield. Both of these adsorbents were characterized by several spectroscopic analyses such as Fourier Transformed Infrared (FTIR) and Nuclear Magnetic Resonance (NMR) spectroscopy.

Both natural and modified pectin were investigated for their potential to remove two heavy metal ions separately (Cu2+ and Pb2+) from aqueous solutions. The study was carried out following different parameters such as pH, contact time, and adsorbent masses to find their impacts on the removal process. Both pectin and modified pectin showed better metal ion adsorption at acidic pH. The Cu2+ ion adsorptions by both pectins were highest at pH 6. However, highest Pb2+ ion adsorption occurred at pH 4 by the adsorbents. At the optimum pH, the maximum adsorption of Cu2+ by pectin and modified pectin occurs at 60 minutes and 30 minutes respectively, whereas the highest removal of Pb2+ ion was obtained at 45 minutes by pectin and 60 minutes by modified pectin. Again, at optimum pH and contact time, the maximum Cu2+ removal was obtained with adsorbent mass of 40 mg for pectin and that of 20 mg for modified pectin. The optimum adsorbent mass for Pb2+ removal was obtained as 40 mg for both pectin and modified pectin. Energy Dispersive X-ray (EDX) analysis and elements mapping confirmed the presence of the adsorbed metal (Cu2+) on the surface of the modified pectin. The findings of the present research revealed that modified pectin removed heavy metal ions more efficiently that natural pectin. This study offers a low cost method for the conversion of waste orange peels into value-added sorbent materials, which will generate a new market for orange peels for treating metal contaminated wastewater and thus will create great economic opportunities and protect the environment. Ultimately, the research will provide a green, viable, cost effective and efficient technique for the treatment of metal contaminated waste water emitted from various types of industries, and consequently will reduce the discharge of heavy metals into the environment