Competitive Adsorption and Displacement Behaviour of Some Heavy Metals on Groundnut (Arachis Hypogaea) Shell

Adsorption is recognized as an effective process of metal ion removal from contaminated water. Groundnut shell has been investigated as a metal adsorbent because of its advantages in terms of both adsorption efficiency and economic viability. In this study, the competitive adsorption of Cd2+, Cu2+, Zn2+, and Pb2+ from groundnut shell and their displacement behaviors were investigated under harmonized optimum adsorption conditions for the metal ions. It was observed from the results obtained that groundnut shell favored adsorption of the ions in the order Pb2+> Zn2+> Cd2+> Cu2+. The extent to which the ions displaced each other showed that Cd2+ had the highest displacement characteristics followed by Zn2+ with Cu2+ being the last. The occurrence and extent of displacement were shown to be closely related to pH, as this influences the metal species present in solution as well as the corresponding ionic charges. The preference of groundnut shell adsorption for one metal over another was also dependent on the solution pH and concentration. Properties such as electron configuration and ionic size also contributed to the effectiveness of the metals in competitive adsorption. Cd2+ and Zn2+ were shown to be more easily displaced than Pb2+ and Cu2+. These findings are important in choosing species for adsorption and displacement in complex solution or mixture with respect to its relevance.