FTIR spectrophotometry, kinetics and adsorption isotherms modeling, ion exchange, and EDX analysis for understanding the mechanism of Cd2+ and Pb2+ removal by mango peel waste

Mango peel waste (MPW) was evaluated as a new sorbent for the removal of Cd2+ and Pb2+ from aqueous solution. The maximum sorption capacity of Cd2+ and Pb2+ was found to be 68.92 and 99.05 mg g−1, respectively. The kinetics of sorption of both metals was fast, reaching at equilibrium in 60 min. Sorption kinetics and equilibria followed pseudo-second order and Langmuir adsorption isotherm models. FTIR analysis revealed that carboxyl and hydroxyl functional groups were mainly responsible for the sorption of Cd2+ and Pb2+. Chemical modification of MPW for blocking of carboxyl and hydroxyl groups showed that 72.46% and 76.26% removal of Cd2+ and Pb2+, respectively, was due to the involvement of carboxylic group, whereas 26.64% and 23.74% was due to the hydroxyl group. EDX analysis of MPW before and after metal sorption and release of cations (Ca2+, Mg2+, Na+, K+) and proton H+ from MPW with the corresponding uptake of Cd2+ and Pb2+ revealed that the main mechanism of sorption was ion exchange. The regeneration experiments showed that the MPW could be reused for five cycles without significant loss in its initial sorption capacity. The study points to the potential of new use of MPW as an effective sorbent for the removal of Cd2+ and Pb2+ from aqueous solution.