ION-EXCHANGE MECHANISM IN BIOSORPTION OF Pb2+ IONS FROM CONTAMINATED WATER BY BANANA STALK WASTE

Banana stalk (BS) waste is used to remove Pb2+ from aqueous solution. Equilibrium data were analyzed with Langmuir and Freundlich adsorption models, which fit better in the former equation. The q(max) (maximum metal uptake capacity) for Pb2+ adsorption was 105.14 mg/g of BS at pH 5.0, which followed pseudo-second order kinetics model. IR spectra confirmed the participation of hydroxyl, amino, and acidic functional moieties in the removal of Pb2+. The major mechanism involved in the biosorption of Pb2+ was ion-exchange as conformed by m(eq) (milliequivalent) ratios of Pb2+ adsorbed and the amount of alkali (Na+, K+) and alkaline earth (Ca2+ and Mg2+) metals released. BS was used in five repeated adsorption-desorption cycles, recovering +99% of adsorbed Pb2+ with 0.5 M HCl as desorbent. The optimized batch experimental parameters were applied to treat large volumes of Pb2+-contaminated wastewater to obtain breakthrough curves in fixed bed columns. The effective removal of Pb2+ by BS, a low-cost and efficient biosorbent to sequester Pb2+, meets the criteria of internationally acceptable maximum discharge limits in wastewaters.