Biosorption of fluoride ion from water using the seeds of the cabbage tree (<i>Moringa stenopetala</i>)

Abstract

Conventional water treatment technologies for the removal of fluoride ion may not be feasible for developing countries due to their high investment and operational costs. The aim of this study was therefore, to investigate the fluoride biosorption potential of the seeds of the cabbage tree (Moringa stenopetala). The influence of Moringa dosage, pH, contact time, and initial concentration of fluoride ion was investigated. The maximum fluoride sorption capacity was found to be 1.32 mg.g^-1 of dry weight of Moringa seeds at a biomass dosage of 2 g L^-1, pH 7.00, initial fluoride ion concentration of 10 mg.L^-1 and a contact time of 60 min. The fluoride level was reduced from 10 to 3.4 mg L^-1. The adsorption of fluoride ion onto Moringa powder was best described by the pseudo-second-order kinetic model (R2 = 0.99). The
adsorption equilibrium data have been fitted well to Langmuir as well as Freundlich adsorption models (R2≥0.97 for both models). The distribution constant (K_d) and maximum adsorption capacity (Bmax) were significantly influenced by the amount of Moringa and equilibrium fluoride ion concentration (p<0.05). The desorption tests indicated that only 20% of the initially bound fluoride ion was regenerated, while the remaining 80% were bounded with the Moringa powder. This suggests that chemisorption was the possible mechanism of fluoride removal.

Key words: Biosorption, chemisorption, desorption, fluoride, isotherm, Moringa stenopetala.