Defluoridation of water using a new biosorbent developed from Ficus glomerata Roxb. bark

Abstract

Defluoridation of water through adsorption using biosorbents is currently attracting attention. A thermo-chemically developed biosorbent derived from Ficus glomerata bark was used in the present study. The adsorption data were analysed using Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models at varying initial adsorbate concentrations (2–25 mg/l). It was found that the adsorption of fluoride onto F. glomerata biosorbent followed the Langmuir isotherm and the Langmuir isotherm constants a and b obtained were 2·27 mg/g and 0·651 l/mg, respectively, at an adsorbent dose of 5 g/l and temperature of 26 ± 1°C. The mean free sorption energy was found to be 8·770 kJ/mol, indicating that the adsorption of fluoride onto F. glomerata bark adsorbent was by a chemisorption mechanism. The kinetic study also supported chemisorption, with the adsorption data fitting well with pseudo-second-order kinetic model. The thermodynamic study indicated the spontaneous and endothermic nature (ΔH° = 15 430·78 J/mol) of fluoride adsorption onto F. glomerata adsorbent. Field scanning electron microscopy and energy dispersive spectroscopy, Brunauer–Emmett–Teller analysis and Fourier transform infrared spectroscopy were used to analyse the surface morphology of the adsorbent before and after the fluoride adsorption process. Practical application of F. glomerata Roxb. biosorbent to a fluoride-contaminated groundwater sample showed encouraging results.