Analysis of equilibrium, kinetic, and thermodynamic parameters for biosorption of fluoride from water onto coconut(Cocos nucifera Linn.)root developed adsorbent

Drinking water with higher fluoride levels results in serious irremediable health problems that have attained a startle all over the world.Researches focused towards deflouridation through the application of biosorbents prepared from various plants are finding greater scope and significance.Present research is done on Cocos nucifera Linn.（coconut tree） one of the very commonly available plants throughout Kerala and around the globe.An adsorbent developed from the root portion of C.nucifera Linn.is used in the present study.Equilibrium study revealed that the fluoride uptake capacity is quite significant and linearly increases with initial adsorbate concentration.The adsorption data is analyzed for Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models at varying initial adsorbate concentrations(2–25 mg·L-1).It is found that the adsorption of fluoride onto C.nucifera Linn.root adsorbent follows Langmuir isotherm.Langmuir isotherm constants "a" and "b" obtained are 2.037 mg·g-1 and 0.823 L·mg-1 at an adsorbent dose of 8 g·L-1 and temperature（26 ± 1） ℃.The mean free sorption energy, E obtained, is 9.13 kJ ·mol-1 which points out that the adsorption of fluoride onto C.nucifera Linn.root adsorbent is by chemisorption mechanism.The kinetic study also supports chemisorption with adsorption data fitting well with a pseudo-second-order kinetic model with an estimated rate constant K2 of 0.2935 g·mg-1 min at an equilibrium contact time of 90 min.The thermodynamic study indicated the spontaneous and endothermic nature(ΔH =12.728 kJ·mol-1) of fluoride adsorption onto the C.nucifera Linn.root adsorbent.Scanning Electron Microscopy（SEM）, BET, FTIR, and EDX methods were used to analyze the surface morphology of adsorbent before and after fluoride adsorption process.Experiments on deflouridation using C.nucifera Linn.root adsorbent application on fluoride contaminated ground water samples from fields showed encouraging results.