Insight into Optimization, isotherm, kinetics, and thermodynamics of fluoride adsorption onto activated alumina

Abstract

Investigation of essential technique to diminish the exceeded limit of fluoride in groundwater is the need of the hour due to severe adverse effects of fluoride on human health. The present study highlights the prospective of activated alumina, a defluoridating agent for the elimination of excess fluoride (F − ) concentration from aqueous solution by using batch adsorption techniques. The adsorptive removal of fluoride was optimized by means of response surface methodology (RSM) considering the parameters in the range of pH (6‐8), contact time (60‐120 min), alumina dose (1‐2 g), agitation speed (200‐300 RPM), and temperature (25‐45°C). The sorbent was instrumentally characterized to study the surface morphology and chemical composition by SEM (Scanning Electron Microscopy), EDX (X‐ray Energy dispersive analysis) and XRD (X‐ray Diffractometry). The optimized condition for the defluoridation procedure was obtained as pH 6, contact time 120 min, alumina dose 2 g, temperature 45°C, and agitation speed of 200 RPM gives 86.1% of fluoride removal. The equilibrium adsorption performances were studied and the data were fitted with both the Freundlich and Langmuir isotherms and showed Freundlich model was fitted well which signifies multilayer adsorption. The defluoridation method followed pseudo‐second‐order kinetics. Gibbs free energy showed that the process is feasible at all three operating temperatures. The statistical parameters proved the significance and applicability of the model for optimization of the defluoridation process using activated alumina as an adsorbent. Hence, alumina could be an eminent adsorbent for the defluoridation of wastewater. © 2017 American Institute of Chemical Engineers Environ Prog, 37: 766–776, 2018