Seawater-Washed Activated Bauxite Residue for Fluoride Removal: Waste Utilization Technique

Abstract

Adsorption of fluoride on seawater-washed activated bauxite residue (SWABR) was studied by using fluoride ion analyzer (ion-selective electrode meter). Bauxite residue from the Bayer process is a waste of aluminium refinery, which is highly alkaline and generated in large quantities, which make its disposal a growing problem. The characterization of SWABR was done by using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy with X-ray microanalysis (SEM/EDS), transmission electron microscope (TEM), and selected-area electron diffraction (SAED) techniques. The adsorption studies indicate the highest fluoride removal efficiency of 95.83% for a SWABR dosage of 50 g/L at pH 5. The effect of pH, SWABR dosage, contact time, and initial fluoride concentration on the fluoride removal efficiency was studied and discussed. Adsorption isotherm experiments showed that fluoride adsorption on SWABR fits Freundlich adsorption isotherm (R2=0.998) better than Langmuir adsorption isotherm (R2=0.983). The field application of SWABR as an adsorbent for defluoridation of groundwater from Gadag District of Karnataka State, India, was also investigated.