Defluoridation of groundwater using mechanochemically-activated clay soil

High concentrations of fluoride in drinking water are reported to be hazardous to human health. This study was conducted to assess the efficiency of mechanochemically-activated aluminosilicate clay soil in removing fluoride from groundwater. The soil was subjected to physicochemical transformation through mechanochemical activation for different time intervals (5, 10, 15 and 30 min). The highest specific surface obtained was about 50 m²/g, with the sample activated for 30 minutes. Fourier Transform Infrared (FT-IR) analyses of samples showed an increase in absorbance by Si-O-H groups at 510 cm⁻¹ with increasing milling time. X-ray diffraction (XRD) analyses revealed that, at 30 minutes milling time, peak broadening was intensified while reflection peak intensities decreased. X-ray fluorescence (XRF) spectrometry showed that silica and alumina were the major clay soil components. Using a dosage of 0.6 g/100 mL of activated clay, a maximum fluoride removal of 41% was achieved using the batch activated for 30 minutes on water spiked with 9 mg-F/L at pH 2.41. The adsorption data fitted both the Langmuir and Freundlich isotherms, but only the pseudo-second-order kinetic, showing chemisorption fluoride removal.