Adsorption-Based Defluoridation of Water Using Volcanic Rock Materials

Abstract

Fluoride (F-) contamination in water poses serious health risks, demanding effective and affordable removal methods. Therefore, this study aimed to evaluate activated pumice, which is a low-cost and ecofriendly adsorbent, for the removal of fluoride via batch adsorption. The pumice was activated by thermal treatment at 550°C followed by acid treatment with 0.1M HCl, enhancing its surface area and reactivity. The material was characterized using Scanning Electron Microscope, X-ray diffraction, and Fourier-Transform Infrared Spectroscopy. SEM images showed fractured, porous, and rough surface morphology favorable for adsorption. XRD analysis revealed a broad hump, indicating an amorphous structure, the FTIR spectra also showed peaks around 3740 cm-1, corresponding to O-H stretching, confirming the presence of hydroxyl groups and surface-bound water molecule; while peaks at 1001 cm-1 and 779 cm-1 confirming the presence of a silicate, aluminosilicate framework. Key parameters, including contact time (15–90 min), pH (3–11), dose (0.5–2.5 g), and initial fluoride concentration (2– 14 mg/L), were optimized at a constant shaking rate (250 rpm) at room temperature. Maximum Fremoval occurred at a contact time of 60 min, a dose of 0.5 g, and an initial F- concentration of 10 mg/L. A UV-visible spectrophotometer was utilized to measure F- using the SPADNS reagent (2- parasulfophenylazo)-1,8-dihydroxy-3,6-naphthalene disulfate. Adsorption kinetics followed the pseudosecond-order model (R2=0.99), described by the Freundlich isotherm model (R2 =0.99), indicating multilayer adsorption on a heterogeneous surface. A field study using a real water sample from Semema, Tigray, Ethiopia, demonstrated a maximum adsorption capacity of 1.59 mg/g. These findings indicated that activated pumice is a promising locally available material for F- removal, offering an effective and sustainable option for community water treatment.