Removal of fluoride from aqueous solution using high surface area activated carbon derived from fish scale solid...

Fluoride contamination in drinking water is a widespread environmental issue that poses a significant threat to human health. In this regard, there is a need to explore low-cost and effective adsorbents for the removal of fluoride from aqueous solution. The low-cost activated carbon (AC) was synthesized via KOH activation using fish scale followed by carbonization at 800 °C under a N₂ atmosphere. The prepared AC was characterized using N₂ adsorption/desorption isotherm, FESEM, XRD, and FTIR analytical techniques. The resulting material AC₂ exhibited a maximum specific surface area of 913 m²/g and a total pore volume of 0.88 cm³/g with a two-to-one KOH to carbonized fish scale ratio. Batch experiments were conducted to understand the effects of various adsorption parameter on the removal of fluoride, such as adsorbent dosages (0.2-1.4 g/L), solution pH (2-11), initial fluoride concentration (2.5-15 mg/L), contact time (0-180 min), and solution temperature (303-323 K). Fluoride removal was found to be pH-dependent, with an optimal pH of 6.0 ± 0.1. The maximum fluoride adsorption capacity of AC₂ was 13.04 mg/g at 303 K, and it decreases with an increase in temperature of the solution. Among the isotherm models applied, the Freundlich model provided the best fit to the equilibrium data. Additionally, the adsorption process followed a pseudo-second-order kinetic model and showed the ca. 75% fluoride removal within the first 5 min at pH 6.0. The change of enthalpy (ΔHº) of the process was -59 kJ/mol. The Gibbs free energy of adsorption (ΔGº) values were negative, indicating that the fluoride removal through AC₂ was spontaneous and feasible. Field water samples from fluoride-affected regions were successfully treated using the fish scale-derived AC, and it reduced the fluoride concentrations in drinking water below the permissible limit recommended by WHO. These results demonstrate that fish scale-derived AC may become a promising adsorbent for fluoride remediation from contaminated water sources.