Ultrasonication-Assisted Defluoridation: An Overview

Batch adsorption experiments were performed to evaluate the removal of fluoride from water using aluminium hydroxide (AHG), aluminium hydroxide monoacetate (AHGMA), and aluminium hydroxide diacetate (AHGDA) as adsorbents. The extent of fluoride removal was influenced by pH, contact time, and the amount of adsorbent used. The studies were conducted at an initial fluoride concentration of 3 ppm, with the solution maintained at pH 6.6, and subjected to 5 minutes of ultrasonication, using adsorbent doses between 0.01 and 0.1 g/L. The use of an ultrasonic bath significantly shortened the treatment duration compared with conventional mechanical stirring. Maximum fluoride uptake occurred within the pH range of 5.5–6.5. The adsorption data followed the Freundlich isotherm model, with linear relationships observed between log (x/m) and log Ce, accompanied by positive intercepts. The corresponding Freundlich constants (K and n) indicated favourable adsorption behaviour. Fluoride adsorption was initially fast and nearly proportional, before gradually slowing as equilibrium conditions were approached. The maximum adsorption capacities achieved were 17 mg/g for AHG, 27 mg/g for AHGMA, and 25 mg/g for AHGDA, confirming that the acetate-modified adsorbents exhibited enhanced performance.