Fluoride removal from water using alumina and aluminum-based composites: A comprehensive review of progress

Abstract

Fluoride concentration in drinking water has become a global challenge due to its effects on the human body. While small level (1–1.5 mg·L−1) strengthens enamel and bone formation, higher concentration (>1.5 mg·L−1) leads to dental and skeletal fluorosis. Globally, over 200 million people drink fluorinated water and more than 70 million people suffer from fluoride related diseases. As such, treating fluorinated water through the adsorption method has been the most ideal method due to its low cost, availability of adsorbents, pollution-free treated water and environmental friendliness. This review article summarizes the use of alumina and aluminum-based composites for fluoride removal. These adsorbents have been classified into three categorize based on their modifications thus: raw alumina-based adsorbents/geomaterials, activated alumina and modified activated alumina and aluminum-based adsorbents. Minimal activation (300–400 °C) and modification improve their overall adsorption capacity by increasing their specific surface area (250–1000 m2·g−1) which ultimately improves the pore size and volume. Also, some can remediate as high as 450 mg·g−1 of fluoride at a wider pH range (3–12) with stable thermodynamic properties. This grants them the ability to easily form aluminumfluoro complexes (AlFx) for enhanced adsorption at near-neutral pH (5.5–6.5) making them the most ideal adsorbents.