Removal of Fluoride Ions from Aqueous Solution Using Ferric Hydroxide

Abstract

Iron hydroxide works as an adsorbent for some metal ions such as arsenic and selenium and is used as a scavenger. In this study, the removal of fluoride in solution by ferric hydroxide powders has been investigated. Ferric hydroxide powders were prepared by adjusting pH in four kinds of ferric salt solutions to 3.0 followed by filtration and drying. Ferric chloride, ferric nitrate, ferric sulfate and ferric polysulfate were used as ferric salts. All the ferric hydroxide powders removed fluoride ions in the pH range between 6.0 and 7.0. Ferric hydroxide powder formed in ferric polysulfate solution was the most efficient. Sulfuric ion concentration increased with increase in the adsorbed amount of fluoride ions. It is known that sulfate ions adsorb on the surface of ferric hydroxide that precipitate in sulfuric solution. Fluorite ions could be removed by ion exchange with sulfate ions on the surface of ferric hydroxide.