Aluminum and calcium effects on the adsorption of fluoride ions by corrosion products

Corrosion products from a hydraulic distribution system of drinking water were obtained, grounded and sifted to a particle size between 0.297 and 0.149 mm. The oxides were modified with aluminum sulfate, calcium hydroxide and aluminum nitrate. The sorption of fluoride ions was studied in a batch system using aluminum and calcium modified materials and the sorption capacities were determined for each material. It was found that the adsorption capacities depend mainly on the content of aluminum in the samples. The kinetic behavior and isotherms were determined with the modified material that gave the highest fluoride sorption capacity using fluoride solutions and drinking water containing naturally fluoride ions. The sorption equilibrium was reached in 24 h and the kinetic results were adjusted to the pseudo-second order model indicating a chemisorption mechanism. A typical isotherm was observed for drinking water, which corresponds to adsorbents that have a wide range of pore sizes. The adsorption capacities determined for drinking water and fluoride solutions were 7.45 and 9.75 mg/g.