Influence of Surface Coating on Fluoride Removal by Magnetite

Al(OH)(3)- and ZrO(OH)(2)-coated magnetites were prepared and used for fluoride removal from aqueous samples. The influence of pH, sorbent mass, and ions such as chloride, sulfate, and phosphate on the removal of fluoride was characterized. The sorption process was highly pH dependent, and the optimal sorption was obtained from pH 4 to 5 for ZrO(OH)(2)- and pH 4 to 7 for Al(OH)(3)-coated magnetites. The sorption isotherm was well described by the Langmuir equation for the sorbents. The maximum adsorption capacity of ZrO(OH)(2)-coated magnetite (57.47mg-Fg(-1)-sorbent) was higher than for Al(OH)(3)-coated magnetite (23.87mg-Fg(-1)-sorbent). The ion-exchange reaction occurred in 5min and more than 99% of fluoride was removed from solution. When the ZrO(OH)(2)-coated magnetite was used, the presence of foreign ions negatively affected the fluoride removal. The prepared sorbents showed an excellent performance for the removal of fluoride in water samples.