Aluminum and lanthanum effects in natural materials on the adsorption of fluoride ions

Abstract

The removal of fluoride ions from aqueous solutions and drinking water with aluminum and lanthanum modified natural materials was studied. Drinking water containing naturally 5.87mg of fluoride ions per liter was characterized. The hematite, zeolitic tuff and calcite were aluminum modified by an electrochemical method. Hematite and a zeolitic tuff were lanthanum modified by ion exchange.The results show that the electrochemical method is useful to modify these materials with aluminum. The presence of this element improves the sorption efficiencies for fluoride ions from drinking water and synthetic solutions. The fluoride adsorption capacities increase with increasing the concentration of the aluminum in the samples. The sorption capacities for hematite 3A-2h (containing 11.92% of Al) and hematite-La (containing 1.24% of La) with drinking water were 0.53mg/g and 0.36mg/g respectively and the sorption capacities for zeolite 3A-3h (containing 34.74% of Al) and zeolite-La (containing 7.15% of La) were 0.56mg/g and 0.36mg/g respectively. The aluminum modified hematite is more effective than aluminum modified zeolitic tuff, the presence of iron may be responsible for this behavior.The presence of lanthanum in hematite and zeolitic tuff improves their sorption efficiencies for fluoride ions, but they are lower than the efficiencies found for aluminum modified materials.