Impregnation of activated alumina with CeO2 for water defluoridation

The fluoride ion is commonly found in groundwater used for water supply and poses health risks when ingested in excess. Several treatments are studied for water defluoridation, with adsorption being one of the most used techniques. Activated alumina is an adsorbent that already has a potential for defluoridation, and can also be subjected to treatments such as impregnation of cations in order to improve its performance. Cerium is a rare earth that has affinity with fluoride. Thus, in this work, an activated alumina adsorbent impregnated with CeO2 was prepared and the defluoridation capacity in synthetic samples and groundwater samples was evaluated. To prepare the material, 10, 15, and 20% mass ratios and calcination temperature were tested. A response surface methodology was applied to determine the best conditions of fluoride removal for synthetic waters and groundwater samples, in addition to kinetic and isothermal tests. The characterization of activated alumina and activated alumina impregnated with cerium oxide was carried out in order to analyze changes in the material. The characterization of the material showed changes in the pore size, specific surface area, and pore volume, in addition to a good distribution of cerium oxide on the alumina surface. The adsorbent that showed the highest adsorption was prepared at a mass ratio of 20% cerium nitrate III and calcined at 350 °C. The best conditions of the experiment occurred at the central point, at pH 7 and dosage of adsorbent 0.3 g L−1 for synthetic sample. The isotherm that best represented the results obtained was that of Langmuir (R2 = 0.781 to 0.958), obtaining a maximum adsorption capacity (Qmax) of 6.157 mg g−1. The kinetic balance occurred in the first 10 min of contact, being best represented by the pseudo-second order model (R2 = 0.999). The results show that adsorption with activated alumina impregnated with cerium oxide is efficient for defluoridation under laboratory conditions, and further studies with groundwater are needed to assess the influence of co-existing ions.