Fluoride removal from water by ceramic oxides from cerium and manganese solutions

Abstract

The excess of fluoride in water has given rise to serious health problems, reason why it is considered a priority pollutant to be removed from drinking water by the World Health Organization (WHO). Several investigations have shown that metal oxides possess a high fluoride adsorption capacity, and recent studies have shown that ceramic oxides are excellent adsorbent materials for various anions in aqueous solutions, which is attributed to their high content of OH– groups. Due to the above, in this research Ce and Mn ceramic oxides were synthesized by a solvothermal method in a microwave to obtain these crystalline oxides: octahedral CeO2, γ-MnOOH and Mn3O4 as rods and nanoparticles, and Ce(OH)SO4 as spherical and plates forms. These ceramic oxides were characterized by Fourier transform infrared spectroscopy (FTIR), potentiometric titrations, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to determine their morphology and composition, the oxides phases were identified by an X-ray diffraction, and their BET surface area was determined by Physisorption. In addition, adsorption and kinetic experiments were carried out to determine fluoride adsorption capacities and rate in aqueous solution. Among the oxides prepared, Ce(OH)SO4 was identified as the material with the highest fluoride adsorption capacity (≈16 mg g−1 at 10 ppm F− equilibrium concentration), although this material showed a low BET surface compared to the other oxides. Finally, the fluoride adsorption mechanism was proposed considering the compounds in the ceramic oxides.