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Ultrasonic Synthesis for the Efficient Zr⁴⁺ Modification of Hydrotalcite Adsorbents for Fluoride Removal
* 1 , 2 , 1 , 3 , 4
1  Mexican Institute of Water Technology, Jiutepec, Morelos 62550, Mexico
2  CONACyT- Antonio Narro Autonomous Agrarian University (UAAAN) Saltillo, Coahuila, México.
3  Polytechnic University of the State of Morelos, Jiutepec, Morelos 62550, Mexico
4  Center for Research and Advanced Studies of the National Polytechnic Institute Saltillo Unit, Ramos Arizpe, Coahuila 25900, México
Academic Editor: Juan Francisco García Martín


Fluoride (F-) that is found in water (used and consumed by humans) is also widely present in the subsoil due to the composition of the Earth's crust in several regions of the world. In Mexico, the problem predominates in the north of the Mexican Republic, causing a potential threat to health, since it exceeds the maximum permissible limit of 1 mg/L, established by the World Health Organization. This work focuses on studying the effect of the molar proportion of zirconium (Zr) on the modification of the structural properties and adsorption mechanisms of lamellar double hydroxide adsorbents (LDHs), obtained by ultrasound-assisted coprecipitation methods and constant pH. Three materials were synthesized with the following molar fractions of Zr: Zr 0.1, Zr 0.075, and Zr 0.05, which were used to remove F- from an aqueous solution. The structural, morphological, and physicochemical properties were characterized by XRD, SEM, EDS, elemental mapping, N2 physisorption (BET), and FTIR. Adsorption tests were carried out, in which the molar fraction of Zr 0.05 showed the best behavior in the removal of F-. Subsequently, an experimental design was applied using the response surface method (RSM), in which the optimal conditions for F- removal were obtained: an initial concentration of F- 12 mg/L, an adsorbent dose of 1 mg/L, and a pH of 5. The maximum adsorption capacity was determined as qt:12.58 mg/g for 180 min. The adsorption kinetics were fitted to the Pseudo-second-order model with an R2 0.99, indicating chemisorption in the F- adsorption process. In conclusion, the Zr 0.05 material is considered potentially efficient by removing 99.9% of the F- present in the solution.

Keywords: Adsorption; Fluoride; Modified hydrotalcite; RSM; Zirconium effect