Polymeric hydrogels for the removal of fluoride ions from natural water and its toxicity

In the present work hydrogels synthetized from polyvinyl alcohol and polyvinyl pyrrolidone (UH) and modified with FeCl 3 (MH) were used to remove fluoride ions from natural water in batch and column systems. The natural water used for this work contained 5 mg/L of F - ions, the maximum permissible limit established by current Mexican regulations is 1.50 mg/L. According to results, the adsorption capacity of the modified hydrogel was higher (MH: 0.342 mg/g) than the unmodified (UH: 0.277 mg/g), based in its application on natural water treatment this value is acceptable; the equilibrium time for MH was 720 min. Three models for each system type (batch and column) were applied, the kinetic data were best fitted to the Ho-McKay model (R 2 = 0.993) for batch test and the Clark model for MH in column experiment. The adsorption process was carried out by ionic exchange between the OH - groups of the adsorbent and the F - ions. The results of toxicity indices obtained from the bioassay on the seeds reported data in moderate toxicity interval (-2.5 to −0.5) for lettuce and low toxicity (0 to −2.5) for radish with respect to minimum concentrations of F - . In general, data showed that UH and MH are promising adsorbent materials to remove F - from natural water and are considered environmentally friendly since they were synthesized with biocompatible materials such as PVA and biodegradable materials such as PVP and citric acid.