Effect of metal ion loaded in a resin towards fluoride retention

Indion FR 10 is a commercially available ion exchange resin with sulphonic acid functionality named as H+ form, has appreciable defluoridation capacity (DC). It has been chemically modified to La3+, Fe3+, Ce3+ and Zr4+ forms by incorporating respective metal ions into the resin in order to know their fluoride selectivity by measuring the DC of the respective resin. The maximum DC of these chemically modified ion exchange resins namely La3+, Fe3+, Ce3+ and Zr4+ forms were found to be 469.7, 467.5, 456.3 and 470.9 mg F−/kg respectively suggests their higher selectivity towards fluoride than H+ form which has the DC of only 275 mg F−/kg at 11 mg/L initial fluoride concentration. The higher DC of the modified resins was explained by electrostatic adsorption and complexation whereas H+ form retains fluoride by hydrogen bond. The functional groups present in the sorbents were identified by FTIR and the existence of fluoride onto the resins was confirmed by EDAX analysis. The experimental data was fitted with both Freundlich and Langmuir isotherms. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° indicate that the nature of sorption is spontaneous and endothermic. The applicability of reaction-based and diffusion-based kinetic models was investigated. A field trial was carried out with fluoride water collected from a nearby fluoride-endemic village to test the suitability of these sorbents at field conditions.