Adsorption of fluoride ion on the zirconium(IV) complexes of the chelating resins functionalized with amine-N-acetate ligands

The reaction of fluoride ion with Zr(IV)-ethylenediamine-N, N, N′, N′-tetraacetate (EDTA) complexes has been examined by ¹⁹F and ¹H NMR spectroscopies and potentiometry using [Zr(H₂O)₂EDTA] and K₂[Zr(CO₃)EDTA] as the model compounds. Ternary complex formation has been suggested as the most plausible mechanism for the retention of fluoride ion on the Zr(IV) complexes. Removal of fluoride ion has been attempted by the use of polymer homologues of Zr(IV)-EDTA complexes. Adsorption characteristics of fluoride ion on Zr(IV) complexes of the chelating resins [CMA (carboxymethylamine) and IDA (iminodiacetic acid) resins] have been investigated. The adsorption capacities and the binding constants for fluoride ion on the Zr(IV) loaded resins have been analyzed using Langmuir model of adsorption. Common anions including chloride, nitrate, acetate, and sulfate ions did not interfere significantly with the adsorption of fluoride ion, whereas the presence of phosphate ion reduced the fluoride capacity markedly. The adsorption rate of fluoride ion uptake by Zr-CMA resin is much faster than that of the Zr-IDA resin. A column process including adsorption, desorption, and regeneration cycles has been demonstrated for the removal of fluoride ion to depict a practical application.