Selective sorption of fluoride ions by anion-exchange resin modified with alizarin fluorine blue-praseodymium(III) complex

Abstract

A new functional resin for selective sorption of fluoride ions was prepared from an anion-exchange resin (Amberlite IRA 400) and a praseodymium(III) complex of alizarin fluorine blue (AFB). The AFB-Pr(III) complex was immobilized by both ion-exchange and nonelectrostatic interaction between AFB molecules and the matrix of the anion-exchange resin. The AFB-Pr(III) complex formed a ternary complex with fluoride ions in the resin. The resin modified with the AFB-Pr(III) complex (AFB-Pr resin) had specific and nonspecific binding sites for sorption of fluoride ions. The former were ligand-exchange sites where fluoride ions replace water molecules coordinated to praseodymium(III) in the resin, and the latter were residual ion-exchange sites where fluoride ions replace chloride ions of quarternary ammonium chloride groups. Fluoride ions were sorbed strongly and specifically in the presence of electrolytes by the former sites. The sorption capacity for fluoride ions was about 0.5 mg/g resin in the presence of 0.1 M sodium chloride when 0.028 mmol of AFB-Pr(III) complex was immobilized per gram of the anion-exchange resin. The effects of pH, buffer, acetone, and foreign ions on fluoride uptake were examined by a batch method. Fluoride uptake decreased with increasing pH. The addition of acetone enhanced fluoride uptake at both binding sites. Interference from the cations and anions studied was negligible except for aluminum(III). Fluoride sorbed on AFB-Pr resin was removed with a dilute sodium hydroxide solution.