Complexation and removal of trace boron from aqueous solution by an anion exchange resin loaded with chromotropic acid (disodium 2,7-dihydroxynaphthalene-4,5-disulfonate)

Abstract

An ion exchanger consisting of disodium 2,7-dihydroxynaphthalene-4,5-disulfonate (chromotropic acid) and strongly basic anion exchange resin has been prepared for the removal of trace boric acid/borate. The reaction of boric acid with chromotropic acid has been examined by ¹¹B, ¹H and ¹³C NMR spectroscopy, and acid–base titration analysis. The NMR study suggests that chromotropic acid preferentially forms a stable bis-chelate type complex (L∶B = 2∶1) in an acidic pH range. The acid–base titration data are consistent with the NMR measurements. Adsorption of boric acid/borate on the resin has been examined with respect to the equilibrium adsorption, kinetics and % extraction of boric acid/borate as a function of pH. The adsorption characteristics have been compared with those of a disodium 4,5-dihydroxybenzene-1,3-disulfonate (Tiron) loaded resin and a commercially available chelating resin containing N-methylglucamine. Boric acid/borate is strongly retained on the chromotropic acid resin in the acidic region (pH 1.8–4.5), allowing quantitative removal of boron. The removal of trace amounts of boron from aqueous solution has been examined.