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)

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.