Ligand exchange sorption of arsenate and arsenite anions by chelating resins in ferric ion form: II. Iminodiacetic chelating resin Chelex 100

Abstract

Arsenate and arsenite are selectively removed by ligand exchange sorption on iminodiacetic chelating resin Chelex 100 used in ferric ion form, the saturation sorption capacities being 45 and 70 mg As / g wet resin with respect to As(V) and As(III) anions, respectively. The liquid sorption of As(V) anions is maximum at pH ∼ 2 and that of As(III) anions at pH ∼ 10. Monovalent anionic species H 2AsO − 3 are mostly involved in ligand sorption on Chelex (Fe 3+), and on average approximately one and two anionic species of As(V) and As(III), respectively, are coordinated to each resin-bound Fe 3+ ion at saturation. The sorbed anionic species are readily stripped with dilute sodium hydroxide into a concentrated form for recovery. An enrichment of more than 40-fold relative to influent concentration (< 100 ppm As) is obtained in ligand exchange column operation for arsenate, as compared to less than 20-fold enrichment for arsenite. Reactivation of the stripped resin is performed in one step by treatment with a mildly acidic solution of ferric chloride (pH ∼ 2), which reconverts the resin to the chelated-Fe 3+ form. The regenerated ligand exchanger exhibits a higher sorption capacity due to additional ion-exchange sorption on the accumulated ferric hydroxide gel. The ligand sorption capacity of the polymer-chelated Fe 3+ ion is, however, several-fold higher than the anion exchange capacity of the ferric hydroxide gel, with respect to both As(V) and As(III) anions.