Removal and recovery of thiocyanate by ligand sorption on polymer-bound ferric ion

Abstract

The sorption thiocyanate anion on polymer-bound ferric ion has been measured, both kinetically and under equilibrium, using ther Dow resin XFS-4195 to bind the ferric ion and has been compared with the purely ion-exchange sorption of thiocynate by the same resin used in the acid-salt form. The thiocyanate is selectively sorbed by the resin in ferric form in preference to other common anions at low concentrations with a maximum sorption capacity of 75 mg SCN -/ g resin and is readily stripped with dilute alkali to yield ion-free thiocyanate in a concentrated form, representing more than 100-fold enrichment compared to the influent concentration. Reactivation of the stripped resin is performed simply by treament with an acidified solution of ferric chloride which reconverts the resin to its original Fe 3+ form. The ferric-form resin has considerably higher sorption capacity and faster sorption kinetics than the same resin in protonated form, and is particularly advantageous for removal of thiocyanate present in low concentrations in wastewater. The sorption rate is film-diffusion controlled at low concentrations (0.2–2.0 nmol l −1) studied. The useful pH range for thiocyanate sorption is 2–7 with the sorption maximum occurring at pH ≈ 2, which is explained by the protonation of the residual free basic sites in the resin.