Separation of Iron from Liquid Media
Iron is the fourth most abundant element in the Earth's crust and is the basis for thousands of useful products from steel to medicine. Generally, ion exchange resins are not employed for the commercial bulk concentration and recovery of iron. Nevertheless, ion exchange resins are commonly used in the control of trace iron in drinking water and commercial process water.
Iron is normally considered as a divalent or trivalent cation that would be easily picked up by standard cation exchange resins, including AmberSep™ G26 H Resin. While this is true, one of the most useful applications of ion exchange for iron removal employs anion exchange resin such as AmberSep™ 21K XLT Resin to capture Fe3+ (ferric) ions as an anionic complex. Similar to zinc, this is possible because these metals form multivalent anionic complexes in the presence of excess chloride ion:
FeCl3+ MCl is at equilibrium with M+FeCl4-
Purification of concentrated HCl is commonly carried out on a commercial scale. Interestingly, the resin is eluted with plain water. In the absence of excess halide ion the equilibrium shifts back to the left and the neutral salt "falls off of the resin".
Iron removal from water via ion exchange is common in chemical and petrochemical processing, oil refining, semiconductor manufacturing and power utility plants.
In waters with low levels of dissolved salts, a strongly acidic cation exchange resin such as AmberSep™ G26 H Resin is employed.
Weak acid cation exchange resins such as AmberLite™ IRC83 H Resin often provide high capacity and good multivalent ion selectivity.
In more brackish waters, however, chelating resins may be required. Chelating resins have reactive units dispersed along their polymer matrix, each of which has multiple metal binding sites. Hence, chelating resins, such as AmberSep™ IRC748 UPS Resin, are selective for multivalent cations over monovalent cations like sodium and potassium.