WaterSolutions Separation of Iron from Liquid Media

Brine/HCl: Normally we think of ionic iron as a di- or tri-valent cation, which would be easily picked-up by standard cation exchange resins. While this is true, one of the most useful applications of ion exchange for iron removal employs anion exchange resin to capture Fe³⁺ (Ferric) ions as an anionic complex. Similar to zinc, this is possible because these metals form multivalent anionic complexes (42KB PDF) 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". For more information, see page 6 of DOWEX™ Ion Exchange Resins  "Powerful Chemical Processing Tools". (164K PDF)

Water/Wastewater: 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 DOWEX G-26 (H) cation exchange resin is employed. Weak acid cation exchange resins such as DOWEX MAC-3 resins often provide high capacity and good multi-valent 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 have multiple metal binding sites. Hence, chelating resins are selective for multi-valent cations over mono-valent cations like sodium and potassium.