Ion exchange resins are employed in the commercial mining and refining of tungsten. Both strong base anion exchange resins and weak base anion resins are employed for tungsten removal from strongly acidic feed streams. The weakly basic anion resins such as AMBERLYST™ A21 Resin is preferred for its high capacity and cleaner elution characteristics. Elution is usually accomplished using 10% sodium hydroxide.
In waters with low levels of W6+, a strongly acidic cation exchanger such as DOWEX™ G 26 (H) Resin is employed.
Weak acid cation exchange resins such as DOWEX MAC 3 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 AMBERLITE™ IRC748i Resin, are selective for multivalent cations over monovalent cations like sodium and potassium.