Separation of Tungsten from Liquid Media
Tungsten is found naturally in combination with wolframite, scheelite, huebnerite and ferberite. Tungsten ore mines, which are located in South Korea, Portugal, Austria, and Australia, produce more than half of the world's supply. The predominant ionic form of tungsten is W6+. Its main industrial uses are in the manufacturing of lighting and heating elements. The ionic chemistry of W6+ is very similar to other Group VIB elements, Mo6+ and Cr6+.
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 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.