Separation of Molybdenum from Liquid Media
Molybdenum occurs naturally as molybdenite and is recovered as a by-product of copper and tungsten mining operations. It is used primarily in steel alloy formulation. The ionic chemistry of Mo6+ is very similar to other Group VIB elements, W6+ and Cr6+.
Ion exchange resins are employed in the commercial mining and refining of molybdenum. Both strong base anion exchange resins and weak base anion resins are employed for Mo removal from strongly acidic feed streams. Nevertheless, 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 Mo6+, 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 water, molybdenum frequently binds with oxygen to form molybdate anions. These species can in turn be removed using both strong base anion exchange resins and weak base anion exchange resins. Strong base anion exchangers, such as AmberSep™ 21K XLT Resin, are well-suited for the removal of molybdate anions across a broad range of solution properties. In acidic solutions, a weak base anion exchange resin such as AmberLyst™ A21 Resin is preferred for its high capacity and cleaner elution characteristics.
In more brackish waters, however, chelating/selective 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 Resin, are selective for multivalent cations over monovalent cations like sodium and potassium.