Aluminous Minerals for Caustic Processing of Scheelite Concentrate

Dry milling of the mixture of scheelite concentrate and solid NaOH is conducted to develop a caustic process for tungsten (W) extraction. Aluminum hydroxide (Al(OH)₃) is further added to the milling to control the calcium dissolution of one reaction product, calcium hydroxide, in the next aqueous extraction of soluble tungstate to form an insoluble substance. For practical application, several aluminous minerals of kaolin, gibbsite, and diaspore with different alumina concentrations and water percentages are used to replace the pure chemical Al(OH)₃, and the feasibility of using these minerals as calcium immobilization additives is confirmed to give rise to the formation of Na₂WO₄ and water-insoluble katoite (Ca₃Al₂(SiO₄)_3−x (OH)_4x ) in the form of powders. Tungsten recovery is found to depend on the compositions of the used mineral, and the conditions for improving W recovery are studied with respect to the compositions of aluminum hydroxide and water inside the minerals. The developed process allows the caustic extraction of W by applying the nearby available aluminous minerals.