Synergistic leaching of scheelite concentrate under atmospheric pressure by a sulfuric-phosphoric acid mixture
Central South University, China
Zhongwei Zhao is the professor of metallurgy at the Central South University, China
Abstract. Scheelite is the main raw material for tungsten metallurgy. Here, an atmospheric acid leaching method based on a tungsten geochemical migration behavior is proposed. The tungsten of sheelite is dissolved into heteropolyacid with H2SO4 and H3PO4, in form of H3PW12O40·nH20, while calcium in form of solid CaSO4. Further research is the competitive coordination between calcium and SO42-, PO42-, WO42- and other oxygenated acid ions, the coarse-grained CaSO4 is generated by adjusting the supersaturation, which can be used to the cement industry. Besides, after filtrating, the phosphotungstic acid crystallize in the mixed acid solution by cooling process which achieves tungsten separation and leaching acid recycling. The new technology has been commercialized in Xiamen Tungsten Industry Co., Ltd, the biggest tungsten metallurgy enterprises in the world, for more than 8 years. Even if the grade of scheelite ore is only 20%, the leaching efficiency is still as high as 99%. The cost of APT per ton is reduced by more than 30%. The technology has shown remarkable economic and environmental benefits.