Leaching tungsten and rare earth elements from scheelite through H2SO4–H3PO4 mixed acid decomposition

Abstract

Rare earth elements (REEs) possess distinctivephysicalandchemical properties and are mainly extracted from several rare earth (RE) and ion-absorbing type RE ores. Traditional RE sources are unable to meet the global demand, making it necessary to explore other resources for the extraction of rare REEs. While this is possible, the recovery of REEs from the leach residue of such resources is uneconomical due to the enormous consumption of mineralacids. H2SO4–H3PO4 mixed acid decomposition is an effective method for leaching tungsten from scheelite and is evaluated in this study for its efficient extraction of tungsten and REEs from the same mineral. The scheelite used in this study contains REEs such as lanthanum, cerium, and neodymium. The properties of the REs in the leaching system are used to evaluate our method. Additionally, the effects of the reaction conditions on the leaching of tungsten and REEs are investigated. The results show that increasing the reaction temperature and H2SO4 concentration favors the leaching process. However, high H2SO4 concentration also promotesthetransformationof gypsumfromCaSO4·2H2OtoCaSO4, which affects the leaching process negatively. Further, excessive H3PO4 concentration increases the viscosity of the leaching solution. Increasing the liquid–solid ratio is beneficial for the dissolution of scheelite. The addition of an appropriate amount of CaSO4·2H2O promotes the leaching of tungsten and REEs but the addition of PEG-400 does not. In terms of the experimental conditions used in this study, the leaching efficiency of W, La, Ce, and Nd can reach approximately 100%, 96.6%, 66.6%, and 57.1%, respectively. After the circulationleaching process, the concentrations of tungsten and the REEs in the leach liquor are increased, which proves these materials can be efficiently leached from scheelite using the H2SO4–H3PO4 mixed acid.