Efficient Extracting of Tungsten from Scheelite Via NaOH-SiO2 Roasting Followed by Water Leaching

Efficient extraction of scheelite using a NaOH-SiO2 roasting and water leaching system was assessed. Initially, the NaOH-SiO2 roasting process was thermodynamically analyzed using Δ GΘ − T diagrams of the possible reactions, which indicated that the CaWO4 transforming to Na2WO4 and Na2CaSiO4 under roasting conditions was feasible. Subsequently, the effect of the thermal decomposition and leaching parameters was investigated. The results showed that the optimal extraction conditions were achieved with a Na2O-to-WO3 molar ratio of 2.2, a SiO2-to-WO3 molar ratio of 1.0, a roasting temperature of 700 °C, a roasting time of 2 h, a leaching temperature of 80 °C, a liquid-to-solid ratio of 3.2:1 and a leaching time of 4 h. Under those conditions, the leaching rate of tungsten was 99.33