Direct Production of Na2WO4-Based Salt by Scheelite Smelting

Tungsten is one of the critical materials with important applications in many areas. Electrolysis of Na2WO4-based salt is a short and green process for the production of tungsten metal and alloys. The conventional process for producing Na2WO4 is expensive and time-consuming. Scheelite (CaWO4) is becoming the most important resource for the extraction of tungsten. Based on thermodynamic calculations and phase equilibrium studies, a novel process is proposed to prepare Na2WO4-based salt directly from scheelite through a high-temperature process. By reacting with silica and sodium oxide, immiscible layers of liquid salt and slag are formed from scheelite between 1200 and 1300 °C. High-density salt containing Na2WO4 is separated from the silicate slag, which is composed of impurities and fluxes. The effects of fluxing agents, smelting temperature, and reaction time on the direct yield of WO3 and purity of sodium tungsten are investigated in combination with thermodynamic calculations and high-temperature experiments. The salt containing up to 99% Na2WO4 is obtained directly in a single process, which can be used for the production of other tungsten chemicals. This study provides a novel research method and detailed information to produce low-cost sodium tungstate directly from scheelite.