Understanding the wet decomposition processes of tungsten ore: Phase, thermodynamics and kinetics

As a strategic rare metal, tungsten is widely used in high-performance metallic materials like cemented carbide. The wet decomposition of scheelite CaWO4 and wolframite (Fe,Mn)WO4 is the primary and important step in tungsten metallurgy. According to the phase separation behaviors of the decomposition products, the wet decomposition processes of tungsten ore MWO4 (M = Ca, Fe, Mn) are summarized into four categories: the processes of producing 1) soluble M and insoluble W, 2) soluble M and soluble W, 3) insoluble M and insoluble W, 4) insoluble M and soluble W, each of which can derive specific decomposition methods with distinct characteristics. In thermodynamics, the equilibrium constant vs. temperature diagrams, predominance-region diagrams and phase diagrams of different acidic or alkaline decomposition methods were calculated and compared. In kinetics, the rate-determining step and targeted process intensification are analyzed and discussed, especially the phase separation/transformation of tungsten ore and decomposition products. Finally, the wet decomposition processes of tungsten ore are evaluated with respect to four aspects: principle and practice, laboratory and plant, resources and environment, and cost and benefit. The alkaline processes represented by the classical NaOH decomposition method and the acidic processes represented by the state-of-the-art H2SO4-H3PO4 synergistic decomposition method will jointly promote the vigorous development of the tungsten metallurgical industry.

Automated summary

Tungsten, a strategic rare metal, is widely used in high-performance metallic materials. The wet decomposition of tungsten ore is an important step in tungsten metallurgy, categorized into four types based on the phase separation behaviors of the decomposition products. Thermodynamic and kinetic analyses were conducted, and the wet decomposition processes were evaluated in terms of principle and practice, resources and environment, etc.