Efficient extracting of tungsten from scheelite via NaOH-SiO₂ roasting followed by water leaching

Abstract

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 G^Θ − 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% and WO₃ mass content in residue was 0.71%. Further mineralogical analysis showed that the CaWO₄ of scheelite was effectively transformed to Na₂CaSiO₄ and Na₂WO₄ under NaOH-SiO₂ roasting process. Broadly, the results of this paper provided a reference for the efficient extraction of scheelite using a pyrometallurgy process.

Keywords

scheelite / sodium hydroxide / roasting / mineral transformation / leaching

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