Sustainable and Efficient Recovery of Tungsten from Wolframite in a Sulfuric Acid and Phosphoric Acid Mixed System

The innovative technology of coleaching scheelite concentrates by a mixture of sulfuric acid and phosphoric acid is an environmentally friendly and low-cost technology. Although the world's first production line for continuous scheelite decomposition has been implemented in recent years, it remains difficult to digest wolframite effectively. To reveal the origin for this behavior and to improve the wolframite leaching process, the leaching mechanism for synthesized and natural wolframite was investigated in this work. The results indicate that synthesized wolframite obtained after the calcination process has a similar crystal structure to natural wolframite and that changes in the cell parameters of the synthesized wolframite are related to the changes in its leaching efficiency. It was also found that the synthesized ferberite is more difficult to leach than the synthesized huebnerite, in agreement with the observed strong relationship between the decomposition (leaching efficiency) of natural wolframite and its Fe/Mn ratio. In addition, a mechanical activation method was used to improve the leaching process; it was demonstrated that the leaching efficiency of wolframite is increased due to the generation of defects in the wolframite crystal lattice, while the leaching efficiency of wolframite concentrates with greater ferberite content remains unacceptable. With the effect of added Ca(OH)(2) in the grinding process, the wolframite concentrates with greater ferberite content were found to be converted into scheelite, which enabled one to obtain a satisfactory leaching efficiency. This study provides an effective countermeasure to make the sulfuric acid and phosphoric acid system suitable for the decomposition of wolframite and scheelite-wolframite mixed ores.