Dissolution Crystallization Recycle of Tungsten Smelting Alkali

With the continuous exploitation of tungsten resources, the reserves of wolframite, especially high-grade wolframite, are getting less and less. The scheelite and the medium ore with high impurity content become the main sources of tungsten smelting raw materials.

Most scheelite smelting is the use of wolframite high-alkali pressure cooker method, but a larger amount of alkali, the theoretical amount of 2.8 to 4 times the general, the mass ratio of excess NaOH to WO₃ in sodium tungstate solution after alkali pressure cooking is 0.7 to 1.2 or even more. If it is not recycled, it will not only exert adverse effects on subsequent processes, but also eventually consume hydrochloric acid to neutralize it. Therefore, it is very necessary to recover excess NaOH from tungsten smelting sodium tungstate solution, regardless of reducing raw material consumption, reducing production cost, or from the perspective of environmental protection, energy saving and emission reduction.

The current method of excess NaOH recycle in tungsten sodium tungstate solution is mainly concentrated crystallization or subsequent neutralization. It has been proved that the recycle of excess NaOH in tungsten sodium tungstate solution by the above method has the advantages of high energy consumption and low efficiency , high operating costs, automation, environmental pressure and other issues. Therefore, how to improve the recycle of excess NaOH is also an urgent and important issue, some scholars proposed the recycle of NaOH by crystallization.

Using sodium tungstate insoluble in ethanol and sodium hydroxide dissolved in ethanol, sodium hydroxide was recycled by dissolution crystallization method. First, the alkaline sodium tungstate solution is mixed with organic alcohol to get the first mixed solution. Then, the first mixed solution was stirred to make sodium tungstate precipitate, and sodium tungstate crystals and second mixed solutions were obtained. Finally, second mixed solutions were evaporated to obtain organic alcohols and sodium hydroxide. Then, the first mixed solution was stirred to make sodium tungstate precipitate, and sodium tungstate crystals and second mixed solutions were obtained. Finally, second mixed solutions were evaporated to obtain organic alcohols and sodium hydroxide.

The crystallization method of alkali waste recycling, not only low operation cost, good stability, convenient operation, high production efficiency, and without hydrochloric acid neutralization process, sodium hydroxide and water recycling can be realized and avoids the waste of sodium hydroxide, the pressure on the environment is small, is worthy of promotion significance. 

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