New Process to Prepare Tungsten Oxide Hydrate from Sodium Tungstate Solution

In the existing tungsten metallurgy system, since the industrial crude sodium tungstate solution contains various impurity elements and must be removed by various steps of removal, the entire process is time-consuming and energy-consuming, and creates some environmental issues. Among them, the process of removing Na is the most cumbersome, and it is unavoidable to increase mid-products of ammonium tungstate and APT.

In the traditional way of thinking, the method of directly depositing tungsten from sodium tungstate solution can only be to prepare tungstic acid. And in the acidification process of tungstate solution to prepare tungstic acid deposit, a variety of complex tungsten polyacid salts and heteropoly are produced. The acid salt, accompanied by the formation of leuco-tungstic acid which is difficult to filter and wash, causes the Na element to be inevitably entrained in the deposit and must be removed by ammonia dissolution. An effective way to solve this problem is to find a tungsten oxide or tungsten hydroxide with a low solubility in an alkaline environment. Some scholars have proposed a process for preparing tungsten oxide hydrate from sodium tungstate solution, including the following steps:

1) Mix a sodium tungstate aqueous solution with concentration of 30% ~ 45%. The temperature of hydrothermal reaction is 100 to 250 ° C, the reaction time is 5 ~ 25 hours, and the pH of the system is controlled between 6.5 ~ 9.0 hours

2) The aqueous sodium tungstate solution and the additive are placed in a high pressure reaction kettle in a suitable ratio to have a hydrothermal decomposition. The pH is stabilized within a certain range during the reaction to obtain a WO3.0.5H2O slurry;

3) Wash, filter and separate the slurry to obtain WO3•0.5H2O filter cake and mother liquor;

4) The filter cake is calcined at a low temperature in a baking furnace; the baking temperature is 300 to 450 ° C;

5) The mother liquor is concentrated by evaporation, cooled and crystallized, separated and filtrated to obtain a solid sodium salt and a crystallized mother liquor; the crystallized mother liquor is returned to the ore leaching step or the sodium tungstate aqueous solution blending step.

The pH of the sodium tungstate hydrothermal system is regulated in the range of 6.5 ~ 9.0, to avoid the complex transformation of sodium tungstate, and to avoid preparing a WO3•0.5H2O deposit without Na element, thus eliminating the ammonium tungstate and APT. The production process greatly reduces energy consumption, reduces environmental burden, and has obvious advantages in preparing ultra-fine powder.

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