Crystallization method is another more scientific and reasonable method of producing sodium tungstate. We can prepare the crude sodium tungstate through salting out crystallization method and prepare the pure sodium tungstate through saturated crystallization method.

1. Prepare the crude sodium tungstate through salting out crystallization method
Experimental materials are the standard black tungsten concentration alkali decomposition industrial sodium tungstate solution. Reagent is industrial caustic soda and the equipment is the sand bath heating stainless steel pot. Methods are that evaporating a certain volume of sodium tungstate solution of the stainless pot on the tempering sand bath. After separation about crystal and mother liquor, take out the sample to analyze respectively. According to the analysis of experimental data, WO3 concentration decreased significantly with the increase of concentration in sodium tungstate solution coexistence of Na2WO4 and NaOH. According to the fact, in the production process, under the boiling temperatures, solution of Na2WO4 and NaOH to sodium supersaturated. Due to the solubility of sodium tungstate is far less than the solubility of sodium hydroxide, sodium tungstate crystallizes from the sodium tungstate solution on Na2WO4 • 2 h2o. It is the so-called salting-out crystallization process in the production of crude sodium tungstate.

2. Prepare the pure sodium tungstate through saturated crystallization method
Usually dissolve crude sodium tungstate in hot water density (1.5), and clarify the filtered sodium tungstate solution under the boiling temperature. And evaporate NA2WO4 supersaturated, cooling solution to less than 50 ℃, pure tungsten acid sodium products can get. When making pure sodium tungstate from crude sodium tungstate, the product won't harden and loose structure less than 60 ℃ filter. Drying products from 70% to 80% range can guarantee the content of WO3 close to 70% and make the pure sodium tungstate in line with the Na2WO4 • 2 H2O chemical formula.

From above these two articles, we know that there’re many kinds of methods to produce sodium tungstate and different kinds of raw materials can be used. For example, we can use waste grinding materials containing tungsten, calcium tungsten powder as raw materials and recycle tungsten dust. Also, the methods of using pyroprocessing, saturated crystallization method or saturated crystallization method are good. Enterprises should find the most scientific method according to specific circumstances. Improve the production efficiency and reduce the production cost and raw material consumption as far as possible to produce high quality sodium tungstate products.
 

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