The Plan of Decomposition and Purification of Sodium Tungstate

Tungsten concentrates are usually treated with acid or alkali. At present, the domestic tungsten smelting enterprises mainly use NaOH decomposition process, in which raw materials such as phosphorus, arsenic, silicon, tin, fluorine and other impurities will be decomposed and get into the sodium tungstate feed liquid.

These impurity components can hinder subsequent processing, result in low yields of tungsten and even affect subsequent ammonium paratungstate product quality and the treatment of smelting wastewater. Take some examples: Silicon will affect the solvent extraction of tungsten; Phosphorus will interfere with the removal of copper impurities; Arsenic and fluorine need follow-up processing once them get into the wastewater; Tin will affect the quality of ammonium paratungstate products.

At present, high-impurity sodium tungstate solution is usually leached by chemical precipitation. This method either has a bad comprehensive effect of impurity removal, or will introduce a large number of anions (such as chloride ions, sulfate ions, nitrate ions, etc.) which will seriously affect the tungsten capacity in the subsequent ion exchange adsorption, and introduce impurity cation which will easily make the cation in the ammonium paratungstate exceed. Therefore, some scholars put forward an effective re-purification program of sodium tungstate. The method can integrate fluoride, phosphorus, arsenic, silicon and other impurities, and will not bring impurities of anion and cation which will affect tungstic acid ion exchange and product purity.

Purify sodium tungstate feed liquid containing WO3 232.7 g / L, F748 ppm, P 0.120 g / L, SiO2 220 ppm:

1. Heat 200ml of sodium tungstate solution to about 80℃; Add tungstic acid under stirring condition; Precipitate the silicon to obtain sodium tungsten mixed solution containing the silicon precipitate and stop adding when pH is from 8 to 9.

2. Add 2.4g of analytical grade magnesium carbonate powder, stirring constantly; The solution should be heated to a temperature of not less than 50 ℃ for 3h to obtain a mixed solution containing the precipitate.

3. Filter the mixed solution obtained in the previous step to gain filtrate and residue, the filtrate was purified sodium tungstate solution.

After testing the purified sodium tungstate solution, we can find that: through the magnesium salt purification, the impurity elements such as F, P, As and SiO2 get fully precipitated in the sodium tungstate solution. The above impurity elements in the filtrate significantly decreased, however, the residue contains a large number of the above impurity elements, which shows that this method has a good purification effect and does not introduce impurity ions, with the significance of promotion.

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