Sodium Tungstate Defluorination with Ion Exchange Method

Alkali process is widely used in tungsten smelting in China. In the process of alkali decomposition of tungsten concentrates, a small amount of CaF₂ and NaOH react with sodium fluoride into sodium wolframidotungstic acid solution. Due to the lack of low cost and effective defluorination technology, the cost of sodium fluoride purification treatment in China's tungsten smelting enterprises is higher.

Some scholars found that the addition of excess calcium carbonate in sodium tungstate solution can precipitate the fluorine precipitation in sodium tungstate solution, which not only improves the purity of sodium tungstate solution, but also reduces the fluorine emission index of the subsequent wastewater. The process of this method is decomposed as follows:

(1) Adjust the pH value of acid sodium solution to 9.0-9.5 and heat it to boiling. The sodium tungstate solution after adjusting the pH value is cooled to 10-30°C and the sodium tungstate solution after cooling is obtained.

(2) Excessive calcium carbonate is added to the sodium tungstate solution after cooling, and the sodium tungstate containing calcium fluoride in a mixed solution is obtained with the reaction of calcium carbonate and fluorine with the stirring.

(3) The excess ferrous sulfate and excess ferrous hydroxide were added into the sodium tungstate solution containing calcium fluoride, and the calcium fluoride was flocculated and precipitated with the stirring, and the defluorinated liquid was obtained. Then the defluorinated liquid was filtered to obtain the purified sodium tungstate solution.

It is found that the removal rate of fluorine can reach 93.0-96.0% after treatment by the above methods, that is, the fluorine content in sodium tungstate solution is decreased from 1000 to 1200mg/l before defluorination to less than 50 ~ 80mg/l after defluorination. Finally, the fluoride content of the sodium tungstate solution after fluoride removal is 5 ~ 8mg/l, which is lower than the national industrial first grade wastewater discharge standard (F < 10mg/l). Compared with the method of defluorination of the tungsten smelting ion exchange wastewater (after crossing liquid), the waste water treatment is reduced by 90% and the cost is reduced by 80%. .

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