A Brief Analysis of the Preparation Process of High Purity Ammonium Paratungstate

Tungsten is a very important strategic resource. With the development of the following products, tungsten wire, tungsten powder, tungsten strip and other high-end cemented carbide require continuous improvement of ammonium para tungstate. The existing national standard zero grade ammonium para tungstate can not meet the requirements of high end cemented carbide, which not only deals with the impurities and physical properties of ammonium para tungstate. A certain requirement can be put forward, and the enterprises that produce some high-end products have put forward special strict requirements for individual impurity elements. Therefore, the high purity tungsten powder is more popular in the market.

In the process of making tungsten powder, its purity is largely influenced by the tungsten oxide in the upstream products, that is to say, the high purity ammonium paratungstate is an important prerequisite for the preparation of high purity tungsten powder. Usually, the preparation method of high purity ammonium parotungstate includes the following steps:

(1) Ore matching and ball milling
After milling the tungsten concentrate and milling with a quantity of tap water, the grinding particle size is controlled to be -325 mesh greater than 95%.

(2)Alkaline boiling decomposition
Sodium tungstate and sodium tungstate slurry was obtained by adding quantitative tablets of alkali, sodium nitrate and water into slurry, then the crude sodium tungstate slurry was obtained. The crude sodium tungstate slurry was pressed through plate frame, and the clarified sodium tungstate filtrate was obtained, and the 16-22g/l sodium tungstate solution was prepared by adding tap water.

(3)Ion exchange
The ion exchange treatment consists of four stages: adsorption, sodium washing, desorption and chlorine washing; the prepared sodium tungstate solution is pumped into the ion exchange column containing strong alkaline anion exchange resin to carry out adsorption operations. After adsorption to saturation, the exchange is stopped.

Wash the sodium using tap water and backwash exchange column 2-3 times, then use air compressor blowing operation, and finally deionized water for 1.5 hours.

The liquid surface in the advanced ion exchange column is added to the ion exchange column and the desorption agent is added to the ion exchange column. When the effluent is dissolved in the solution containing tungsten, the former peak liquid, the peak liquid and the back section liquid are removed respectively. When t
he outflow is not contained in the solution of tungsten, it turns to chlorine washing operation. Change the column 2-3 times, and use the air compressor to blow the air.

(4) Molybdenum removal
The analytical peak liquid pump is sent to the molybdenum removal bucket, after adding the quantitative ammonium sulphide, then adding copper sulfate, then CuMoS₄ precipitates, and the peak liquid after removing molybdenum is filtered through the filter tank containing the filter cloth after precipitation, and then into the ion exchange column containing the strong alkali anion exchange resin, and the high purity ammonium tungstate is dissolved.

(5)Crystallization and drying
When the high purity ammonium tungstate solution is concentrated and crystallized, when the concentration of WO₃ in the concentration is 24g/l, the crystallization is stopped, and the filtered cake from the filtrate is washed by deionized water for 2-3 times and the Gao Chunzhong ammonium tungstate is obtained by drying.

Through the above process, the standard of the finished product of ammonium para tungstate is far below the requirement of the total impurity content in the NH₄ standard zero grade product, which is less than 177ppm, and can be more satisfied with the actual demand of the high purity secondary ammonium sulfate of the large alloy enterprises.

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