High-purity Ammonium Paratungstate Preparation Process

Ammonium paratungstate hydrate is an intermediate for the production of tungsten metal, tungsten-containing catalysts, tungsten-based hard materials (such as tungsten carbide) or sputtering targets. The preparation is carried out mainly by digesting or melting a slag containing tungsten concentrate or tungsten with acid or base, followed by purification, and the purification stage includes a precipitation process and a liquid-liquid extraction. The purified solution is usually concentrated by evaporation to finally crystallize the ammonium paratungstate hydrate.

Ammonium paratungstate tetrahydrate is a high-purity ammonium paratungstate product mainly used for tungsten powders required by the electronics industry. However, a major disadvantage of the known method for producing such ammonium paratungstate is the purity for specific applications (eg sputtering). Target) is not enough. In addition, because of the high energy consumption required for evaporation crystallization, ammonium paratungstate hydrate is extremely expensive to manufacture.

In view of this, the researchers have published an economical process for preparing high-purity ammonium paratungstate in high yield and simple process by converting ammonium ammonium paratungstate decahydrate suspended in an aqueous phase to ammonium paratungstate tetrahydrate. The preparation process is as follows:

First, ammonium paratungstate decahydrate is prepared, and in the preparation process, the separation of the phase mixture is carried out by stirring in a settler having a stirrer, wherein the rotational speed of the stirrer is set such that the precipitate of ammonium paratungstate hydrate The entrained organic phase is separated and removed, and the phase mixture from the mixer is introduced into the phase boundary region between the organic phase and the ammonia-containing aqueous phase in the settler. So that the organic phase and the ammonia-containing aqueous phase in the mixer can be evenly distributed.

A 100 liter solution containing ammonia and tungsten containing 3.5 grams per liter of NH3, 45.2 grams per liter of W, and 50 liters of deionized water was placed in a heated 200 liter stirred reactor. 200 kg of APT decahydrate was added with stirring. The suspension was then treated at 85 ° C for three hours with stirring. At a molar ratio of NH3:W of 0.83:1, the NH3 concentration of the liquid phase was 3.5 g/l. The pH at room temperature was 6.9. The mass ratio of solid to aqueous solution was 1.14:1. After the treatment, the suspension was filtered, the product was washed with 10 liters of deionized water, and finally dried at 100 °C. The amount of high-purity ammonium paratungstate product was 190 kg. The equivalent yield is 98.1%.

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