a Brief Review of Ammonium Para Tungstate Preparation Closed Circuit Mode

In the existing technology, the production of ammonium para tungstate is not recycled, and the consumption of auxiliary materials is large, and the environmental pollution is heavy. The main reason is that a large amount of high salt waste liquid is produced during the transformation process of tungstate solution, and the evaporation crystallization mother liquor is difficult to recycle economically and produce ammonia nitrogen wastewater. In the existing technology, if the enterprise is changed to "cycle" model, then the enterprise will lose money, so the tungsten metallurgical enterprises all over the world have to choose sewage discharge.

The main research and development directions include three types: strong alkaline sodium tungstate solution direct extraction, tungsten ore roasting ammonia leaching method, ammonium phosphate or ammonium fluoride leaching method.

(1) Some scholars have developed the technology of caustic soda or soda leaching - quaternary ammonium salt medium extraction directly from tungsten evaporation crystallization to produce APT. The process can realize the recycling of alkali, thereby greatly reducing the consumption of waste water, acid and alkali and other chemical reagents.

(2) The tungsten ore roasting ammonia leaching method is to roast the tungsten concentrate and silica, and the sintering of tungsten trioxide and calcium silicate and / or ferrous silicate are obtained, and ammonium tungstate solution is obtained by leaching ammonia with ammonia water. However, silicon dioxide can not be recycled, especially the pressure of leaching system is higher (100°C 6atm), and no industrial application has been reported.

(3) Ammonium phosphate or ammonium fluoride leaching method. The main steps are ammonium phosphate or ammonium fluoride leaching - purification of coarse ammonium tungstate solution - crystallization of APT. A method of decomposing scheelite by ammonium salt has been invented. Ammonium scheelite is decomposed by ammonium phosphate and liquid ammonia, and the temperature is decomposed at 180~220°C. This method is only suitable for the treatment of scheelite, and the use of liquid ammonia is corrosive and easy to volatilize, belongs to the 2.3 type of toxic substances, chemical accident rate is very high, in the process of industrialization, the need for strict safety and environmental protection facilities.

Therefore, the existing technology, although the idea of green metallurgy, hope to achieve the whole process of pollution free emissions, but in the R & D stage, and the process is complex, the production site personnel are not easy to master, so far there is no precedent for industrial application. 

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