Ultra Pure Ammonium Paratungstate Preparation

Ammonium tungstate is mainly used for the preparation of WO₃ and W powder. At present, the main methods of producing ammonium tungstate are neutralization, evaporation, extraction and ion exchange. The main process of preparing ammonium tungstate is evaporation method.

In view of the relatively large liquid solid ratio and long evaporation time of ammonium tungstate, some impurities, such as iron, are brought into ammonium tungstate because of the long time stirring of ammonium tungstate solution in the stainless steel reaction axe. In addition, the growth rate of the micro particles of ammonium tungstate is caused by the unequal balance of temperature gradient and alkalinity mass transfer. It is difficult to exceed the national standard zero of ammonium tungstate, even it is difficult to exceed the national standard of ammonium tungstate, and can not meet the growing electronic industry, chemical synthesis, and stone. The demand for high purity and ultrapure pure ammonium tungstate in the fields of oil catalysis and so on.

In order to achieve the above purpose, some researchers have proposed that, on the basis of existing technology, one or more tungsten sources of tungsten, ammonium tungstate, ammonium parastate, ammonium para tungstate and ammonium tungstate are used as the raw material on the basis of the national standard of ammonium tungstate, adding pure water and liquid ammonia (or ammonia water) at normal temperature to make ammonia solution and mix well, and no extra heating is needed. After the extraction, Superacid was added to the acid to precipitate the acid after the extraction, and the solid and liquid separation was carried out after the end of acid precipitation. The separated ammonium tungstate was dried until the moisture content of ammonium tungstate decreased to less than 1.08g/cm3. The specific process was as follows:

The technical conditions of 300kg are in accordance with one or more tungsten sources of tungsten oxide, ammonium perotungstate, ammonium parastate, ammonium para tungstate and ammonium tungstate, adding pure water and liquid ammonia (or ammonia) at normal temperature for ammonia solution and mixing, without extra heating, and controlling the tungsten ion concentration in the main body of solution at 240g/L at the time of 300kg. At the same time, the pH of the main solution remained in the effective range of 9.0~11.0 before controlling the crystallization. Then super acid is added under normal pressure for acid precipitation crystallization. The pH of the acid precipitation endpoint is controlled at 6.0-7.0. Solid-liquid separation is performed after the acid precipitation is completed. The separated ammonium tungstate is dried for 1~2 h until ammonium tungstate. The moisture content in the water drops to ≤ 1.08 g/cm³, the crystallization rate of the final product exceeds 96%, and the purity of the prepared ammonium tungstate product exceeds the national standard of ammonium tungstate APT-0.

The new technology avoids the way of evaporation and crystallization of ammonium tungstate solution by using coal or gas to produce steam. A new method to clean the production of ultra pure ammonium paratungstate is found. It is green, environmental and low carbon, and the process is stable and the quality of the product is reliable.

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