Ammonium metatungstate (AMT) is an important compound product in the process of tungsten smelting. It is widely used.
The preparation methods of ammonium acid are heat degradation and ion exchange, extraction, electrodialysis and neutralization.
The neutralization method called ammonium tungstate acid, ammonium paratungstate production is one of the commonly used method, but this method can also be used for the preparation of ammonium metatungstate, it is used in acid solution and the crystallization of APT, by controlling the pH value of 3-4, heating, stirring and other means to strengthen the ammonium tungstate solution is gradually converted into ammonium metatungstate solution then, the precipitation of AMT crystals.
Some scholars use ammonium paratungstate as raw material, adopt continuous solution conversion method,compare the effect of two kinds of acidizing agents, nitric acid and cationic resin on the basis of experiment. After that, nitric acid is selected as an acid agent, at a temperature of 95 degree and a stirring rate of 80 r/min,then obtained ammonium tungstate with similar impurity content as ammonium tungstate, the product quality is stable after the several tests. The direct yield of tungsten metal is 88%, and the total yield is 98.4%.
The most important characteristic of neutralization process is simple process and high rate of solution conversion, It is a common preparation process of ammonium tungstate at early stage. But it is a pity that acid consumption of neutralization method is large, It hashigh cost and environmental risks. Compared with Thermal degradation method and Ion exchange method, Now it has no more advantages.