Ammonium metatungstate (AMT) is an important tungsten compound, mainly used in the manufacture of tungsten oxide, tungsten and tungsten carbide powder and their downstream products ect., also it can be used as catalyst in fields of petroleum cracking, organic synthesis, nitration and so on; besides, with the rapid development of oil refining, petrochemical and other industries, the demand amount of ammonium metatungstate is growing fast. There are many preparation methods for ammonium metatungstate which can be divided into two catalogues of solid and liquid phase transformation method, such as thermal decomposition method, neutralization method, solvent extraction and ion exchange method, wherein the thermal decomposition method which is depending on raw material of ammonium paratungstate (APT) is the mainstream process for preparing AMT in industrial.

 

For manufacturing AMT with high solubility to meet the requirement of tungsten contained catalyst, an invention has pointed out a liquid phase transformation method to produce ammonium metatungstate which took ammonium paratungstate as raw material; and the result of experiment have shown that this method has the advantages of short process, little investment of equipment ect., furthermore, the product – AMT is highly dissolve in water with the stable quality. The preparation steps are shown as following:

1. Leaching the wet ammonium paratungstate: Mixing the material of wet ammonium paratungstate (which the water content is among 5~10%) and dilute nitric acid (HNO₃) to prepare ammonium metatungstate solution, the chemical reaction is like bellow:

5(NH₄)₂•12WO₃•5H₂O+4HNO₃=(NH₄)₆•H₂W₁₂O₄₀•6H₂O+4NH₄NO₃

2. Converting the dilute ammonium metatungstate solution to concentrated AMT solution: The dilute ammonium metatungstate solution is carried out standing for aging, filtering, heating for concentrating and again filtering for many times to finally get concentrated AMT solution;

3. Spraying and drying the concentrated AMT solution obtained in step 2 with an spray dry tower which will dry AMT feed liquid into powder quickly, thus to get product of AMT powder.

 

Compared to the traditional method, this kind of liquid phase transformation method requires no calcination step, so it is no need to use rotary kiln which will reduce the fixed investment; at the same time, product per ton will save 120KWH, while the recovery efficiency can be improved for 3%.