Ammonium Metatungstate Improvement Process

Ammonium metatungstate powder is widely used in chemical industry as raw material of petroleum cracking catalyst, corrosion inhibitor (anticorrosive coating or coating) for electronic components, and as important raw material for preparing composite powder, doped tungsten wire and tungsten-cerium electrode in the production of tungsten products.

In order to improve the content of WO₃ and the yield of tungsten metal on the basis of ensuring the high purity of the product, reduce the energy consumption and the labor intensity and production cost of operators, the researchers improved the process on the basis of evaporative crystallization method. According to the characteristics of ammonium metatungstate crystal, such as being very soluble in water and easily deliquescent, etc. The obtained wet crystal material is heated and dehydrated at low temperature by far infrared, and then dried at high temperature by far infrared after cooling. The operation process includes:

A.Evaporative crystallization: The solution of ammonium metatungstate produced by conventional method is indirectly heated in evaporative crystallization (concentration) tank, evaporative crystallization is carried out at boiling temperature. During evaporation, the PH value of the feed liquid is controlled between 2.0 and 5.5 by adding nitric acid. When the density of the feed liquid reaches 2.5g/cm³ or the crystallization rate reaches 80%, the heating is stopped and the cooling is over. Ammonium metatungstate crystal material containing free water was filtered.

B.De-free water: The material obtained from process A is fed into the far-infrared steel strip heating furnace, and the temperature is gradually raised from low to high in the temperature range of 50-70 ℃. The moisture content of free water in the material is 3-5 wt% after 40-80 minutes of dehydration treatment.

C.Drying and packaging: The material after dehydration in process B is fed into the far-infrared steel strip heating furnace, which is gradually warmed up from low to high in the temperature range of 100-170 ℃. The material is dried for 50-90 minutes and then sifted and packed after cooling. Ammonium metatungstate powder is obtained.

The improved process has the advantages of convenient temperature adjustment, good stability and control accuracy less than (+2.0 ℃). Water molecules are driven out from the inside of the material, dehydration and drying are uniform and non-caking. After drying, the particle size of the material reaches 15-20 micron and is uniform, and the thermal efficiency is high. It can save about 40% energy compared with the traditional technology, while the product is of high purity and quality. Good volume, WO₃ content as high as 91.0-92.5wt%, both low production costs, good working environment, low labor intensity of operators and so on.

B.De-free water: The material obtained from process A is fed into the far-infrared steel strip heating furnace, and the temperature is gradually raised from low to high in the temperature range of 50-70 ℃. The moisture content of free water in the material is 3-5 wt% after 40-80 minutes of dehydration treatment.

C.Drying and packaging: The material after dehydration in process B is fed into the far-infrared steel strip heating furnace, which is gradually warmed up from low to high in the temperature range of 100-170 ℃. The material is dried for 50-90 minutes and then sifted and packed after cooling. Ammonium metatungstate powder is obtained.

The improved process has the advantages of convenient temperature adjustment, good stability and control accuracy less than (+2.0 ℃). Water molecules are driven out from the inside of the material, dehydration and drying are uniform and non-caking. After drying, the particle size of the material reaches 15-20 micron and is uniform, and the thermal efficiency is high. It can save about 40% energy compared with the traditional technology, while the product is of high purity and quality, good volume, WO₃ content as high as 91.0-92.5wt%, both low production costs, good working environment, low labor intensity of operators and so on.

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