Ammonium metatungstate (AMT) is an important intermediate compound in tungsten metallurgy industry, which is mainly used for manufacturing tungsten oxide, tungsten powder, tungsten wire and other tungsten compound, also, it is used in catalyst of petrochemical industry. Researches have indicated that ammonium metatungstate and ammonium sulfide solution can be used for preparing ammonium dithiotungstate under some specific environment.

 

There are two methods of ammonium metatungstate preparing ammonium dithiotungstate, as following:

The first method:

1. Dissolve ammonium metatungstate in the deionized water with stirring;

2. Add ammonia water and stir for 20 minutes to speed up the reaction speed under the temperature of 60°C, at this time, the pH value of reaction system may be 9;

3. Add ammonium sulfide solution and stir for 30 minutes under 60°C, then carry out vacuum filtration until the reaction is stop to remove a small amount of blue precipitation which generated during the reaction process;

4. Stand the filtrate for 24 hours under 0°C to get yellow crystal;

5. Carry out vacuum filtration and the precipitation is washed respectively with deionized water and anhydrous ethanol for three times, and finally we get the ammonium dithiotungstate crystal after drying, with the yield of 45%.

 

The second method:

1. Place the 5g of industrial grade ammonium tungstate which contains 83% of tungsten trioxide into conical beaker, and add 8 wt% of ammonium sulfide solution 35ml slowly, at this time the color of the solution will slowly turns from blue to light yellow;

2. Stir for 30 minute at room temperature after all the ammonium sulfide solution is poured into the conical beaker, and then stand the reactant solution for 12 hours to generate yellow crystal;

3. Precipitate, and wash the precipitation respectively with deionized water and anhydrous ethanol for three times, dry at room temperature in vacuum environment to finally get ammonium dithiotungstate crystal, the yield is 93% in accordance with tungsten content.

 

Ammonium dithiotungstate [(NH₄)₂WO₂S₂] is an important class of thiometal ammonium salt, and the decomposition products include {WOS₂}, vulcanization intermediate of tungsten oxide. Studies have found that the thermal decomposition of ammonium dithiotungstate crystal under the atmosphere of hydrogen is mainly occurred among 160～450℃, which firstly transfers to {WOS₂} and then to tungsten disulfide.