Ammonium tungstate, ammonium metatungstate and ammonium paratungstate are the same, they are all tungsten compounds, they are all a kind of tungstate, which can be used to make tungsten trioxide, blue tungsten oxide, purple tungsten oxide or dioxide Tungsten and other tungsten compounds. But the three others are also different.
Ammonium tungstate is a white crystalline powder, the English name is Ammonium tungstate, the molecular formula is (NH4)10W12O41~xH2O, and the molecular weight is 3042.58. Ammonium metatungstate is a crystalline powder with a white or yellowish appearance. Its Chinese alias is ammonium metatungstate hydrate, and its English name is Ammonium (Meta) tungstate Hydrate (abbreviated as “AMT”). Its molecular formula is H28N6O41
W12 and its molecular weight is 2974.32.
Ammonium paratungstate is a white crystalline powder, the English name is Ammonium paratungstate (“APT” for short), the molecular formula is H8N2O4W, and the molecular weight is 283.9145. According to different crystallization conditions, it can be divided into the following four types: 3(NH4)2O-7WO3-6H2O , 5(NH4)2-12WO3-5H2O, 5(NH4)2O-12WO3-5H2O and 5(NH4)2O-12WO3-11H2O.
From the perspective of physical and chemical properties
Ammonium tungstate is soluble in water but insoluble in alcohol. It will lose tetramolecular crystal water at 100°C, and its solubility in water at 20°C is less than 2%. Ammonium metatungstate can dissolve in water, and this feature is the most obvious difference between it and ammonium paratungstate.
The crystal structure of ammonium paratungstate is flake and needle, and it is slightly soluble in water, the solubility in water is less than 2% at 20°C, and insoluble in alcohol. In addition, when it is heated to 220-280°C, it will lose part of ammonia and crystallization water and transform into AMT, and when heated above 600°C, it will lose all ammonia and crystallization water and completely transform into yellow tungsten oxide.
The three are also different in terms of production process.
The preparation method of ammonium tungstate is the neutralization method, that is, after wolframite is subjected to alkali hydrolysis, it reacts with calcium chloride to synthesize calcium tungstate, and the calcium tungstate undergoes acid hydrolysis, and then reacts with ammonia water to obtain tungstic acid. Ammonium.
The main production methods of ammonium metatungstate are: (1) Using ammonium tungstate/sodium tungstate as raw material, ammonium metatungstate solution is prepared by solvent extraction or ion exchange method, and then AMT is obtained by evaporation and crystallization. (2) Heating ammonium paratungstate to make it lose part of ammonia and crystal water, transform into ammonium metatungstate solution, and then obtain AMT through evaporation and crystallization. (3) Stir ammonium paratungstate in water and neutralize it with acid to pH 3-4 to convert ammonium paratungstate into ammonium metatungstate solution, and then obtain AMT through evaporation and crystallization.
The main production methods of ammonium metatungstate are: (1) black tungsten concentrate (scheelite concentrate) high pressure alkali (sodium hydroxide) boiling – solvent extraction (ion exchange) – evaporation crystallization method; (2) scheelite concentrate Caustic soda fluorine salt pressure cooking-ion exchange (solvent extraction)-evaporation crystallization method; (3) scheelite concentrate hydrochloric acid decomposition-ammonia dissolution-evaporation crystallization method.
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