Ammonium Tungstate,
Ammonium Metatungstate and ammonium paratungstate are all compounds of tungsten and can be used to make other tungsten compounds such as tungsten trioxide, blue tungsten oxide, purple tungsten oxide or tungsten dioxide. So what's the difference between them?
1. Definition
Ammonium tungstate is a white crystalline powder, the English 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 slightly yellow appearance. Its Chinese alias is ammonium metatungstate hydrate, English is ammonium (meta)tungstate hydrate ("AMT" for short), its molecular formula is H28N6O41W12, and its molecular weight is 2974.32.
Ammonium paratungstate is a white crystalline powder, the English is Ammonium paratungstate (referred to as "APT"), the molecular formula is H8N2O4W, and the molecular weight is 283.9145. According to the 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.
Ammonium Paratungstate
Second, the nature
Ammonium tungstate is soluble in water but insoluble in alcohol, loses four molecules of crystal water at 100°C, and has a solubility in water of less than 2% at 20°C.
Ammonium metatungstate is soluble in water, and this characteristic is the most obvious difference between it and ammonium paratungstate.
Ammonium paratungstate has two crystal structures: flake and needle, and it is slightly soluble in water, the solubility in water is less than 2% at 20 °C, and it is insoluble in alcohol. In addition, when heated to 220-280 °C, it will lose part of ammonia and crystal water, and convert it into AMT. When heated to above 600 °C, it will lose all ammonia and crystal water, and completely convert it into yellow tungsten oxide.
Ammonium metatungstate
Third, the production process
The preparation method of ammonium tungstate is the neutralization method, that is, after alkali hydrolysis of wolframite, calcium tungstate is synthesized by the action of calcium chloride, and
Tungstic Acid can be obtained by acid hydrolysis of calcium tungstate and then with ammonia water. Ammonium.
The main production methods of ammonium metatungstate are as follows: (1) Using ammonium tungstate/
Sodium Tungstate as raw materials, firstly prepare ammonium metatungstate solution by solvent extraction or ion exchange method, and then obtain AMT through evaporative crystallization. (2) Heating ammonium paratungstate to make it lose part of ammonia and crystal water, convert it into ammonium metatungstate solution, and then evaporate and crystallize to obtain AMT. (3) Neutralize ammonium paratungstate with acid to pH 3-4 under stirring in water to convert ammonium paratungstate into ammonium metatungstate solution, and then obtain AMT through evaporative crystallization.
The main production methods of ammonium metatungstate are: (1) wolframite concentrate (scheelite concentrate) high pressure alkali (sodium hydroxide) cooking - solvent extraction (ion exchange) - evaporation crystallization method; (2) scheelite concentrate Caustic soda fluoride salt pressure cooking-ion exchange (solvent extraction)-evaporative crystallization method; (3) hydrochloric acid decomposition of scheelite concentrate-ammonia dissolution-evaporative crystallization method.
