Metatungstate is a class salts containing with tungstate partial tungstate, the important compound in tungsten production process, including ammonium metatungstate (AMT), sodium metatungstate and lithium metatungstate ect., partial tungstic acid and most of its salts can be well dissolved in water. Metatungstate ion is stable in weak acid solution of PH value equals to 4; while, decomposition of it will be carried out when adding alkali or getting boiling and to generate positive tungstate. Once the metatungstate ion is formed in the aqueous solution, it can not precipitate tungstic acid even add the acid, while adding calcium chloride (CaCl2) will not suppose to precipitate the scheelite. Therefore, the way of adding alkali and boiling for a long time is generally taken to turn metatungstate to tungstate in the tungsten metallurgical industry.
Ammonium metatungstate (AMT) is a very common metatungstate, with the high solubility in water which helps it to prepare tungstate solution with high concentration and free of the alkali metal ions. AMT is mainly used for producing catalyst substrate; in addition, it also used as a corrosion inhibitor for nuclear shielding; precursor for preparing other tungsten compounds. The preparation methods of AMT are neutralized, ion exchange, electrodialysis method ect..
Sodium metatungstate, [Na6(H2W12O40)•3H2O]the white crystalline, soluble in water, and its preparation process is firstly preparing sodium tungstate solution, then concentrating to obtain the solution with high concentration (density up to 3.1g/mL). Sodium metatungstate can be used in oil drilling; as an important intermediate product used in the manufacturing process of heteropolytungstate; also it used as a fuel cell electrode and in the cigarette filters; and for fireproof textiles.
Lithium Metatungstate, [Li6(H2W12O40)•3H2O] has the density higher than sodium metatungstate which will up to 3.5g/mL at maximum, although lithium is an alkali metal with the smallest density.
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