Preparation and Structure of Sodium Tungstate

The predominant route to this salt is the extraction of tungsten ores, almost all of which are tungstates. Thus, the ores are treated with a base to give sodium tungstate, as illustrated in the case of wolframite:
Fe/MnWO₄ + 2 NaOH + 2 H₂O → Na₂WO₄•2H₂O + Fe/Mn(OH)₂

Scheelite is treated similarly using sodium carbonate.

Sodium tungstate can also be produced by treating tungsten carbide with a mixture of sodium nitrate and sodium hydroxide in a fusion process which overcomes the high exothermicity of the reaction involved.

Several polymorphs of sodium tungstate are known, three at only one atmosphere pressure. They feature tetrahedral orthotungstate dianions but differ in the packing motif. The WO₄²⁻ anion adopts a structure like sulfate (SO₄²⁻).


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