Pure Sodium Tungstate Preparation from Alkali Leaching Solution

At present, in the process of producing ammonium tungstate solution by tungsten mine, the technology of separating P, As, Si and Mo from tungsten ore to produce high pure ammonium tungstate solution has the classical chemical method, the current extraction method and the ion exchange method. The current extraction process is the free alkali in the inorganic acid neutralization solution, the silicate hydrolysis, most silicon is removed by silicic acid precipitation, then the P, As and the remaining silicon are removed by the magnesium salt or ammonium magnesium salt, and the Mo is separated by the precipitated MoS₃ method, and the purified sodium tungstate solution.

In order to overcome the shortcomings of the above methods, this paper introduces a method for preparing high purity sodium tungstate from tungsten ore base decomposition solution, such as pure sodium tungstate and pure ammonium tungstate.

Material: tungsten ore caustic leaching solution WO₃ 150g/l, Mo 0.40g/l, As 0.006g/l, P 0.009g/l, Si 0.08g/l.

The pH of crude Na₂WO₄ solution was adjusted by naphthenic acid extraction, then NaHS was added to control certain conditions to treat the vulcanization, so that the molybdenum and arsenic were fully converted into thioacid. The Na₂WO₄ solution treated by vulcanization was adjusted to a certain concentration with deionized water and adjusted to pH to 8~9 by NaOH solution.

CO2-3 quaternary ammonium salt was used as a mixture of organic phase and liquid for reverse flow extraction, the concentration of extractant in organic phase was 380g/l, compared with 2.5: 1, series 9, the loaded organic phase was washed step by step after deionized water washing, 2.5mol/l NH₄HCO₃ solution was first used, W with high purity (NH₄) ₂WO₄ solution compared with 1.5: 1,10 counter current reverse extraction W. After the solution was oxidized, the organic phase was oxidized with H₂O₂ solution, then Mo and As were extracted by NaHCO₃ aqueous solution. Finally, the organic phase was treated by NaOH aqueous solution, so that the organic phase could be regenerated.

The product (NH₄)₂WO₄ solution crystallized to produce ammonium parotungstate, the crystallization rate was 91%, the content of all elements in the product reached APT-0 grade standard.

The advantages of the above process are that the low molybdenum tungsten concentrate can directly treat the caustic soda decomposition solution of tungsten ore, it can separate P, As and Si at the same time, and obtain purified (NH₄)₂WO₄ or Na₂WO₄ solution, which can directly crystallize high pure APT or solid Na₂WO₄ products. The process does not consume acid, and can return the residual liquid to the leaching use and recovery of tungsten. The free alkali in the leaching solution of caustic soda can shorten the whole process, reduce the tungsten loss, reduce the consumption of manpower and reagents, and reduce the pollution of the environment, thus reducing the cost of the product.

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