Recovery of Ammonium Paratungstate from Tungsten-containing Soft Waste

The traditional tungsten soft waste recovery and treatment process is firstly to convert the soft waste into sodium tungstate solution by NaOH solution cooking, and then crystallize the sodium tungstate crystal; then dissolve the crystal in the circulating mother liquor, regenerate the sodium tungstate solution, and then extract the tungsten from the solution by organic extractant and purify the ammonium tungstate. The ammonium salt of ammonium tungstate is evaporated. It can be seen that the recovery method is no different from the conventional treatment process, but in fact, because of the waste, there are some defects such as high operating cost, environmental pressure and so on.

In view of this, a new method is needed to overcome the shortcomings of traditional thinking mode and process route, shorten process flow, improve tungsten recovery, reduce production cost and prevent environmental pollution. For example, some scholars have put forward the following measures.

The tungsten-containing soft waste produced in the hydrometallurgical process of tungsten is directly mixed with dilute ammonia water, and is converted into ammonium tungstate solution by airtight reaction at set temperature and pressure, and then ammonium paratungstate product is obtained by filtering residue, evaporating crystallization and solid-liquid separation.

A. Pressure ammonia water leaching: the tungsten soft waste produced in the hydrometallurgical process of tungsten is mixed with dilute ammonia water and leached at 0.2-0.6 Mpa and 120-200 ~C for 1-3 hours; the dilute ammonia water in the material is NH3; the tungsten in the tungsten soft waste is WO₃; the molar ratio of the two is 2.5-4.5:1;

B. Filtration  and deslagging: feed the liquid after leaching through the A process and filter it to filter.

C. Crystallization and separation: The filtrate from process B is sent to the evaporator, evaporated and concentrated at 50-100 ℃ to the density of mother liquor in slurry is 1.02-1.10 g/ml, and ammonium Paratungstate Crystal is obtained by solid-liquid separation.

The soft waste containing tungsten is the leaching residue produced in the production of ammonium metatungstate (AMT), the ground material and air duct material produced in the production of ammonium paratungstate and yellow tungsten in the production of tungsten oxide, and the mother liquor of evaporation in the production of ammonium paratungstate or its mixture. The concentration of dilute ammonia water is 4 ~ 15wt%.

Ammonium paratungstate crystals can be obtained by direct pressure leaching of tungsten-containing soft waste with dilute ammonia water and regular filtration, evaporation, crystallization and separation. Therefore, it has the advantages of short process flow, low equipment investment, high productivity and yield, zero emission and no pollution, and the cost of recovery and treatment is only 30-40% of the traditional technology.

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