The new technology yields a high-quality product, is ecologically clean, and is characterized by a high degree of metal extraction (over 99%).

At plants manufacturing various products from metallic tungsten (small bars, wire, etc.) and its alloys, up to 20% of the products are, for technical reasons, lost as wastes in the form of chunks, tangles, shavings, etc. Such secondary raw materials are at present mainly processed by the method of fusing with sodium nitrate followed by multistage hydrometallurgical conversion. In industrial production, moreover, different types of tungsten wastes, as a rule, tend to blend, and this affects the quality of the product and the degree of metal regeneration. It should also be remembered that the nitrogen oxides released in the production process substantially worsen the environmental situation in the vicinity of the plant.

These limiting factors are absent in the new technology of electrochemical processing of metallic tungsten wastes, which is based on the direct anodic dissolution of the wastes in an ammonia electrolyte with the subsequent evaporation of the solution and the isolation of ammonium paratungstate (APT), a marketable salt.

The new process has been implemented on an industrial scale. The industrial electrolyzer for processing the metallic tungsten wastes is shown schematically in Fig. I. It is made of titanium with a stainless steel cathode.

The ammonia electrolyte is continuously recycled in the apparatus; when it becomes saturated with tungsten (over 120 g/l, density over 1.10 g/cm³), it is removed for evaporation and APT precipitation.

The process can also be employed to regenerate wastes of metallic molybdenum. Two versions of this technology have been developed: for d.c. and a.c. industrial-frequency currents.

Particularly promising is the application of the electrochemical technology to processing carbide wastes of solid alloys: tungsten-cobalt, tungsten-cobalt-tantalum, etc. In this case electrochemical oxidation causes cobalt to pass into the nitrate solution (the electrolyte), while tungsten in the form of wolframic acid accumulates in the anode mud, which is then leached with ammonia liquor to obtain a high-quality APT product. If the initial material contains tantalum (wastes of alloys of tungsten-cobalt-titanium-tantalum), the latter is concentrated in the ammonia-leached tungsten sludge.

Up to 99% of the metals is extracted into the marketable products. The process is conducted with an industrial-frequency a.c. The current efficiency in the optimal mode ranges from 96 to 98%, the conditions of electrolysis ensuring the absence of any harmful escape of nitrogen oxides; this is achieved by adjusting the various variable parameters (temperature, nitric acid concentration in the electrolyte, current density, etc.).

Industrial electrolyzer shown schematically:

I - electrolyzer lid; 2 - exhaust ventilation duct; 3 - cathode; 4 - soluble anode basket; 5 - recycled solution collector; 6 - electrolyzer housing.

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