Low Cost Chemical Method for Waste Tungsten Recovery

At present, waste tungsten is recycled by re-grinding inserts. But beyond a certain point, it is impossible to grind them again and the purity can not be improved. Therefore, further process is usually needed to complete the recovery of tungsten scrap.

The follow-up process of recovery of tungsten scrap mainly adopts chemical methods, and there are various technological schemes, including alkali leaching of tungsten oxide scrap to convert the scrap into sodium tungstate, and crude tungsten can be recovered from sodium tungstate. Sodium nitrite or sodium nitrate are also used as oxidant and sodium carbonate as diluent to recover tungsten compounds. The tungsten carbide powder can also be recovered directly by zinc method. But these are high-cost methods and require a lot of investment. Therefore, a cost-effective method is needed to extract tungsten carbide.

Recently, some scholars have proposed a chemical method for recovering carbide alloys. The main method is to grind tungsten carbide alloys to obtain powders, and treat the powders with carburized gas mixture to obtain purified tungsten carbide alloy powders. Its specific operations include:

Oxidation of 10 kg tungsten carbide waste in air for 10 hours at atmospheric pressure and 950 ℃. The oxidized powder is then ground in a ball mill for about 2 hours. The oxide powders were carburized by a carburizing mixture consisting of 10% natural gas and 90% nitrogen for 6 hours, then cooled in nitrogen to 200 ℃, and then cooled in air to room temperature.

Analysis of carburized and reduced powders reveals that reduction is complete and that the carbon content is 6.3%, which is the correct stoichiometric composition. It is also found that cobalt is about 9% and titanium is about 1.3%, which is consistent with the requirement of tungsten carbide powder for compression.

The main principle of this method is to convert elements into their oxides, and then use carbothermal reduction to convert oxide powders back to the original elements. Carbon existing in tungsten carbide alloys as carbide will escape as carbon dioxide during oxidation. The results show that this method can produce high quality powder mixtures at a lower cost without any expensive equipment or consumables.

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