Oxidation Method for Recycling Tungsten Carbide

The demand for tungsten, driven significantly by its recycling from various waste materials, has led to the development of several effective recycling methods. Among these, the oxidation method stands out due to its efficiency in processing tungsten carbide-cobalt metal (hard alloy) or residual tungsten metal. This method converts these materials into valuable reusable forms through a series of chemical reactions and processes.

Overview of the Oxidation Method

The oxidation method for recycling tungsten carbide involves two main steps: oxidation and alkali treatment. Initially, waste tungsten carbide is reacted with oxygen to form tungsten and cobalt oxides. Subsequently, these oxides react with alkali to produce water-soluble sodium tungstate, which is easily separated from the solid cobalt oxide. Common oxidants used in this process include potassium nitrate or oxygen-enriched air, leading to two primary variations of the method: the Potassium Nitrate Smelting Method and the Oxygen-Enriched Air Oxidation Method.

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1. Potassium Nitrate Smelting Method

Process Description

• Reaction Mechanism: Potassium nitrate (or sodium nitrate) and atmospheric oxygen serve as oxidants, transforming tungsten in the waste into tungsten trioxide (WO3). This reacts with sodium oxide, a decomposition product of sodium nitrate, to form soluble sodium tungstate (Na2WO4).
• Operational Details: The process is conducted in a reverberatory furnace, which is fueled by heavy oil or gas. Once the potassium nitrate reaches its melting point, it reacts vigorously with the waste tungsten materials, elevating the temperature to between 1073-1173 K. After about an hour of stirring and fusion, the molten product is processed to extract Na2WO4 and Co2O3 slag.

Advantages

• High tungsten recovery rate (up to 99% from certain slags).
• Fast reaction and high production capacity.
• Suitable for various types of tungsten-containing waste.

Limitations

• Generates significant amounts of NO2, posing environmental challenges.
• Alternative oxidants like sodium sulfate reduce pollution but require higher temperatures and longer processing times.

2. Oxygen-Enriched Air Oxidation Method

Process Description

• Operational Mechanism: Oxygen-enriched air is introduced into a preheated oxidizing furnace, where temperatures range from 1073 to 1173 K. Tungsten oxides form and dissolve in alkali to produce Na2WO4.
• Efficiency: The oxidation process is self-sustaining in terms of heat once initiated, eliminating the need for external heating. The process typically takes 2 to 7 hours depending on the waste material’s form and composition.

Advantages

• Suitable for a variety of tungsten-containing materials including rods, bars, wires, and plates.
• Allows for the recovery of cobalt from the insoluble residue post-alkali treatment.

Limitations

• Some tungsten loss due to WO3 sublimation, with typical recovery rates for Na2WO4 production ranging from 94% to 97%.

Conclusion

Both the potassium nitrate smelting method and the oxygen-enriched air oxidation method provide robust solutions for recycling tungsten carbide. While the potassium nitrate method is noted for its rapid processing and high recovery rates, it does pose environmental challenges. Conversely, the oxygen-enriched air method, though slightly less efficient in tungsten recovery, offers a more environmentally friendly alternative with its self-sustaining heat mechanism. Each method’s suitability varies depending on the specific types and forms of tungsten-containing waste, allowing for flexible application in recycling practices.