Why is recycling of tungsten important?
Tungsten (W) is a rare metal element known for its high melting point (3422°C) and boiling point (5930°C) such that tungsten is widely used in the manufacturing industry as welding electrodes. Besides, tungsten alloys such as Cemented Tungsten Carbide (WC-Co) and High-speed Steel (HSS) have also been used as hard materials for cutting tools and wear-resistant applications. However, tungsten is one of the limited resources in the periodic table regarding current mineral extraction rate, and tungsten ores are mostly located in countries such as China, Canada, and Russia. Thus, to mitigate the shortage of tungsten supply, recycling of spent tungsten scarps becomes more important in terms of secondary resources and strategic concerns.
Example of Tungsten Scraps [1]
How do we recycle tungsten scraps?
There are three categories of tungsten recycling approaches: Direct recycling (Zn-process), Semi-direct recycling (Chemical or Electrochemical process), and Melting metallurgy (Thermal Remelting). Among these methods, semi-direct recycling is commonly used because of its scalability and flexibility to form high-purity tungsten compounds such as ammonium paratungstate (APT) based on the chemical property of tungsten. The other two methods are only applicable in a few countries under specific conditions due to high energy consumption.
Tungsten Recycling Approaches [2]
What are the problems during tungsten recycling?
The conventional process of tungsten recycling by chemical approaches usually has multiple steps and high reagent/energy requirements. The secondary waste and emission during recycling are also a big concern. Therefore, to develop a more efficient and more environmentally-friendly process for tungsten recycling is critical in the near future. In our lab, we have utilized novel electrochemical methods for the recycling of tungsten, which realizes the effective and efficient removal of impurities.
New Recycling Process for Tungsten Scraps [3]
[1] Burghard Zeiler, et al., 2021. Recycling of tungsten: Current share, economic limitations, technologies and future potential. International Journal of Refractory Metals and Hard Materials, 98, 105546.
[2] International Tungsten Industry Association, 2019. Recycling of Tungsten - The technology - History, State of the Art and Peculiarities. ITIA News, August 2019.
[3] Takahiko Makino, et al., 2018. Recovery and Recycling of Tungsten by Alkaline Leaching of Scrap and Charged Amino Group Assisted Precipitation. ACS Sustainable Chem. Eng., 6, 4246−4252.