Everyone knows that common metals like steel, aluminium, and copper are recyclable – but what about special metals like tungsten?
This rare metallic element has a variety of highly resistant properties that make it very useful in a range of industries around the world. From light bulb filaments and electric contacts to sports equipment, heavy-duty tools and machinery to jewellery, highly durable tungsten can be found in many places and forms.
However, it’s in limited supply, which makes it even more important for as much tungsten to be recycled as possible. There are several ways that tungsten can be extracted from scrap and processed into pure tungsten again to be reused in new tungsten products.
Here’s what you should know about recycling tungsten metal.
Why is recycling tungsten important?
Due to its high demand and relatively low abundance, tungsten is what’s known as a ‘critical raw material’ – a metal or mineral whose supply is essential for industry and society. Europe alone is responsible for the consumption of 25% of global raw materials, despite only producing 3%.
Based on its consumption rates, it’s predicted that the world’s supply of tungsten ore will only last for around 140 years. Currently, 76% of tungsten is newly produced (though about 10% is lost in the process of manufacturing final tungsten products). This means that recycled and reused tungsten only accounts for around 24% of the remaining tungsten in circulation.
Sourcing the raw material can have its difficulties, as its production is limited to several countries with viable tungsten mines. China in particular seems to have a monopoly on the tungsten market, as it has the largest natural supply in the world – producing an estimated 71,000 metric tons in 2022 compared to just 13,100 metric tons from all other countries that year.
If other countries don’t want to be dependent on China for raw tungsten production, then recycling it from scrap metal is a crucial step in maintaining a supply of usable tungsten. It’s also in keeping with sustainability efforts, following ever-increasing pressures to reduce environmental damage.
Recycling processes are typically lower-cost and have less of an environmental impact than sourcing new tungsten ore, with newer technologies helping to avoid the pollution and potential health hazards caused by older methods of separating tungsten from alloys.
Which types of tungsten can be recycled?
First-use or semi-finished tungsten products require more manufacturing steps to be ready for final use, such as tungsten alloy rods or drill bits that may require cutting or assembly with further pieces to become an end-use product.
When this end-use product is no longer useful for its intended purpose, such as a worn-out drill head, the metal pieces become scrap. New scrap can also be produced during the first-use process, such as chips and burrs, and parts that don’t pass quality checks.
Most scrap materials containing tungsten can be processed to extract even a small amount of tungsten for reuse, including tungsten carbide parts, tungsten alloy scrap, tungsten catalyst waste, and production residue like sludge (grinding swarf).
According to research published in the International Journal of Refractory Metals and Hard Materials, the annual input of tungsten material contains 35% new and old scrap, with the old scrap generated from the consumption of end-use products having a 30% end-of-life recycling rate.
Only a third of metals have a recycling input rate of 25% or more, making tungsten one of the more recyclable metals. With today’s technologies, there are methods of treating nearly every type of tungsten scrap generated during production and the end-use cycle.
How much tungsten is recycled?
The largest contributor to tungsten’s high recycling rates is tungsten carbide, which is one of the most commonly used forms of tungsten in the world. This tungsten-carbon alloy, which may be combined with cobalt to form a hardmetal or cemented carbide, accounts for two-thirds of tungsten use. It’s typically found in heavy-duty cutting tools for a range of industries, which contribute over half of tungsten carbide’s estimated global recycling rate of 46%.
The second largest use of tungsten is in steels and superalloys, but there were no figures available for their average recycling rates. However, we can assume they are fairly high, as production scraps from smelting, casting, and forming these metals are easily collected and re-melted for other uses in-house, without having to outsource to a recycling company.
Other tungsten metal products that account for the third largest usage of the element include metallurgical powders and heavy metals used in lighting, electronics, switches, and high-temperature applications. This segment has an estimated global recycling rate of 22%, with heavy metals accounting for 30% of this total.
The smallest sector is tungsten chemicals, which are used as catalysts, pigments, lubricants, and semiconductors. These are harder to recycle because they typically become highly contaminated with non-recyclable materials in their line of use, leaving tungsten chemicals with the lowest estimated global recycling rate at just 5%.
How is tungsten recycled?
As their atoms don’t disappear, metals largely remain reusable over and over again – but they can still be exhausted as a resource when mismanagement causes them to dissipate or dilute beyond the point of being able to access them again.
This is why the ‘reduce, reuse, recycle’ principle is just as important with metals like tungsten as it is with other materials. Efficiency in the first-use stage is key to reducing the amount of waste, and reconditioning products after wear and tear can prolong their lifecycles. Only then should scrap tungsten be recovered from well-used products.
Recycling tungsten scraps involves processing the material to extract the element in as raw a form as possible, so it can then become a first-use material again, without compromising its resistant properties. There are three primary types of tungsten recycling, with varying methods for each.
Direct recycling
Direct recycling means transforming the scrap material to a powder with a final composition as close to the original as possible, being highly pure without contamination from foreign materials. This can be achieved through physical or chemical treatments, but must involve minimal energy consumption, waste generation, and processing costs.
Examples of tungsten direct recycling methods include zinc melting and mechanical pulverisation. During zinc melting, zinc is added at a high temperature to form an alloy, then removed through vacuum distillation, with the leftover product ground into a powder. Pulverisation involves the traditional method of manually crushing the material into powder.
Chemical recycling (indirect)
Chemical recycling requires the chemical conversion of scrap material into good-as-new ammonium paratungstate (APT), which is a high-purity source for most tungsten products. In some cases, only part of the scrap may be chemically converted, recovering the by-products while leaving the tungsten or tungsten carbide in a powder form suitable for reuse.
One common method, alkaline fusion, uses sodium compounds and high temperatures to create sodium tungstate through oxidation and digestion. The mixture is then leached in heated water and filtered to remove water-insoluble materials. Though it requires careful control of potentially explosive reactions, this method is versatile enough to oxidise even hardmetal scraps.
Another two-step method involves oxidation and alkaline digestion. Soft or hard scrap metal is first oxidised in air to form tungsten oxides and tungstates, then the product is digested in a sodium hydroxide solution under high temperature and pressure to recover the tungsten.
A third option is electro-dissolution, which uses a leaching agent to dissolve binder metals such as cobalt from tungsten alloys like tungsten carbide. The product is dissolved in an acidic solution under an electric field to separate the component materials, which can then be crushed into powder.
Melting metallurgy (semi-direct)
Scrap from tungsten steels and superalloys is perhaps the most straightforward to recycle, as it’s easier to melt down and add to other products, depending on the composition required. The scraps can be melted in an electric arc furnace, then refined in an argon oxygen decarburisation converter.
Highly pure tungsten scraps can be added to superalloys, while less pure tungsten scraps can be used for steels, often as a substitute for ferrotungsten (iron-tungsten alloy). When re-used in this way, tungsten can only be recycled again by further re-melting.
Can all refractory metals be recycled?
Tungsten is part of a group of special metals with highly resistant qualities that make them useful in challenging environments – known as refractory metals. Some have more widespread uses than others, making them easier to re-use, like niobium and molybdenum, while others have more health hazards to consider, such as chromium.
According to the Handbook of Recycling (2014), the recovery of other refractory metals for steel production is also quite high – around 50% for chromium, manganese, and niobium, and 25% or more for molybdenum. For other speciality applications, this changes to around 50% for rhenium and titanium, and at least 1% for tantalum and zirconium.
Tungsten remains one of, if not the, most commonly used and recycled refractory metal. With many recycling processes available, it’s possible to recover highly pure tungsten from a variety of scrap types, maintaining its properties and the performance of the material throughout future uses.
The best way to recycle tungsten depends on the particular material and type of scrap, and the intended use for the recycled product. If you work with tungsten parts that can’t be recycled in-house, it’s definitely worth looking into professional tungsten recycling facilities or scrap buyers to improve the sustainability and cost-effectiveness of your business.
