Electronic waste (e-waste) is a growing problem, with a record 62 million tonnes (Mt) of it being generated worldwide in 2022.
At the same time, there is a growing demand for critical raw materials (CRMs), including rare metals, to sustain the rapid growth of existing and emerging technologies.
Recycling as much metal as possible from e-waste plays a crucial role in mitigating shortages of critical metals, as well as reducing the need for damaging mining operations.
There are a number of drawbacks to current metal recycling techniques, however.
Hydrometallurgy – a process that uses liquids to first dissolve and then reclaim the metals – involves substantial water and chemical consumption, and also produces secondary waste streams.
Existing heat-based pyrometallurgy, meanwhile, lacks selectivity and requires substantial energy input.
Now, researchers in Texas have detailed a newly developed technique that they say is able to recycle metals from e-waste more efficiently and with reduced environmental impact.
The new technique uses flash heating and chlorination, an industrial process that involves reacting chlorine and oxygen with specific metals in a mixture.
While still reliant on heat and additional chemicals, it allows both to be deployed in a more controlled manner.
Flash Joule heating uses electric current to produce high temperatures
The technique, detailed in the journal Nature Chemical Engineering, is built on a method known as flash Joule heating (FJH) that lead researcher Professor James Tour had previously used in waste disposal.
FJH involves passing an electric current through a material to rapidly heat it to extremely high temperatures, transforming it into different substances.
It enabled extremely fast and precise levels of heat to be applied to the e-waste, allowing the team to successfully recover a number of different metals.
Tests saw the team effectively separating tantalum from used capacitors, gallium from discarded light-emitting diodes (LEDs), and indium from used solar conductive films.
The precise control over reaction conditions provided by the technique allowed the team to achieve a metal purity of more than 95% and a yield of over 85%.
The researchers now intend to adapt the process to recover other critical metals from waste streams and believe that their method holds promise for extracting lithium, a crucial ingredient in many battery technologies.
It could also potentially be used on other industrial waste and even crude ores from mining.
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