Researchers have developed a process for recovering the precious metals in our electronic devices using the astonishing properties of water heated to 500 degrees.
The printed circuits in our electronic devices contain precious metals including among other things gold (one metric ton of electronic boards contains as much as a kilo of gold!), silver, copper and a variety of less well known strategic metals such as tantalum, which are commonly referred to as "rare earths".
Separating and recovering these resources, intertwined and welded onto layers of conductive or insulating material, is no easy task. In Orleans in France, a team of researchers from the CNRS institute of combustion aerothermal reactivity and environment (Icare) has attempted to meet this challenge... using water! When subjected to extreme conditions (in this case, heated beyond its critical temperature and subjected to very high pressure), the water in fact reaches a so-called "supercritical" state and acquires new physical properties.
Supercritical water is obtained at more than 374 degrees Celsius at a pressure greater than 218 bar. It then becomes a very powerful solvent, capable of breaking down organic substances. France’s atomic energy commission (CEA) makes use of this super water, for example to "clean" and recycle radioactive waste. It is also used in the food industry to dissolve the caffeine in coffee beans.
In the Orleans laboratory, water is heated to 500 degrees and is pressurized at 250 bar in order to extract the raw materials from the printed circuits. The aim is to "destroy" the polymers which support and hold these components on the electronic circuit board. Made of carbon, they are unable to resist the corrosive effect of the supercritical water.
An alternative to incineration
Ultimately, the treatment of waste using supercritical water (hydrothermal oxidation) could be an interesting ecological alternative - notably to industrial incineration, which releases pollutants and does not allow all the waste to be treated.
This process could provide a new source of precious metals. Europe spends billions of euros every year on importing strategic metals, but they are becoming scarcer. It could also be another useful technique for recycling electronic waste - which is challenging from an environmental, technical and economic point of view.
However, the process developed in Orleans has not been fully perfected and has to be adapted to the materials that will be treated. The CNRS reports that an industrial scale pilot project is underway in northern France. If the tests prove successful, the project promoters could become the leading European producers of tantalum.
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