Electronic cards and boards contain valuable metals. image credit: piqsels.com.
A group of engineers at the University of Iowa were inspired by nature's work to grow stalagmites and stalactites in caves, which are spike-like structures formed by chemical precipitation. Through the controlled application of oxygen and temperature, researchers have reported that they can separate a metal from the rest of the components by slowly moving more reactive components to the surface, where they grow by forming spikes of metal oxides, similar to stalagmites in caves.
According to the research results, the less reactive components are left in a liquid core of purified metal surrounded by fragile spikes of metal oxides, forming a structure they call a "ship in a bottle." Their results were recently reported in the journal Materials Horizons.
The method makes use of the inherent gradient of free energy and composition that form the thin surface layers of metallic alloys, taking advantage of this gradient to drive the order and selective separation of materials on the surface, allowing the enrichment of the core with the materials of lower oxide reduction potential. Thus demonstrating that purification can be achieved through surface oxide engineering and selective core enrichment.
On the surface of the alloy, the growth of metal oxides in the form of peaks is promoted as the nucleus is enriched. Image designed by @emiliomoron.
This method has a great potential to achieve metal de-alloying and purification by controlling the surface oxidation, adjusting the oxidation by regulating the temperature, oxidant composition and composition, achieving particles of different morphology. This would offer an alternative to conventional electrochemical separation methods, which require high temperatures and consume a lot of energy.
On the other side, the researchers assure that the method could also be applied to achieve the distribution of certain metallic species on a surface, which would open immense possibilities in the design of more selective and specialized catalysts.
There is no doubt that we need new procedures for the recovery of precious metals from electronic waste, methods that allow economically viable recovery in order to take advantage of the metals in these components and reduce the exploitation of the earth's minerals, in addition to using methods with much lower energy consumption, something that would also have positive effects on the environment.
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