Inspired by nature’s work to build spiky structures in caves, engineers have developed a method to recover precious metals from electronic waste. Using controlled applications of oxygen and relatively low temperatures, the engineers say they can de-alloy a metal by slowly moving the most reactive components to the surface, where they form stalagmitelike spikes of metal oxides. That leaves the least-reactive components in a purified, liquid core surrounded by brittle metal-oxide spikes.
The structure formed when the metal is molten is analogous to filled cave structures such as stalactites or stalagmites. Instead of water, the team used oxidation to create the structures. The work demonstrates the controlled behavior of surface oxidation in metals and its potential in design of new particle structures or purification/de-alloying. By tuning oxidation via temperature, oxidant partial pressure, time, and composition, a balance between reactivity and thermal deformation enables unprecedented morphologies that could be useful in recovering precious metals from e-waste or mixed-metal materials.
The team demonstrated that traditional electrochemical or high-temperature methods (above 1,832 °F) may not be necessary in metal purification, as the metal’s reactivity can be used to drive separation. The oxidation technology works well at temperatures of 500 to 700 °F.
Besides metal purification and recovery, the method could also be applied to metal speciation — the ability to dictate creation and distribution of certain metal components. One use could be production of complex catalysts to drive multi-stage reactions.