Researchers at the Iowa State University, Ames, USA, have developed a technology capable of recovering pure and precious metals from the alloys found in electrical waste. The process, which the team refers to as ‘metal whispering’, uses controlled applications of oxygen at relatively low temperatures to de-alloy a metal by slowly moving the most reactive components to the surface.
The technique leaves the least reactive components in a purified, liquid core surrounded by brittle metal-oxide spikes “to create a so-called ‘ship-in-a-bottle structure,’” states Martin Thuo, the leader of the research project and an associate professor of materials science and engineering at Iowa State University.
“The structure formed when the metal is molten is analogous to filled cave structures such as stalactites or stalagmites,” Thuo added. “But instead of water, we are using oxidation to create these structures.”
Thuo and the engineers in his research group want to control exactly how and where alloy components fall apart, or de-alloy. “It’s like being a metal whisperer,” he said. “We make things go the way we want.”
The engineers offered a more precise description in their paper ‘Passivation-driven speciation, dealloying and purification,’ published by the journal Materials Horizons. “This work demonstrates the controlled behaviour of surface oxidation in metals and its potential in design of new particle structures or purification/dealloying. By tuning oxidation via temperature, oxidant partial pressure, time and composition, a balance between reactivity and thermal deformation enables unprecedented morphologies.”
The technology works at lower temperatures of between 260°C and 370°C. Thuo continued, “What we demonstrate here is that the traditional electrochemical or high-temperature methods (above 1000°C) may not be necessary in metal purification as the metal’s reactivity can be used to drive separation.”
Besides metal purification and recovery, this new idea 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.