Green metallurgical process uses surface energy to extract and refine metals from waste alloys

A team of scientists from the University of Melbourne and King Fahd University of Petroleum and Minerals (KFUPM) has made a discovery that could transform how metals are extracted and purified from crude metals and waste alloys. This new method, based on electrocapillary principles, enables the selective separation of metals from liquid alloys using differences in their surface energy, a concept previously unexplored in metallurgy.

Traditional metal refining relies on chemical differences between elements that often require high temperatures and produce harmful waste. Thermal methods, exploiting differences in melting and boiling points, are also used but tend to be energy-intensive and inefficient. However, the newly discovered process utilizes the differences in the surface energy of metals to separate them from one another.

In molten alloys, certain metals naturally migrate to the surface, enriching the interface based on their surface energy levels. In the new technology, crude metals and alloys can be dissolved into low-melting-point post-transition metals (like gallium, Ga) to form liquid alloys that remain fluid at or near room temperature.

When liquid alloys are placed in a special solution, they create a boundary layer (liquid-liquid interface). By applying a small electric charge to this layer, the surface tension of the alloy is reduced. This causes certain metals, specifically those with lower surface energy, like bismuth (Bi), tin (Sn), and lead (Pb), to move to the surface and separate from the mixture in a specific sequence. This process achieves high-purity metal separation without the need for high temperatures or harmful chemicals.

This innovation represents a shift towards greener low-energy metal recovery techniques. Unlike conventional smelting or chemical extraction, this method minimizes energy consumption and reduces environmental impact.

“The commercial application of our metal expulsion technology is expected to utilize proven renewable energy sources for achieving a net-zero process,” said Dr. Mohannad Mayyas, the lead scientist of the research. He added, “This discovery opens the door to sustainable metallurgy. We can now think about refining metals more efficiently, with far less energy and without chemical waste.”

Xichao Zhang, the study’s first author and a Ph.D. student at the University of Melbourne, highlighted the efficiency of the process: “The metal separation in our process is very rapid and allows us to achieve precise control over purity and particle size.”

The research team envisions future applications in processing several “hard-to-process” waste and metallurgical reject streams, including solder alloys, crude Ga, Pb dross, Pb bullion, and Betts anode slimes. The next phase of research aims to scale up the technology for industrial use at KFUPM. This breakthrough not only advances the field of materials science but also supports global efforts towards greener industrial processes and circular economy initiatives.

The paper “Electrocapillary-Driven Metal Expulsion in Post-Transition Metal-Based Liquid Alloys” is published in the journal of Advanced Functional Materials.

The research was conducted by scientists from the Departments of Chemical Engineering and Mechanical Engineering at the University of Melbourne, along with the Department of Materials Science and Engineering and the Interdisciplinary Research Center for Sustainable Energy Systems (IRC-SES) at King Fahd University of Petroleum and Minerals.

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King Fahd University of Petroleum & Minerals