While working with the molten semiconductor, antimony sulphide, it found that by adding another layer that is a very good ionic conductor on top of the material, electrolysis began to work very well, separating the metal out of the sulfide compound to form a pool of 99.9% pure antimony at the bottom of their cell. Antimony can’t normally be processed using the electrolytic method, which is used to produce aluminium by applying an electric current.
Lead researcher, Donald Sadoway, explained: “Antimony sulfide is a very good conductor of electrons. But if you want to do electrolysis, you only want an ionic conductor – that is, a material that is good at conducting molecules that have a net electric charge.”
In typical smelting processes, the sulfur would immediately bond with oxygen in the air to form sulfur dioxide, a significant air pollutant and the major cause of acid rain. But instead this contained process provides highly purified metal without the need to worry about scrubbing out the polluting gas.
“Electrolysis is much more efficient than traditional heat-based smelting methods, because it is a single-step continuous process,” Sadoway said. “The discovery of that process is what transformed aluminium, more than a century ago, from a precious metal more valuable than silver into a widely used inexpensive commodity.”
If the process could be applied to other common industrial metals such as copper, nickel and other metals, it would have the potential to significantly lower prices as well as reduce the air pollution and greenhouse gas emissions associated with traditional production.
“Though the higher melting temperatures of other metals add complication to designing an overall production system, the underlying physical principles are the same, and so such systems should eventually be feasible,” concluded Sadoway.