New 'green' way to produce metals found

MIT scientists have discovered a new 'green' and less expensive method to produce metals without causing air pollution.
Researchers were trying to develop a new battery, but thanks to an unexpected finding in their tests, they discovered a whole new way of producing the metal antimony - and potentially a new way of smelting other metals.
The discovery could lead to metal-production systems that are much less expensive and that virtually eliminate the greenhouse gas emissions associated with most traditional metal smelting, researchers said.
Although antimony itself is not a widely used metal, the same principles may also be applied to producing much more abundant and economically important metals such as copper and nickel.

"We were trying to develop a different electrochemistry for a battery. We wanted to investigate the utility of putting a second electrolyte between the positive and negative electrodes of the liquid battery," said Donald Sadoway from Massachusetts Institute of Technology (MIT) in the US.
However, the experiment did not go as planned.

"We found that when we went to charge this putative battery, we were in fact producing liquid antimony instead of charging the battery," said Sadoway.
The material they were using, antimony sulfide, is a molten semiconductor, which normally would not allow for the kind of electrolytic process that is used to produce aluminium and some other metals through the application of an electric current.

"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," said Sadoway.
By adding another layer on top of the molten semiconductor, one that is a very good ionic conductor, it turned out the electrolysis process worked very well in this "battery," separating the metal out of the sulfide compound to form a pool of 99.9 per cent pure antimony at the bottom of their cell.
In typical smelting processes, the sulphur would immediately bond with oxygen in the air to form sulphur dioxide, a significant air pollutant and the major cause of acid rain.

However, instead this contained process provides highly purified metal without the need to worry about scrubbing out the polluting gas.
"The thing that made this such an exciting finding is that we could imagine doing the same for copper and nickel, metals that are used in large quantities," said Sadoway.
The research was published in the journal Nature Communications.