New method to produce metals developed

MIT researchers attempting to create a new battery have uncovered a new way to produce antimony, as well as smelting other metals.

According to MIT, “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.”

While antimony is not a commonly used metal, MIT says the method can be applied to more economically important metals such as copper and nickel.

Writing in academic journal Nature Communications, the John F. Elliott professor of materials chemistry Donald Sadoway explained, “We were trying to develop a different electrochemistry for a battery.”

The work was investigating an extension of the variety of chemical formulations for the all-liquid, high temperature storage batteries that his lab has been developing for several years.

“We wanted to investigate the utility of putting a second electrolyte between the positive and negative electrodes” of the liquid battery, he said.

However, much like the discovery of penicillin, the experiment did not go to plan and created an unexpected result.

“We found that when we went to charge this putative battery, we were in fact producing liquid antimony instead of charging the battery,” Sadoway said.

Sadoway, along with Huayi Yin and Brice Chung then tried to figure out what had happened.

The material they used was antimony sulphide, a molten semiconductor, which typically does not allow for the electrolytic processes used to produce aluminium and other metals.

“Antimony sulfide is a very good conductor of electrons,” Sadoway said.

“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.

However, through 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 sulphiide compound to form a pool of 99.9 percent pure antimony at the bottom of their cell, while pure sulphur gas accumulated at the top, where it could be collected for use as a chemical feedstock, MIT stated.

This process now reduces the potential for sulphur dioxide to form as it provides the highly purified metal without the need to scrub out the gas.

Sadoway added electrolysis is a better smelting method than traditional processes as it is a single step continuous process, and if it could now be applied to industrial metals such as copper it could drive down processing costs as well as emissions.

“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,” he said.

“Antimony was a good test vehicle for the idea, but we could imagine doing something similar for much more common metals,” Sadoway said.

“We see no reason why this approach couldn’t be generalised to oxide feedstocks,” which represent the other major category of metal ores. Such a process would produce pure oxygen as the secondary product, instead of sulphur.”

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