New Smelting Process Can Produce Metals With Less Air Pollution And Greenhouse Gas Emission


MIT researchers were conducting experiments with the aim of building better batteries when they discovered something different instead: a new and better way to smelt metal.

Study researcher Donald Sadoway said that they were attempting to come up with a different electrochemistry for a battery, but their experiment did not work out as planned. Instead, they found a new way to produce the metal antimony.

Although antimony is not a widely used metal, the method used to produce it can be applied to more important metals such as nickel and copper, which are commonly used in electronics.

The discovery, which was published in the journal Nature Communications on Aug. 24, could pave the way to more cost-efficient metal production systems that can also virtually reduce the emission of planet-warming greenhouse gas associated with traditional metal smelting.

Sadoway said that when they attempted to charge the supposed battery, they found out that instead of charging the battery, they were actually producing liquid antimony so they set out to know what happened.

The material Sadoway and colleagues used was antimony sulfide, a molten semiconductor considered as a good conductor of electrons. Under normal conditions, antimony sulfide would not allow the kind of electrolytic process used for producing aluminum and other metals when an electric current is applied.

Sadoway said that to do electrolysis, it is ideal to only use an ionic conductor, a material with a strong ability to conduct molecules that have a net electric charge. However, by adding a layer of a good ionic conductor on top of the antimony sulfide, the researchers found that the electrolysis process separates the metal out of the sulfide compound.

The process produced a pool of 99.9 percent pure antimony, which gathered at the bottom of the cell. Pure sulfur gas, on the other hand, accumulated at the top where it can be gathered and used as a chemical feedstock.

In a traditional smelting process, sulfur would immediately bond with the oxygen present in the air to form sulfur dioxide, an air pollutant that is known to cause damaging acid rain. The new process, however, offers purified metals sans the need to remove the polluting gas.

If the method can be used in the production of other industrial metals, it could potentially lower the cost of the process and reduce air pollution and greenhouse gas emissions that are associated with traditional metal production.

"As opposed to conventional extraction practices, direct sulfide electrolysis completely avoids generation of problematic fugitive emissions (CO2, CO and SO2), significantly reduces energy consumption, increases productivity in a single-step process (lower capital and operating costs) and is broadly applicable to a host of electronically conductive transition-metal chalcogenides," Sadoway and colleagues wrote.

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