Selective separation could help retrieve rare metals that are costly to mine

Image Credit: Rick Rothenberg

MIT researchers have developed a new processing method to help retrieve rare metals that are costly to mine and are getting increasingly harder to find. The technique is called “solid selective separation”, and it could replace liquid separation for at least 56 elements, 15 of which have already been tested successfully.

Compared to liquid separation, “selective separation” costs between 65% and 95% less, and it also reduces greenhouse gas emissions by 60% to 90%. It all boils down to using significantly less energy for the separation process, particularly for retrieving lithium and cobalt from batteries and performing rare-earth magnet recycling.

The MIT team has been experimenting with sulfides for over a decade and found that common materials during metal-sulfur compound formation behave very predictably in extremely high temperatures such as 3,000 degrees Fahrenheit (1,650 degrees Celsius). By adjusting gas pressure and adding carbon in the process, the scientists discovered that they could selectively create a variety of sulfide solids that can then be physically separated.

This neoteric process absolves retrieval procedures from using acids, organic solvents, distilled water, and large quantities of energy and time to go through tedious liquid separation stages. Also, the team proved that it’s possible to retrieve five or six rare earth metals from the same processed batch, which is significant.

For example, in conventional methods, engineers have to define a target metal and follow a process that retrieves a particular material. This limitation often makes smaller concentrations of other, potentially more valuable metals unretrievable or not worth the extra effort and generally increases the cost.

The best part of using sulfidation for the separation process is that the techniques, equipment, and involved materials already exist and aren’t highly sophisticated, exotic, experimental, or untested. As such, “selective separation” can be adopted at scale right away.

Bianca Van der Watt

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