MIT develops selective rare metal separation technology with lower costs and lower emissions

The new processing method developed by researchers at the Massachusetts Institute of Technology (MIT) can help alleviate the urgent shortage of basic metals in everything from telephones to automotive batteries, as it makes it easier to separate these rare metals from ores and recycled materials.

Metallurgy professor Antoine Allanore and his graduate student Caspar Stinn made selective adjustments in a chemical process called sulfidation, successfully targeting rare metals in mixed metal materials such as cobalt in lithium-ion batteries and separating them.

As they reported in Nature, their processing techniques allow metals to remain in solid form and separate without dissolving the material. This avoids traditional but expensive liquid separation methods that require a lot of energy. Researchers developed processing conditions for 56 elements and tested these conditions on 15 elements.

They pointed out in their paper that their vulcanization method can reduce the capital cost of metal separation from mixed metal oxides by 65% to 95%. In addition, compared to traditional liquid based separation, their selective treatment can also reduce greenhouse gas emissions by 60% to 90%.

"We are pleased to find alternatives to processes with very high water consumption and greenhouse gas emissions, such as lithium-ion battery recycling, rare earth magnet recycling, and rare earth separation. These are all processes for manufacturing materials for sustainable applications, but these processes themselves are very unsustainable," said Stinn.

These findings provide a way to alleviate the growing demand for small metals such as cobalt, lithium, and rare earth elements. It is reported that these small metals are used in "clean" energy products such as electric vehicles, solar cells, and wind turbines for power generation. According to a report by the International Energy Agency (IEA) in 2021, since 2010, with the expansion of renewable energy technologies using these metals, the average amount of minerals required for a new power generation capacity unit has increased by 50%.

Selective opportunities

For over a decade, the Allanore team has been researching the use of sulfide materials to develop new electrochemical routes for metal production. Sulfides are common materials, but MIT scientists are conducting experiments on them under extreme conditions. Extreme conditions include conditions such as extremely high temperatures - from 800 to 3000 degrees Fahrenheit - which are used in manufacturing plants but not in a typical university laboratory.

"We are studying very mature materials whose conditions are not common compared to what we have done before. That's why we are looking for new applications or new realities," Allanore said.

Stinn pointed out that in the process of synthesizing high-temperature sulfide materials to support electrochemical production, "we understand that we can have very selective and very controlled control over the products we manufacture. It is based on this understanding that we realize, 'Okay, maybe there is an opportunity for selectivity here'."

Researchers use chemical reactions to cause a material containing mixed metal oxides to react and then form new metal sulfur compounds or sulfides. By changing temperature, gas pressure, and adding carbon during the reaction process, Stinn and Allanore found that they can selectively create various sulfide solids that can be physically separated through various methods, including crushing materials and sorting sulfides of different sizes or using magnets to separate sulfides from each other.

Stinn stated that current rare metal separation methods rely on a large amount of energy, water, acids, and organic solvents, all of which have expensive impacts on the environment. "We are trying to use abundant, economical, and easily available materials for sustainable material separation, and we have expanded this field to include sulfur and sulfides now."

Stinn and Allanore use selective sulfidation to separate economically important metals, such as cobalt from recycled lithium-ion batteries. They also used their technology to separate dysprosium from rare earth boron magnets - a rare earth element used in applications ranging from data storage devices to optoelectronics, or to separate dysprosium from typical oxide mixtures of mining minerals such as fluorocarbon cerium ore.

Utilize existing technology

Allanore pointed out that metals such as cobalt and rare earths only exist in small amounts in the mined materials, so the industry must process large amounts of materials to retrieve or recover enough of these metals to be economically feasible. "Clearly, these processes are inefficient. Most of the emissions come from a lack of selectivity and low concentrations at which they operate."

By eliminating the need for liquid separation and the additional steps and materials required for dissolution and re precipitation of individual elements, MIT researchers have significantly reduced the costs and emissions required during the separation process.

"One benefit of using vulcanization to separate materials is that many existing technologies and process infrastructure can be utilized," Stinn said. "This is a new condition and new chemistry in existing reactor styles and equipment."

The next step is to demonstrate that the process can be applied to a large number of raw materials, such as separating 16 elements from rare earth ore streams. Allanore said, "We have now indicated that we can handle three, four, or five of them together, but we have not yet processed the actual flow from existing mines at a scale that meets deployment requirements."

It is reported that Stinn and colleagues in the laboratory have built a reactor that can process about 10 kilograms of raw materials per day, and researchers are starting discussions with several companies about the possibility.

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