New processing methods developed by researchers at MIT could help alleviate looming shortages of essential metals that power everything from phones to automotive batteries, by making it easier to separate these rare metals from mining ores and recycled materials.
Selective adjustments within a chemical process called sulfidation allowed metallurgy professor Antoine Allanore and graduate student Caspar Stinn to successfully target and separate rare metals, such as cobalt in a lithium-ion battery, mixed materials.
As they report in the newspaper Nature, their processing techniques allow metals to remain in solid form and to be separated without dissolving the material. This avoids the traditional but expensive methods of separating liquids which require significant energy. The researchers developed processing conditions for 56 items and tested these conditions on 15 items.
Their sulfurization approach, they write in the article, could reduce the investment costs of separating metals to between 65 and 95 percent of mixed metal oxides. Their selective treatment could also reduce greenhouse gas emissions by 60 to 90% compared to traditional liquid separation.
“We were excited to find alternatives for processes that consumed a lot of water and generated greenhouse gas emissions, such as recycling lithium-ion batteries, recycling rare earth magnets and separating rare earths, ”says Stinn. “These are processes that fabricate materials for durability applications, but the processes themselves are very unsustainable.”
The results offer a way to reduce the growing demand for minor metals like cobalt, lithium and rare earth elements that are used in clean energy products like electric cars, solar cells and wind turbines producing electricity. electricity. According to a 2021 report by the International Energy Agency, the average amount of minerals needed for a new unit of power generation capacity has increased by 50% since 2010, as renewable energy technologies using these metals extend their reach.
Selectivity opportunity
For more than a decade, the Allanore group has been studying the use of sulfur-containing materials in the development of new electrochemical pathways for the production of metals. Sulphides are common materials, but scientists at MIT experiment with them under extreme conditions such as very high temperatures – from 800 to 3,000 degrees Fahrenheit – which are used in manufacturing plants but not in a typical university lab.
“We are looking at very well established materials under unusual conditions compared to what has been done before,” explains Allanore, “and that’s why we find new applications or new realities”.
In the process of synthesizing sulfur-containing materials at high temperatures to support electrochemical production, says Stinn, “we’ve learned that we can be very selective and very controlled over the products we make. And it was with this understanding that we realized, “OK, maybe there is an opportunity for selectivity in separation here.”
The chemical reaction exploited by researchers causes a material containing a mixture of metal oxides to react to form new metal-sulfur or sulphide compounds. By altering factors such as temperature, gas pressure, and the addition of carbon in the reaction process, Stinn and Allanore found that they could selectively create a variety of sulphide solids that could be physically separated by various methods, including grinding the material and sorting different sulfides of reduced size or using magnets to separate the different sulfides from each other.
Current methods of separating rare metals rely on large amounts of energy, water, acids and organic solvents that have costly environmental impacts, says Stinn. “We are trying to use abundant, economical and readily available materials for sustainable material separation, and we have expanded this area to now include sulfur and sulphides. “
Stinn and Allanore used selective sulfurization to separate economically important metals like cobalt in recycled lithium-ion batteries. They also used their techniques to separate dysprosium – a rare earth element used in applications ranging from data storage devices to optoelectronics – from rare earth boron magnets or the typical mixture of oxides available from mining minerals such as bastnaesite.
Leverage existing technology
Metals like cobalt and rare earths are only found in small amounts in mined materials, so industries must process large volumes of materials to recover or recycle enough of these metals to be economically viable, Allanore explains. “It’s pretty clear that these processes are not efficient. Most of the emissions come from the lack of selectivity and the low concentration at which they operate.
By eliminating the need for liquid separation and the additional steps and materials required to dissolve and then reprecipitate individual elements, the process of MIT researchers dramatically reduces costs incurred and emissions produced during separation.
“One of the advantages of separating materials using sulfurization is that many existing technologies and process infrastructures can be exploited,” says Stinn. “These are new conditions and new chemistries in established reactor styles and equipment. “
The next step is to show that the process can work for large amounts of raw materials, for example by separating 16 elements from rare earth extraction streams. “Now we have shown that we can handle three, four or five of them together, but we have yet to process an actual flow from an existing mine at a scale corresponding to what is required for deployment. Says Allanore.
Stinn and his colleagues in the lab have built a reactor that can process around 10 kilograms of raw material per day, and the researchers are starting conversations with several companies about the possibilities.
“We are discussing what it would take to demonstrate the performance of this approach with existing mineral and recycle streams,” said Allanore.
