Many rare earth elements and metals are mixed together in low-grade rare earth elements (REE) sources, such as industrial waste. The new method of extraction and separation relies on a protein called Lanmodulin (LanM), which first binds all the rare Earth elements in the source. After that, other metals can be drained and then removed. Individual rare earth elements can be collected by altering the conditions of the sample. This includes changing the acidity of adding chelators or changing the pH. This new method can extract and separate heavy rare earth elements from samples with low levels of rare Earth elements. Credit: Dong et al. 2021, ACS Central Science
A new method allows for the separation and extraction of rare earth elements. This group of 17 elements is critical to technologies like smart phones and electric cars batteries. Researchers at Penn State and Lawrence Livermore National Laboratory have demonstrated that a protein extracted from bacteria can be used to extract these metals as well as to separate them from other elements and each other in a more eco-friendly way. This method could be scaled up in the future to provide a domestic supply for rare earth metals.
Joseph Cotruvo Jr. is assistant professor and Louis Martarano career development Professor of Chemistry at Penn State. He was also a member Penn State's Center for Critical Minerals and one of the co-corresponding authors on the study. This includes improving the efficiency of these metals' extraction and separation processes and reducing the environmental impact. This study demonstrates a promising new method that uses a natural protein to extract rare earth elements from low-grade, industrial wastes.
The United States imports the majority of its rare earth elements. This has led to a renewed focus on creating a domestic supply from alternative sources. These include industrial waste from coal mining and other metals, as well as cell phone and other electronic waste. These rare earths can be found in many different metals, and are therefore considered low-grade. Additionally, the current methods of extraction and separation are labor-intensive, often involve hundreds of steps and produce large amounts of waste.
This new method uses a bacterial protein called Lanmodulin that was previously discovered by the research team. It is nearly a billion times more effective at binding to rare metals than other metals. The process is described in a paper published online by ACS Central Science on Oct. 8.
First, the protein is immobilized on tiny beads in a column, a vertical tube that is commonly used in industrial processes. Next, the liquid source material is added. The protein binds to the rare Earth elements in the sample. This allows only the rare earths in the column to be retained and any liquid to be drained. You can then change the conditions by adding or changing acidity, and the metals will no longer bind to the protein. The metals can then be removed from the column and can be collected. Individual rare earth elements can be separated by carefully altering the sequence of conditions.
Cotruvo said that they first showed that the method was extremely effective at separating rare earth elements from other metallics. This is crucial when working with low-grade sources with a lot of metals. Even in complex solutions where less than 0.1% are rare earths, which is an extremely low percentage, we were able to extract and separate a grouping the lighter rare Earths from a grouping the heavier rare earths in just one step. This is a crucial step in simplifying the process because rare earths must be separated into their individual elements so that they can be integrated into technology.
The research team isolated yttrium from neodymium, which are both abundant in primary rare Earth deposits and coal byproducts with greater than 99.9% purity. The research team also separated dysprosium (Dy), a critical pairing found in electronic waste with greater than 99.9% purity, in one or two cycles depending on the initial metal composition.
Ziye Dong (a postdoctoral researcher at LLNL) said that the high-purity of the reclaimed neodymium or dysprosium was comparable to other methods. The separation process took as few steps as possible without the use of harsh organic solvents. The protein can be used for multiple cycles and is therefore an eco-friendly option to current methods.
Researchers don't believe their method will replace the current liquid-liquid extraction method that is used to produce lighter rare earth elements in large quantities from high-grade resources. It will instead allow for efficient use and separation of rarer, more valuable heavy rare Earths.
"Other methods can extract rare earth elements from low grade sources, but they usually stop at a total' product which contains all the rare Earths. This has relatively little value and must then be funnelled into more conventional schemes to further purify individual rare earth elements," Dan Park, staff scientist at LLNL, and co-author of the study. "The real value lies in the production and use of individual rare earths, especially those with heavier elements."
Cotruvo said, "Our process is especially convenient because these high value metals can be purified from the column first."
Researchers plan to optimize the process so that it requires fewer cycles to produce the highest-purity products. Then, the process can be scaled up to industrial use.
Cotruvo stated that if we can create derivatives of the Lanmodulin protein with greater selectivity to specific elements, we could extract and separate all 17 rare Earth elements in a relatively short number of steps even from complex mixtures. This would be a huge deal without using any organic solvents and toxic chemicals. Our work supports this goal.
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Ziye Dong et. al., Bridging Hydrometallurgy & Biochemistry: A Protein Based Process for Recovery & Separation Rare Earth Elements. ACS Central Science (2021). Information from the Journal: ACS Central Science Ziye Dog et. al., Bridging Hydrometallurgy & Biochemistry: A Protein Based Process for Recovery & Separation Rare Earth Elements. (2021). DOI: 10.1021/acscentsci.1c00724
