New research from scientists at Penn State and Lawrence Livermore National Laboratory (LLNL) demonstrates how a protein isolated from bacteria can provide a more environmentally friendly way to extract rare earth elements from unconventional sources such as mine tailings and electronic waste and separate them from other metals and from each other. An open access article on the work is published in the journal ACS Central Science.
Low Rare Earth Element (REE) sources, for example from industrial waste, usually contain many rare earth elements and other mixed metals. The new method relies on a protein called lanmodulin (LanM) which first binds to all rare earth elements in the source. Then the other metals are drained and removed. By changing the conditions of the sample, for example changing the acidity or adding ingredients called chelators, individual types of rare earth elements are no longer bound and can be collected. Even when a sample contains very low amounts of rare earth elements, this new procedure successfully extracts and separates heavy rare earth elements with high purity. Credit: Dong et al. 2021, ACS Central Science
In order to meet the growing demand for rare earth elements for use in emerging clean energy technologies, we need to address several challenges in the supply chain. This includes improving the efficiency and reducing the environmental burden of the extraction and separation processes of these metals. In this study, we demonstrate a promising new method using a natural protein that could be extended to extract and separate rare earth elements from low-grade sources, including industrial waste.
—Joseph Cotruvo Jr., Assistant Professor and Louis Martarano Career Development Chemistry Professor at Penn State and Co-Corresponding Author
Since the United States currently imports most of the rare earth elements it needs, a new emphasis has been placed on establishing a domestic supply from unconventional sources, including industrial waste from the burning of coal and the extraction of other metals as well as electronic waste from cell phones and many other materials. These sources are large but considered to be low grade, as the rare earths are mixed with many other metals and the amount of rare earths present is too low for traditional processes to work properly. In addition, current extraction and separation methods rely on harsh chemicals, are labor intensive, sometimes involve hundreds of steps, produce a high volume of waste, and are expensive.
The new method takes advantage of a bacterial protein called lanmodulin, previously discovered by the research team, which binds almost a billion times better to rare earth elements than to other metals.
The extraction and subsequent separation of individual rare earth elements (REEs) from raw materials containing REEs is a difficult but essential task for the growth and sustainability of renewable energy technologies. As an important step in overcoming the technical and environmental limitations of current rare earth processing methods, we demonstrate a scheme for extracting and separating biobased and fully aqueous rare earths using the earth-selective lanmodulin protein. rare.
Lanmodulin has been conjugated to porous support materials using thiol-maleimide chemistry to allow purification and tandem separation of rare earths under continuous flow conditions. The immobilized lanmodulin maintains the attractive properties of the soluble protein, including remarkable rare earth selectivity, the ability to bind rare earths at low pH, and high stability over many low pH adsorption / desorption cycles.
We further demonstrate the ability of immobilized lanmodulin to achieve high purity separation of the critical rare earth pair for clean energy Nd / Dy and transform low grade leachate (0.043 mol% rare earth) into fractions. heavy and light rare earths (88 mol% total rare earth purity) in a single column run while using ∼ 90% column capacity. This ability to achieve, for the first time, tandem extraction and pooled separation of rare earths from highly complex aqueous raw material solutions without the need for organic solvents makes this anmodulin-based approach an important advance for hydrometallurgy. sustainable.
The protein is first immobilized on tiny beads inside a column – a vertical tube commonly used in industrial processes – to which the liquid source material is added. The protein then binds to the rare earth elements in the sample, which allows only the rare earths to be retained in the column and the remaining liquid to be evacuated. Then, by changing the conditions, for example changing the acidity or adding additional ingredients, the metals break off from the protein and can be drained and collected. By carefully changing the conditions in order, the individual rare earth elements could be separated.
The research team separated yttrium (Y) from neodymium (Nd) – both abundant in primary deposits of rare earths and coal byproducts – with a purity greater than 99%. They also separated neodymium from dysprosium (Dy) – a crucial pairing common in electronic waste – with purity above 99.9% in just one or two cycles, depending on the initial composition of the metal.
The high purity of the recovered neodymium and dysprosium is comparable to other separation methods and was achieved in as many or fewer steps without the use of harsh organic solvents. Because the protein can be used for many cycles, it offers an attractive environmentally friendly alternative to the methods currently in use.
—Ziye Dong, LLNL postdoctoral researcher and first author
The researchers don’t think their method will necessarily supplant the current liquid-liquid extraction process that is commonly used for high-volume production of lighter rare earth elements from high-quality sources. Instead, this will allow efficient use of low grade sources and in particular for the extraction and separation of the rarer and generally much more valuable heavy rare earths.
Other recent methods are capable of extracting rare earth elements from low content sources, but they usually stop at a “total” product which includes all the rare earths, which is relatively low in value and must. then be channeled into more conventional schemes. for further purification of individual rare earth elements. The value really lies in the production of individual rare earths and especially the heavier elements.
—Dan Park, LLNL researcher and co-corresponding author
The researchers plan to optimize the method so that fewer cycles are required to obtain the purest products and that it can be extended to industrial use.
If we can design derivatives of the lanmodulin protein with greater selectivity for specific elements, we could recover and separate the 17 rare earth elements in a relatively small number of steps, even from the most complex mixtures, and without any organic solvent or toxic chemicals, which would be very serious. Our work shows that this goal must be achievable.
—Joseph Cotruvo Jr.
This work was supported by the Critical Materials Institute, an energy innovation center funded by the US Department of Energy and the DOE Office of Science.
Ziye Dong, Joseph A. Mattocks, Gauthier J.-P. Deblonde, Dehong Hu, Yongqin Jiao, Joseph A. Cotruvo and Dan M. Park (2021) “Bridging hydrometallurgy and biochemistry: a protein-based process for the recovery and separation of rare earth elements’ ACS Central Science do I: 10.1021 / acscentsci.1c00724