A protein mines, sorts rare earths better than humans, paving way for
green tech

Date:
May 31, 2023
Source:
Penn State
Summary:
Rare earth elements, like neodymium and dysprosium, are a critical
component to almost all modern technologies, from smartphones to
hard drives, but they are notoriously hard to separate from the
Earth's crust and from one another. Scientists have discovered
a new mechanism by which bacteria can select between different
rare earth elements, using the ability of a bacterial protein to
bind to another unit of itself, or 'dimerize,' when it is bound
to certain rare earths, but prefer to remain a single unit, or
'monomer,' when bound to others.


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FULL STORY ==========================================================================
Rare earth elements, like neodymium and dysprosium, are a critical
component to almost all modern technologies, from smartphones to hard
drives, but they are notoriously hard to separate from the Earth's crust
and from one another.

Penn State scientists have discovered a new mechanism by which bacteria
can select between different rare earth elements, using the ability of
a bacterial protein to bind to another unit of itself, or "dimerize,"
when it is bound to certain rare earths, but prefer to remain a single
unit, or "monomer," when bound to others.

By figuring out how this molecular handshake works at the atomic level,
the researchers have found a way to separate these similar metals from
one another quickly, efficiently, and under normal room temperature
conditions. This strategy could lead to more efficient, greener mining
and recycling practices for the entire tech sector, the researchers state.

"Biology manages to differentiate rare earths from all the other metals
out there -- and now, we can see how it even differentiates between
the rare earths it finds useful and the ones it doesn't," said Joseph
Cotruvo Jr., associate professor of chemistry at Penn State and lead
author on a paper about the discovery published today (May 31) in the
journal Nature. "We're showing how we can adapt these approaches for rare
earth recovery and separation." Rare earth elements, which include the lanthanide metals, are in fact relatively abundant, Cotruvo explained,
but they are what mineralogists call "dispersed," meaning they're mostly scattered throughout the planet in low concentrations.

"If you can harvest rare earths from devices that we already have,
then we may not be so reliant on mining it in the first place," Cotruvo
said. However, he added that regardless of source, the challenge of
separating one rare earth from another to get a pure substance remains.

"Whether you are mining the metals from rock or from devices, you are
still going to need to perform the separation. Our method, in theory,
is applicable for any way in which rare earths are harvested," he said.

All the same -- and completely different In simple terms, rare earths
are 15 elements on the periodic table -- the lanthanides, with atomic
numbers 57 to 71 -- and two other elements with similar properties that
are often grouped with them. The metals behave similarly chemically,
have similar sizes, and, for those reasons, they often are found together
in the Earth's crust. However, each one has distinct applications in technologies.

Conventional rare earth separation practices require using large amounts
of toxic chemicals like kerosene and phosphonates, similar to chemicals
that are commonly used in insecticides, herbicides and flame retardants, Cotruvo explained. The separation process requires dozens or even hundreds
of steps, using these highly toxic chemicals, to achieve high-purity
individual rare earth oxides.

"There is getting them out of the rock, which is one part of the problem,
but one for which many solutions exist," Cotruvo said. "But you run into
a second problem once they are out, because you need to separate multiple
rare earths from one another. This is the biggest and most interesting challenge, discriminating between the individual rare earths, because
they are so alike.

We've taken a natural protein, which we call lanmodulin or LanM, and
engineered it to do just that." Learning from nature Cotruvo and his lab turned to nature to find an alternative to the conventional solvent-based separation process, because biology has already been harvesting and
harnessing the power of rare earths for millennia, especially in a class
of bacteria called "methylotrophs" that often are found on plant leaves
and in soil and water and play an important role in how carbon moves
through the environment.

Six years ago, the lab isolated lanmodulin from one of these bacteria,
and showed that it was unmatched -- over 100 million times better -- in
its ability to bind lanthanides over common metals like calcium. Through subsequent work they showed that it was able to purify rare earths as
a group from dozens of other metals in mixtures that were too complex
for traditional rare earth extraction methods. However, the protein was
less good at discriminating between the individual rare earths.

Cotruvo explained that for the new study detailed in Nature, the team identified hundreds of other natural proteins that looked roughly like
the first lanmodulin but homed in on one that was different enough
-- 70% different -- that they suspected it would have some distinct
properties. This protein is found naturally in a bacterium (Hansschlegelia quercus) isolated from English oak buds.

The researchers found that the lanmodulin from this bacterium exhibited
strong capabilities to differentiate between rare earths. Their studies indicated that this differentiation came from an ability of the protein
to dimerize and perform a kind of handshake. When the protein binds
one of the lighter lanthanides, like neodymium, the handshake (dimer)
is strong. By contrast, when the protein binds to a heavier lanthanide,
like dysprosium, the handshake is much weaker, such that the protein
favors the monomer form.

"This was surprising because these metals are very similar in size,"
Cotruvo said. "This protein has the ability to differentiate at a scale
that is unimaginable to most of us -- a few trillionths of a meter,
a difference that is less than a tenth of the diameter of an atom."
Fine-tuning rare earth separations To visualize the process at such
a small scale, the researchers teamed up with Amie Boal, Penn State
professor of chemistry, biochemistry and molecular biology, who is a
co-author on the paper. Boal's lab specializes in a technique called
X-ray crystallography, which allows for high-resolution molecular imaging.

The researchers determined that the protein's ability to dimerize
dependent on the lanthanide to which it was bound came down to a single
amino acid -- 1% of the whole protein -- that occupied a different
position with lanthanum (which, like neodymium, is a light lanthanide)
than with dysprosium.

Because this amino acid is part of a network of interconnected amino
acids at the interface with the other monomer, this shift altered how
the two protein units interacted. When an amino acid that is a key player
in this network was removed, the protein was much less sensitive to rare
earth identity and size.

The findings revealed a new, natural principle for fine-tuning rare earth separations, based on propagation of miniscule differences at the rare
earth binding site to the dimer interface.

Using this knowledge, their collaborators at Lawrence Livermore National Laboratory showed that the protein could be tethered to small beads in
a column, and that it could separate the most important components of
permanent magnets, neodymium and dysprosium, in a single step, at room temperature and without any organic solvents.

"While we are by no means the first scientists to recognize that metal- sensitive dimerization could be a way of separating very similar
metals, mostly with synthetic molecules," Cotruvo said, "this is
the first time that this phenomenon has been observed in nature with
the lanthanides. This is basic science with applied outcomes. We're
revealing what nature is doing and it's teaching us what we can do better
as chemists." Cotruvo believes that the concept of binding rare earths
at a molecular interface, such that dimerization is dependent on the
exact size of the metal ion, can be a powerful approach for accomplishing challenging separations.

"This is the tip of the iceberg," he said. "With further optimization of
this phenomenon, the toughest problem of all -- efficient separation of
rare earths that are right next to each other on the periodic table --
may be within reach." A patent application was filed by Penn State based
on this work and the team is currently scaling up operations, fine-tuning
and streamlining the protein with the goal of commercializing the process.

Other Penn State co-authors are Joseph Mattocks, Jonathan Jung, Chi-Yun
Lin, Neela Yennawar, Emily Featherston and Timothy Hamilton. Ziye Dong, Christina Kang-Yun and Dan Park of the Lawrence Livermore National
Laboratory also co- authored the paper.

The work was funded by the U.S. Department of Energy, the National
Science Foundation, the National Institutes of Health, the Jane Coffin
Childs Memorial Fund for Medical Research, and the Critical Materials Institute, an Energy Innovation Hub funded by the DOE, Office of Energy Efficiency and Renewable Energy, Advanced Materials and Manufacturing Technologies Office. Part of the work was performed under the auspices
of the DOE by Lawrence Livermore National Laboratory.

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========================================================================== Story Source: Materials provided by Penn_State. Original written by
Adrienne Berard. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Mattocks, J.A., Jung, J.J., Lin, CY. et al. Enhanced rare-earth
separation with a metal-sensitive lanmodulin dimer. Nature, 2023
DOI: 10.1038/s41586-023-05945-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/05/230531150125.htm

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