Magnetics Business & Technology - September/October 2022 - 22

RESEARCH & DEVELOPMENT
Game-Changing Rare-Earth Elements Separation Technology Licensed to Marshallton
ogy. " We're excited to further explore what these new extractants
can achieve. "
REEs are commercially separated using liquid-liquid extraction,
which uses ligands - organic molecules composed of carbon,
hydrogen, oxygen, and nitrogen atoms - as extractants to selectively
bind the REE ions. An oily solvent containing the extractant
is vigorously mixed with an REE-rich aqueous solution, then
allowed to separate in the same manner as oil and vinegar for
salad dressing. During this process, the REEs get transferred
into the organic solvent forming complexes with the extractant
molecules. DGAs show higher affinity for lanthanides with smaller
ionic radius, which allows individual REEs to be separated from
one another in multiple stages.
Santa Jansone-Popova, left, and Ilja Popovs quantify rare-earth element
concentrations in liquid samples using a spectroscopy instrument.
Credit: Genevieve Martin/ORNL, U.S. Dept. of Energy
A new technology for rare-earth elements chemical separation
has been licensed to Marshallton Research Laboratories, a North
Carolina-based manufacturer of organic chemicals for a range of
industries.
Developed by scientists from Oak Ridge National Laboratory and
Idaho National Laboratory in the Department of Energy's Critical
Materials Institute, or CMI, the technology provides insight into
how to cost-effectively separate in-demand rare-earth elements,
which could dramatically shift the industry to benefit producers in
the United States.
The unique electronic properties of rare-earth elements, or REEs
- a group of 17 metallic elements that includes 15 lanthanides
plus yttrium and scandium - make them critical for producing
electronics, optical technologies, alloys and high-performance
magnets. These powerful, permanent magnets are vital to clean
energy technology and defense applications.
Individual REEs do not occur in minable concentrations in the
Earth's crust, but are naturally mineralized together and must be
chemically separated to use for technological applications. Their
physical and chemical similarities make them extremely difficult
and costly to separate while generating a lot of waste. Extraction
and separation of REEs for technological applications occurs
largely overseas.
To meet the growing need for these materials and to limit the
nation's reliance on foreign sources, ORNL and INL scientists
working under the banner of CMI, a DOE Energy Innovation Hub
led by Ames Laboratory, have applied their deep expertise in
chemical synthesis, separations, and engineering to design and
produce new extraction agents based on diglycolamide, or DGA,
ligands and a corresponding process for separating lanthanides
that outperforms current technology.
" At Marshallton, our purpose is to become a domestic, strategically
reliable supplier of DGA extractants for rare-earth elements.
We expect to service pilot-plant and commercial operations in ore
processing, recovery from mining tailings and recycling, " said Mac
Foster, co-owner of Marshallton and a collaborator on the technol " Our
goal was to identify an extractant that surpasses the performance
of the state-of-the-art ligands that are currently used in
industry, " ORNL's Santa Jansone-Popova said. " The compound
widely used is a phosphorous based extractant, called PC88A,
and since its selectivity is relatively low, a lot of separation stages
are required along with generation of additional waste throughout
the process. "
Selectivity refers to the degree to which a solvent prefers one
metal over another and is described by a unit called separation
factor. For example, when seeking to separate adjacent lanthanides
neodymium and praseodymium - both used in high-powered
magnets - the phosphorus-based extractant's separation
factor is around 1.2, which is very low.
" You have to run the extraction many, many times to separate adjacent
lanthanides completely. We need to improve the economics
of the process, reduce the waste, reduce the complexity - limit
the steps it takes to achieve separation, " Jansone-Popova said.
ORNL's Chemical Science Division had been experimenting
with an alternative DGA called TODGA, which has a separation
factor of 2.5 - already a big improvement over the phosphorusbased
extractant. However, a key variable in the economics of
the process is loading capacity - how many grams per liter of
extractants can be held in the organic solvent without adverse
reactions. TODGA could only handle about one-fifth of what the
phosphorous-based extract could.
" The extractant concentrations we were limited to were not
adequate compared to the industry standard. At higher concentrations,
we run into things like gelling or precipitation, which are
detrimental to the process, " said Kevin Lyon, an INL chemical
engineer with expertise in applied solvent extraction who tested
and developed the process design for the licensed technology. " If
you think of the process as a conveyor belt, we want to be able to
load that conveyor belt up as high as we can, or at least competitive
with what industry does, to make it cost effective. "
Jansone-Popova recognized that by chemically modifying the
structure of DGAs, she might improve their properties and their
efficiency in extracting REEs.
Her team at ORNL began a systematic approach to making
structural changes to the DGA ligands by adding a range of
substituents known as alkyls - fatty organic groups that exclusively
contain hydrogen and carbon atoms. These groups can
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