Chemical Engineering May 2020 - 11

MOFs and nanochannels enable lithium extraction from brines
UiO-66
L
is a key raw material
for batteries that power
electric vehicles, portable
electronics and more, but traditional
methods for obtaining it are
plagued by poor lithium recovery (a
large portion of Li is lost in the recovery
process), slow speed (thermal
evaporation of large brine ponds
takes months) and poor selectivity
(co-precipitation of magnesium
makes isolation difficult).
Now, development is progressing
on a technology that uses metalorganic
frameworks (MOFs) embedded
inside nanoscale channels
in a polymer membrane to selectively
separate lithium ions from salt
brines. The method is envisioned
as a more environmentally friendly
lithium-harvesting alternative to conventional
methods, such as mining
lithium-containing ores and evaporating
brine ponds under the sun.
Described in a recent paper in Nature
Materials, the technique was
pioneered by a collaborative team
ithium
nanocrystals). The MOFs form
complexes
MOFs (zirconium
with
carboxylic
oxide
acid
groups on the interior surface of the
PET nanochannels.
EnergyX
from the University of Texas (Austin),
Monash University (Melbourne, Australia)
and others, and is licensed for
commercialization by Energy Exploration
Technologies (EnergyX; Fort Lauderdale,
Fla.; www.energyX.com).
EnergyX is developing a system,
known as LiTAS, for separating Li
from brine that scales up the membrane
technique demonstrated by
the research team. To make the
membrane, nanoscale channels
are chemically etched into a thin
polymer film, such as polyethylene
terephthalate (PET), and filled with
A key aspect of the assembly is
an asymmetric nanochannel that allows
the MOFs to be packed at the
smaller end of the channel, while the
larger end is open for faster ion transport,
explains UT chemical engineering
professor Benny Freeman, who
is working with EnergyX. The result
is ion-sieving action at the MOF end
of the channel that is capable of selectively
transporting lithium ions. The
MOFs can sort ions based on their
dehydrated Bohr radius, so the membrane
is more permeable for Li ions
than for larger ions.
Along with industrial R&D partners,
EnergyX is scaling up membrane production
and integrating it into a commercial-scale
system. Pilot testing
using real-world brines is expected to
begin in the first quarter of 2021, says
Teague Egan, EnergyX CEO.
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Chemical Engineering May 2020

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