Everyone knows that China's strategic rare earths monopoly
is not built on top of mines but refinement.
China's extraction and purification dominance not
only grants them economic leverage they are more than willing to use;
But also puts them first in line for future breakthroughs and new
applications using these elements since Chinese researchers have such a plentiful supply of it.
Rare earths refinement as it is done now is dirty and damaging. And since we don't need
a lot of rare earths, it is hard to find scale. How to get around this? So let's talk bacteria.
## Beginnings
There are about 15 to 17 valuable rare earth elements.
They are used in a variety of industries. Like magnets for the green energy and EV
industries. They are also used in flat screens, fiber optics, MRI machines, and more. Their
roles are small but critical. You don't need a lot of them, but nothing works without them.
The ironic thing about rare earth elements is that a few of them are
found everywhere. In China they are added to fertilizers to encourage plant growth. Thus,
we have seen concentrations of it accumulating in plants, animals, and people.
Anyway, so they are everywhere. The problem is finding them in
large enough concentrations to economically pull out. Generally
that is from ore deposits of minerals like bastnasite, monazite, and xenotime.
Unfortunately their chemical properties are very similar to one another,
which makes separating and purifying them challenging.
## Refinement
These ores need to undergo a refinement process in order to get the desired elements.
The exact process depends on the specific element and the ore they are refining,
but what follows is a brief conceptual review.
After the ore rocks are mined, we roast them in different ways at over
300 degrees Celsius in the presence of acids. We want to remove moisture,
decompose some of the minerals, and prepare them for later steps.
Here, we may do some extra steps like gravitation or Flotation to further concentrate the ores in
preparation for refinement. Flotation is pretty gross. We add a bunch of chemicals
to a slurry of ore and water which causes the stuff we want to rise to the surface as froth.
Gravitation is where we use centrifuges to separate specific minerals or elements
from others based on their weight. After gravitation and flotation, we have a more
concentrated slurry that is ready for the core hydrometallurgical steps - starting with leaching.
Leaching is where we pour acids over the cracked and roasted rocks with
the goal of dissolving the elements out of the ores. What acid we leach
with again depends on the element - could be either hydrochloric or sulfuric acids.
Now we have a liquid of acid and some rare earth elements. We can use either
ion exchange or solvent extraction to do the core work of separating the REEs. The former is
still sometimes used for specialty elements, but solvent extraction is more commercially scalable.
The basic concept behind solvent extraction is that we mix the leached liquid with a second,
organic liquid in such a way to cause ions to travel from the first to the
second liquid. After this is done, you have a reasonably pure rare earth
concentration that undergoes further work for 99% purity.
We know little about how China performs these processes at scale, but we do
know that it is a massive ecosystem involving over a hundred companies.
Processing is also energy intensive and potentially damaging to the environment
due to the chemicals involved. For instance, I just mentioned flotation.
Solvent exchange also leaves behind a real mess that is not easy to clean up.
Needless to say, the whole processing chain is a formidable capital-intensive
foundation that is difficult to match. Can we find a better way to get around all this?
## Bacteria
In recent years, there has been a lot of work done in using bacteria in an
industrial setting to produce or refine specific chemicals.
For instance, Hyaluronic Acid or HA is a chemical found in the body's connective
and neural tissues. Because it is an important component in repairing skin,
we use it for cosmetics, skincare, and tissue engineering products.
To produce it at industrial scale, we extract it from animal tissues. Namely, the combs of
roosters. Which seems to me like ... well, at least they are using every part of the bird.
Another, less-bird-deforming way was discovered in the 1990s,
when we identified a gene in the Streptococcus bacteria that made
HA. We smash that gene like it's the YouTube Like button and let it rip.
Furthermore, there has been a lot of work done with regards to using bacteria as an eco-friendly
method for cleaning up heavy metal pollution, especially in sewage runoff from mines. There
is a lot of overlap here with rare earths refinement so let us take a look into it.
## Biosorption
There are several mechanisms by which we can use bacteria to separate rare earths from a
liquid but I think there are two economical options. I like one more than the other.
The first and most well studied is biosorption,
which is a subcategory of a process called adsorption.
This is where ions floating around in a liquid attach themselves onto a solid,
biological surface. Like hair to a balloon.
Adsorption happens because of a passive chemical or physical interaction between
the target rare earth element and something on the cell's outer membrane called a biosorbent.
Key is that the organism doesn't have to use energy. In other words, the bacteria can be dead,
which helps because REEs are toxic and often kill bacteria at higher concentrations.
Killing the bacteria might be preferable if we have to modify the biosorbents using
physical methods to improve their specificity and effectiveness.
I know there may be serious ethical questions about killing bacteria for
capitalist profit but let us set those aside for
now. And it is not always the case we need to kill the bacteria first.
Bacteria do not even necessarily have to be involved. There have been promising experiments
with biological materials like algae, fungi, bamboo charcoal and even leaf powder. Algae-based
methods seem particularly promising, but using bacteria offers various advantages.
First, the bacteria can be pre-treated to be very selective to a particular element. Second,
the ratio of each bacteria's cell membrane surface area to its weight is very high. Since
biosorption happens on the cell wall, the more cell wall that we have available, the better.
## Bioaccumulation
Another studied methodology has been bioaccumulation.
Bioaccumulation refers to when certain chemicals and metals accumulate within
an organism over time. The example that I always think of is mercury in tuna.
Bioaccumulation is different from biosorption because in order for
it to work the bacteria has to be alive and actively taking in the rare earth
elements. This makes it particularly difficult to study, scale and predict,
since it requires that we also understand the complexities of cell metabolism.
Science has discovered some bacteria living in extreme situations that
actively interact with various metal and rare earth ions. We can use this.
One interesting 2019 study done in South Africa brought up some of these bacteria up from hot
vents and cultivated them in low-concentration mixes containing the rare earth element europium.
They discovered that the bacteria thrived in the presence of low levels of europium.
And electron microscope readings discovered the presence of small
granules of europium carbonate collected by the bacteria and stored inside itself.
Europium is used for scintillators for X-rays and as a phosphor for producing the blue light
in LEDs. Before it can be used for that, it needs to be further refined, of course.
At the heart of it though, I see some economic challenges with bioaccumulation. Sourcing and
growing these unique, special bacteria will be hard. Moreover the challenge of keeping
them alive as they slowly accumulate rare earths inside their bodies.
## A Promising Biosorption Option
So let us go back to biosorption. Can we really use such a system to separate rare earths?
There was a fascinating 2017 techno-economic analysis done
by the Idaho National Laboratory. They built an airlift bioreactor, which is a vessel designed
to cultivate a good cell environment through a constant injection of air.
The reactor is used to grow some bacteria - Caulobacter crescentus and E. coli - that
have been previously bio-engineered to have on their cell wall surface,
a tag that attaches to the lanthanides.
Other studies have identified Arthrobacter nicotianae - a Gram
Positive soil bacteria sometimes found in cheese - or Bacillus subtilis - a
well studied bacteria used for industrial production.
The lanthanides are a subcategory of 15 rare earths from lanthanum
to lutetium. It includes the most widely used rare earth, neodymium.
The Idaho team studied several candidates for "feedstock" of various types, sources,
and qualities into the reactor. Candidates included the traditional ores, coal ash,
rare earth clays that have been leached with acids, and fracking wastewater.
To do the biosorption, they secured the bacteria in biofilms on top of a
solid substrate of high density polyethylene discs. Having them
secured and immobilized like this makes it easier to remove them later on. Future
studies would move to beads rather than discs due to higher adsorption capacity.
You load them into the reactor along with the REE-containing solution. Inside, the reactor
bubbles air through a chamber such that the discs can gently circulate around the chamber.
This is done until the cells have reached 90% of their adsorption capacity. Then
we take the discs out and then strip the rare earths using a citrate solution. The
biofilm discs can then be reused - about ten cycles before needing a new biofilm.
After the rare earths are desorbed out of the discs,
we solidify them and then roast them to achieve increasingly higher purities.
All of these are well-established technologies. The Idaho team discovered that rare earth ores had
the cheapest cost of production but the recovered REEs did not command high prices on the market.
So surprisingly, it was the coal fly ash collected from
22 coal fired plants around the United States that was most profitable. This
was due to the presence of higher value REEs - scandium and cerium.
## Scandium
The identifying of coal fly ash as a potential feedstock for certain high
value REEs was very interesting. But there are several caveats.
The most significant item is that 90% of the REE
sale proceeds from the 2017 coal fly ash test came from scandium.
Scandium is widely used in ceramics, glass, and certain steel alloys, but its market price
is volatile. Furthermore, the global market need is minuscule - about 10-25 tons a year.
Not a lot compared to the most widely used rare earth - neodymium. In 2022,
we used an estimated 16,000 tons of it for permanent magnets alone. Would be
nice to source and process some of that locally.
And the dark irony of it all is that scandium is one of the
few rare earths not monopolized by China. Gosh.
Now, there are other feedstocks that we can use. For instance,
low-grade lignite coal from North Dakota is known to have very small
amounts of neodymium - far less than the ores of China's Bayan Obo mine. There
also seems to be potential in pulling REEs out of mining waste and electronic waste.
## Economics
Biosorption has been studied for over sixty years, with over 13,000 published papers.
However the technology - even outside of REE refinement - has still not yet
been widely implemented in industrial practice. In various feasibility studies,
costs exceed revenues especially when scandium prices are low.
Significant cost factors include the use of acid in order to leach the feedstocks
before they go into the bioreactor. One of the feasibility studies pointed to
not only the economic benefits of using less acid, but also environmental ones.
Second, there was the cost of sourcing and preparing the immobilizing biofilm
matrix for the bacteria - another 2019 study at Idaho National Laboratory highlighted the
cost savings of using silica nanoparticle gel beads over polyethylene to embed the bacteria.
Third, is the general need to streamline and optimize the biosorption process itself. Notably,
the number of times we can reuse the microbe beads before needing to be
replaced. The more cycles they last, the more profitable the final enterprise is.
None of these seem like insurmountable obstacles and feels like something that
some well-targeted policy might be able to solve.
## Conclusion
Even if we decide that REE refinement by bacteria is not able to take down
the Chinese rare earths giant, it might be still worth pursuing for two reasons.
First, is the need to build local supply chain independence for these valuable rare
earth elements. The threat continually hangs over other technology areas and
biosorption looks to be a greener and cheaper way to do processing.
And second, we should consider them anyway for the sake of safety. These were built from
wastewater technologies. It is known that REEs are toxic and carcinogenic. Being able to get
these out of e-waste and other products for future reuse is a win for everyone.
I hope to start seeing more work and efforts done in moving these rare earth
element biosorption technologies towards mass commercialization.