Rare earth elements, or REEs, are very much in the news these days.
That’s because China continues to control 96% of the world’s REEs, which are crucial for today’s technology, including America’s F-35 stealth fighter.
Both the US and EU are scrambling to close that gap, but it’s clear China will maintain its REE dominance for years to come, though it has so far not used it as a political bargaining chip.
The fact is, although REEs are not actually rare, they tend to be spread thinly throughout the earth’s crust rather than concentrated in a single place, which limits opportunities for mining them at scale.
And the elements are often found together in the ground and share similar chemistry, requiring separation processes that involve large amounts of energy and organic solvents.
These difficulties mean that it is neither economically feasible nor environmentally friendly to extract and separate REEs from anything but high-grade ores using existing technology.
The same challenges apply to waste materials containing low but potentially valuable concentrations of REEs, including ash left by burning coal, runoff from mines, and waste electronic items.
A team led by Joseph A. Cotruvo Jr. at Pennsylvania State University and Dan M. Park at Lawrence Livermore National Laboratory has now developed an alternative process that could tap these sources without requiring organic solvents, improving access to REEs while helping to avoid industrial waste, Chemical & Engineering News reported.
According to the team, a protein that binds REEs could be used to extract and separate these valuable metals from low-grade sources, such as coal ash or even electronic waste.
The REEs include the 15 lanthanides, along with scandium and yttrium, and many are in high demand for products such as electric vehicles, wind turbines and light-emitting diodes.
The new process relies on lanmodulin, a small acid-resistant protein with a very strong affinity for lanthanides. It is produced by certain methane-digesting bacteria.
The researchers attached the protein to porous microbeads in a column.
As an acidic solution of metal ions passes through the column, lanmodulin snatches the REEs out of the solution while allowing others, such as copper or zinc, to pass right through, the report said.
The REEs can then be freed by changing the pH of the solution or by adding a counterion such as citrate to chelate the REEs. Acid from the process, and the columns themselves, can be reused many times, Cotruvo says.
The team tested the purification column on a solution leached from coal ash. One pass through the column was enough to produce an enriched solution in which 88% of the metal ions were REEs, a 2,000-fold improvement in purity.
“It’s impressive, because it’s starting at less than 0.1% rare earths, so it’s a really large upgrading,” Cotruvo says.
By carefully adjusting the pH, the researchers could draw REEs from the column in two separate batches containing lighter and heavier REEs, respectively.
The technique could also completely separate mixtures of two REEs, including neodymium and dysprosium, which are commonly found together in electronic waste containing rare-earth magnets, the report said.
“If we’re going to recycle electronic waste, this is one of the most important separations,” Cotruvo says.
Starting with a solution that mimicked the composition of such waste, the researchers used several separation cycles to recover more than 80% of each element, each at more than 99% purity.
“It’s a nice demonstration of how a natural system can be used, pretty much unaltered, to solve this problem of separating lanthanides,” says bioinorganic chemist Lena J. Daumann of Ludwig Maximilian University Munich.
“This protein-based approach, once scaled up and optimized for a continuous process, could be a really promising technique for low-grade sources.”
REE are almost ubiquitous in modern technology because they’re incredibly useful.
They are the “vitamins of chemistry,” says Daniel Cordier, a mineral commodities specialist for rare earths at the U.S. Geological Survey.
“They help everything perform better, and they have their own unique characteristics,” he says, “particularly in terms of magnetism, temperature resistance and resistance to corrosion.”
Those characteristics have helped REEs find homes in everything from flat-panel TVs and smart phones to anti-lock brakes and air bags in cars, from sunglasses and crystal to lasers and smart bombs.
Each stealthy F-35 strike fighter requires 920 pounds of rare-earth material, according to DOD. Each Arleigh Burke DDG-51 destroyer requires 5,200 pounds. An SSN-774 Virginia-class submarine needs 9,200 pounds.
However, there are many environmental and health issues associated the production, processing, and utilization of REEs.
Which is why Cotruvo’s discovery could be of great importance.
At a larger scale, multiple separation columns could be linked to run continuously, and tweaking conditions such as pH, flow rate and other factors should also improve the column’s performance, the report said.
Sources: Chemical & Engineering News, Smithsonian magazine, Air Force magazine, US Department of Defense