Rare earth elements like neodymium and lanthanum make possible technologies that many have come to rely on like smartphones and computer hard drives. They’re also used in solar panels and wind turbines that generate cleaner, more sustainable energy.
These elements are not actually that rare. But mining and isolating them relies on fossil fuels and creates toxic waste.
“So we’re actually kind of destroying the environment to make a green economy to get these metals,” said Colleen Doherty, an associate professor at North Carolina State University.
In a greenhouse in West Raleigh, Doherty is exploring an alternative to the harsh practices of mining rare earth elements.
“And plants are actually really quite good at taking up these metals that we need,” she said.
Doherty’s working with a plant called pokeweed which can grow to be over 10 feet tall with red stalks and purple berries. It is native to North America and typically grows along the edges of wooded areas.
And this prolific plant has a special power.
Plants absorb a variety of nutrients through their roots, eventually ‘taking them up’ into their stalks and leaves, Doherty explained. Along with essential nutrients, pokeweed is particularly good at taking up rare earth elements as well.
These metals are usually not found in high enough quantities in regular soil for the pokeweed to do much with. But researchers have found an unexpected source: coal waste.
Using toxic waste instead of creating it
Edmaritz Hernandez Pagan, a PhD student who works with Doherty, explained that the lab grows the pokeweed in acid mine drainage. This is a type of industrial waste that results from water becoming contaminated by coal mining activity.
“And it's shown to contain a lot of toxic metals, but also rare earth elements. And we are basically testing how pokeweed uptakes the rare earth elements,” Hernandez Pagan said.
This process would involve isolating rare earth elements from existing industrial waste, instead of creating more waste to mine them. Doherty said this is just the kind of low-carbon footprint solution she envisioned.
But while pokeweed is relatively good at absorbing rare earth elements, the elements still need to be extracted and isolated to be used for manufacturing. Doherty said researchers have been developing methods to do that.
“So right now, the current method of extraction is just to incinerate the plants, and that just contributes to the CO2,” she said.
Doherty and her team are collaborating with researchers at Virginia Tech to develop alternatives to extracting the elements that don’t involve burning the plants.
This group is not alone in trying to tap into acid mine drainage as a source of rare earth elements. But drawing on the power of plants sets them apart. And while other efforts could potentially do this at a larger scale, they would also require more extensive infrastructure. Doherty sees the pokeweed as part of a smaller-scale and complementary solution that could be implemented closer to sites of contamination.
She said this work is a long way from providing these elements for our smartphones and solar panels. But the progress she and her team have made working on this project so far has made her optimistic.
“We came into this as kind of skeptics that this is unrealistic and not going to happen,” Doherty said. “And the more we dig into it, the more we're like, 'wait, this isn't that unrealistic.'”
Doherty hopes that someday mining the rare earth elements from this acid mine drainage could even incentivize efforts to clean up areas the waste has polluted.
