These Plants Could Mine Valuable Metals From the Soil With Their Roots

The renewable energy transition will require a huge amount of materials, and there are fears we may soon face shortages of some critical metals. US government researchers think we could rope in plants to mine for these metals with their roots.

Green technologies like solar power and electric vehicles are being adopted at an unprecedented rate, but this is also straining the supply chains that support them. One area of particular concern includes the metals required to build batteries, wind turbines, and other advanced electronics that are powering the energy transition.

We may not be able to sustain projected growth at current rates of production of many of these minerals, such as lithium, cobalt, and nickel. Some of these metals are also sourced from countries whose mining operations raise serious human rights or geopolitical concerns.

To diversify supplies, the government research agency ARPA-E is offering $10 million in funding to explore “phytomining,” in which certain species of plants are used to extract valuable metals from the soil through their roots. The project is focusing on nickel first, a critical battery metal, but in theory, it could be expanded to other minerals.

“In order to accomplish the goals laid out by President Biden to meet our clean energy targets, and support our economy and national security, it’s going to take [an] all-hands-on-deck approach and innovative solutions,” ARPA-E director Evelyn Wang said in a press release.

“By exploring phytomining to extract nickel as the first target critical material, ARPA-E aims to achieve a cost-competitive and low-carbon footprint extraction approach needed to support the energy transition.”

The concept of phytomining has been around for a while and relies on a class of plants known as “hyperaccumulators.” These species can absorb a large amount of metal through their roots and store it in their tissues. Phytomining involves growing these plants in soils with high levels of metals, harvesting and burning the plants, and then extracting the metals from the ash.

The ARPA-E project, known as Plant HYperaccumulators TO MIne Nickel-Enriched Soils (PHYTOMINES), is focusing on nickel because there are already many hyperaccumulators known to absorb the metal. But finding, or creating, species able to economically mine the metal in North America will still be a significant challenge.

One of the primary goals of the project is to optimize the amount of nickel these plants can take in. This could involve breeding or genetically modifying plants to enhance these traits or altering the microbiome of either the plants or the surrounding soil to boost absorption.

The agency also wants to gain a better understanding of the environmental and economic factors that could determine the viability of the approach, such as the impact of soil mineral composition, the land ownership status of promising sites, and the lifetime costs of a phytomining operation.

But while the idea is still at a nebulous stage, there is considerable potential.

“In soil that contains roughly 5 percent nickel—that is pretty contaminated—you’re going to get an ash that’s about 25 to 50 percent nickel after you burn it down,” Dave McNear, a biogeochemist at the University of Kentucky, told Wired.

“In comparison, where you mine it from the ground, from rock, that has about .02 percent nickel. So you are several orders of magnitude greater in enrichment, and it has far less impurities.”

Phytomining would also be much less environmentally damaging than traditional mining, and it could help remediate soil polluted with metals so they can be farmed more conventionally. While the focus is currently on nickel, the approach could be extended to other valuable metals too.

The main challenge will be finding a plant that is suitable for American climates that grows quickly. “The problem has historically been that they’re not often very productive plants,” Patrick Brown, a plant scientist at the University of California, Davis, told Wired. “And the challenge is you have to have high concentrations of nickel and high biomass to achieve a meaningful, economically viable outcome.”

Still, if researchers can square that circle, the approach could be a promising way to boost supplies of the critical minerals needed to support the transition to a greener economy.

Image Credit: Nickel hyperaccumulator Alyssum argenteum / David Stang via Wikimedia Commons

Edd Gent
Edd Gent
I am a freelance science and technology writer based in Bangalore, India. My main areas of interest are engineering, computing and biology, with a particular focus on the intersections between the three.
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