Can Green Plants Mine Key Minerals?

As demand for electric vehicles spikes, so does the demand for nickel — a key ingredient in lithium-ion batteries.

But extracting nickel from the ground is difficult, and its presence depends on geology. The U.S. currently operates just one active domestic mine, the Eagle Mine located in Michigan’s remote Upper Peninsula; as a result, the nation’s manufacturers needed to import $3.6 billion worth of the metal last year, nearly half from Canada alone.

Now Stevens professors Dibs Sarkar and Christos Christodoulatos, working with researchers from Michigan Technological University (MTU) and NJIT, are testing a sustainable alternative to supply the metal domestically while also leaving a light footprint on the landscape. It’s called phytomining — and it uses plants to extract useful metals from stubborn or exhausted soils.

The U.S. Department of Energy was impressed enough with the idea to recently award MTU, Stevens and NJIT $1.9 million, through its Advanced Research Projects Agency (ARPA-E), in support of the effort to conduct a demonstration project that could prove this innovative concept works in real life.

Plant biology to do the heavy lifting

How can green plants do the work of picks, shovels and heavy equipment? It all comes down to plant biochemistry.

Certain plants, known as hyperaccumulators, draw proportionally larger amounts of nickel into their leaves and stems as they grow, explains Sarkar. The class of flowering plants known as Phyllanthacea, for instance — which includes bushweed and bishopwood — are particularly adept at chemically locating and extracting bits of nickel from soil they grow in. However, nickel has to exist in a soluble, phytoavailable form before plants can take it up through their roots.

In a Stevens greenhouse, the team will grow combinations of nickel-friendly plants in boxes of waste soils brought from former mining sites as well as soils sampled from serpentine barrens — small pockets of metallic, nutrient-poor soils that occur in an arc from southern New Jersey to northern Virginia on the east coast and from California to Washington on the west coast.

The research group will also tinker with the plants’ growing environment.

“There are various ways we can modify and study plants’ inherent biological and chemical phytomining mechanisms,” Sarkar explains. “Natural, biodegradable compounds such as citric acid added to a soil, for instance, make any nickel compounds in it more soluble and available.” “You can also introduce specific bacteria that release organic acids as they grow, helping break down the nickel-rich minerals in soils so that plants can absorb them more easily.”

Biosensors will enable the team to monitor nickel levels in the test plants in real time, giving the group — and the nation — a window into the optimal combinations of chemical and microbiological systems that might one day usefully extract the metal while also sustaining the grown to extract it.

If the pilot project proves successful, Sarkar adds, the team will conduct larger-scale field studies and begin new research into plants’ properties as natural cleansers and filters of contaminated soils.