On a field in northern Albania, farmers are working between rows of yellow mustard plants, bringing in their harvest: nickel.

What's planted here is one of about 700 hyperaccumulating species — plants that accumulate high amounts of metals from the ground, such as nickel, zinc, copper, even gold and rare earth elements.

They evolved to store these metals in their shoots, leaves or sap. It's their little toxic trick, a defense against predators and pathogens. For the plants themselves, the metals are harmless.

From cleaning up contaminated soil to mining metals

Scientists first used such plants in the 1980s to clean up soils that had been contaminated by mines or smelters. One plant was even able to remove small amounts of radioactive cesium from the soil of the Chernobyl nuclear disaster site.

But it wasn't until the 1990s that the scientists asked: what if we used all those precious metals collected by the plants? They called the idea: phytomining.

Fast forward 30 years, and planting flowers to actually "mine" metals is on the brink of becoming a business. But can this really take on huge industrial mines?

Phytomining as a business model

On the field in Albania, there is too much nickel in the soil to grow food crops with good harvest. But then there's also not enough nickel to set up a conventional mine. This makes it an ideal place for phytomining, according to Eric Matzner, co-founder of startup Metalplant, which is behind the 10-hectare field near the town of Tropoje.

"The minimum target we are looking for is around a third of a ton of nickel per hectare," he said.

The Odontarrhena plants suck up the metal and store it. Once harvested and dried, about 2% of their dry weight is nickel. Metalplant grind and burn the plants, leaving an ashy concentrate, or "bio-ore." The ash gets washed and, by using sulfuric acid, turned into a liquid. It's then filtered and crystallized into nickel sulfate, a resource that is in high demand for use in large batteries, like those in electric cars.

Toxic tailings and waste in conventional mining

"The environmental impact of phytomining is low," said Antony van der Ent. A researcher with Wageningen University in the Netherlands, he is one of the world's busiest phytomining researchers and adviser to Botanickel, another company in the field.

Conventional metal mining can severely harm the environment, and often involves deforestation of large areas of land. It may produce toxic tailings and waste that can leak into the environment and poison people and wildlife. Because of the energy-intensive processing, it often comes with high greenhouse gas emissions. With 10 to 59 tons of emissions per ton of metal, nickel is especially polluting.

Phytomining, on the other hand, is climate-friendly. "A tremendous amount of carbon is captured by the metal crop. It is released back into the atmosphere during incineration of the plants, but that means you obtain highly pure nickel at close to zero carbon emission," said van der Ent.

Phytomining also targets land that lies barren and is deemed unsuitable for agriculture because of the metals in the ground.

"This land is being cleaned from the metals in the soil. Afterwards, it could probably be used for forestry or for recreational purposes," said Rupali Datta, a biochemist with Michigan Tech University who's done extensive research on phytomining.

World hunger for EV batteries fuels nickel demand

While plants are able to suck out different types of metal, scientists and companies have been applying phytomining almost exclusively to nickel harvesting: The metal is known to be abundant in the topsoil in many parts of the world, in countries like Indonesia, the Philippines, Brazil, South Africa, or the US.

Meanwhile, demand for nickel is set to grow rapidly, according to the International Energy Agency, expected to double by 2050 fueled by the global hunger for EV batteries. However, most of the supply comes from Chinese-owned mines in Indonesia where concentrations in soils are high. Phytomining could serve as an alternative in countries with lower nickel contents, helping them to secure their own supply.

Is phytomining worth it?

Strategic research firm BloombergNEF estimated that phytomining would be too expensive for buyers of nickel. Metalplant wouldn't disclose how much it cost them to harvest the metal, but say they aim to match the price of any other nickel on the market.

"The goal is to get demonstrations of the price parity. We call it a green advantage or green dividend where you get a better product for equally the same cost," said Metalplant's Matzner. The startup also combines farming with carbon capture, for which they can sell carbon credits, to make it worth their while.

In their now third season, Metalplant said they harvested more than three tons of nickel on their 10-hectare field in Albania. That is what scientists elsewhere hope to achieve, too. But it pales in comparison to conventional mines where the same amount is being extracted in just about half an hour. 

Can phytomining replace conventional mines?

To match the annual output of one conventional nickel mine, a field would need to be the size of about 200,000 hectares. That's 2.5 times the size of New York City. To replace the current global conventional nickel production entirely, 15 million hectares of fields would be needed — an area the size of Tunisia.

"Economies of scale really play a key role," said Kwasi Ampofo, a metals market analyst at BloombergNEF. "The bigger it gets, the cheaper it gets. But for phytomining, the challenge hasn't been the cost. It has been land."

"Phytomining can definitely not replace conventional mining. It can be an additional process," biochemist Datta told DW. And monoculture fields at the scale of thousands of hectares would not be so environmentally friendly after all. "Wherever you're doing intensive farming, you're using fertilizer, pesticides, water — all of these are also applicable for phytomining," said Datta. 

According to researcher van der Ent, smaller communities struggling to grow food crops stand the most to gain from this type of mining. "That's where I see the potential," he said, adding that locals could turn a small profit from selling nickel while cleaning up their soil.

Edited by: Sarah Steffen