On a recent afternoon in northern Albania, workers gathered armfuls of freshly cut shrubs covered in yellow flowers, leaving them to dry in the sun like hay. But this was no ordinary harvest. The farm is both a mine, growing plants that accumulate nickel metal in their leaves and stems, and a carbon sink, its soil spread with crushed rocks that remove carbon dioxide from the atmosphere.
“We’re able to turn the lowest-grade land in the world into some of the most lucrative land in the world,” says at Metalplant, the start-up behind the flower farm.
The idea of mining with plants and other metal-gobbling organisms isn’t new. Several companies and researchers aim to use greenery as a more environmentally friendly source of nickel for applications like electric vehicle batteries, and many other projects have used such plants to clean up contaminated soil. But only Metalplant is combining so-called “phytomining” with a method of removing CO2 from the atmosphere called enhanced rock weathering, which involves spreading large volumes of rock dust on farms. This dust can both capture CO2 and replenish the nickel taken up by the plants.
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Previous harvests have contained about 1 tonne of nickel, from which the company has extracted less than a kilogram of usable metal. But if the fields of yellow flowers perform as claimed, future harvests with larger yields could offer a supply of carbon-negative nickel that would avoid the worst impacts of mining.
Nickel is essential to power the transition away from fossil fuels, with demand to double to more than 6 million tonnes per year by 2040. Yet mining and refining it is environmentally destructive and emissions intensive: depending on where and how it is produced, a tonne of nickel now generates between of CO2. In Indonesia, the world’s largest supplier of the metal, have damaged ecosystems and working conditions at the plants have led to human rights abuses.
Phytomining for nickel avoids these problems, but it only works in places where there is a lot of the metal in the soil. For instance, a French company called Econick now has 100 hectares under cultivation in the Baltic states and is expanding in Malaysia, according to at Econick. Albania has long attracted interest due to the high nickel content of its soils: the mantle rocks that compose its mountains are made up of a mineral called olivine, which contains too little nickel for conventional mining, but enough to accumulate in certain plants.
Metallic soil is toxic for some flora, but native plants have adapted to tolerate it. “They take in nickel like a macronutrient,” says at the Agricultural University of Tirana in Albania, who is working with Metalplant. Some species – such as the yellow-flowered Odontarrhena decipiens that the company is growing on its farms – are capable of accumulating around 2 per cent of their dry weight as nickel.
Metalplant also uses Albania’s abundant olivine for its approach to carbon removal – its largest farm, in Tropojë, is adjacent to a quarry of olivine-rich rocks owned by , an Albanian-American mining industry magnate who is a co-founder of the company. According to Matzner, Muja has not invested in the company, which has so far raised $3.7 million from climate tech investors.
This enhanced rock weathering technique involves spreading olivine, or another silicate rock like basalt, onto fields. As the rocks dissolve, they react with CO2 in the atmosphere to form bicarbonate minerals that can store the planet-warming gas for millennia. Olivine’s high nickel content generally makes it unsuitable for use with food crops – it could contaminate the soil – but that could be an advantage in this case.
In June, company workers harvested the crop from 3 hectares, each of which was spread with a few dozen tonnes of olivine dust. After drying on the field, the plants will be heated to break down organic material. The ash will then be sent to a lab in Germany, where a chemical process will extract a greenish nickel salt, which can be used in existing EV battery production processes.
Depending on how efficiently the plants accumulated the nickel, the farm should yield between 200 to 400 kilograms of nickel per hectare says Matzner, enough for a handful of EV batteries. He says each tonne of nickel produced this way would be associated with as much as 200 net tonnes of CO2 removed, depending on how much olivine was put down.
Companies like those that produce electric vehicles could then include the resulting carbon-negative metal in their supply chains to offset their overall environmental impact, suggests Matzner. Selling the nickel could also be a way to subsidise CO2 removal, which has struggled to gain the investment needed to remove billions of tonnes of the greenhouse gas.
However, even if companies like Metalplant and Econick can cultivate very large areas with nickel farms, the volume of metal that could feasibly be produced is far too small to compete with conventional nickel mining, says at the University of Lorraine in France, who has extensively phytomining and is involved with Econick. Any environmental benefit “also depends on the way it is done”, she says.
Expanding phytomining farms on ecologically sensitive land could have the same environmental impacts as any other form of agriculture, for instance. Metalplant’s approach – using olivine dust from a quarry – also doesn’t avoid conventional mining. “I’m still worried about mining, extracting, crushing, transporting and spreading something,” says Echevarria. Based on his research on phytomining in Albania, he says adding the extra rock may even be unnecessary to replenish supplies of nickel in the soil, which are recharged over time by natural erosion and runoff.
But Matzner argues that mining olivine in Albania, where the rock is abundant at the surface, is a better option than stripping ecosystems in a place like Indonesia to get at high-grade nickel ore. And once it is spread on the fields, the normally energy-intensive process of refining the ore is as simple as tending to the farm, he says. “That is the energy of the sun concentrating the nickel in the plant.”
Article amended on 5 July 2024
We clarified Sahit Muja’s relationship to Metalplant.
