Harvesting metal from plants looks promising
Some of Earth’s plants have fallen in love with metal. With roots that act practically like magnets, these organisms — about 700 are known — flourish in metal-rich soils that make hundreds of thousands of other plant species flee or die.
Slicing open one of these trees or running the leaves of its bush cousin through a peanut press produces a sap that oozes a neon bluegreen. This “juice” is actually one-quarter nickel, far more concentrated than the ore feeding the world’s nickel smelters.
The plants not only collect the soil’s minerals into their bodies but seem to hoard them to “ridiculous” levels, said Alan Baker, a visiting botany professor at the University of Melbourne who has researched the relationship between plants and their soils since the 1970s. This vegetation could be the world’s most efficient, solar-powered mineral smelters. What if, as a partial substitute to traditional, energy-intensive and environmentally costly mining and smelting, the world harvested nickel plants?
Baker and an international team of colleagues have set their sights on convincing the world that the idea is more than just a fun thought experiment. On a plot of land rented from a rural village on the Malaysian side of the island of Borneo, the group has proved it on a small scale. Every six to 12 months, a farmer shaves off 1 foot of growth from these nickel-hyperaccumulating plants and either burns or squeezes the metal out. After a short purification, farmers could hold in their hands roughly 500 pounds of nickel citrate, potentially worth thousands of dollars on international markets.
Now, as the team scales up to the world’s largest trial at nearly 50 acres, their target audience is industry. The researchers hope that in a decade a sizable portion of insatiable consumer demand for base metals and rare minerals could be filled by the same kind of farming that produces the world’s coconuts and coffee.
Phytomining, or extracting minerals from hyperaccumulating plants, cannot fully replace traditional mining techniques, Baker said. But the technology has the additional value of enabling areas with toxic soils to be made productive. Smallholding farmers could grow on metal-rich soils, and mining companies might use these plants to clean up their former mines and waste and even collect some revenue.
“It’s icing on the cake,” Baker said.
The father of modern mineral smelting, Georgius Agricola, saw this potential 500 years ago. He smelted plants in his free time. If you knew what to look for in a leaf, he wrote in the 16th century, you could deduce which metals lay in the ground below.
Rufus Chaney, an agronomist at the U.S. Department of Agriculture for 47 years, coined the word “phytomining” in 1983 and with Baker helped begin the first trial in Oregon in 1996. His name is immortalized in one of the nickel-sucking plants used in the Malaysian plot.
“The hope is that we can show it off and have proof of concept and show people how it works, and that it works,” added Antony van der Ent, a plant scientist at the Sustainable Minerals Institute at the University of Queensland in Australia. His dissertation began the Malaysian project.
Nickel is a crucial element in stainless steel. Its chemical compounds are increasingly used in batteries for electric vehicles and renewable energies. It is toxic to plants, just as it is to humans in high doses.