Harvesting metal from plants that suck it out of the ground

"Hyperaccumulator" plants grow in metal-rich soil—and suck a huge amount of metal out of the ground.

If you cut open the leaf of a hyperaccumulator plant, you get sap that's blue-green, because it's fully 25% nickel. That's an astonishingly high concentration; it's higher than the ore that goes into a nickel smelter.

This leads to a fun idea: What if, instead of mining rare minerals the traditional way—digging into the ground, a technique that requires tons of energy and damages the local ecosystem—you farmed them? Plant huge farms of hyperaccumulators on metal-rich soil, cut 'em when they mature, and extract the minerals. It even has a badass name: "Phytomining".

A group of scientists and farmers are currently experimenting with this wild idea. They've published a paper about it here—"The first tropical 'metal farm'"—and the New York Times recently covered their experiments:

They have the potential to remedy the mining industry's biggest problem: abandoned mines, which pollute waterways. A leftover mine, planted with hyper-accumulators, could salvage the remaining metals for additional revenue. That incentive could persuade companies to invest in rehabilitation or mine-waste cleanup.

Currently, the most common way to extract nickel for electronics requires intense energy — often derived from coal and diesel — and creates heaps of acidic waste. A typical smelter costs hundreds of millions of dollars and requires increasingly scarce ore that is at least 1.2 percent rich with nickel.

In contrast, plants on a small nickel farm could be harvested every six months on land where the nickel concentration is only 0.1 percent. After two decades, the roots would struggle to find enough nickel, but the land would have been sucked dry of its toxic metals, and fertile enough to support more common crops.

If you want to dive into the academic literature, there are a ton of papers and book chapters at the web sites of two of the researchers noted in that story, Alan Baker and Antony van der Ent.

(That CC-4.0-licensed photo of a hyperaccumulator tree, above, is courtesy Antony van der Ent!)