Down on the Farm That Harvests Metal From Plants

Proponents of phytomining see the greatest potential in Indonesia and the Philippines, two of the world’s biggest nickel ore producers, where hundreds of mines shovel topsoil into smelters. The two countries likely harbor many nickel-hyper-accumulating plants, but research has been scant.

Hyper-accumulators don’t just tolerate metals; their roots crave them. To what benefit? The nickel may help the plant fight off pests, or perhaps it enables the plant to more readily take up potassium, a scarce resource, from the soil. Regardless, there has been no need to genetically modify or selectively breed to increase the plants’ nickel-philia. Nature’s smelters are already as efficient as the extractive industry would want.

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.

That the nickel crop might be so productive and lucrative has led to fears that farmers might push for opening tropical forests for cultivation, foreshadowing another case such as palm oil, a cash crop that has devastated Borneo’s native forests. But that isn’t a likely outcome, the researchers said. Areas with the most phytomining potential tend to be grassy, and few other plants are likely to grow on land selected for mineral farming.

“We can grow these plants on soils where it’s already been deforested,” Dr. Baker said. “It’s a way of putting back, rather than taking away.”

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