Scientists look to mine metals from plants

A hyperaccumulator plant in northern Boreno suit able for phytomining. (Antony van der Ent)

Inside a lab at the University of Queensland in Brisbane, Australia, soil samples sit under a row of a glowing light bulbs hanging from a track only a short distance above them. In another room, a centrifuge hums as beakers of Nyquil-colored liquids sit on a nearby shelf. Standard white lab coats hang on hooks outside.

This generic-looking lab feels worlds away from the gritty, dusty mines of Australia—but this is where scientists hope to chart a new path for the industry here, and across the world.

If work being done at the Centre for Mined Land Rehabilitation catches on, it could mean new futures for global communities affected by resource-hungry strip-mining, and new ways for the mining industry to do business.

Australian scientists hope to accomplish this with phytomining—harvesting valuable metals from plants. Essentially, it’s growing plants containing nickel, zinc and cobalt—the bread and butter of the world’s mines, and harvesting the metals above ground, not below.

“We have identified a whole lot of new species which could be used for phytomining which weren’t previously known to science,” said Dr. Peter Erskine, one of the researchers working to make the process suitable for conventional mining companies.

So far, Erskine and his colleague Dr. Antony van der Ent, have discovered about 25 species of plants called ‘hyperaccumulators’ that take up high concentrations of metals from soil, that could form phytomining farms.

Erskine and van der Ent’s latest experiments with phytomining in remote northern Borneo show just how useful the emerging mining practice can be. It’s there that some of these hyperaccumulators thrive in soils rich in nickel. Just one mature tree of the right species can contain up to 11 pounds of nickel.

“I think nickel is the most promising type of metal for phytomining because it’s worth quite a bit of money—almost $20,000 per ton—and, there are very strong hyperaccumulators known for nickel,” van der Ent said.

So planting these hyperaccumulators in land that has already been strip-mined in places like the tropics, where the leftover soil is still rich in nickel but not worth exploiting through conventional mining, could allow for a new future for these otherwise barren areas.

“Stripping mining is pretty devastating for landscapes,” van der Ent said. “You essentially end up with land that’s not useful for many things. The soil is very nutrient-poor, so it’s very difficult to do any normal agriculture on it.”

But it is suitable for phytomining.

“These plants very happily grow in these types of soil,” van der Ent said.

That means locals who’ve reclaimed the barren land can harvest valuable metals, and also prevent erosion in these critically important rainforest areas.

It also gives mining companies another alternative for their post-mine land use, according to Erskine.

Harvesting the metal in the plants is simple, according to researchers. Just trim the leaves and shoots from the tops of the crops—like at a tea plantation—burn them to access the metal in the ashes, and allow the plants to regrow.

Researchers also believe phytomining has potential in places like South Africa, the U.S., Turkey, Greece, and Australia.

Money metals

Beyond nickel, researchers say valuable metals like zinc and cobalt are also suitable for phytomining.

Zinc is widely used in manufacturing and construction, nickel is used in stainless steel and coins, and cobalt is highly valued for its use in batteries.

Other potential applications of phytomining, and what’s called biorecovery, are for rare earth metals used in electronics, and platinum metals in cars and the chemical industry.

Gold is one other option that could be mined from plants. But researchers say chemicals like cyanide are needed to dissolve the metal to make it acceptable to plants.

“I think it would be quite a niche market,” van der Ent said. “You’d need to contain it in a [sealed or fully contained] environment. You can’t just add cyanide to the soil, it’s very toxic.”

Industry skepticism

While the idea of phytomining has been around for decades, it hasn’t been used commercially. Despite efforts by the mining industry to improve its sustainability and minimize environmental impacts, it has shown little interest in investing in phytomining.

University of Sydney professor Dr. Andrew Harris, who has also studied phytomining, isn’t sure there’s much value to the emerging mining technique. He says it’s often easier for companies to clean up mine sites by transporting the used soil to a sealed landfill.

Phytomining “is a niche solution to a small part of the mining value chain,” Harris said. “And I think the sum total of all of that means it just hasn’t progressed very much in the last few years.”

Even as research into its possibilities increases, there have still been no large-scale trials of phytomining anywhere in the world.

“I think if there is a successful large-scale demonstration, then it would be much more acceptable to conventional miners,” van der Ent said. “I guess there is a bit of skepticism at the moment to alternative ways of mining metals and minerals.”

Until those trials are successful, it could be difficult to convince an industry hesitant to adopt change.

“The mining industry isn’t famous for being quick off the mark, in terms of taking on new ideas,” according to Melbourne-based mining consultant Gerald Whittle. “Like any new technology, it doesn’t matter how wonderful it is, it is going to take a while.”

But Erskine and van der Ent are optimistic. They say phytomining is a low-cost, sustainable way to grow new life in areas around the world left for dead.