Scientists Perfect Technique to Harvest Metals from Trees

Nickel-rich sap being taken from a tree in Malaysia.

Image: Nickel-rich sap being taken from a tree in Malaysia. Image: Antony van der Ent

While metallic soils often kill plants, scientists have been studying certain species of trees that are able to thrive in these soils and store metals–like nickel–in their tissue and seeds as a result. As the New York Times recently wrote, “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?”

While this sounds like something straight out of Star Trek, there’s already a small scale tree farm in Borneo that’s shown these “metal crops” are feasible,

  • Every six to 12 months, a farmer shaves off one foot of growth from these nickel-hyper-accumulating 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.

How This Works: Extracting metals from trees is done through a process called “phytomining.” As the Ausimm Bulletin explained,

  • Phytomining is a method for literally ‘farming’ metals by growing hyperaccumulator plants (plants that are capable of growing in soil or water with very high concentrations of metals) and then harvesting the biomass rich in a particular metal.
  • The potential for phytomining is greatest for nickel because of the occurrence of specific soils that are naturally enriched in nickel and occur around the world.
  • Rufus Chaney from the United States Agricultural Department first envisaged phytomining in the early 1980s. He and Robert Brooks, Alan Baker, Roger Reeves and colleagues later embarked on extensive laboratory and field trials in the United States and elsewhere. This work has demonstrated that phytomining is not only possible, but also highly efficient in extracting metals from the soil.

The Opportunity: The Times also explained that “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. Where nickel is mined and refined, it destroys land and leaves waste.” Around the world in soils that are naturally rich in nickel scientists already know of numerous species of trees that absorb and store the metal.

Why This Matters: As the Guardian explained, extraction of nickel – predominately mined in Australia, Canada, Indonesia, Russia and the Philippines – comes at an environmental and health cost. In a clean energy future, we’ll need even more lithium-ion batteries which are largely made out of nickel and having a sustainable way to extract this metal will be critical. Researchers hope that developing methods of metal extraction from trees could eventually provide industry with enough base metals and rare minerals alike to meet its needs. In the future, if we’re able to extract metals from plants instead of traditional environmentally-taxing mining practices then we’ll be all the better for it.

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