Botany professor Alan Baker finds 9 percent nickel in the sap of the Phyllantus balgooyi tree
In the future, some metals may be available not through mining, but simply through cultivation. Scientists have discovered “superaccumulator” plants in nature that can grow in metal-rich soil that is toxic to other plants, sucking metals from the land and storing them in sap and leaves, among other things, in what scientists are calling “phytomining. In fact, there are already “plant mines” in trial operation.
Scientists anticipate that the plants could also be used in medicine to bring health benefits to people.
Plants absorb large amounts of metals
Alan Baker, a visiting botany professor at the University of Melbourne, discovered a peculiar plant in the Philippine jungle that oozes a bright green glowing sap when cut from the side of the trunk. The sap was tested and found to contain 9% nickel.
This is a newly discovered species, named Phyllanthus Balgooyi, a rare plant that can absorb large amounts of metals from the soil.
Professor Baker said, “These plants can take up metal elements from the soil at rates several orders of magnitude higher than normal plants.”
The discovery of this new species is encouraging, as Professor Baker has actually been working on what he calls “superaccumulator” plants for many years.
Plant mining
Antony van der Ent, a plant expert at the University of Queensland, has also been working on this, which he calls “agroponics”.
It is also known as “plant mining”.
In recent years, Dr. van der Ent has traveled the world in search of new hyperaccumulator species: “We’ve found them in Southeast Asia, New Caledonia, and Cuba and Brazil.”
Very few plants have this property, and Dr. van der Unter estimates that only about seven hundred of the 300,000 known plant species on Earth have this hyperaccumulation property. About two-thirds of these species specialize in nickel uptake, including three species found in New Caledonia that have sap concentrations of about 25 percent nickel, much higher than in conventional nickel ores. Traditional nickel oxide ores contain 1% to 2% nickel in nickel laterite and 1.6% to 4.0% nickel in nickel silicate.
Nickel is a popular metal and is an important component of lithium-ion batteries and stainless steel.
The “super accumulation” plant branches are dried and burned to produce a “bio-ore” ash.
This is an extremely high-quality ore that can be processed using standard hydrometallurgical techniques,” says Dr. van der Unter.
Today, scientists are looking at ways to use the plant’s characteristics as an alternative to traditional mining.
Researchers at the University of Lorraine have established a demonstration “metal farm” in Malaysia, which has been operating for five years.
The farm reportedly produces 200 to 300 kilograms of nickel per hectare per year.
Plants accumulate metals as a self-protection requirement
The trace elements of metals found in these plants are more than needed for plant growth and are even harmful to the plants in general.
So why do these plants take them up in large quantities?
Baker says, “Many ideas have been proposed [for this phenomenon], but the most plausible explanation is that it is a self-protective mechanism they have developed to defend themselves against herbivorous insects and animals.”
Superaccumulator plants help restore ecology
Dr. Baker says that extracting minerals from superaccumulator plants is not a complete substitute for traditional mining techniques. However, the technology has the added value of making areas with toxic soils productive. Farmers could grow crops in metal-rich soil, and mining companies might use the plants to clean up former mines and wastes and even generate some revenue.
For medical care
Growing and harvesting superaccumulator plants may also boost people’s health, Dr. van der Unter says.
He said many people in developing countries are deficient in elements such as zinc and selenium, which are vital to maintaining good health.
We can grow biomass (a variety of organisms formed through photosynthesis, including all plants, animals and microorganisms) rich in these elements to supplement people’s needs; or use biofortification to increase the concentration of zinc or selenium in staple crops, Dr. van der Unter said.
Scientists predict that in the future hyperaccumulation plant cultivation may be as important as mining, animal husbandry and crop cultivation.
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