In the 1970s, people discovered a magical tree on a small island in the Pacific. When its bark is cut, turquoise-colored sap flows out.
Pycnandra acuminata, a tree growing in New Caledonia, exudes bright blue-green sap (Photo: Atony van der Ent)
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Scientists found that the sap contained up to 25 percent nickel, which they believe may be a strategy used by plants to fend off insect attack.
Dr Atony van der Ent from the University of Queensland, one of those who specializes in studying the plant, said the tree can only be found in remnants of ancient rainforest.
It is difficult for ordinary plants to survive in places with excessive levels of heavy metals such as nickel, let alone accumulate them in their own body tissues.
This plant can absorb metals that are toxic to most other plants into its trunk, leaves and even seeds.
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The tissue contains a large amount of nickel compounds, which gives the tree's sap a turquoise color (Image source: narido)
Since then, other plants that can accumulate metals have been discovered, known as “hyperaccumulators.”
For Dr. van der Ent, studying green sap plants is not easy because they grow very slowly.
“It can take decades for them to come to fruition,” Dr. van der Ent said. And this plant is currently under various threats. With the expansion of mining, logging and forest fires, the living space of these trees is getting smaller and smaller.
The green sign on the right is where the Pycnandra acuminata tree is found (Image source: Google map)
Scientists don't yet understand how the green sap trees evolved the ability to accumulate such high concentrations of nickel in order to adapt to the harsh soil, but they believe it is not the result of human interference.
“Different populations of hyperaccumulator plants have evolved many times over millions of years, meaning they have grown in metal-rich soils,” says Dr. van der Ent.
Still, people see the potential of these plants in remediating soil contaminated with metals or organic compounds.
The process of phytoremediation (Image source: wiki)
For most plants, metal elements are mainly concentrated in their roots. However, among hyperaccumulators, metal concentrations are unusually high in leaves and much lower in roots.
Scientists believe this is because they somehow transfer metal elements from the roots to the leaves, thereby protecting the roots from metal toxicity.
The high metal content in the leaves of these plants can also attract herbivores as well as harmful insects and pathogens.
Hyperaccumulator plants can use this method to concentrate harmful compounds from the environment and then break them down into a variety of smaller compounds without causing additional pollution.
There are also many phytoremediation methods used to absorb heavy metal pollution in soil, such as cadmium, lead and other elements.
Some plants can remove metals, such as copper and zinc, from the soil by moving them to their roots and then on to their leaves (Image source: wiki)
However, when absorbing heavy metals, plants cannot further decompose them, so more care must be taken in the subsequent processing to prevent these plants from being made into consumer products such as food or cosmetics.
It is precisely this characteristic that gives hyperaccumulator plants another employment direction:Go be a miner.
Simply put, phytomining involves harvesting plants after they are mature, and then drying, burning and processing them to recover the target metal.
Some plants and their products that can extract certain metals (Image source: Reference[9])
The U.S. Bureau of Mines (now defunct) conducted the first phytomining experiments in Nevada using a hyperaccumulator plant that could enrich nickel. The tests were carried out in soil with a nickel content of 0.35%, a level that is far from worth extracting using conventional mining techniques.
The results show that plant mining can produce 100 kilograms of nickel per hectare, which is equivalent to a profit of about 10,000 yuan. The return is comparable to other cash crops.
In Dr. van der Ent's research, it was also mentioned that because metal-rich soil makes it difficult to increase the yield of food crops such as wheat or rice, plant mining can be a viable alternative that can bring better economic benefits to the local area. .
“Pytomining does not replace food crops, but serves as a temporary planting option to wait until soil quality improves before growing food crops,” van der Ent said.
Some plant miners mine in Australia (Image source: Reference[9])
For the new energy transformation, this is something worth looking forward to. Green technologies such as electric vehicles are developing at an unprecedented speed, and cobalt and nickel required for new energy batteries are also among the metals that can be collected by hyperaccumulating plants.
Some scientists believe that plant mining could concentrate nickel at levels several orders of magnitude higher than in soil, with far fewer impurities. Plant mining also causes less damage to the environment than traditional mining. In addition, it can repair soil contaminated by metals. This mining method has a promising future.
Although there have been a large number of successful trials, scientists say that plant mining is still difficult to commercialize. Large-scale trial operations are needed to conduct risk assessments and a comprehensive analysis of the profitability of plant mining is required.
From biological extracts (left) to high-value nickel compounds or pure nickel (right) (Image source: Reference[10])
van der Ent also said that only plants with nickel content above a certain proportion of leaf dry matter are commercially viable.
“Not all plants are suitable for mining, and to make this a viable option, overall yields and metal enrichment rates need to be increased.”
There is another constraint on plant mining, which is that these hyperaccumulating plants are generally not productive plants. Some plants are very demanding on the climate, and some are slow-growing, making them unsuitable for commercial use.
Researchers are still looking for solutions to help plant miners officially start working.
Some scientists have previously summarized hyperaccumulator plants that can specifically collect certain minerals. Among them, there is mustard (Brassica juncea) that can collect gold. It is recommended that everyone grow this.
It’s the kind that makes mustard (Image source: alliance for science)
Reference link
[1]https://theintelligentminer.com/2021/12/09/how-to-grow-metals-using-plants/
[2]https://www.bbc.com/news/science-environment-45398434
[3]https://www.techwalker.com/2020/0906/3128742.shtml
[4]https://en.wikipedia.org/wiki/Pycnandra_acuminata
[5]https://en.wikipedia.org/wiki/Hyperaccumulator
[6]https://en.wikipedia.org/wiki/Phytoremediation
[7]https://en.wikipedia.org/wiki/Phytomining
[8]https://singularityhub.com/2024/03/28/these-plants-could-mine-crucial-battery-materials-from-the-soil-with-their-roots/
[9]Antony van der Ent, Anita Parbhakar-Fox, Peter D. Erskine, Treasure from trash: Mining critical metals from waste and unconventional sources, Science of The Total Environment, Volume 758, 2021, https://doi.org/10.1016/j. scitotenv.2020.143673.
[10]Environ. Sci. Technol. 2015, 49, 8, 4773-4780
Planning and production
Source｜Bring science home (ID: steamforkids)
Author丨Ziv
Editor in charge丨Wang Mengru
Reviewer丨Xu Lai Linlin