The rare plants that ‘bleed’ nickel

Though necessary for many of the products we use on a daily basis, traditional nickel mining is not very environmentally-friendly. This soil biologist has been working tirelessly since 2004 to find these special plants that naturally “mine” nickel to work on an alternative called phytomining. So far, the results are promising. (1)

The Search for Nickel Hyper-accumulators

The Indonesian island of Sulawesi was once filled with thriving vegetation. The town of Sorowako in its center was home to a rich diversity of plants. When the vast amounts of nickel were discovered in its soil, however, the town quickly became the center for one of the largest nickel mining operations in the world, and the land around it was quickly stripped of essentially all of its plant life. Only dusty roads and dirt were left behind. (1)

In 2004, soil biologist Aiyen Tjoa from Tadulako University in Central Sulawesi went to Sorowako in an attempt to find the few surviving plants. These rare bushes and young trees are known as nickel hyper-accumulators. (1)

What Are Nickel Hyper-accumulators?

Nickel hyper-accumulators are plants that have adapted to the nickel-rich environment that they are living in and are able to take up and store large quantities of the metal. Normally, nickel is highly toxic to plants and can kill them in too-high quantities. Nick hyper-accumulators are plants that have the ability to concentrate at least 1,000 micrograms of nickel per 1 gram of dried leaf. 

Not only do these pants clean the soil of nickel, a natural toxin, but they also can be “mined” as an alternative source of nickel without damaging the environment. In fact, these plants might be able to restore the ecosystem back to its former green, lush glory. (1)

Hyper-accumulators bind nickel inside their cell walls or vacuoles in either their leaves, shoots, roots or sap. Different species have different storage capacities, and they show it in different ways. For example (1):

• Alyssum murale, native to Italy, can handle up to 30,000 micrograms of nickel per gram of dried leaf.
• Phyllantis baligoyii, native to Malaysia, have such a high nickel content that their sap turns a vibrant green color.

There are about 450 species of nickel hyper-accumulators documented currently around the world, however, most are found in places with far less plant diversity and far less soil nickel than Indonesia. These are (1):

• Cuba (130 species)
• Southern Europe (45 species)
• New Caledonia (65 species)
• Malaysia (24 species)

Interestingly enough, very few species have been found in Indonesia, despite it having some of the most nickel-rich soils and biologically diverse countries in the world. According to Tjoa, this is because few people besides her have spent any time actually looking for them. (1)

Tjoa’s Search

Once Tjoa had the permits she needed from the mining company in Sorowako, she quickly set out to search the area for the rare plants. In the beginning, it was tough: For the first four years everything was on her own dime, and it was largely fruitless. (1) 

She was finally able to find two indigenous hyper-accumulators in 2008: Knema matanensis and Sarcotheca celebica. Each of these can store between 1,000 and 5,000 micrograms of nickel per gram of dried leaf. (1)

Why Are Nickel Hyper-accumulators So Hard to Find?

The issue is that these plants are difficult to spot because they look largely just like any other plant. Thankfully once you do identify one, there is a fool-proof test you can do using a circle of white detection paper that’s both fast and easy. When leaves of nickel-containing plants are pressed against it, it instantly turns pink. (1)

The next step is then to analyze the concentration of nickel in the lab. This is important because just because a plant contains some nickel does not mean it is a hyper-accumulator. (1) Once tested for concentration, it can be determined if the plant is or isn’t what you are looking for. (1)

Phytomining

Phytomining is the process of cultivating these plants for the purpose of mineral extraction. In order to do so in a way that is economically feasible, each plant needs to be able to accumulate at least 10,000 micrograms of nickel per gram of dried leaf. (1) So while the first two species Tjoa found were exciting, they weren’t enough.

Her research and findings, however, attracted the attention of Bandung Institute of Technology rock magnetism professor Satria Bijaksana. He was researching the relationship between Sulawesi’s geology and ecology and thought that he could lend his expertise to the phytomining project. (1)

Why Magnetism Can Help

These hyper-accumulators have high quantities of metals, and so do their ashes after they’ve been burned. Some of these metals are magnetic, in particular, iron. It has been shown that nickel and iron uptake in these plants happen simultaneously, so Tjoa and Bijaksana created an experiment to see whether or not the plants become more magnetic the higher the nickel concentration. (1)

They tested the ashes of two well-known hyper-accumulators and compared them with 10 plants indigenous to the Sulawesi and Halmahera areas. They found that one of the indigenous plants was high in both metals. (1)

This test is important because it speeds up the process of testing for hyper-accumulators because it gives less false positives than other methods. (1)

“We think using magnetism could speed up the process because it only detects high concentrations of nickel,” says Bijaksana (1)

Their study, which was published this past May, also identified two more species of nickel hyper-accumulators. The goal is that their study, along with continued research, will help people understand the value of phytomining in Indonesia. (1)

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The Environmental Benefits of Phytomining

Phytomining is positive for the environment and for industry (1):

• It collects a natural toxin from the soil, protecting the environment,
• That metal (nickel) is used in products we use every single day, like the tap in your kitchen or the battery in your car.

The actual process of phytomining is also much easier on the ecosystem than traditional methods, which produce a ton of carbon dioxide, release radioactive elements, metallic dust, and naturally occurring asbestos-like substances into the ecosystem, all on top of stripping the area of its plant life. The extraction of nickel from the plants doesn’t do any of that and is also quite easy to do (1):

1. Prune the shoots (these have the highest nickel concentration)
2. Burn the shoots
3. Separate the nickel from the ash

Though the burning does release carbon dioxide, as the pruned plants continue to grow, they recapture it within a few months. This makes phytomining a net-zero carbon emissions process.(1)

The plants can also help to rehabilitate the land that has been ravaged by traditional mining methods. In the past, attempts have been made using other, non-hyper-accumulating plants, which do not work very well on account of the high nickel content of the soil. The hyper-accumulators thrive there, effectively removing nickel from the soil and returning it to a more nutritive state. This will eventually allow other plant species to return to the area. (1)

Economic Benefits

It is estimated that hyper-accumulators can produce roughly 120kg of nickel per hectare every year, which is valued at about $1,754 per hectare. (1) In addition, traditional nickel mining can only extract the metal from soil that is at least 1% nickel. A hyper-accumulator, however, can take up high levels of the metal from soil that is only 0.1% nickel. (1)

This means that not only can phytomining help to restore traditionally-mined land, but it can also be used to “mine” land that hasn’t been used before. (1)

Not a Complete Replacement

Phytomining cannot fully replace traditional or open-pit nickel mining in Indonesia. The country produces 5% of the world’s nickel and exported 73 million tons of the metal in 2019. (1) The goal is for phytomining to be implemented as an alternative form of agriculture for people living in rural areas on nickel-rich land. (1)

Difficulty Gaining Traction

So far, Tjoa has been frustrated by the lack of development of phytomining in Indonesia. She tried to connect Indonesia’s state-owned mining firm PT Aneka Tambang (Antam) in 2009, who at first supported her field trials. The collaboration was later terminated by Antam, in part due to company restructuring. Over 10 years later, she still has not been able to re-open that partnership. (1)

Despite this, Tjoa has not lost hope. They’ve found an untouched forest in the Morowali Nature Reserve in central Sulawesi that is made up of the exact type of soil hyper-accumulators love. Until now, no one has thought to look for them. (1)

She was also contacted by an American investor in 2017 who is planning on funding her 5,000-hectare trial in Sulawesi. (1) For this trial, she will use a native Italian species, because it is a safe bet. From there she hopes to transition into using native Indonesian species that will be better for the natural ecosystem. (1)

“Maybe we have to use it first to convince Indonesian government that phytomining works,” she says. (1)

The eventual goal is to have phytomining included in every mining zone. Firms would be required to reserve a section of the rainforest in each of their zones and use the plants instead. This would create less waste, both toxic and non-toxic, and ultimately, preserve the ecosystem. (1)

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