For millions of years, Plantlife on land has evolved to survive and to thrive. Trees are the results of these millions of years of evolution of Plantlife. In the process of this evolution and diversification of Plantlife on land, each species of Plant went through different experiences with unique problems in every phase of their lives according to the environment they were adapting to. Based on these experiences and the problems they faced to survive and to thrive over millions of years, they have gained certain abilities. Every species of Plant has a unique set of abilities that have been passed over many generations.
In this sense, every Tree is like a book, and every feature or characteristic of a Tree has its own story that has been developing for millions of years. Over the years, driven by curiosity and necessity, humanity has been discovering many hidden stories, abilities, and wisdom of Trees that have shaped every aspect of human life. Phytomining is one of the hidden abilities of Trees that the scientific world is recently becoming aware of.
The concept of Phytomining is not completely new; over 500 years ago, the father of modern mineral smelting Georgius Agricola perceived this hidden ability of Trees. In his free time, he used to smelt Plants. In the 16th century, he wrote, if you knew what to look for in a leaf, you could deduce which metals lay in the ground below.
What is Phytomining?
In simple terms, the process of extracting underground metals by growing Plants is called Phytomining. So, Phytomining is the production of a crop of a metal by growing high-biomass Plants that accumulate high metal concentrations. Some of these Plants are natural hyperaccumulators, and in others, this characteristic can be induced.
From 320,000 recognized Plant species, only about 700 are identified as “hyperaccumulators”—for example, Kinabalu’s Phyllanthus Rufuschaneyi. Over time, they absorb the metals like nickel, zinc, cobalt, and even gold from the soil.
The word “phytomining” was first put forth in 1983 by an agronomist at the U.S. Department of Agriculture named Rufus L. Chaney. His name is now immortalized in one of the nickel-absorbing Plants used in Sabah, Malaysia.
According to the experts, pioneering experiments in this field might lead to a green alternative to currently existing, environmentally destructive mining practices.
The Process of Phytomining
According to Aiyen Tjoa, a soil biologist and lecturer at Tadulako University in Central Sulawesi, who has been studying nickel hyperaccumulators for more than a decade, most Plants draw up small amounts of heavy metals from the underground to activate some important enzymes. Over time it is observed that nickel is needed to activate one crucial enzyme for Plants’ flowering process, but even a slightly excessed amount of nickel can poison and kill most Plants. However, nickel hyperaccumulators like Phyllanthus Rufuschaneyi have evolved the ability to withstand this excess by wrapping the metal inside their cell wall or storing excess of it in their vacuoles. But they primarily store the absorbed nickel in their shoots, roots, leaves as sap.
Over time experts observed that some nickel-absorbing species that are native to Italy, like Alyssum Murale, can take up to 30,000 micrograms of nickel per 1g dried leaf. Others like Phyllanthus Balgoyii from Malaysia have such a high nickel content that their sap turned into a remarkably bright blue-green color.
So far till now, around 450 species of nickel-loving hyperaccumulating Plants have been documented globally. Most of these Plants grow in countries with less Plant diversity and lower nickel deposits than Indonesia, such as Cuba (130 species), southern Europe (45), New Caledonia (65), and Malaysia (24).
A new way to mine
The miracle of nickel hyperaccumulating Plants is that they absorb and use something that is both a toxic pollutant if left alone in the soil and valuable material. Currently, nickel is used in making stainless steel products from kitchen taps to electric car batteries. Over the years, researchers have been perfecting the process of collecting nickel from Plants, which is relatively an easy process compared to the traditional energy-intensive and environmentally costly mining and smelting process.
Dr. Alan Baker, a visiting botany professor at the University of Melbourne who has researched the relationship between Plants and their soils since the 1970s, and an international research team of colleagues have set their visions on convincing the world that the idea is more than just a fun thought experiment. To do this on a plot of land rented from a rural village on the Malaysian side of the island of Borneo, the research team has proved it at a small scale. Every 6 to 12 months, a farmer shaves off one foot of growth from these nickel-hyperaccumulating Plants and either burn or squeezes the metal out. After a short purification, farmers could hold roughly 500 pounds of nickel in their hands, potentially worth thousands of dollars on international markets.
The University of Queensland’s van der Ent has estimated that a hyper-accumulator like Phyllantus Balgoyii can provide an estimated 120kg of nickel per hectare every year. According to the current market value, that translates to around $1,754 per hectare. Phytomining extracting nickel involves pruning the shoots; according to the experts, Plants’ shoots hold the highest concentrations of metal. Burning them, after which the nickel can be isolated from the ash.
Though this involves releasing carbon dioxide through burning, the continuous cultivation of nickel hyperaccumulators can be considered carbon-neutral, says van der Ent. According to his calculation and estimation, all carbon released from the burning shoots will be recaptured by the newly growing crop in a few months.
What happens next
According to Dr. Baker, Phytomining, or extracting minerals or metal by cultivating hyperaccumulating Plants, cannot fully replace the traditional mining techniques, but the process has the potentiality to make the toxic soils productive again. Smallholding farmers from the land polluted areas could use Phytomining, and big mining companies might use these Plants to clean up their former mines and waste, and even in this process could collect some revenue.
But the nickel-absorbing crop cultivation can be so productive and lucrative for the smallholding farmers that it led to fears that farmers might push for opening tropical forests for cultivation, foreshadowing another case such as palm oil, a cash crop that has devastated Borneo’s native forests. But according to the researchers, that is not a likely outcome. Areas with the most phytomining potential tend to be grassy, and few other Plants are likely to grow on land selected for mineral farming.
Dr. Baker pointed out that these hyperaccumulating Plants will be grown on soils where it has already been deforested, so, in this context, it is a way of putting back, rather than taking away.
References
- Chaney, R., et al. (2016). Growth and Metal Accumulation of an Alyssum murale Nickel Hyperaccumulator Ecotype Co-cropped with Alyssum montanum and Perennial Ryegrass in Serpentine Soil. Frontiers in Plant Science, [online] Available at: https://doi.org/10.3389/fpls.2016.00451 [Accessed 9th September 2021].
- Deng, THB., van der Ent, A., Tang, YT. et al. (2018). Nickel hyperaccumulation mechanisms: a review on the current state of knowledge. Plant Soil, [online] Volume, 423, 1–11. Available at: https://doi.org/10.1007/s11104-017-3539-8 [Accessed 9th September 2021].
- Ghasemi, R., et al. (2014). A preliminary study of the role of nickel in enhancing flowering of the nickel hyperaccumulating Plant Alyssum inflatum Nyár. (Brassicaceae). Elsevier, [online] Volume, 92, p. 47-52. Available at: https://doi.org/10.1016/j.sajb.2014.01.015 [Accessed 9th September 2021].
- Ghori, Z., et al. (2016). Chapter 15 – Phytoextraction: The Use of Plants to Remove Heavy Metals from Soil. Elsevier, [online] Volume, 16, p. 385-409. Available at: https://doi.org/10.1016/B978-0-12-803158-2.00015-1 [Accessed 9th September 2021].
- van der Ent, A., et al. (2013). Ultramafic nickel laterites in Indonesia (Sulawesi, Halmahera): Mining, nickel hyperaccumulators and opportunities for Phytomining. Geochemical Exploration, [online] Volume, 128, p. 72-79. Available at: http://dx.doi.org/10.1016/j.gexplo.2013.01.009 [Accessed 9th September 2021].
- van der Ent, A., et al. (2019). The first tropical ‘metal farm’: Some perspectives from field and pot experiments. Elsevier, [online] Volume 198, p. 114-122. Available at: https://doi.org/10.1016/j.gexplo.2018.12.003 [Accessed 9th September 2021].
