The idea of extracting valuable metals with the help of plants has gone from science fiction to a real line of research. Today we know that there are species capable of accumulating large quantities of critical elements in their biomass and that they can even promote their mineralization under environmental conditionsWhat's interesting is not just the technology, but also the new approach: producing raw materials with less impact, while restoring damaged soils.
In recent years, discoveries have been made that have changed the game: from ferns that crystallize strategic minerals to pilot projects for phytomining and phytomanagement In Europe, Asia, and Oceania, biochar is being used to accelerate metal extraction and improve soils. If you're interested in the energy transition, electronics, or the circular economy, here's a clear, rigorous, and comprehensive overview of what's already possible.
What is phytomining and why does it matter?
Phytomining is the deliberate use of plants to extract metals from the soil and concentrate them in their aboveground biomass. These species, known as hyperaccumulators, can store extraordinary quantities of metals without showing apparent toxicity, allowing the biomass to be harvested and the metal subsequently recovered. physical-chemical processes or suitable metallurgical.
The relevance of this strategy has two clear aspects. On the one hand, it offers an alternative or complementary supply of key metals for modern technologies: wind turbines, electric vehicles, high-performance magnets, electronics, lasers, and photophores. On the other hand, it opens a path to environmental remediation with economic return, taking advantage of degraded soils or mining tailings where conventional mining is unfeasible or too expensive.
Furthermore, the geopolitical context is pressing. In the case of rare earth elements, more than 60% of world production is concentrated in ChinaThis creates supply risks. Phytomining, along with phytoremediation and phytomanagement, points to a more distributed and resilient model, with regional value chains and a smaller ecological footprint.
The discovery: monazite inside a living plant
A research team from the Guangzhou Institute of Geochemistry (China) and Virginia Tech (United States) documented for the first time the natural formation of a rare-earth mineral within a living plant. The study, published in Environmental Science & Technology, identified monazite on a nanoscale in a perennial fern, Blechnum orientale, collected from rare earth deposits in the city of Guangzhou, in southern China.
Monazite is a phosphate rich in rare-earth elements such as cerium, lanthanum, and neodymium. This mineral typically forms under high pressures and temperatures of hundreds of degreesHowever, in this case, it crystallized under ambient conditions, within the fern's extracellular tissues. Analysis showed that the concentration of these elements is highest in the pinna (part of the leaf), followed by the root system and the petiole. Thus, the plant, as a defense and detoxification mechanism, immobilizes non-nutritive elements in stable mineral phases outside the cells.
The authors compare the process to a “chemical garden”: when a seed of metallic salt enters a solution with anions (silicate or phosphate, for example), complex, non-equilibrium structures self-organize, reminiscent of plant forms. In the fern, the high local concentration of metallic salts and phosphates in an aqueous medium favors the nanoscale monocyte nucleation and growth, a phenomenon as elegant as it is powerful due to its technological implications.
The properties of monazite are particularly interesting: it has a high melting point, high optical emissivity, and resistance to corrosion from molten glass and radiation damage. These characteristics make it ideal for applications such as coatings and diffusion barriers, luminophores, lasers, light emitters, ionic conductors and even matrices for the immobilization and management of radioactive waste.
This finding validates something essential: the viability of phytomining applied to rare earth elements. Not only can rare earth elements be extracted from biomass, but some plants can promote their direct mineralization into useful forms, opening the door to recover functional materials with less subsequent transformation already scaling up more efficient bioextraction schemes.
Hyperaccumulating plants: how they work and where to apply them
Hyperaccumulators are species capable of concentrating metals or metalloids in their tissues at levels hundreds or thousands of times higher than those found in the soil. Their physiology allows them to take up ionic forms of metals, transport them through the vascular system, and store them without damage. This trait makes them candidates for cultivation in metal-rich soils, allowing for the subsequent recovery of the target elements. biomass harvested using low-impact techniques.
In practical terms, phytomining can be deployed in contaminated soils, abandoned mines, or areas where conventional mining faces environmental, social, or geopolitical restrictions. There are already pilot projects in Australia, Malaysia and the Philippines all with nickel and cobaltAnd the case of the fern with monazite opens up new opportunities for rare earths, a group of elements critical for the energy transition.
The strategy does not aim to replace industrial mining entirely, but rather to complement it with regenerative options. Reducing the need for excavation or the use of aggressive chemicals means fewer emissions, less water consumption, and less soil degradation. In parallel, the vegetation used It helps to stabilize and restore ecosystemscombining extraction with environmental services.
Gold, nickel and more: from eucalyptus to mustard and mushrooms
Beyond rare earth elements, there are species that allow for the extraction of valuable metals such as gold, platinum, palladium, and nickel. Experiments in Australia showed that eucalyptus trees growing on gold deposits can accumulate up to 80.000 parts per billion (ppb) of gold in its leaves, well above the levels in areas without mineralization. In low-grade soils, agents that mobilize gold have been tested to facilitate its absorption by plants such as Indian mustard (Brassica juncea), which is then harvested and burned to concentrate the metal.
Meanwhile, biotechnology is providing unexpected protagonists. The fungus Fusarium oxysporum has been shown to transform minerals into gold nanoparticles on its surface, a finding published in Nature Communications by the CSIRO. This biological process suggests pathways of biofabrication of metals at the nanoscale, with applications in phytomining and precious metal recovery, even in controlled and small-scale environments with treated soils.
Phytomining has other uses: eco-efficient exploration. Analyzing tree leaves can act as a natural sensor for hidden deposits, reducing invasive drilling. And not just with gold. Agromining specialist Antony van der Ent has documented tropical species with sap containing up to 25% nickel"Metal farms" have been tested in Malaysia with yields of 200 to 300 kilograms of nickel per hectare per year.
Plant management in Murcia: restoring with native species and biochar
In the Region of Murcia, a project by the Polytechnic University of Cartagena (UPCT) is exploring the phytomanagement of waste from former mining activities in the Sierra de Cartagena-La Unión. The premise is simple: to use plants—alone or combined with soil amendments—to stabilize or extract metallic contaminants. preventing its dispersion and restoring soil functionality.
The aridity of the semi-arid climate and the low fertility of these soils complicate plant establishment. To improve the substrate, the team uses amendments derived from human waste—municipal solid waste (MSW) and pruning debris—and a biochar made from organic waste. Biochar is more stable than traditional compost and retains a lot of moisture, which aids plant establishment. in environments with water deficit.
In a novel approach, native tree species such as Aleppo pine and Cartagena cypress (a species of high botanical interest that in continental Europe only grows naturally in the Region of Murcia) have been tested. The study was conducted in a greenhouse for almost two years, controlling growth conditions, MSW/biochar mixtures, and soil and plant parameters. At the end of the trial, the biomass was analyzed to determine which combinations They better promote establishment, stability, and security.
To complete the environmental safety cycle, the team assesses ecotoxicity using soil invertebrates as bioindicators. The goal is to identify mixtures that minimize the transfer of metals to the food chain, so that, when recommending practices, plant productivity is combined with risk reduction and ecological restoration.
Agromine: European demonstration of nickel in Galicia
The European project Agromine, with the participation of the CSIC in Galicia (Microbiology Group of the IIAG), aims to demonstrate the feasibility of cultivating hyperaccumulator plants in nickel-rich ultramafic soils to produce biomass from which high-purity nickel compounds can be obtained. The fieldwork will be carried out in Agolada (Pontevedra), with pilot tests to measure productivity, metal accumulation and effects on the physical-chemical properties and microbial activity of the soil.
The plan is organized into four phases: 1) optimization of cultivation systems and selection of species according to climate; 2) metallurgical improvements to produce compounds such as nickel and ammonium sulfate from biomass ash, as well as recovering energy during combustion; 3) evaluation of the improvement in soil fertility and biological quality; and 4) socioeconomic analysis to assess the viability and sustainability of the whole.
This consortium, funded by the LIFE program, is coordinated by the University of Lorraine and brings together partners from France (including the start-up Microhumus SARL), Austria (Universität für Bodenkultur Wien and alchemia-nova GmbH), Belgium (Universiteit Hasselt), Greece (Eastern Macedonia and Thrace Institute of Technology and Technological Institute of Thessaly), Albania (Agro-Environment and Economic Management Center), and Spain (CSIC). It provides a multidisciplinary approach: botany of ultramafic soils, physiology of hyperaccumulators, phytotechnologies, green metallurgy and economics.
For context, only about 500 hyperaccumulator species are known worldwide, most of them nickel-focused and adapted to ultramafic soils rich in nickel, chromium, and cobalt. These plants allow for the extraction of high-value metals from the soil, and after controlled combustion of the biomass, subsequent metallurgy recovers up to [amount missing]. 99% of the stored metal in the ashes using appropriate techniques.
Circular economy and new materials: the UCLM path
The EARTH (Integrated Environmental Recovery Technologies) group at UCLM is exploring an interesting concept: decontaminating soils and water with plants and then repurposing that biomass to manufacture carbon black without petroleum, and designing materials for sodium-ion batteries and catalysts, or even propose alternatives for rare earth mining without breaking up the earth.
Working with vegetation that grew in mines like San Quintín, they have found that certain species can accumulate many metals within them. The major challenge of all phytoremediation is what to do with the biomass laden with contaminants: the circular economy approach proposes transforming it into valuable industrial productssolving the initial environmental problem and simultaneously creating a chain of utilization.
In collaboration with universities and companies, the carbons obtained from these plants are tested in electrodes for sodium-ion batteries (more affordable than lithium-ion batteries), in the production of hydrogen peroxide with a lower environmental impact, in hydrogen production trials, and in the capture of CO2 with functional carbonaceous materialsThe development requires validating that the process is competitive with fossil carbon and that it manages the metals present well.
To ensure control, some of the work is done in greenhouses on the Ciudad Real Campus, using species such as red sandwort, sedge, common reed, and cattail, measuring how much of certain pollutants they remove and how they accumulate heavy metals. The risk of this biomass entering the food chain is also monitored, reinforcing safe handling and treatment measures before its release. valuation as material.
Biochar: manufacturing, uses and real cases
Biochar is produced by the pyrolysis of biomass between 300 and 600 °C in the absence of oxygenIt is a very stable material, with high porosity and a great capacity to retain water and nutrients. Its application in soils has been proposed as a climate mitigation tool (it promotes carbon sequestration) and as an amendment to improve structure, fertility, and microbial activity.
In Spain, livestock farming generates around 121 million tons of manure per yearMuch of it is used as a soil amendment after composting, but some is lost in landfills or incinerated. Recent estimates place the potential for biochar production from waste above 15 million tons per year, an opportunity to valorize livestock and agricultural waste with multiple environmental and phytotechnological applications.
An illustrative case is Riotinto, in the Iberian Pyrite Belt. There, mining sludge with high concentrations of heavy metals accumulates in ponds. In the laboratory, it has been observed that combining biochar (for example, from rabbit manure) with rapeseed as an extraction crop can increase arsenic extraction above [percentage missing]. 1.000%and for chromium and nickel above 200%, in addition to zinc above 150%. This approach increases the availability or flow of metals to the biomass and improves the performance of the phytoremediation and phytomining.
Biochar, by improving soil properties, can increase plant biomass production by over 10%, making the operation more profitable. The technique is scalable and can be implemented in large areas, especially in heavily contaminated soils where the costs of physicochemical methods Traditional costs are high, and the environmental return of phytotechnologies is greater.
Environmental and geopolitical implications
The supply of rare earth elements and other critical metals has been marked by significant environmental impacts and concentrated production. Phytomining, phytomanagement, and phytoremediation, supported by biochar and clean metallurgy, point toward a more sustainable system. diversified, decentralized, and compatible with regenerationHarvesting metals from plants reduces emissions, water consumption and soil degradation, while vegetating and stabilizing degraded areas.
The discovery of nanoscale monazite in a living fern, the impetus of European projects like Agromine, nickel pilot projects in Asia, and the circular economy initiatives of groups like EARTH (UCLM) all fit into the same vision: using biology to extract value where previously there were only environmental liabilities, with less aggressive and more circular processes.
This entire process demonstrates that a scientific and technical basis already exists for a hybrid model: cultivating hyperaccumulator plants in problematic soils, recovering metals (including rare earth elements) from their biomass, utilizing biochar to multiply yields and convert waste into industrial materials, all while restoring the land. If nature is capable of crystallizing a strategic mineral like monazite in fern leaves, we can aspire to a mining industry that prioritizes the environment. soil health, climate and communitieswithout giving up the metals that make current technology possible.
