A Chinese-led team of scientists says it has found a naturally formed mineral with rare earth elements in a fern, a world first that offers a “green circular model” for extracting high-value rare earths, according to an institution behind the study.
The researchers said the discovery of nanoscale monazite in a living plant “opens new possibilities for the direct recovery of functional rare earth element materials”.
“To our knowledge, this is the earliest reported occurrence of rare earth elements crystallising into a mineral phase within a hyperaccumulator,” they said.
“This work substantiates the feasibility of phytomining and introduces an innovative, plant-based approach for sustainable rare earth element resource development,” the team wrote in the peer-reviewed journal Environmental Science & Technology this month.
The researchers from the Guangzhou Institute of Geochemistry under the Chinese Academy of Sciences collaborated with an earth scientist in the geosciences department at Virginia Tech in the United States for the work.
Phytomining is a green method using so-called hyperaccumulator plants to extract metals from soil. The underexplored strategy offered potential for sustainable rare earth supply, the team said.
In the paper, the scientists described hyperaccumulators as plants that could concentrate heavy metals or metalloids in their tissue at levels hundreds to thousands of times higher than the surrounding soil.
“Leveraging this remarkable capacity, phytomining involves cultivating these plants on metal-rich soils and recovering the target metals from harvested biomass. This strategy reduces reliance on conventional mining while mitigating associated environmental and geopolitical risks,” they said.
Monazite is a phosphate mineral rich in rare earth elements, including cerium, lanthanum and neodymium.
While monazite typically formed under high pressure and temperature hundreds of degrees Celsius, plants presented an alternative for their mineralisation under ambient Earth-surface conditions, the scientists said.
The mineral has a high melting point, excellent optical emissivity and exceptional resistance to corrosion from molten glass and radiation damage.
Its outstanding mechanical, physical and thermal properties make it highly suitable for applications such as coatings and diffusion barriers, luminophores, lasers and light emitters, ionic conductors and matrices for radioactive waste management, according to the team.
In the study, the researchers collected plant samples of a known rare earth hyperaccumulator – an evergreen fern named Blechnum orientale – and the soil surrounding them.
The samples were picked and transported from rare earth deposits in the southern Chinese city of Guangzhou.
The team’s analysis showed that rare earth elements were concentrated in the pinna, followed by the root system and leaf stalk. The minerals crystallise within extracellular tissues under ambient conditions for the plants to prevent non-nutrient elements from entering cells and to detoxify, according to the paper.
The researchers said monazite formation occurred via a process similar to a chemical garden, which features plantlike structures that form when a metal-salt seed is dropped into an aqueous solution containing anions, such as silicate or phosphate.
It also serves as an example in chemistry of a self-organising nonequilibrium process that creates complex structures.
“This phenomenon is the newly recognised occurrence of a chemical garden in a plant, driven by the high local concentration of metal salts (rare earth element and phosphate) in an aqueous environment,” they wrote.
In a statement on Thursday, the Guangzhou Institute of Geochemistry said the study offered “a new path for the sustainable use of rare earth resources”.
“By planting hyperaccumulator plants, high-value rare earths can be recovered from the plants while remediating polluted soil and restoring the ecology of rare earth tailings, thus realising a green circular model of ‘remediation and recycling at the same time’,” it said. -- SOUTH CHINA MORNING POST
