Sift through phyto: rare earth metals will be extracted using mustard
Scientists have developed a technique for extracting rare earth elements using plants. The technology involves extracting valuable components from man-made landfills. In particular, it has already been tested on samples from phosphogypsum mining and loparite enrichment sites. Experts plan to get up to two harvests per season and have selected crops adapted to Russian conditions. Pilot plantings will begin next year. At the same time, plots for growing plants will require special preparation and fertilization, which may make the technology more expensive than expected, experts noted.
How plants extract rare earth metals from the soil
In Russia, it was proposed to extract rare earth metals using hyperaccumulative plants. They are planted on man-made landfills, where they extract useful elements from the soil themselves and accumulate them in their biomass. The technology was developed at the Giredmet Institute (part of Rosatom).
— Similar methods are used to clean up territories. For example, crops are planted along roads or near chemical plants to remove heavy metals and other harmful compounds from the ground. Species that extract radionuclides from the soil are also being studied. We have the opposite approach — we want to extract the maximum amount of useful elements from the earth with the help of plants," Vitaly Sanin, head of the Metallurgical processes laboratory at the Giredmet Institute, told Izvestia.
In science, this process is called phytomining. Unlike traditional methods, the new technology involves minimal capital expenditures, since the construction of expensive processing plants will replace conventional agricultural work, the scientist explained.
According to him, the researchers selected white mustard, sunflower, corn, flax, buckwheat, fern, hogweed and a number of other plants for experiments. In addition to the ability to accumulate metals, the choice is due to their rapid growth, climate resistance in Russia, as well as the availability of agricultural techniques that allow mechanization of sowing and harvesting of these crops.
Rare earth metals are a group of 17 elements that possess unique magnetic, electrical, and chemical properties. They are used in the production of permanent magnets, batteries, electronics, medical equipment, aerospace and defense industries. Despite the name, many of these elements are often found in the earth's crust, but they rarely form deposits with high concentrations.
Where will valuable elements be mined in Russia
The developers tested the technology on phosphogypsum mining waste from deposits in the vicinity of Voskresensk (Moscow region) and Balakovo (Saratov region), as well as at the loparite ore processing tailing dumps from the Lovozersky Mining and Processing Plant in the Murmansk Region.
According to the estimates made, under optimal conditions, up to 630 kg of various rare earth metals can be extracted from one hectare of plantings in one harvest. At the same time, the climate in central Russia allows for up to two harvests per year.
As explained by Vitaly Sanin, in the experiments, experts also selected auxiliary organic substances that convert metals into a form easily absorbed by plants. At the same time, it is important that the bulk of the elements accumulate in stems and leaves, which makes it possible to collect biomass in a mechanized manner.
In the future, the plants are dried and burned to obtain ash. The total concentrate of rare earth metals is extracted from it using chemical reactions. The next stage is its separation into individual elements by obtaining oxides, followed by reduction to pure metals.
As the scientists noted, these technologies already exist in Russia, and they are being actively developed to an industrial level. In particular, the corresponding production complex will be built in Solikamsk in 2028-2029.
— Plants grow worse in pure phosphogypsum, therefore, in experiments, scientists determined the optimal ratios of mixtures with ordinary earth. The one-to-three ratio proved to be the best. Scaling this process is not difficult. To prepare for planting, soil is brought to the surface of the man—made dump, then the "field" is plowed and seeds are sown," said Vitaly Sanin.
He added that a similar approach is being worked out for the Lovozersky Mining and Processing plant, but with an emphasis on the use of hyperaccumulative plants from the local flora. In particular, they consider willow, a shrub that is resistant to harsh climates and a short growing season. The use of wood molds will make it possible to process them into sawdust and make fuel briquettes.
Experimental field plantings for phytomining will begin next year, Vitaly Sanin said. According to him, the technology will not replace mining, but will complement it, allowing it to extract valuable elements where classical methods are unprofitable. In addition, the technology will help to reclaim territories at the sites of former deposits.
The development can also be exported, the scientist noted. In particular, in countries with a warm climate, the technology will potentially allow for 3-4 harvests per year. Such projects are already being worked out with foreign partners.
— Back in the 19th century, it was noticed that plants can accumulate metals in themselves. However, it was only in 2003 that gold phytomining tests were conducted in New Zealand and Brazil, and the technology entered industrial use for nickel accumulation last year," Lyudmila Komarova, head of the Department of Biology at the Obninsk Institute of Atomic Energy at the National Research Nuclear University MEPhI, told Izvestia.
In her opinion, the commercial implementation of phytomining is hindered by the difficulty of selecting species with the right qualities, creating the necessary growth conditions and economically justified methods for obtaining rare earths from biomass.
— The main problems of phytomining are related to the fact that hyperaccumulating plants, as a rule, have a small biomass. Accumulated REM can be toxic and also limit growth. In addition, it is difficult for plants to grow in man—made landfills, so the technology requires agrotechnical soil preparation — creating a soil layer, applying fertilizers (nitrogen, phosphorus, potassium, and others), which makes the whole process not as cheap as it seems," added Irina Kiseleva, head of the Department of Experimental Biology and Biotechnology at Ural Federal University.
It is promising to use perennial tree forms, such as willow, the expert noted. Such plants can accumulate REM for several years and produce a greater yield of elements. However, there are few such species in Russia.
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