Rare Earth Production Research Articles

Analysis of Unstable Supply and Demand of Rare Earths from Korea to China and Countermeasures against Regulations: Based on Quad-system Subscriptions

Purpose – This study investigates the impact of regulations over Rare earth that recently China had carried out agianst USA. This discussion examines the definition of essential strategic resources called rare earths, China’s precedent of declaring resource weaponization, and its influence. Furthermore, it analyzes the possibility of China’s rare earth export regulations in trade between South Korea and China, and also suggests Korea’s countermeasures to them, focusing on joining the QUAD system. Furthurmore, POSCO Group, which is pushing for ‘E-Autopos’, a next-generation electric vehicle platform, will be analyzed as a concrete example to discuss the impact on not only the Korean electric vehicle industry but also automakers doing business with POSCO Group. Design/Methodology/Approach – To this end, we used d ata f rom China’s rare earth production, actual cases of damage suffered by POSCO at the time of the restriction on rare earth imports from Japan and the United States. Findings – The quad system is a U.S.-centered security talks planned since the Trump administration and is preparing for China’s exclusive exercise of rare earth hegemony. Moreover we discuss about the high probability that China’s export regulations would be imposed on Korea, considering the domestic economy, which is highly dependent on the Chinese economy. As a result , we insist it is essential for Korea to join the QUAD in preparation for existing rare earth-related risks. In order to elaborate its discussion, we will also link up with the domestic electric vehicle industry, which is essential to have rare earths. To this end, POSCO Group, which is pushing for ‘E-Autopos’,a next-generation electric vehicle platform, will be analyzed as a concrete example to discuss the impact on not only the Korean electric vehicle industry but also automakers doing business with POSCO Group. Research Implications – Through this analysis process, we will analyze the impact of China’s rare earth export regulations on the Korean economy, approach and develop the phenomenon on Korea in terms of resource factors, and present solutions.

Surface chemistry considerations of gangue dissolved species in the bastnaesite flotation system

Inefficient flotation of bastnaesite remains a challenge in the production of rare earth elements. This study aimed to investigate the dissolution and adsorption behaviour of species that are commonly released into bastnaesite flotation pulp from Ca/Ba-bearing gangue minerals. The influence and corresponding mechanisms on the bastnaesite mineral surface and collectors, namely sodium oleate (NaOL), were evaluated experimentally based on micro-flotation, zeta potentials, in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and X-Ray photoelectron spectroscopy (XPS) analyses. The flotation recovery of bastnaesite significantly decreased from ∼95% to ∼25%, ∼15%, ∼80%, ∼25% when exposed to calcite, fluorite, barite, and mixed dissolved species, respectively. The zeta potential of bastnaesite was pH sensitive, indicating that H+ and OH- determine the surface potential of bastnaesite. Solution chemistry analyses revealed that the presence of the dissolved species differed at various pH values. In situ ATR-FTIR demonstrated the different effects of the dissolved species from calcite, fluorite, and barite on collector adsorption. The former two dissolved species mainly depressed the chemisorption of the NaOL monomers (RCOO‒), whereas calcite also affected the physical adsorption of the oleic acid molecular dimer (RCOOH·RCOO‒). Moreover, the barite dissolved species only affected the physical adsorption of the NaOL species. The results of XPS analysis revealed that dissolved species from these three gangues could pre-adsorbed onto bastnaesite and affected the interaction with the collector. Density functional theory calculations were employed to provide further theoretical insights into the interactions between the dissolved species from calcite, fluorite, and barite and NaOL.

Process optimization for acidic leaching of rare earth elements (REE) from waste electrical and electronic equipment (WEEE).

E-waste (EW) from discarded electrical and electronic devices is a potential source of rare earth elements (REEs) that might be recovered from urban and industrial wastes. REEs are essential raw materials for emerging and high technologies. China currently dominates global REE production with a proportion of 97%. To increase the independence of REE supply and eliminate the environmental impacts related to REE mining, methods for an efficient REE recovery from secondary sources like EW are needed. In this work, we examine improvements in pre-treatment and acidic leaching processes to recover REEs and other valuable metals. EW was crushed and ground prior to the sieving. The materials obtained were then subjected to acid leaching. The parameters used to optimize the conditions for leaching were as follows: acid type (HCl, HNO3, and aqua regia), particle size, and waste-to-acid ratio. The maximum leaching efficiency was obtained from the ground, sieved, and undersized part of e-waste by using HCl with a W:A of 12.5 mg/mL. The total REE concentration was 435 mg/kg. Several treatment scenarios are identified with promise for improving REE recovery at full scale in EW recovery plants and thereby advancing goals for a sustainable, circular economy.

Phosphate Polymer Nanogel for Selective and Efficient Rare Earth Element Recovery.

Demand for rare earth elements (REEs) is increasing, and REE production from ores is energy-intensive. Recovering REEs from waste streams can provide a more sustainable approach to help meet REE demand but requires materials with high selectivity and capacity for REEs due to the low concentration of REEs and high competing ion concentrations. Here, we developed a phosphate polymer nanogel (PPN) to selectively recover REEs from low REE content waste streams, including leached fly ash. A high phosphorus content (16.2 wt % P as phosphate groups) in the PPN provides an abundance of coordination sites for REE binding. In model solutions, the distribution coefficient (Kd) for all REEs ranged from 1.3 × 105 to 3.1 × 105 mL g-1 at pH = 7, and the sorption capacity (qm) for Nd, Gd, and Ho were ∼300 mg g-1. The PPN was selective toward REEs, outcompeting cations (Ca, Mg, Fe, Al) at up to 1000-fold excess concentration. The PPN had a Kd of ∼105-106 mL g-1 for lanthanides in coal fly ash leachate (pH = 5), orders of magnitude higher than the Kd of major competing ions (∼103-104 mL g-1). REEs were recovered from the PPN using 3.5% HNO3, and the material remained effective over three sorption-elution cycles. The high REE capacity and selectivity and good durability in a real waste stream matrix suggest its potential to recover REEs from a broad range of secondary REE stocks.

The Behaviour of Rare Earth Elements from South African Coal Fly Ash during Enrichment Processes: Wet, Magnetic Separation and Zeolitisation

Rare earth elements (REEs) are essential raw materials in a variety of industries including clean energy technologies such as electric vehicles and wind turbines. This places an ever-increasing demand on global rare earth element production. Coal fly ash (CFA) possesses appreciable levels of REEs. CFA, a waste by-product of coal combustion, is therefore a readily available source of REEs that does not require mining. CFA valorisation to zeolites has been achieved via various synthesis pathways. This study aimed to evaluate one such pathway by monitoring how REEs partition during CFA processing by the wet, magnetic separation process and zeolitisation. South African CFA was subjected to wet, magnetic separation and subsequent zeolitisation of the nonmagnetic fraction (NMF); solid products were characterised by XRD, SEM, XRF and LA-ICP-MS. The wet, magnetic separation process resulted in the partitioning of a specific set of transition metals (such as Fe, Mn, Cr, V, Ni, Zn, Cu, Co and Mo) into the magnetic fraction (MF) of CFA, while REEs partitioned into the NMF with a total REE content of 530.2 ppm; thus, the matrix elements of CFA were extracted with ease. Zeolitisation resulted in a solid zeolite product (hydroxysodalite) with a total REE content of 537.6 ppm. The process of zeolitisation also resulted in the selective enrichment of Ce (259.1 ppm) into the solid zeolite product (hydroxysodalite), while other REEs were largely partitioned into the liquid phase. CFA valorisation by wet, magnetic separation and zeolitisation therefore allowed for the partitioning of REEs into various extraction products while recovering the matrix elements of CFA such as Fe, Si and Al. The findings of this study highlight the geopolitical importance of REEs in terms of the development of alternative processes for REE recovery from waste and alternative sources, which may potentially give countries that employ and develop the technology a key advantage in the production of REEs for the global market.

Methodology applied to ensure compliance with the remediation goals of an old rare earth production plant contaminated with radionuclides in Brazil

In the past, Brazil has already exploited its immense mineral reserves of rare earth elements. The industrial plants that processed these rare earth ores were contaminated with radionuclides, this happened because at that time there was no legal framework to prevent it. When it was necessary to close these sites, the areas contaminated with radionuclides were remedied during the decommissioning process. This article reports on the steps in the remediation process of an area in one of these facilities and also describes and discusses the methodology applied to ensure that the final planned and authorized radiation levels were effectively achieved during the remediation of this area, located in the largest city in the country. For that, results of the analyses carried out by the operator were the object of comparative analytical tests to verify the quality of the reported data. In order to avoid contaminated and abandoned facilities in the future, it is recommended that the financial planning of industrial facilities with specific environmental and radiological characteristics take into account all the associated costs to be considered environmentally sustainable.

Enhanced leaching recovery of rare earth elements from a phosphatic waste clay through calcination pretreatment

Phosphatic clay is a waste material produced during the beneficiation of phosphate ore, which likely poses severe environmental problems. In this study, a phosphatic clay containing 258 ppm of total rare earth elements (REEs) was used as a feedstock for REE recovery. By reacting with 0.1 M HCl at 75 °C for 3 h, around 36 % of light REEs and 65 % of heavy REEs were extracted from the raw material. However, after calcination pretreatment at 600 °C for 2 h, the recovery was increased to 73 % and 81 %, respectively, which are close to the recoveries obtained from the raw material using a much higher acid concentration of 1.2 M. Based on the findings from sequential chemical extraction tests and scanning electron microscopy analysis, the positive impact was explained by the decomposition and conversion of REE-bearing minerals into more leachable species. Using a higher calcination temperature of 900 °C, recovery of both the light and heavy REEs was largely reduced relative to the raw material. Mineralogical analyses showed that the dominant minerals existing in the material, such as muscovite, were fused and sintered during the calcination at 900 °C. These reactions likely caused the decreases in the recovery. The results and findings from this study will contribute to the beneficial uses of phosphatic clay and the production of REEs.

The spillover effect of trade policy along the value Chain: Evidence from China's rare earth‐related sectors

AbstractThis study examines the heterogeneous spillover effects of an export control policy from an upstream sector to its related downstream sectors. In 2010, China implemented tough policies on rare earth production and export that created a significant price premium for rare earth in foreign markets, thus offering downstream sectors in China cost advantages over their foreign competitors. This study exploits China's policy as an exogenous shock and performs a detailed examination of Chinese customs data. The results show that the export control policy has increased the export price of rare earth downstream products from China, whereas the effects on export quantity and value have been heterogeneous across sectors: they are significant for sectors in which the rare earth cost share is high, and the elasticity of substitution is low.

Toward the Circular Economy of Rare Earth Elements: A Review of Abundance, Extraction, Applications, and Environmental Impacts.

Rare earth elements (REEs) are increasingly critical to the high-technology and low-carbon economy. With a shift to sustainable socioeconomic development that aims to be less fossil fuel dependent, global demand for REEs continues to rise, despite their uncertain supply chain and high environmental impact of production. Here, we review recent research on REEs, including global reserve assessment, REE-based applications, major REE production pathways, environmental impacts, and the potential to leverage circular economies within the REE industry. The main objective of this review is to provide an overall socioeconomic and environmental perspective of the REE industry with a central focus on environmental impacts of various REE-related activities. The literature reveals significant interest in extracting REEs from secondary materials(e.g., tailings, bauxite residues, coal combustion ash) and electronic wastes. However, some of these REE recovery processes are not yet economically profitable and environmental-friendly. Continued technological advancements and increasing demands for REEs may entice countries with recently discovered REE reserves to break the current monopolistic REE supply chain. Furthermore, the sustainability of REE usage may also depend on consumer awareness of environmental and human health impacts associated with end-of-life electronics that contain REEs. On the other hand, REEs may show promise in sustainable agriculture and environmental applications. Nevertheless, further research on REE ecotoxicological impacts is required to establish environmental regulations that protect the environment and human health.

Rare earth elements (REEs) recovery and porous silica preparation from kaolinite

A kaolinite containing 245 ppm of REEs was used as a feedstock for REE recovery. Acid leaching test results showed that less than 20% of the REEs were leached using 1.2 mol/L HCl. However, after thermal treatment at 600 °C, a recovery of over 80% was obtained with a much lower acid concentration (0.01 mol/L). Meanwhile, only 3.91% Al, 2.34% Fe, 8.63% K, 9.32% Mg, 0.08% Ti, and 5.34% Ca were simultaneously extracted. Therefore, high-purity rare earth products are likely produced from the kaolinite. To achieve a more comprehensive utilization of the kaolinite, the residual solid after REE recovery was subjected to a selective leaching process to prepare porous silica. Comparisons among three different types of mineral acids showed that H2SO4 provided the best performance. The effects of different factors were investigated using the response surface methodology. A porous silica with as high as 336.95 m2/g specific surface area was ultimately produced.

Recovery of rare earths, lithium and fluorine from rare earth molten salt electrolytic slag via fluoride sulfate conversion and mineral phase reconstruction

To solve the problem of rare earths (RE) lithium (Li) and fluorine (F) recovery in rare earth molten salt electrolysis slag, a recovery method was developed based on magnetic separation, sulfuric acid leaching, HF recycling, water leaching, fluorination precipitation. First, RE, Li and iron-containing phases in a slag sample were separated using a magnetic separation method. Second, sulfuric acid-leaching was used to reconstruct the phases of RE and Li in the non-magnetic fraction, which were transformed into a rare earth sulfate easily dissolved in water. At the same time, the HF generated in the sulfuric acid leaching process is recovered by multistage adsorption. Finally, qualified fluoride rare earth products were obtained by HF cycle precipitation. The results show that the recovery of iron is 85.30% under the condition that the magnetic separation intensity of 0.668 T, particle size of 58–75 μm, and the main phase in the non-magnetic fraction is the rare earth phase, and the iron content is only 2.90%. Under the conditions of a concentrated acid concentration of 98.00%, a temperature of 633 K, a liquid–solid ratio of 2:1, a particle size of 58–75 μm, a constant stirring speed of 300 r·min−1, and reaction time of 3 h, the removal rate of F is 95.30%, and the transformation rates of Nd, Pr, Dy, and Li reached more than 95.00%. Through water immersion and fluorination precipitation, rare earth fluoride products can be obtained. The purity, particle size, and water content of the products met the standards required for industrial rare earth molten salt electrolysis.

Naturally Derived Organic Dyes for LED Lightings of High Color Rendering and Fidelity Index

AbstractLight‐emitting diodes (LEDs) are a lighting technology with a huge and ascending market. Typically, LED backlights are often paired with inorganic phosphors made from rare‐earth elements (REEs) to tune the emission lineshapes for different applications. However, REE production is a resource‐intensive process with many negative environmental impacts. Herein organic hybrid LEDs are developed using organic dyes synthesized from an abundant and non‐toxic natural product (theobromine) to replace REE phosphors. The resulted hybrid LED generates continuous emission from 400–740 nm, resulting in a high color rendering index (the current industry standard) of 90 and a color fidelity index (the most advanced and comprehensive standard) of 92, challenging commercial LEDs based on REE phosphors. In addition, the light‐converting composite is made from 99 wt% SBS, an inexpensive industrial polymer, and 1 wt% theobromine dyes, reducing the cost of the light converter to ¢1.30 for a 1 W LED, compared to approximately ¢ 19.2 of commercial products. The light converting efficiency of the dye‐SBS composite is 82%. Excited state kinetics experiments are also conducted to provide guidance to further increase the light‐converting efficiency of the theobromine dyes while maintaining excellent color rendering and fidelity.

Industrial waste—A valuable source of rare metals or a reclamation object?

The scope of the analysis embraces nine types of industrial waste: low-grade ore piles, pyrite cinder dumps, tailings dumps, wet magneti c separation and flotation tailings ponds, phosphogypsum piles, red mud ponds, as well as dumps of metallurgical and electric power industries. The prospects of using the industrial waste as a source for production of rare metals, rare earths and other by-products are discussed. The practical interest lies only in the use of low-grade ore and pyrite cinder. Recovery of valuable components from the other types of industrial waste is incapable to solve the problem connected with the waste management but can only aggravate it. It is expedient to extract valuable components from waste of current processing, in amount to be sufficient to satisfy the related demand. To this effect, it is necessary to create new no-waste technologies. This is the way taken by Russia’s largest companies RUSAL and ROSTEC: reduction in cost of the main production releases finds for the implementation of environmental and nature-oriented activities.The problem connected with the use of many millions of tons of ecologically hazardous old waste is solved in a big way by means of reclamation, which is only possible in association with the government, through establishment of a public institution on industrial waste management.

Ultra-selective ion sieve for thorium recovery from rare earth elements using oxygen-rich microporous carbon adsorption

The ultra-selective extraction of thorium ions (Th(IV)) from lanthanides is of significance to both solve the radioactive pollution issue in rare earth (RE) production and sustainably provide thorium fuel for the liquid fluoride thorium reactors (LFTR). However, it remains a great challenge. Here, we reported an oxygen-rich microporous carbon for ultra-selective extraction of Th(IV) from rare earth elements (REEs) in a wide pH range. This selectivity was derived from the synergy of the oxygen-rich nature, microporous structure of the carbons, the chemical valence, and the ionic size of Th(IV) species. This oxygen-rich microporous carbon presented an ultra-high distribution coefficient (Kd) of 1.15 × 108 mL g−1 for Th(IV) at pH 4.9 in the presence of 15 REEs and revealed outstanding performance for Th(IV) extraction from three simulated RE solutions with high ionic strength of lanthanides. Meanwhile, an exceptional adsorption capacity of 624.98 mg g−1 was obtained in the single Th(IV) solution. Both values were superior to those of reported adsorbents. More importantly, the new adsorbent developed here could be prepared from cigarette butts. These features ensured the oxygen-rich carbon as a promising and cost-effective adsorbent for high-purity thorium extraction from REEs.

The thermodynamics of rare earth element liberation, mobilization and supergene enrichment during groundwater-regolith interaction

Rare earth elements (REEs) mobilize, fractionate, and are re-distributed during supergene processes, and thus provide a powerful tool with which to quantitatively reconstruct the effects of chemical weathering. Moreover, under certain conditions, the REEs can concentrate to levels in the regolith sufficient to form giant regolith-hosted REE deposits, that are now responsible for much of the World’s production of heavy REEs (HREEs). Understanding the supergene behavior of the REEs is an important first step towards applying the REEs as a geochemical tool and meeting the growing global demand of the REEs.Thermodynamic calculations predict that dissolution of the main REE minerals in REE-rich protoliths, namely synchysite-(Y), gadolinite-(Y), hingganite-(Y), yttrialite-(Y), allanite-(Ce), eudialyte, chevkinite-(Ce), britholite, euxenite and loparite-(Ce), should occur spontaneously during weathering. It therefore follows that a high abundance of these minerals in the protolith implies high mobility of the REEs during weathering and consequently a high potential for the discovery of economic REE resources. Dissolution of apatite is promoted by metamictization or structural distortion and could be also important at low pH. In contrast, some LREE-fluorocarbonate minerals, notably bastnäsite-(Ce) and parisite-(Ce), and monazite-(Ce) are likely thermodynamically stable in acidic environments. Thus, they would be preserved in the regolith. Zircon, titanite, aeschynite, fergusonite, and xenotime-(Y) are resistant to acidic dissolution, consistent with their common occurrence as residual minerals.In the cases of the world-class regolith-hosted REE deposits in South China, the groundwater is mildly acidic to circumneutral and carbonate-rich. The REEs are consequently transported dominantly as hydrated cations and carbonate complexes, depending on the pH. The general inheritance of the REE pattern of the regolith groundwater in the clay-sorbed fraction in the regolith indicates that the REEs in regolith are scavenged from the regolith groundwater. Elemental anomalies of specific REEs in the clay-sorbed fraction are very likely caused by an anomalously high REECO3+ fraction in the corresponding regolith groundwater, suggesting a preferential uptake of the REECO3+ complexes by the clay minerals, feasibly by halloysite through intercalation as interlayer complexes. This reaction is expected to be particularly important for the sorption and enrichment of the HREEs in the regolith. Depending on the pH and carbonate concentration of the water, surface complexation on clay minerals or interlayer intercalation particularly in halloysite control the pattern of REE enrichment. Mixing of the regolith groundwater with the alkaline and carbonate-rich aquifer groundwater increases the pH and carbonate concentration and, in turn, affects the ability of the mixed water to transport the HREEs. Interplay of aqueous complexation with the regolith mineralogy significantly affects the REE fractionation and re-distribution during groundwater-regolith interaction.

Recovery and Enhanced Upgrading of Rare Earth Elements from Coal-Based Resources: Bioleaching and Precipitation

Rare earth elements (REEs) are of great importance to modern society and their reliable supply is a major concern of many industries that utilize them in metal alloys, semiconductors, electrical equipment, and defense equipment. REEs in the coal waste have been revealed to be an alternative resource for REEs production. In this study, the extraction, recovery, and upgrading of the REEs from coal waste has been realized with the bioleaching and precipitation processes. Reliable and sustainable acid and oxidant production from the oxidation of the pyrite with Acidithiobacillus ferrooxidans to generate acid for leaching were realized in this research. The acidified bioleaching solution was used to extract REEs from coal waste, with 13–14% yields for most REE elements (~72 h of leaching). However, recovery for longer duration tests was significant higher (varies from 40–60% for individual REEs). After extraction, precipitation and separation processes were designed with the aid of Visual Minteq calculations and modeling to concentrate the REEs. With the procedures designed in this research, a final REEs precipitate product containing 36.7% REEs was produced.

How environmental regulation affects China's rare earth export?

China’s rare earth export trade has developed so rapidly since 1990s that China has gradually occupied a leading position in the international market. However, this fast development was proceeding at the cost of the rare earth energy consumption and environmental devastation. Now China begins to attach great importance to environmental protection, which attracts many researchers. This study aims to analyze the influence of environmental regulation on China’s rare earth export trade. And the original study is amongst the few to examine the relationship between environmental regulation and China’s rare earth export with the product-level data. Different from previous studies, this paper selects China’s rare earth export data from 1995 to 2015 and introduces product heterogeneity based on the rare earth production process. Moreover, this study uses the entropy weight method to measure the intensity of environmental regulation. The core conclusions are as follows: (1) Environmental regulation significantly promotes rather than restrains China’s rare earth export. (2) According to the rare earth production process, this paper divides rare earth products into 3 kinds, that is, rare earth raw materials, rare earth useful components and rare earth end-use applications. Then, it is found that rare earth useful component export in processing and smelting is positively affected by environmental regulation. Rare earth raw materials and end-use applications in China’s export are hardly affected. (3) Technological innovation has a mediating effect on the impact mechanism of environmental regulation on China’s rare earth export, which means that environmental regulation significantly promotes technological innovation of enterprises, and thereby the rare earth export is increased. The findings are helpful for policymakers to resolve the issue of environmental devastation.

A cleaner recovery of rare earth bearing minerals by Pickering emulsification: Improvement of processing conditions toward an economic operation

The production of rare earth elements (REE) is crucial in modern world. They are increasingly utilized in numerous applications, especially in clean- and high-tech sectors. The froth flotation is commonly considered for the concentrate production of REE, from their bearing ore, in the course of mine-to-metal production chain. However, various environmental drawbacks are present in conventional flotation processes such as large amounts of tailings, chemical reagents and surfactants all released in the surroundings of the operations. In our previous work, we introduced the Pickering emulsification as a novel approach, and cleaner alternative to the froth flotation, which potentially offers multiple ecologic and economic advantages, where we achieved a recovery of about 50% of REE, and an enrichment ratio of 2.9. Here, we investigated the effects of two essential process parameters such as mixing intensity (i.e., changing the impellers speed), and shear uniformity (i.e., comparing the performance of two hydrodynamically different impellers) to improve the process performance. We achieved an optimum rotational speed and energy consumption with a Maxblend impeller, where the size of the emulsion droplets showed much more uniform distribution. Thus, the recovery and the enrichment ratio rose up to 65% and approximately 3.85, respectively, after one single stage of emulsification. We have shown that such conditions outperform the froth flotation besides the environmental advantages.

Hypothetical Soil Thresholds for Biological Effects of Rare Earth Elements

Objectives: Anthropogenic exposures to rare earth elements are poorly known and there is limited information on their toxicity and ecotoxicity. At the same time, world production of rare earth elements has doubled every 15 years over the last half-century, and high environmental concentrations of gadolinium and lanthanum have already been found. The current review aims to give some estimates of overall exposures and an initial in-depth appraisal of thresholds for effects on agricultural soil. The results are envisaged to be used in initial assessments of agricultural soil where the natural concentrations have been anthropogenically enhanced.
 
 Methods: An extensive review has been made of available scientific literature. Criteria have been established for the selection and analysis of eligible research. For instance, only effects on soils with vegetation have been included in the assessment of biological effects. A species sensitivity distribution based on 25% inhibition of organism functions has been used to establish thresholds for effects on soil organisms. 
 
 Results: Around the year 2000, mean anthropogenic contributions of lanthanides in European soil regions were at most a few per cent of the total soil content. Since then, they should have increased considerably. The proposed hypothetical threshold for agricultural soils is 1125 mg total rare earth element per kg of soil. This threshold is about 8 times the natural soil concentration.
 
 Conclusions: If this result holds up to scrutiny, it implies that general anthropogenic pollution by rare earth elements will not be a threat to agricultural sustainability for the coming generation. A preliminary assessment suggests that this threshold would also protect humans from adverse effects due to secondary exposure.

PURIFICATION OF RARE EARTH ELEMENTS FROM THORIUM, URANIUM, AND RADIOACTIVE ISOTOPES

This article presents the results of industrial tests of the technology of sorption, precipitation and extraction purification of the concentrate of rare earth elements (REE) from radioactive decay products of the uranium and thorium series. It has been shown that the combination of sorption, selective precipitation, and extraction processes makes it possible to effectively purify REE from U, Th, Po, Ra, RaD, and Ac and to obtain radiation-safe nitrogencontaining solutions for the production of fertilizers and individual REE.