Rare Earth Resources Research Articles

Leaching of Rare Earth Elements (REEs) from lake sediments around Eppawala phosphate deposit, Sri Lanka: A secondary source for REEs

Rare earth elements (REEs) are widely employed in a spectrum of high-tech applications. Since primary REE resources are limited, secondary REE sources will be crucial to reduce future supply chain gap between REE demand and supply, which is currently about 3000 t per year. In this context, lake sediments around Eppawala Phosphate Deposit (EPD) in Sri Lanka could be considered as a potential secondary REE source since a man-made water canal running across the EPD transports REE-rich materials to the lake sediments. The average total REE (ΣREE) concentration of the downstream surface lake sediments was 804 mg/kg. The REEs were present in lake sediments as 3 fractions, namely, ion-adsorbed, colloidal, and mineral bound fractions. Ion-adsorbed fraction was assessed using less expensive, easy, and environmentally friendly ion-exchangeable leaching by a solution of (NH4)2SO4 under optimum conditions. Experimental results revealed that 34% of ΣREE was leached as ion-adsorbed fraction. In addition, the maximum leachable REE content (i.e. ion-adsorbed and colloidal fractions) was determined as 78% of ΣREE through HCl leaching under optimum conditions. Therefore, acid leaching was proven to be the best leaching process and the results in this preliminary study could be useful to assess low-grade geological resources, especially sediments and soils around major phosphate deposits with similar geological settings.

Mine waste from carbonatite deposits as potential rare earth resource: Insight into the Phalaborwa (Palabora) Complex

The Phalaborwa (Palabora) Igneous Complex (PIC), South Africa, has been mined for the last six decades for copper and phosphate, among others commodities. As a result, more than 4500 Mt. of mining wastes have been deposited in waste rock dumps (WRDs) and tailing impoundments. This study aims to investigate the potential of the PIC wastes (WRDs and tailings) as a secondary resource of rare earth elements (REE) and its possible processing options, by means of both mineralogical and geochemical determinations, using X-ray diffraction (XRD), petrographic and scanning electron microscope with energy dispersive spectroscopy (SEM–EDS) and electron probe micro-analyzer (EPMA). The samples were also submitted to a REE leachability assay based in a sequential extraction procedure. Phoscorites and carbonatites are major lithologies in the WRDs and contain a notable concentration of REE, of which 0.2 and 0.1 wt%, respectively, would be easily extractable. The mineralogical results show monazite as the main REE-mineral (∑REE 60 wt%), while fluorapatite and calcite are the most important REE-bearing minerals (∑REE 1 and 0.5 wt%, respectively) for their abundance. On the other hand, the tailings are comprised mostly by monomineralic particles of calcite, dolomite, pyroxene, fluorapatite, magnetite and phlogopite. Based on the geochemical results, the extraction of REE from monazite, fluorapatite, calcite and dolomite, from tailings produced by both the Cu and the phosphate mines, might produce up to 5.65 and 1.75 kg of REE per ton, respectively. Therefore, tailings from PIC have the potential to become an asset. An approach to circular economy by re-processing mining wastes would extend the lifetime of the PIC mines and their benefits, while reducing the waste of resources and their environmental impact.

Advances in solid lithium ion electrolyte based on the composites of polymer and LLTO/LLZO of rare earth oxides

AbstractComposite solid electrolyte is a promising solution for the development of new generation of safe and high‐performance all‐solid‐state lithium batteries (ASSLBs). It combines both the advantages of inorganic electrolyte and organic polymer electrolyte, having high ionic conductivity, mechanical strength, good contact with the electrodes and high processability. In the recent decades, rare earth oxides have attracted wide attentions from researchers because of their high ionic conductivity. China is abundant in rare earth resources, so has a good chance to provide the world with high quality rare earth containing functional materials. This review paper focuses on the recent progress in the studies of composite solid electrolyte of polymer and rare earth containing lithium lanthanum zirconium and lithium lanthanum titanium oxides, and gains insights into the challenges in the field, and hopefully helps in the rational design of high performance electrolyte for the development of ASSLBs.

Coal characterization and occurrence of rare earth elements in coal and coal-ash of Sohagpur Coalfield, Madhya Pradesh, India

ABSTRACT Coal is a valuable source for power energy as well as for metal contents within it. Coal and its by-product are considered a promising resource for the critical elements and rare earth elements (REEs). The study of REEs in coal is in its infancy. This paper focuses on REEs’ occurrence, qualitative, and quantitative in coal and its by-products (shale coal, shale coal ash, and coal ash) of Sohagpur Coalfield, Madhya Pradesh, India. The collected coal samples were analyzed by scanning electron microscope with energy-dispersive X-ray analysis, inductively coupled plasma mass spectrometry, bomb calorimeter, thermogravimetric analysis, and ultimate analysis. The REEs’ concentration of Sohagpur Coalfield was also compared with the Chinese coal, US coal, and world coal average. The average content of critical REEs for Y is 51.49 ppm, for Nd is 79.34 ppm, for Eu is 2.67 ppm, for Tb is 1.71 ppm, and for Dy is 9.76 ppm in samples. The highest average values of REEs reported for Ce are 58.15 ppm in coal and 187 ppm in coal ash by-products. Coal by-products of the collected samples are a good resource for REEs than the Chinese coal, US coal, and world coal averages.

Igneous genesis of the Bayan Obo REE–Nb–Fe deposit: New petrographical and structural evidence from the H1–H9 cross-section and deep-drilling exploration

Rare earth elements (REEs) are a focus of global attention because of their unique properties and high-tech applications. Bayan Obo is the world's largest REE deposit and is hosted in the Paleoproterozoic Bayan Obo Group, Inner Mongolia. The REE resources are concentrated in unit H8, “dolomite marble.” However, whether unit H8 has an igneous or sedimentary origin is debated, and relationships among units H1–H9 are unclear, hindering our understanding of the formation of such a giant REE deposit. It was previously assumed that the unit H8 orebody is located in both limbs of the Bayan syncline and unit H9 in the core, which also needs to be confirmed because it is a guide for ore exploration. Field observations and petrographic studies of units H1–H9 were undertaken to re-evaluate the petrology and structure of the Bayan Obo Group. It was found that some units (e.g., H5–H7) are missing from the studied cross-section, with the two sides of unit H9, across the hinge of the so-called syncline, not being directly comparable. Unit H8 displays petrological, mineralogical, and whole-rock REE geochemical characteristics distinct from those of the other units investigated, suggesting they are of different origin. Moreover, deep-drilling exploration indicates major differences between the two limbs of the orebodies in terms of thickness, occurrence, and spatial distribution. The East orebody has a steep dip angle of 70°–80° and continuously extends to depth without reduction of angle, suggesting the syncline is probably nonexistent. These results, combined with the reported intrusion relationship of unit H8 with surrounding rock and in situ isotopic studies previously reported, indicate that the orebody is a carbonatitic igneous conduit rather than being of sedimentary origin. SHRIMP U–Pb dating of detrital zircons from the units H2–H9 yielded ages of 2574 ± 25 to 132 ± 2 Ma, overlapping the ages of units H1–H9 and the main REE mineralization periods reported previously. These protracted and complicated ages of the orebody likely represent fluid-aided resetting ages.

Ecological footprints jeopardy for mineral resource extraction: Efficient use of energy, financial development and insurance services to conserve natural resources

The commodity and resource markets played an important role in attaining the country's economic development via energy efficiency, economic insurance prices and sound financial development. However, the enormous pressure of human demand on natural capital exhausts many important rare earth's resources that demolished the global resource conservation agenda. This study examines the stated factors in the top 10 mineral abundant economies by using their latest available data series from 1990 to 2019. The results of the study show that ecological footprints on mineral resources confirmed the hump-shaped relationship between them. The enormous human demand for natural capital is viewed further in the environmental accounting system. Ecological footprints cause a greater extraction of mineral resources that jeopardize future stocks of rare earth's resources. The panel estimates show that insurance and financial services, massive population growth, and continued economic growth decreases mineral resource rents. In contrast, energy efficiency and trade policies increase mineral resource rents across countries. In general, the results support the economic policies that help reduce human demand for natural capital by efficient insurance services, sustainable economic growth, energy efficiency, and trade fair policies. These factors required more sustainable efforts to mitigate adverse environmental externalities by adopting the latest technology in extractive industries to prevent unsolicited mineral losses.

Removal of Trace Aluminum Impurity for High-Purity GdCl3 Preparation using an Amine-Group-Functionalized Ionic Liquid

Aluminum, as an associated metal with rare-earth resources, is a common impurity in rare-earth separation products. In the traditional P507-kerosene-HCl system, tremendous aluminum impurity (8875 mg/L herein) is often enriched in GdCl3 solutions because of the similar extraction sequence during rare-earth separation. In this work, a new amine-group-functionalized ionic liquid (IL) was developed to remove trace aluminum impurity from high-purity GdCl3 solutions, overcoming the drawbacks of strong hydrophilicity and complicated compositions of the organic phase, as well as other impurities introduced and tremendous saline wastewater produced inevitably. Methyltrioctylammonium hydroxide (N1888OH), instead of the water soluble ammonium hydroxide (NH4OH), was used to dissociate the dimer of sec-octylphenoxy acetic acid (CA12) and synthesize cation- and anion-bifunctionalized IL [N1888][CA12]. The separation factor of Al/Gd was as high as 36. The influences of pH, salting-out agent, extraction time, temperature, and stripping efficiency on the extraction efficiency were evaluated. The result showed that high-purity GdCl3 solution was obtained with low aluminum impurity of 10 ppm after five-stage countercurrent extraction. Due to the weak interaction between the metal and IL, very dilute HCl solution (0.07 mol/L) and NaOH solution (0.07 mol/L) were in favor of metal stripping and IL regeneration.

Enrichment of rare earth elements in the early Cambrian Zhijin phosphorite deposit, SW China: Evidence from francolite micro-petrography and geochemistry

The Zhijin phosphorite deposit is a giant early Cambrian rare earth element (REE) deposit, with particular enrichment in heavy REEs, and is of high economic significance. The REEs of the deposit occur almost entirely in apatite, which, on the basis of petrographic characteristics, can be divided into francolite grains (90%), amorphous apatite, and phosphate fossils. In this paper, we report an investigation into francolite grains in different types of phosphorite from ore sections of the Zhijin deposit. Detailed petrographic and transmission electron microscopy observations reveal that the francolite grains are composed of nano-apatite crystals measuring 120–160 nm long. Trace-element contents of pyrite and whole-rock geochemical indicators (such as Cr/Zr and V/Ni ratios and Th/U–Co/Ni plots) suggest that the Zhijin phosphorite formed in an anoxic hydrothermal sedimentary environment. However, the negative Ce/Ce* and Eu/Eu* anomalies indicate that the diagenetic environment of the francolite grains was oxidic. Different diagenetic redox environments and the presence of transportation fractures in francolite grains identified under back-scattered electron imaging reveal that the francolite grains underwent prolonged abrasion and transportation in seawater before sedimentation. Petrographic observations and laser ablation–mass spectrometry element surface scanning analyses indicate that the REEs are uniformly distributed in nano-apatite in isomorphic form, and no nano-inclusions or REE minerals were found, implying that late mineralization was not the cause of REE enrichment. The higher (La/Yb)N ratios of francolite grains relative to seawater indicate that the francolite grains captured abundant REEs during the early diagenetic stage. We infer that prolonged exposure to seawater and the high specific surface area of francolite grains are the key factors that led to the enrichment in REEs. Combining the timing of the metallogenic epoch (543 Ma), Sr–Nd isotopic data, and the Y/Ho ratio, which is close to those of modern seawater, indicates that the REEs were sourced from paleo-seawater. Paleogeographic information suggests that during the early Cambrian, extensive continental collisions caused great amounts of continental weathering products to enter the paleo-ocean, leading to the production of abundant amounts of hydrothermal–sedimentary phosphorus and REEs in shallow seas, thus forming an ideal sedimentary environment for generating the REE resources of the Zhijin phosphorite deposit.

China's rare earth industry technological innovation structure and driving factors: A social network analysis based on patents

Based on patent information, the paper analyzes the technological comparative advantages from the perspective of industrial chain, and adopts the Social Network Analysis (SNA) method and knowledge production function model to explore technological innovation network structure of China's rare earth industry and its driving force. The results show that, overall, China's rare earth industry technological innovation ability has continued to increase in terms of the breadth and depth, and the industrial chain has shown the characteristics of “strong upper and weaker lower”. The network structure analysis show that the overall technical connection network tends to be close and stable, but it is still in a state of weak connection. In terms of individual networks, technologies represented by the development, extraction and smelting of rare earth resources constitute the core participants in the innovation network, and play the role of the power and control center of the technological innovation network. Further factors identification shows that China's innovation environment is the biggest driving force for technological innovation in the rare earth industry, followed by R&D investment and resource retention capacity. Additionally, the development of strategic emerging industries related to rare earths and resource production capacity have obvious lag effect on the technological innovation level.

Investigating the performance of oxalic acid for separating bastnaesite from calcium-bearing gangue minerals based on experiment and theoretical calculation

Bastnaesite is a major light rare earth resource in the earth, which is difficult to separate from calcium-bearing gangue minerals in flotation because of their similar flotation characteristics as the semisoluble salt minerals. To address this problem, in 3-hydroxy-2-naphthyl hydroxamic acid (H205) system, the selective inhibition mechanism of oxalic acid on common calcium-bearing gangue minerals (calcite and fluorite) in bastnaesite flotation was studied by flotation tests, solution chemistry analysis, zeta potential measurements, and X-ray photoelectron spectroscopy (XPS) measurements, combined with thermodynamics and density functional theory (DFT) calculation. After the analysis of those tests and calculation results, it can be known that the hydrophilic oxalic acid can selectively compete with H205 for the active site (Ca2+) on the surface of the calcium-bearing gangue minerals, thus reducing its surface hydrophobicity and inhibiting its floating, while bastnaesite is not susceptible. In this process, fluorite is more inhibited than calcite.

Adsorption behavior and mechanism of Serratia marcescens for Eu(III) in rare earth wastewater.

Directly discharging low-concentration rare-earth wastewater not only wastes rare-earth resources but also pollutes the environment. In this study, the biosorption behavior of Serratia marcescens for Eu(III) was studied with emphasis on the optimization of adsorption conditions, adsorption kinetics, and adsorption isotherm. It was shown that the maximum adsorption capacity of Serratia marcescens reached 115.36 mg·g-1 under an optimal condition, indicating the good adsorption capability of Serratia marcescens for Eu(III). The adsorption kinetics and adsorption isotherm analysis showed that the adsorption process conforms to the pseudo-second-order kinetic model and Langmuir adsorption isotherm, indicating that the adsorption of Eu(III) by Serratia marcescens is a monolayer chemical adsorption process. In addition, the adsorption mechanism was investigated by using characterizations of zeta potential, scanning electron microscope-energy dispersive spectrometer (SEM-EDS), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS) analyses. It was revealed that the adsorption of Eu(III) by S. marcescens is a combination of electrostatic attraction, ions exchange and coordination. These findings indicate that S. marcescens can be used as a potential biosorbent to recover rare earth elements from rare earth wastewater.

The Use of Mining Tailings as Analog of Rare Earth Elements Resources: Part 1 – Characterization and Preliminary Separation

ABSTRACT The rapid depletion of high-grade rare earth elements (REE) resources implies that future supplies may be augmented with low-grade ores, mining tailings and other unconventional resources to meet cutoff grades and subsequently supply demands. In this work, detailed characterization of tailings from a copper processing plant was carried out to expand the knowledge of their chemical and mineralogical characteristics for REE recovery. The results showed that the REE are mainly mineralized as bastnäsite, monazite, and stetindite, along with uncommon minerals, such as brannerite, stillwellite, and florencite, for which there is limited processing data. In a preliminary effort to recover the REE, the tailings were subjected to gravity, magnetic, and froth flotation separation. Over 90% REE recovery was achieved via froth flotation, whereas magnetic and gravity separation tests recovered up to 86% and 54% REE, respectively. The results from this study suggest that, with systematic optimization studies, REE recovery and upgrade could be enhanced, with significant efforts of minimizing the recovery of key gangue minerals, such as goethite, hematite, and quartz. Overall, the study confirms that the tailings used in this work could be regarded as unconventional REE resources subject to tactical development and optimization of beneficiation methods.

Lanthanum Diffusion in Fluorapatite at 400 °C, 50 MPa and 4–16 wt %

Apatite is an important carrier of rare earth elements (REEs) and phosphorite is a potential REEs resource. However, the influence of hydrothermal fluids on the migration and enrichment of REE in apatite remains controversial. The experimental study of the interaction between REE-bearing fluid and apatite is one of the essential ways to understand the chemical behavior of rare earth elements in apatite. In this study, we conducted the fluid–mineral reaction experimental study (at 400 °C, 50 MPa and 4–16 wt %) between high lanthanum (La) content hydrothermal solution and low REE content to reveal the influence of different salinities on the diffusion of rare earth elements in fluorapatite. Based on in situ geochemical analyses of experimental products, we show that the diffusion coefficients of La in fluorapatite are between 3.24 × 10−15 and 5.88 × 10−15 m2/s. The salinity of the fluid has a great influence on the diffusion coefficient, with the increase of salinity, the diffusion coefficient increase.

Electrochemical treatment of spent NdFeB magnet in organic acid for recovery of rare earths and other metal values

The spent Neodymium-Iron–Boron (NdFeB) magnet is potential secondary resource of rare earth elements. Conventional hydrometallurgical processing of spent NdFeB magnet requires energy intensive steps viz. crushing, grinding, roasting etc. and is associated with the discharge of acidic effluents in the environment. The chemical dissolution of waste magnet using biodegradable organic acids is also associated with the major drawback of poor leaching efficiency. The present study is focused on the electrochemical dissolution of spent NdFeB magnet in organic acid for the recovery of rare earths and other metal values. The electrochemical dissolution studies were carried out using citric acid as an electrolyte. The dissolution of spent NdFeB magnet in citric acid was studied with and without electrochemical effect. It was found that the dissolution of NdFeB magnet in citric acid enhanced significantly under electrochemical effect as compared to chemical dissolution. The reaction mechanism of electrochemical dissolution was also determined. The effect of various parameters such as citric acid concentration, current density, stirring speed, bath temperature etc. were studied for electrochemical dissolution of spent NdFeB magnet. The anodic dissolution efficiency and energy consumption were also evaluated. A solvent extraction method using 1M di-(2-ethylhexyl) phosphoric acid (D2EHPA) as an extractant was developed to extract rare earths selectively and quantitatively from the electrolytic liquor. From the loaded organic, mixed oxalates of rare earths were recovered quantitatively by precipitation stripping using oxalic acid solution as stripping agent. Mixed oxides of neodymium, praseodymium and dysprosium of purity 99.9% were obtained by calcination at 1073 K. Iron oxide (98.6% pure) was also produced as by-product of the process. The solid products were characterized by chemical analysis, XRD, SEM and TG-DTA. Enhanced dissolution of metals in citric acid under electrochemical effect is the main advantage of this electrochemical process. The developed process is clean and avoids energy intensive steps viz. crushing, grinding and roasting.

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.

Effect of Oxidation Behavior of (Nd,Dy)-Fe-B Magnet on Heavy Rare Earth Extraction Process

Rare earth magnets with excellent magnetic properties are indispensable in the electric device, wind turbine, and e-mobility industries. The demand for the development of eco-friendly recycling techniques has increased to realize sustainable green technology, and the supply of rare earth resources, which are critical for the production of permanent magnets, are limited. Liquid metal extraction (LME), which is a type of pyrometallurgical recycling, is known to selectively extract the metal forms of rare earth elements. Although several studies have been carried out on the formation of intermetallic compounds and oxides, the effect of oxide formation on the extraction efficiency in the LME process remains unknown. In this study, microstructural and phase analyses are conducted to confirm the oxidation behavior of magnets pulverized by a jaw crusher. The LME process is performed with pulverized scrap, and extraction percentages are calculated to confirm the effect of the oxide phases on the extraction of Dy during the reaction. During the LME p rocess, Nd i s completely e xtracted a fter 6 h, w hile D y remains as D y2Fe17 and Dy-oxide. Because the decomposition rate of Dy2Fe17 is faster than the reduction rate of Dy-oxide, the importance of controlling Dy-oxide on Dy extraction is confirmed.

Simulation Solvent Extraction of Rare Earth Metal Source Origin from Marine Sediment

Ocean mining probably one of the world’s largest untapped resources of rare earth elements. Specifically, the rare earth resources from polymetallic nodule which receive less attention from industry due to the various challenges. This article studied the simulation HDEHP-HCl system fractional cascade extraction strategy for extraction of rare earth elements from polymetallic nodule. HDEHP-HCl was capable of complete extract very high purity rare earth elements (99.9%). The fractional cascade extraction strategy simulation designed for the separation of rare earth elements could be momentous for practical application. The simulation data shows high purity of products at both outlets, aqueous and organic are obtainable. All these will provide the promising industrial applications of HDEHP-HCl system in extracting rare earth elements from polymetallic nodule with more fundamental data and guidance.

Leaching Kinetics of Rare Earth Elements in Phosphoric Acid from Phosphate Rock

Phosphate rock has been considered as one of the most significant secondary rare-earth resource, and the utilization of rare earth elements (REEs) in phosphate rock has attracted increasing attention. In this study, the leaching kinetics of REEs from a phosphate ore from China was studied with the variation of temperature and phosphoric acid concentration under the conditions: ratio of liquid to solid of 12 mL/g, stirring speed of 120 r/min, and phosphate particle size of −0.074 mm amounts 61.1%. The results suggest that there were two distinct stages in leaching process and kinetics of both stages followed shrinking core model. At fast reaction stage, the semi-empirical equation describing the kinetics was 1 − 3(1 − α)2/3 + 2(1 − α) = 1.885CH3PO40.89exp(−11220/8.31T)t. The semi-empirical equation for slow reaction stage was 1 − 3(1 − α)2/3 + 2(1 − α) = 0.299CH3PO42.50exp(−18720/8.31T)t. Using shrinking core model and time-to-a-given-fraction method, we found that leaching rate of fast reaction stage was controlled by solid product layer diffusion, and both solid product layer diffusion and chemical reaction determined slow reaction stage.

Ocean-Floor Sediments as a Resource of Rare Earth Elements: An Overview of Recently Studied Sites

The rare earth elements (REE), comprising 15 elements of the lanthanum series (La-Lu) together with yttrium (Y) and scandium (Sc), have become of particular interest because of their use, for example, in modern communications, renewable energy generation, and the electrification of transport. However, the security of supply of REE is considered to be at risk due to the limited number of sources, with dependence largely on one supplier that produced approximately 63% of all REE in 2019. As a result, there is a growing need to diversify supply. This has resulted in the drive to seek new resources elsewhere, and particularly on the deep-ocean floor. Here, we give a summary of REE distribution in minerals, versatile applications, and an update of their economic value. We present the most typical onshore methods for the determination of REE and examine methods for their offshore exploration in near real time. The motivation for this comes from recent studies over the past decade that showed ΣREE concentrations as high as 22,000 ppm in ocean-floor sediments in the Pacific Ocean. The ocean-floor sediments are evaluated in terms of their potential as resources of REE, while the likely economic cost and environmental impacts of deep-sea mining these are also considered.

The Feedback Effect of Rare Earth Development Policy on Economy and Society

China is rich in rare earths (RE). However, the exploitation of rare earths not only promoted the social and economic development, but also produced negative environmental externalities, so the relevant departments issued policies and regulations to carry out pollution control work. This paper made a macroanalysis of China firstly. And then this paper took Jiangxi province as the main research area, which compared with Inner Mongolia, Guangdong, Sichuan and Fujian. This paper used the method of non-radial SBM to measure policy execution efficiency. Based on calculating the social and economic development indicator, economic development and social development indicator, this paper explored the feedback correlation of policy execution efficiency and the development of society and economy by grey relational analysis. The results showed that China reduced its dependence on rare earth resources. However, the efficiency of policy implementation needs to be improved. Effective implementation of rare earth industry policy has a feedback effect on social and economic development. From the perspective of case analysis, the implementation efficiency of vegetation destruction policy in Jiangxi province is higher than that of air pollution policy. The overall policy implementation efficiency of Jiangxi province has a strong feedback effect on the overall level of social and economic development, among which the air pollution and water pollution policy implementation efficiency has a relatively obvious feedback effect on social and economic development.