Rare Earth Resources Research Articles

Rare earth elements and yttrium in coal ash from the Luzhou power plant in Sichuan, Southwest China: Concentration, characterization and optimized extraction

Coal ash is considered as a promising alternative resource for rare earth elements and yttrium (REE + Y or REY) recovery. Coal ash samples (fly ash and bottom ash), as well as corresponding feed coals, collected from the Luzhou coal-fired power plant in Sichuan, southwestern China were analyzed for their chemical and mineralogical characteristics. The fly ash was further tested for its feasibility of REE extraction. The feed coals are characterized as a low-volatile bituminous, medium‑sulfur, and high-ash coal, sourced from the Guxu coalfield (Late Permian Longtan Formation) in Sichuan, SW China. REE and Y, along with high-field-strength elements Zr(Hf) and Nb(Ta), and Li, F, Sc, V, Cr, Co, Cu, Zn, Ga, Ge, Se, Sr, Cd, In, Sn, Hg, Th, U, are all enriched in the feed coal. The mineralogical compositions of the feed coals are dominated by kaolinite and illite/smectite (I/S) mixed layers, followed by the carbonate minerals including calcite, siderite, ankerite, and minor amounts of anatase and jarosite.The combustion of the feed coals produces a Class F fly ash, characterized by an aluminosilicate composition with a low CaO content. The bottom ash is compositionally similar to the fly ash, except that it is more enriched in high-density elements (Fe and Mn), and more depleted in volatile elements. REY are enriched in both the fly ash and bottom ash, although heavy REY (HREY) are notably more enriched in the fly ash. Mineralogical analysis shows that the fly ash consists of >70% amorphous glass and <30% mineral phases such as mullite, quartz and iron oxides. The bottom ash is composed of ~60% amorphous glass but with a more complex mineralogical composition than the fly ash. Dissolution of the fly ash and bottom ash with 4% hydrofluoric acid (HF) showed that ~90% of all the REY are associated with the amorphous glass in the fly ash, whereas <50% of REY in the bottom ash is contained in the glassy component. An alkaline-acid-combined (NaOH-HCl) sequential leaching process was employed to test the extractability of REY in the Luzhou fly ash. The experimental variables, including extractant concentration, liquid-to-solid ratio, leaching temperature and leaching time, were optimized by an orthogonal array design. The optimal NaOH leaching conditions results in 41.10% of active silica removal from the fly ash and 39.43% of REY enrichment. The HCl leaching of desilicated fly ash achieves 88.15% of REY extraction efficiency under the optimal conditions, which is a dramatic increase as compared to the same leaching of raw fly ash. Even though the extraction efficiency may vary between different coal ashes from various sources, a complete REY extraction procedure from fly ash is suggested for future use.

Simultaneous recovery of rare earth elements and phosphorus from phosphate rock by phosphoric acid leaching and selective precipitation: Towards green process

Phosphate rock has been considered as one of the potential promising resources for rare earth elements (REEs). But the cost issues and the technical challenges caused by the low content of REEs in ores did hinder the further development of REEs recovery technologies. In order to explore a green process for the recovery of REEs from phosphate rock, this study investigates the effects of phosphoric acid concentration, liquid-to-solid ratio (L/S ratio), leaching time and temperature on the leaching efficiencies of the major components from phosphate rock. A REEs recovery of 94.3% and a phosphorus recovery of 95.3% are achieved under the optimal conditions of attacking phosphate rock using 30%P2O5 acid with an L/S ratio of 10:1 and a stirring speed of 250 r/min at 25 °C for 4 h. Then, the selective precipitation of REEs with 81.3% REEs recovery is realized by heating up the leaching solution from 25 to 90 °C and keeping for 4 h. Thereafter, more than 95% phosphoric acid is recovered by H2SO4 and high purity gypsum, more than 95% CaSO4 (tested by XRF), is also produced at the same time. Ultimately, a green process that leaches phosphate rock with H3PO4, selectively precipitates REEs from leaching solution by heating up, recovers H3PO4 with H2SO4 is proposed. Compared with REE recovery in traditional processes, this process owns the merits of simple operation, energy saving and minimum wastes.

Geochemistry and Geophysics of Iron Oxide-Apatite Deposits and Associated Waste Piles with Implications for Potential Rare Earth Element Resources from Ore and Historical Mine Waste in the Eastern Adirondack Highlands, New York, USA

Abstract The iron oxide-apatite (IOA) deposits of the eastern Adirondack Highlands, New York, are historical high-grade magnetite mines that contain variable concentrations of rare earth element (REE)-bearing apatite crystals. The majority of the deposits are hosted within sodically altered Lyon Mountain granite gneiss, although some deposits occur within paragneiss, gabbro, anorthosite, or potassically altered Lyon Mountain granite gneiss. The IOA deposits and the waste and/or tailings piles associated with them have potential as an unconventional resource for REEs. Reprocessing of these piles would have the advantage of partial recycling of the waste material to produce a set of critical elements. Thirty-four ore, nine rock, 25 waste-pile, and four tailings-pile samples were collected and analyzed for major, minor, and trace elements. At the tailings- and waste-pile sites, composite samples were collected by combining 30 to &gt;50 subsamples randomly distributed over each pile. The total REE content of the waste and tailings piles varied from approximately 10 to 22,000 ppm, whereas the ore sample concentrations ranged from approximately 15 to 48,000 ppm total REEs. A positive correlation exists between the total REE content of ore and its associated waste pile. Median light REE/heavy REE values were 2.14 for waste/tailings piles and 2.25 for ore, which is a substantial relative enrichment in the heavy REEs in comparison to many developed REE mines, such as the mined carbonatites of Bayan Obo, China, and Mountain Pass, California. Importantly, the ore and waste samples are significantly enriched in both Y and Nd compared to other REEs in the samples. Other minor components such as Th are also elevated. Airborne radiometric surveys show large positive eTh and eU anomalies corresponding to tailings piles. Although it is a limited data set, geochemical data of unaltered and altered host rocks suggest a speculative new model for IOA ore formation in the Adirondack Highlands that is consistent with the geology and previously published data. The ferroan ore-hosting Lyon Mountain granite gneiss underwent localized potassic alteration that enriched the altered rock in Fe, REEs, Th, and other metals. A later sodic alteration event affected the previously potassically altered Lyon Mountain granite gneiss, which increased rock porosity and remobilized Fe, REEs, and other elements from the host rock into the iron ore seams. The sodic fluids responsible for ore formation were enriched in F and Cl.

Distribution of Rare Earth Elements plus Yttrium among Major Mineral Phases of Marine Fe–Mn Crusts from the South China Sea and Western Pacific Ocean: A Comparative Study

Marine hydrogenetic Fe–Mn crusts on seamounts are known as potential mineral resources of rare earth elements plus yttrium (REY). In recent years, increasing numbers of deposits of Fe–Mn crusts and nodules were discovered in the South China Sea (SCS), yet the enrichment mechanism of REY is yet to be sufficiently addressed. In this study, hydrogenetic Fe–Mn crusts from the South China Sea (SCS) and the Western Pacific Ocean (WPO) were comparatively studied with mineralogy and geochemistry. In addition, we used an in situ REY distribution mapping method, implementing laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and a sequential leaching procedure to investigate the partitioning behavior of REY in the Fe–Mn crusts. The typical Fe–Mn crusts from SCS were mainly composed of quartz, calcite, vernadite (δ-MnO2), and amorphous Fe oxides/hydroxides (FeOOH). The Fe–Mn crusts from the Central SCS Basin and the WPO contained quartz, δ-MnO2, FeOOH, todorokite, and phillipsite. Furthermore, geochemical analysis indicated that the typical SCS crusts had a higher growth rate and lower REY concentrations. The LA-ICP-MS mapping results showed that the δ-MnO2 and FeOOH dominated the occurrence phases of REY in the SCS crusts. Four mineral phases (i.e., easily exchangeable and carbonate, Mn-oxide, amorphous FeOOH, and residual aluminosilicates) in these Fe–Mn crusts were separated by a sequential leaching procedure. In the SCS and WPO crusts, the majority of total REY (ΣREY) was distributed in the Mn-oxide and amorphous FeOOH phases. The post-Archean Australian shale-normalized REY patterns showed that light REY (LREY) and heavy REY (HREY) were preferentially adsorbed onto δ-MnO2 and FeOOH, respectively. It is noteworthy that ~27% of ΣREY was associated with the residual aluminosilicates phase of the WPO crusts. The La/Al ratios in the aluminosilicates phase of the typical SCS crusts were the values of the upper crust. We conclude that large amounts of terrigenous materials dilute the abundance of REY in the SCS crusts. In addition, the growth rates of Fe–Mn crusts have a negative correlation with the FeOOH-bound and aluminosilicate-bound REY. As a result of the fast growth rates, the SCS crusts contain relatively low concentrations of REY.

Perspective of availability and sustainable recycling prospects of metals in rechargeable batteries – A resource overview

The growing need for strategic and rare earth elements (REE) led to an enormous interest in the development of new technologies for the recycling and recovery of these metals from secondary resources especially batteries. The primary reserves, production scenario and possible secondary resources of cobalt, lead, lithium, manganese, nickel, REE, and zinc, with respect of metal content, quantity, the source of generation is discussed. The purpose of this review is to depict the status of the recycling technologies for the extraction of metals inherent in primary and secondary batteries from secondary resources like process wastes, catalysts, effluents, metal and alloy scrap, e-wastes, mine tailings, and metallurgical slags and spent batteries, depicting a summary of those under-utilized wastes. Also, the problems and the prospect of the studies of their recycling technologies especially focused on the hydrometallurgical and pyrometallurgical processes have been put forward. The future avenues in spent battery recycling are also discussed with respect to the directions of research needed for their sustainable utilization and environmental management.

Geochemistry and Mineralogy of Rare Earth Elements (REE) in Bauxitic Ores of the Catalan Coastal Range, NE Spain

Karst bauxite deposits are currently investigated as a new resource for rare earth elements (REE) in order to avoid present and future supply shortfalls of these critical metals. The present work focuses on the geochemistry and mineralogy of the REE in karst bauxite deposits of the Catalan Coastal Range (CCR), NE-Spain. It is revealed that the studied bauxitic ores have a dominant breccia and local ooido-pisoidic and pelitomorphic texture. The bauxitic ores are mostly composed of kaolinite and hematite, as well as of lesser amounts of boehmite, diaspore, rutile and calcite. The mineralogy and major element composition indicate incomplete bauxitization of an argillaceous precursor material possibly derived from the erosion of the Mesozoic Ebro massif paleo-high. The studied bauxites are characterized by ∑REE (including Sc, Y) between 286 and 820 ppm (av. 483 ppm) and light REE to heavy REE (LREE/HREE) ratios up to 10.6. REE are mainly concentrated in phosphate minerals, identified as monazite-(Ce) and xenotime-(Y) of detrital origin and unidentified REE-phosphates of a possible authigenic origin. REE remobilization presumably took place under acidic conditions, whereas REE entrapment in the form of precipitation of authigenic rare earth minerals from percolating solutions was related to neutral to slightly alkaline conditions. During the bauxitization process no significant REE fractionation took place and the REE distribution pattern of the bauxitic ores was governed by the REE budget of the precursor material. Finally, adsorption as a main REE scavenging mechanism in the studied CCR bauxite deposits should not be considered, since the presented data did not reveal significant REE contents in Fe-and Mn-oxyhydroxides and clay minerals.

The recovery of rare earth elements from coal combustion products by ionic liquids

Rare earth elements (REEs) are essential for hundreds of applications in the fields of permanent magnets, batteries, fluorescent materials, laser crystals, alloys, ceramics, catalysts, superconductors, etc. With the need of environmental protection increasing, the novel resource utilization and separation technology for REEs have caused widespread concerns. The reclamation of REEs from coal combustion products (CCPs) were proposed as a way to supply rare earth mining. However, the effective REEs extraction technology from CCPs has still been less reported. In this article, the REE contents of some Chinese CCPs from Jiangxi, Guizhou and a power plant were investigated. Then the ionic liquid type extractants of [N1888]Cl, [P6,6,6,14]Cl, [P6,6,6,14][SOPAA] and [P6,6,6,14][SOPAA] were studied for the purification of REEs from the leaching solutions of CCPs. Using the purification and recovery procedures, the purification multiples of Al, Fe, Ca arrived at 94, 40,588 and 8.7 times, and the recovery rate of REE was 37.4%. The development of recovery technology in this study contributes to the REEs resource utilization from CCPs.

Evaluation and Policy Research on the Sustainable Development of China’s Rare Earth Resources

As rare earth resources are indispensable raw materials for modern society, they have become strategic global reserve resources. Even though China is the world’s largest producer and exporter of rare earth, the industry has low efficiency and severe problems with over-exploitation and environmental pollution; therefore, there needs to be a greater focus on the sustainable exploitation of rare earth resources. This paper establishes an innovative evaluation index system for the sustainable development of China’s rare earth resources from six main aspects; economic development, social progress, environmental protection, technological innovation, rare earth development and utilization, and rare earth protection in which the indicators are assessed using an entropy method. Grey correlation analysis was used to evaluate China’s rare earth sustainable development level from 2006–2016, from which it was found that sustainable development was poor from 2006–2010 and marginally better from 2011–2016. The main factor affecting rare earth sustainable development in China was found to be the lag in the development of environment protection system and rare earth protection system. Policy recommendations for improving China’s rare earth protection, environmental protection, and technological innovation are proposed to guide government regulations and assist rare earth industry personnel.

Phase equilibria in medium basicity region of CaO-SiO2-Nb2O5-(5%, 10%, 15%) La2O3 system

The thermodynamic information, such as primary phase fields and liquidus temperatures, in the CaO-SiO2-Nb2O5-La2O3 quaternary system phase diagram is important for the comprehensive utilization of niobium and rare earth resources. In the current work, the phase equilibria of CaO-SiO2-Nb2O5-(0–15%)La2O3 system within medium basicity region at 1373–1673 K were experimentally studied. X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectrometer (EDS) were used to identify the type and composition of equilibrium phases in the quenched samples after thermodynamic equilibrium experiment. According to the experimental results, the univariate line between CaNb2O6-Ca2Nb2O7-LaNbO4 primary phase fields, the bivariate interface between CaNb2O6-Ca2Nb2O7 primary phase fields, the bivariate interface between CaNb2O6-LaNbO4 primary phase fields, and isothermal liquidus surfaces in CaNb2O6 and Ca2Nb2O7 primary phase fields were determined, respectively. Finally, CaO-SiO2-Nb2O5-La2O3 phase diagram within specific region was spatially constructed, and the results were also presented in the form of CaO-SiO2-Nb2O5 pseudo-ternary system phase diagram with w(La2O3) = 5%,10% and 15%. The research results are important for the comprehensive utilization of Nb and RE resources, meanwhile, they are also important for the improvement of related phase diagrams.

Rare Earth Elements in Planetary Crusts: Insights from Chemically Evolved Igneous Suites on Earth and the Moon

The abundance of the rare earth elements (REEs) in Earth’s crust has become the intense focus of study in recent years due to the increasing societal demand for REEs, their increasing utilization in modern-day technology, and the geopolitics associated with their global distribution. Within the context of chemically evolved igneous suites, 122 REE deposits have been identified as being associated with intrusive dike, granitic pegmatites, carbonatites, and alkaline igneous rocks, including A-type granites and undersaturated rocks. These REE resource minerals are not unlimited and with a 5–10% growth in global demand for REEs per annum, consideration of other potential REE sources and their geological and chemical associations is warranted. The Earth’s moon is a planetary object that underwent silicate-metal differentiation early during its history. Following ~99% solidification of a primordial lunar magma ocean, residual liquids were enriched in potassium, REE, and phosphorus (KREEP). While this reservoir has not been directly sampled, its chemical signature has been identified in several lunar lithologies and the Procellarum KREEP Terrane (PKT) on the lunar nearside has an estimated volume of KREEP-rich lithologies at depth of 2.2 × 108 km3. This reservoir therefore offers a prospective location for future lunar REE exploration. Within the context of chemically evolved lithologies, lunar granites are rare with only 22 samples currently classified as granitic. However, these extraterrestrial granites exhibit chemical affinities to terrestrial A-type granites. On Earth, these anorogenic magmatic systems are hosts to U-Th-REE-ore deposits and while to date only U-Th regions of enrichment on the lunar surface have been identified, future exploration of the lunar surface and interior may yet reveal U-Th-REE regions associated with the distribution of these chemically distinct, evolved lithologies.

The Rare Earth Elements Potential of Greek Bauxite Active Mines in the Light of a Sustainable REE Demand

More recent data of Greek bauxites from the Parnassos-Ghiona active mines prove that rare earth elements (REEs) occur mainly in the form of authigenic/diagenetic LREE3+ carbonate and phosphate minerals (bastnasite/parisite group and florencite). Bulk geochemistry of representative samples, from underground mines and open pits, showed an increased content in LREE (ΣLREE—from La to Gd—varying between 106 and 913 ppm; avg. ΣLREE = 321 ppm; n = 17), and lower HREE (ΣHREE—from Tb to Lu including Y—varying between 45 and 179 ppm; avg. ΣHREE = 95; n = 17). The overall REE concentration (ΣREE + Y+Sc) varies from 192 to 1109 ppm (avg. 463 ppm; n = 17). The most abundant REE is Ce (min: 67 ppm; max: 655 ppm; avg. 193 ppm; n = 17), exhibiting in general a positive geochemical anomaly (avg. Ce/Ce* -CeA-: 2.6), identical to the case of marine Fe–Mn-crust and terrestrial desert vanish, implying also that Ce4+ may exist either in REE-oxides and/or epigenetically sorbed in Fe-oxides. On the other hand, Nd content, which is more interesting for the industry, is lower (avg. 41 ppm; n = 17). The concentration of REEs is much higher in Fe-rich (red) bauxite, compared to Fe-depleted (white) bauxite (avg. ΣREE + Y+Sc = 569 ppm and 268 ppm, respectively). The new data presented herein show a rather lower REE potential of Parnassos-Ghiona bauxites, compared to previous literature, but similar values compared to karst-type bauxites of the globe. Although their REE concentration is higher compared to that of various geochemical reference materials (i.e., positive REE geochemical anomalies in comparison with chondrites, UCC, PAAS, NASC, and ES), it is vitally lower compared to REE resources being mined, such as REE–Fe–Nb–Th deposits. A trend similar to REE geochemical trend also stands for most of the trace elements that are present in Greek bauxites—mainly HFSE—except for LILE. Besides, Greek bauxite metallurgical residue’s (red mud) REE content seems to be remarkably increased by almost two times compared to that of the Parnassos-Ghiona bauxite parent material. Scandium is another critical element. In the studied bauxites, it varies from 29 to 73 ppm (avg. 47 ppm; n = 17); it is typical for the Mediterranean and EU bauxites and laterites, but much lower compared to the exploitable Australian laterites. The Fe-rich samples contain higher concentrations of Sc compared to Fe-depleted (avg. 54 and 33 ppm, respectively). This means that common red Greek bauxite is rather more exploitable, with regard to Sc (and the rest REE), but not the white one (which is of high quality in terms of Al). Bulk geochemistry indicates that Sc is correlated to Fe but not to Zr, while microscale observations demonstrated the presence of fine-grained scandian-zircons. This is in line with a very recent study proving that Sc is mainly present in Fe-oxide minerals (mainly hematite and goethite) and zircons. Bulk geochemical Fe–Pb and Fe–As positive correlations are also verified among the associated trace elements. Finally, the investigation of the REE vertical distribution in a characteristic deposit of the B3 horizon (i.e., Pera Lakkos mine case study), showed that the REE concentration is increased in the Fe-rich domain (lying above the footwall limestone), as well as in the coal layer interstratified between the Fe-depleted domain and the hanging wall limestone. However, it is revealed that the Ce/Ce* (CeA) is increased in the coal layer and is raised to the uppermost Fe-depleted domain, but not the lowermost Fe-rich bauxite domain. This might be attributed to the Ce3+ ↔ Ce4+ and the LREE re-mobilization during the supergene/epigenetic processes.

Reflectance spectroscopy and geochemical analysis of rare earth element-bearing tailings: A case study of two abandoned tin mine sites in Bangka Island, Indonesia

Rare Earth Elements (REEs) are indispensable in the manufacturing of renewable energy and clean technologies. Due to the high demand for REEs, mine waste, called “tailings”, are sought because they could be a possible resource for REEs. In this study, tailing samples were collected from two tin mine tailings in Bangka Island, Indonesia, and analyzed using inductively coupled plasma optical emission spectrometry, x-ray powder diffraction, and Fourier transform infrared - attenuated total reflectance. Results showed that the tailing samples were identified as quartz and contained a high amount of erbium between 111.6 and 3768.4 μg/g. Absorption features in infrared reflectance spectra were related to REE concentrations. We found a positive correlation between erbium and two absorption features that have not been reported before: One feature is centered at 500 nm with a correlation of 0.685, and one is centered at 674 nm with a correlation of 0.829.

Rare Earth Elements on the A-type Unggan Granite and Its Comparison to the A-type Section of Sibolga Granite

Rare earth elements are often correlated to A-type granite. Unggan Granite is A-type granite which is located in Sijunjung Regency, West Sumatra. This study discusses the rare earth elements composition on A-type Unggan Granite and compares the element abundance to the nearest A-type granite from Sibolga. Total REE of the studied location in the part of Solok Quadrangle is averagely 860 ppm. XRF and ICP-MS at Center for Geology Survey were applied to measure the composition of major oxides, trace elements, and rare earth elements in the selected granite. Megascopically, the samples are dark red and coarse grain granites with quartz and feldspar as major minerals. Major oxides content of the samples affirms the samples as granite based on geochemistry composition. Ga, Nb, and Y amounts in the granites reveal the A-type affinity. The average REE abundance of Unggan Granite is higher than the A-type section of Sibolga Granite. The selected rock are classified in shoshonitic series with lanthanum and neodymium as the major REE. Negative Ce and negative Eu anomalies in normalized spider plot are detected in the samples. The granite characters are worth to be explored more for national income from rare earth elements resource.

SOME TRENDS OF THE WORLD REE MARKET AND PROSPECTS FOR RUSSIA

The paper presents a review of some trends observed on the world market of rare-earth elements (REE). This review takes into account actual changes in the commercial and industrial policy of China and the current trends of REE consumption. Main characteristics of the modern REE markets are considered. The paper provides an assessment of world production volumes, world trade and prices. The article describes the REE market behavior in 2000–2020 and provides a forecast of main indicators and prices up to 2020. It contains a description of current world REE resources, production and trade over the main countries. In addition, the prices and the main buyers of REE are specified indicating the forecast of consumption. The prospects of the Russian REE market are estimated taking into account the «Development of the Rare and Rare-Earth Elements Industry» subprogram implemented as part of the State Program of the Russian Federation «Industry Development and Competitiveness Improvement». The purpose of the subprogram is to create a competitive rare-earth industry of an integrated production cycle in the Russian Federation in order to satisfy the needs of the domestic defense industry complex, civil industries and enter the foreign markets. It is noted that this subprogram should be upgraded with regard to changes in the market conditions and development of rare-earth elements production in the Russian Federation including by means of statutory, non-tariff and technical regulation. Loparite and apatite will remain the main sources of rare-earth elements as raw materials for industrial processing in Russia in the near future, while REE production from apatite will increase. It is emphasized that the prospects of REE development in Russia consist not so much in increasing the primary production as in establishing new plants consuming rare-earth products.

Reducing Dy content by Ce substitution in nanocomposite Nd-Dy-Fe-B/α-Fe alloys

To alleviate Dy and Tb shortage and develop permanent magnets with high performance/cost ratio, the abundant and inexpensive rare earth (RE) element Ce has been suggested to be employed in Nd-Fe-B alloys. In this work, the effects of Ce substitution for Dy on the microstructure, magnetic properties, and thermal stability of melt spun nanocomposite [Nd0.8(Dy1-xCex)0.2]10Fe82.5B6Zr1.5 alloys are systematically investigated. The refined XRD results show the existence of 2:14:1 phase and α-Fe in all alloys, and the c-axis expansion for the 2:14:1 phase is observed in the alloy with x = 0.2. With Ce substitution, the alloys exhibit a lightly increased grain size and more uniform microstructure. An abnormal increase of coercivity Hc = 833 kA/m and a sudden decrease of temperature coefficients of coercivity |β| = 0.323%/°C are observed in x = 0.8 alloy, which is only slightly lower than those of x = 0.25 alloy, 865 kA/m and 0.321%/°C, respectively. With increasing Ce content, the Curie temperature Tc of 2:14:1 phase monotonically decreases from 550 K to 535 K, and the exchange coupling effect is weakened. The [Nd0.8(Dy0.5Ce0.5)0.2]10Fe82.5B6Zr1.5 alloy with 50% Dy reduction exhibits a high (BH)max of 133 kJ/m3 with an acceptable β value of −0.348%/°C and an Hc of 769 kA/m. It is expected that these investigations could be beneficial for developing Ce-containing nanocrystalline Nd-Fe-B magnets with saved heavy RE resources.

Rare earth elements and yttrium in ferromanganese deposits from the South China Sea: distribution, composition and resource considerations

Ferromanganese nodules and crusts contain relatively high concentration of rare earth elements (REE) and yttrium (REY), with a growing interest in exploitation as an alternative to land-based REY resources. On the basis of comprehensive geochemical approach, the abundance and distribution of REY in the ferromanganese nodules from the South China Sea are analyzed. The results indicate that the REY contents in ferromanganese deposits show a clear geographic regularity. Total REY contents range from 69.1×10–6 to 2 919.4×10–6, with an average value of 1 459.5×10–6. Especially, the enrichment rate of Ce content is high, accounting for almost 60% of the total REY. This REE enrichment is controlled mainly by the sorption of ferromanganese oxides and clay minerals in the nodules and crusts. Moreover, the total REY are higher in ferromanganese deposits of hydrogenous origin than of diagenetic origin. Finally, Light REE (LREE) and heavy REE (HREE) oxides of the ferromanganese deposits in the study area can be classified into four grades: non-enriched type, weakly enriched type, enriched type, and extremely enriched type. According to the classification criteria of rare earth resources, the Xisha and Zhongsha platform-central deep basin areas show a great potential for these rare earth metals.

Concentration of rare earth elements during high temperature pyrolysis of waste printed circuit boards

An in-depth investigation was carried out on the recovery of rare earth elements (REEs) from a variety of waste printed circuit boards (PCBs). High temperature pyrolysis was carried out at 850 °C for 15 min using horizontal resistance and thermal plasma furnaces with different levels of turbulence. The concentration of REEs in key pyrolysis residues, namely, copper rich red metallic fraction, lead/tin rich white metallic fraction and slag rich carbonaceous residues, were determined using ICP analysis. Most of the REEs were found concentrated in the carbonaceous residue with negligible levels of REEs recovered in the two metallic fractions. Most of the recovered REEs showed a high affinity towards to refractory oxides silica and alumina, and little affinity towards metals Cu, Pb and Sn. The yield of REEs was significantly higher from the plasma furnace indicating the important role of turbulence in the dissociation & subsequent diffusion of REEs during pyrolysis. While La, Pr, Sm and Y required turbulent conditions for their recovery, Nd, Gd, Ce and Dy were relatively easy to dissociate and extract from the waste. Significant amounts of REEs could thus be recovered from waste PCBs as concentrated recyclates for further processing and extraction of individual rare earths. This study has shown that PCBs could prove to be a valuable urban mining resource of REEs. The recovery of REEs, in addition to precious and other metals, could play an important role towards enhancing the economic and environmental sustainability of e-waste recycling.

Study on Influence Factors of Leaching of Rare Earth Elements from Coal Fly Ash

Rare earth elements (REEs) are very important strategic resources, but the traditional high-quality rare earth resources are becoming increasingly scarce. Coal fly ash (CFA) in some areas in the world has a high REE content, which can be a potential supplement to the rare earth resources. CFA samples collected from the Panbei Power Plant in Guizhou Province of China, in which the REE content is 489 ppm, was used as the research object in this study. Taking three REEs (lanthanum (La), cerium (Ce), and neodymium (Nd)) with the highest content in this CFA sample as the representative and hydrochloric acid as the leaching reagent, the effects of various factors on the leaching efficiencies of REEs from CFA were investigated systematically. Further, two unreacted core shrinkage models (chemically controlled model and diffusion controlled model) were used to study the leaching kinetics of REEs from CFA. The results showed that, except for the small influence of the stirring speed, the temperature, acid concentr...

Preparation and properties of polyethylene-coated terbium complex/calcium carbonate composite fluorescent material

A reaction of terbium chloride hexahydrate and 4-chlorobenzoic acid was used to form a terbium complex on the surface of an alkaline calcium carbonate core. Different concentrations of high-density polyethylene (HDPE) toluene solution were then coated onto the prepared terbium complex/calcium carbonate composite fluorescent material (referred to as Material I), which resulted in a series of core-shell HDPE/terbium complex/calcium composite fluorescent materials (referred to as Material II). The structures of these materials were identified and analyzed using UV spectroscopy, IR spectroscopy, X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectroscopy and inductively coupled plasma-optional emission spectrometry. The thermal stability and fluorescence of these materials were also examined, and results showed that both Materials I and II were shown to have high thermal stability and high levels of fluorescence. These new types of composite fluorescent materials not only offer economic savings on expensive rare earth resources through reduced production costs, they also offer an effective alternative method for the preparation of highly fluorescent, highly temperature resistant binary terbium complexes. Further, the use of the polymer polyethylene coating on the fluorescent material significantly enhanced the emission intensity of the composite fluorescent materials and offers new possibilities for the production of high-end rare earth fluorescent materials.

A New Look at the Occurrences of the Rare-Earth Elements in the Georgia Kaolins

AbstractThe high-density siliciclastic minerals (e.g. zircon) in the coarse fractions (&gt;44 mm, informally known as grit) of the mined Georgia kaolins are potential and significant sources of the rare-earth elements (REE). The abundances and provenance of the REE signature have not been studied extensively for the Georgia kaolins. The objective of the present study was, therefore, to define the contribution of these heavy minerals (e.g. zircon) to the REE inventory of the coarse fractions of Georgia kaolins. Heavy-mineral subfractions separated from the coarse fractions contained 1647 mg/kg REE from the Jeffersonville Member of the Lower Tertiary Huber Formation and 5012 mg/kg REE from the Buffalo Creek Kaolin Member of the Upper Cretaceous Galliard Formation, respectively. These heavy-mineral subfractions were enriched 10–100 times in the heavy rare-earth elements (HREE, Gd—Lu,), Hf, and Zr relative to the concentrations of these elements in Upper Continental Crust. The heavy-mineral subfractions comprised 5% of the coarse fractions (grit) of these two kaolin-producing formations. The heavy-mineral subfractions consisted of zircon, anatase, rutile, kaolinite, and minor amounts of muscovite, trace ilmenite, and staurolite. The large concentrations of REE were obtained by separating the dense heavy minerals from the coarse fraction (grit) obtained during the typical production of kaolin-group minerals (kaolinite) from kaolin ore. The amount of zircon (estimated from the 6–11 wt.% Zr) and the absence of monazite did not explain the high concentrations of REE in the heavy-mineral subfractions. The large amounts of REE could have resulted from the sorption of REE released during weathering reactions, or from the presence of small amounts (0.025 wt.%) each of monazite and xenotime in addition to the presence of zircon. This heavymineral subfraction represented a novel domestic resource of extractable REE, especially the HREE, of a grade as high as 0.50 wt.% total REE.