Source Of Rare Earth Elements Research Articles

Metasomatism and REE mineralization of the Zilair Formation sedimentary rocks in the Khudolaz complex gabbro massif exocontact zone (Chebarkul area, Southern Urals)

Relevance. West-Magnitogorsk zone (Southern Urals) hold a lot of Early Carboniferous gabbroic and granitoid intrusions which associated with various mineralization types (Ti-Fe, Cu-Ni-PGE, Au), but information about REE mineralization is scarce. Contact hydrothermal-metasomatic processes rarely form the economic REE mineral deposits, but they can provide valuable information about the behaviors of rare earth elements. Aim. Mineralogical and geochemical characteristics of metasedimentary rocks from exocontact zone of the Khudolaz complex gabbro massif, study of rare earth minerals, determination of the formation conditions and sources of mineralizing fluids. Methods. Minerals were studied using optical and scanning electron microscopy; the bulk composition of the rocks was determined by XRF and ICP-MS analytical techniques; vapor-liquid fluid inclusions in calcite were studied using microthermometry and Raman spectroscopy; the isotopic composition of carbon and oxygen was determined for metasedimentary silicate-carbonate metasomatites. Results and conclusions. In the Khudolaz complex gabbro massif exocontact zone, the Zilair Formation sedimentary rocks undergo recrystallization associated with hydrothermal-metasomatic processes and manifested as the formation of globular and granoblastic textures, stylolites, the formation of metacrystals of various rock-forming and accessory minerals, including rare earth minerals (synchisite-(Ce), CaCe(CO3)2F, and REE-rich clinozoisite, (Ca,REE)2Al3O[Si2O7][SiO4](OH)). According to microthermometry of vapor-liquid fluid inclusions in calcite, the formation of REE-bearing minerals occurred at temperatures not lower than 150 °С. The sources of rare earth elements could be both the Zilair Formation sedimentary rocks and gabbro, as evidenced by the increase in REE concentrations and isotopic composition of oxygen and carbon in silicate-carbonate metasomatites (δ18OSMOW =13.80…15.98 ‰, δ13С = –5.64…–2.18).

Mining and industrial processing wastes of phosphate rocks in Egypt: potentiality of rare earth elements

Abstract Globally, Egypt ranked the eighth position in the production of phosphorus with about 5 million tons annually. Phosphate ore is considered one of the commonest sources of rare earth elements (REEs). Mining and industrial processes (beneficiation) of phosphate ore produce huge amounts of wastes in different sizes. The present study aims to evaluate the potentiality of the phosphate ore wastes as a source of rare earth elements (REEs). The study targeted some phosphate production sites in Egypt, including: Abu Tartur, West and East El-Sebaiya phosphate mines, in addition to the fertilizers factory in Assiut. The collected waste samples, during 2023, were analyzed in terms of mineralogical composition using XRD (X-Ray Diffraction) and chemical composition using XRF (X-Ray Fluorescence). The results of chemical analysis recorded the highest concentrations of Y, Ce, La, Nd, Sc, Sm, U, and Th in Abu Tartur waste samples, while the lowest concentrations were recorded in the fertilizers factory waste samples. These wastes contain higher concentrations of REEs than the Algerian and USA wastes. Furthermore, an enrichment of the mostly environmental hazardous elements As, Cr, Cd, Pb, and Se are detected in Abu Tartur and West and East El-Sebaiya. Thus, the wastes from the industry and mining processing of phosphate represented a vital economic source for the production of REEs. The use of wastes for production of trace and rare earth elements represents an economic and environmental add value for phosphate industry.

Rare earth element (REEs) imprints and provenance of wetland sediments from Oaxaca coast, Mexico.

REEs in wetland sediments from the Oaxaca coast in southern Mexico were used to infer the sources and depositional processes by involving both the geochemical characteristics and geostatistical approaches. Statistically strong positive correlation between REEs confirmed similar origin in all the cores. Light REEs (LREEs) represented >84% of ΣREE mean concentrations varies between 47.95 (C1) and 87.84mg/kg (C3). NASC normalized La/Yb, La/Sm, and Gd/Yb ratios indicated more Middle REEs in sediments of C1 and C3 cores and more LREEs in C2 and C4 cores indicating the different mineralogical associations. The absence of Ce anomaly and significant negative Eu anomalies is due to the presence of Fe/Mn oxy-hydroxide, humid subtropical conditions and a strong leaching process. Comparison with REE and possible sources revealed contributions from the Sierra Madre del Sur Mountains with major influences of igneous rocks such as andesite, basaltic andesite, dacite, rhyolitic tuff and rhyolitic vitrophyre.

Electrochemical reduction method for leaching terbium and cerium from waste phosphors.

Rare earth elements are commonly used in various fields due to their unique physical and chemical properties. Waste phosphors represent an important secondary source of rare earth elements, and their recovery is a crucial means of improving the utilization of these resources. When using FeCl2 as a reducing agent to reduce Tb4+ and Ce4+ from washed phosphors, a large amount of reducing agent is required, and the Fe2+ cycle becomes complicated. In this study, the electrochemical reduction process was employed to treat washed phosphors. Under optimum conditions of FeCl2 concentration of 0.10 mol L-1, current density of 100 A m-2, HCl concentration of 3 mol L-1, temperature of 80 °C, L/S ratio of 30 mL g-1, and time of 60 min, the leaching efficiencies of Tb and Ce reached 99.2% and 98.5%, respectively. The apparent activation energies of Tb and Ce were calculated as 17.71 and 18.46 kJ mol-1, respectively, illustrating that the leaching processes of Tb and Ce depend on the diffusion. By applying an external electric field, Fe2+ can be recycled in the system, thereby reducing the amount of reducing agent needed and achieving a higher leaching efficiency for Tb and Ce. These results are beneficial for the resource utilization of waste phosphors and have significant implications for the sustainable development of rare earth resources.

An investigation of rare earth elements in sewage sludge generated in Poland

According to Statistics Poland, an average of around 1 million tonnes DM of sewage sludge has been generated in Poland annually over the past several years, of which approximately 30% has been used in nature, e.g. in agriculture, to grow plants for compost production, or for land reclamation (Statistics Poland 2004–2022). Most research on sewage sludge has focused on investigating its fertilizing value (nitrogen, phosphorus), identifying the composition of organic matter and determining the total content of heavy metals (including primarily cadmium, copper, nickel, lead, zinc, mercury and chromium) and the forms of their occurrence that determine their mobility and bioavailability. The occurrence of rare earth elements (REEs) in sewage sludge has hardly been addressed in research, even though their presence in production processes and everyday objects is increasingly common. The results presented in this article of studies of the concentrations of individual REEs in sewage sludge from selected industrial and municipal wastewater treatment plants located in Poland indicate that they are significantly lower than the average lanthanide level in the Earth’s crust. This may suggest that anthropogenic sources of REEs do not affect the composition of the wastewater and sludge studied. The calculated median concentration of ΣREE in sludge from industrial wastewater treatment plants is 9.47 mg/kg, whereas in municipal sewage sludge, the midpoint value for REE concentration is 13.5 mg/kg. Normalization of the obtained results with respect to Post-Archean Australian Shale (PAAS) and to topsoil and subsoil from Poland shows that the sludge is generally depleted in REE relative to the standards used. An assessment of the contamination of sewage sludge with rare earth elements, based on the calculated values of the geoaccumulation index (Igeo) for these elements, also shows that the content of lanthanides in the studied sewage sludge is lower than in the soils of Poland.

Micro-Topographic Controls on Rare Earth Element Accumulation and Fractionation in Weathering Profiles: Case Study of Ion-Adsorption Rare Earth Element Deposit in Hedi, Zhejiang Province, China

Ion-adsorption rare earth element (REE) deposits are a major source of REEs and are found mainly in China. The formation of such deposits is affected by a combination of endogenic and exogenic factors. This study investigated the effect of micro-topography on the REE distribution in four weathering profiles at different topographic sites on a knoll in Hedi, Zhejiang Province, China. The weathering profile and REE accumulation are both most developed at mid-slope positions of the knoll. The intensity of chemical weathering decreases in the order of mid-slope > base > summit. As weathering progressed, REE enrichment initially increased but later decreased, with a progressive increase in light/heavy REE fractionation. REE fractionation is more pronounced on the north-facing slope than on the south-facing slope. Weathering degrees and clay mineral characteristics are key factors influencing the varying REE distributions on the knoll. Water leaching and the evolution of clay minerals towards higher maturity reduce REE adsorption capacity. Clay minerals also play a significant role in REE fractionation; the abundance of these minerals and the presence of illite enable the retention of more HREEs with minimal desorption. Taking into account water content, it is inferred that hydrological conditions, modulated by the micro-topography, strongly affect the depth and extent of REE accumulation, as well as fractionation.

Rare Earth Elements enrichment in Triassic coals deposits and associated argillaceous rocks in Lesotho

The demand for rare earth elements has increased around the world due to their application in a variety of technological advancements. Previous studies have evaluated the potential of the rare earth elements and yttrium (REY) hosted within the Permian coal deposits of the main Karoo Basin (MKB) in Southern Africa. However, not a lot of scientific research has gone into the Triassic coal deposits. The Triassic coals in South Africa were the first coals to be exploited for their thermal use in the 1880s, but the discovery of the higher rank and more abundant Ecca coal deposits led to the Triassic coals remaining largely unexplored. The demand for rare earth elements has sparked interest in these coal deposits as potential sources for valuable minerals. Late Triassic coal deposits in Lesotho have previously not been well documented and these low-rank coals can be a potential source of rare earth elements. This study aims to characterize and evaluate the potential of REY in the Taung coal deposit, southwest of Lesotho. Coal and associated argillaceous samples from the Taung coal deposit were analyzed using microscopic petrography for coal characterization and an inductively coupled plasma mass spectrometry (ICP-MS) to determine the amount of rare earth elements. Taung coal is classified as middle medium rank D bituminous coal. The total REY content in Taung coal and its associated rocks range from 162.9 ppm to 855.1 ppm, which is significantly higher than the upper continental crustal (UCC) average. The average critical REY concentration of samples from the Taung coal deposit is 189.4 ppm, which is three times higher than that of the Chinese Bayan Obo deposit. Samples classified as very promising and promising because of their outlook coefficients, are found to contain up to 77% of critical REY. It is envisioned that the area could be a prime deposit for these REY.

A novel method for leaching rare earth element from fluorescent lamp waste via acid fusion

Spent fluorescent lamps are alternatives to primary sources of rare earth elements. For recycling, the most common hydrometallurgical processes involve leaching with mineral acids, combined or not with alkaline fusion, which must be followed by another acidic leaching step for terbium, cerium, and lanthanum recovery. This study proposes a novel method employing acid fusion with potassium pyrosulfate (K2S2O7) and leaching with water at 25 °C. A full factorial design (23) was employed to study the following variables for the fusion process: temperature (450–550 °C), flux/sample mass ratio (2.2–3.0), and time (30–120 min). Under the optimal experimental conditions, the maximum recovery for La was 56.0 %. Recoveries were close to or greater than 70 % for Y, Ce, Eu, and Tb, at lower temperatures compared to those used in alkaline fusion, without the need for additional reagents and heating in the REE leaching step after fusion.

Combining APCS-MLR model to evaluate the distribution and sources of rare earth elements in a large catchment

Rare earth elements (REEs), functioning as indicators for environmental tracking, revealing the impacts of human activities on changes in aquatic ecosystems. However, systematic research on the geochemical characteristics of REEs in large river basins remains relatively scarce. Therefore, this research investigates the geochemical properties of REEs within the Yangtze River basin, analyzing the quantity and spatial distribution of REEs in surface aquatic environments across the upstream, midstream, and downstream segments of the Yangtze River, and quantitatively assessing their sources. Results indicate that the REE concentration in the upstream and downstream areas are significantly higher than in the midstream, with average concentrations of 0.69 μg/L, 0.56 μg/L, and 0.39 μg/L, respectively. REEs in the Yangtze River basin are enriched in light rare earth elements (LREEs), exhibiting a slight negative cerium (Ce) anomaly and a pronounced positive europium (Eu) anomaly. The Ce anomaly correlates with pH levels, and the Eu anomaly is largely attributed to the selective chemical decomposition and solubilization of feldspar minerals. Correlation analysis indicates that REE sources are related to manganese (Mn). Utilizing the Absolute Principal Component Scores-Multiple Linear Regression (APCS-MLR) model, the principal sources of REEs are further determined to be mineral sources (36.80%), industrial sources (45.61%), and mixed sources (17.59%). Further analysis suggests that mining and dissolution of Mn-bearing feldspar minerals, along with the discharge of industrial wastewater, considerably influence REE concentrations in the basin. This study reveals the anthropogenic and natural factors influencing the distribution of REEs in the Yangtze River basin, laying a foundational framework for investigating how human activities affect the dispersion of REEs in aquatic environments.

Valorisation of acid mine drainage through effective recovery of selected rare earth elements using cationic resins

Acid mine drainage (AMD) presents a challenge to the environment if not well managed, but it also presents an opportunity for the recovery of economically valuable products, including rare earth elements (REEs), which are critical for the development of advanced, and green technologies. REE concentrations in AMD samples from coal and gold mines were determined using inductively coupled plasma optical emission spectroscopy (ICP-OES) and their sorption by different cationic resins (CHT4083, CHP4502 and CHP00712) was evaluated. Optimum conditions for the sorption of the REEs by these resins were determined through batch experiments and desorption of the REEs from the resins using different concentrations of sulphuric acid (H2SO4) solutions. Coal mine drainage (CMD), with a low pH of 2.37, had higher amounts of REEs (ΣREE 226.3732 mg/L) than AMD from the gold mines (ΣREE 4.9705 mg/L), with a pH of 3.21. A REE sorption efficiency of up to 98% was obtained with CHP4502 and CHP00712 resins and further optimisation of CHP00712 revealed that a resin volume of 250 mL and a contact time of 10 min were required to successfully remove REEs from 500 mL AMD. The sorption capacities of the resin for the selected REEs were 3.88 mg/g, 0.88 mg/g, 1.37 mg/g, 3.18 mg/g, 0.67 mg/g, 0.01 mg/g and 0.27mg/g for Pr, Gd, Nd, Ce, Sm, Eu and Y, respectively. Elution of the resin with a 0.5 N solution of sulphuric acid desorbed the REEs. AMD from coal mines could be an alternate source of REEs and cationic resins can be used to recover these REEs from the CMD. Further investigations, including impregnation of resin to improve its sorption capacity, and temperature effects on the sorption process, are recommended.

Mineralogy and geochemical controls on the distribution of REY-Ga-Se-Nb enrichment in the No. 6 Coal Seam, Soutpansberg Coalfield, South Africa

Coal is being explored as a potential alternative source for rare earth elements (REY + Sc), which are critical for advancing modern technology. Previous research has mainly focused on assessing the concentration and distribution of REY + Sc in coals from South Africa. However, the modes occurrence of these elements in coal is yet to be investigated. This study offers new insights on the mineralogy and inorganic geochemistry of the No. 6 Seam coal from the Soutpansberg Coalfield (South Africa). The objective is to investigate the distribution, enrichment, and modes of occurrence of critical elements such as Ga, Se, Nb, and REY + Sc within this coal. The No. 6 Seam is a medium rank-B, moderate vitrinite (avg. 41.5 vol%) coal, and contains major minerals such as kaolinite, quartz, and minor minerals including muscovite, siderite, dolomite, pyrite, and calcite. The total REY + Sc concentrations in the coal samples range from 79.9 to 332.1 mg/kg (avg. 213.2 mg/kg; whole-coal/rock basis), higher than global averages for hard coal. The upper continental crust (UCC) normalized concentration coefficients (CC) of the coal shows enrichment of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, and Y. Distinct REY + Sc enrichment patterns are observed across different coal horizons, divided into two categories: light-REY (LREY) and medium-REY (MREY) in the bottom horizon coal [bottom-upper (BU) and bottom-lower (BL)], whereas the middle horizon coal [middle-upper (MU) and middle-lower (ML)] are enriched in medium-REY (MREY) and heavy-REY (HREY). The BU and BL samples show greater REY + Sc enrichment relative to the MU and ML samples. The samples also contain elevated concentrations of Ga (max. 106.1 mg/kg), Se (max. 50.9 mg/kg), and Nb (max. 14.8 mg/kg), exceeding the average values reported for Chinese coals.When considering the correlations between REY + Sc and major oxide elements, minerals, and organic petrographic assemblages, REY + Sc appears to be more closely associated with inorganic fraction, particularly aluminosilicate (such as kaolinite) and carbonate minerals (like dolomite), rather than with the organic fraction. The kaolinite and dolomite represent mostly detrital input and epigenesis, respectively. Gallium in the coal is primarily associated with aluminium oxide-hydroxide, Nb with minerals such as clay, rutile/anatase, and zircon; and Se with pyrite. Redox-sensitive elemental ratios of Al2O3/TiO2 andTiO2/Zr suggest that the detrital components of the No. 6 Seam coals were predominantly derived from a source consisting of felsic-intermediate rocks. These materials likely represent the weathering products of magmatic rocks from the passive-continental margin tectonic framework of the Limpopo Mobile Belt. Paleoclimatic conditions are inferred to be warm-humid to hot, with the peat deposited under suboxic-to-oxic environments. High values of critical REY percentage (REYdef,rel%: 29.85 to 39.75 %) and an outlook coefficient ≥ 0.7 suggest these Soutpansberg coal samples to be promising for REY + Sc recovery along with Ga.

Characterisation and Hydrochloric Acid Leaching of Rare Earth Elements in Discard Coal and Coal Fly Ash

Rare earth elements (REEs) have been identified as valuable and critical raw materials, vital for numerous technologies and applications. With the increasing demand for and supply gap in REEs, many research studies have focused on alternative sources of REEs. This study involved an elemental and mineralogical characterisation of discarded coal from a coal plant and coal fly ash (CFA) from a power station in South Africa for REE presence. XRD results revealed that the discard coal sample consisted mainly of kaolinite, pyrite, siderite, quartz, calcite, gypsum, and muscovite, whereas CFA contained abundant glassy amorphous phases, alumina silicates, quartz, gypsum, calcite, and minute levels of muscovite and hematite. SEM-EDAX showed REE-carrying grains containing phosphorus in both discard coal and CFA samples. This was followed by investigating the leaching potential of REEs using hydrochloric acid from discard coal and CFA. This research’s potential impact is possibly providing a new and sustainable source of REEs. For that purpose, multiple batch leaching tests were performed to investigate the effects of temperature and acid concentration on the leaching efficiencies of REEs from discard coal and CFA. The experimental results indicated that temperature strongly influences REE leaching efficiency, while acid concentration has a lesser impact. This study identifies the best leaching conditions for the total REE recovery as 1 M HCl and 80 °C for discard coal and CFA.

Rare earth elements enrichment and extraction potential of bauxite deposits in Samar, Philippines

Abstract Rare earth elements (REE) play an integral part of modern life, from smartphones to satellites. Dubbed ‘critical metals’, the demand for REE has significantly increased, driven by the growth in global production for green technologies such as e-vehicles, solar panels, wind turbines, and other energy-economic infrastructure. Therefore, there is a need to explore alternative REE sources to ensure continued development of emerging green technologies. A possible alternative REE source is bauxite, which is soil that forms from intense weathering of aluminum oxide-rich rocks exposed to tropical climate. This paper investigates the REE enrichment and extraction potential from bauxite deposits in Paranas, Samar, Philippines. The sampling survey included collection of rock and soil on surface exposures, test pits, and drill cores from accessible portions of the bauxite mineral reservation site. The soil and parent rock samples collected were then subjected to various geochemical and mineralogical analyses. The main ore minerals of aluminum are gibbsite and boehmite; with minor goethite, hematite, and magnetite. Investigation of the geochemical composition of the bauxite reveals a total REE content of up to ~300 ppm, which is one of the highest REE and critical metal content among geological deposits in the country. These results will provide inputs in the design of a green and economical process to recover REE from bauxites. If the bauxite deposits prove to be a valuable REE resource, this study will help maximize the economic potential of the mineral resource in the Philippines and contribute to an economically efficient and environment-friendly way to produce e-tech elements for the country.

Garnet as a carrier of HREEs in highly fractionated peraluminous granite: Implications for the formation of ion-absorption HREE deposits

Ion-absorption rare earth element (REE) deposits in South China are the world’s most important source of heavy REEs (HREEs). These deposits were formed by the weathering of granitic rocks whose formation involved primary HREE enrichment. Previous studies have identified the key role of late-stage magmatic evolution, especially the magmatic–hydrothermal transition stage played in HREE enrichment, but the detailed processes need further investigation. Garnet is a common HREE carrier in parent rocks and also a main contributor of these elements in formation of ion-absorption HREE deposits. Here, we investigate textural and compositional variations in garnets from parent rock (muscovite granite) of the Dabu ion-absorption HREE deposit to constrain the primary HREE enrichment of the parent rock during late-stage magmatic evolution. Mass-balance calculations reveal that garnet accounts for ∼67 % of the Y and 64 % of the REEs in the Dabu muscovite granite. The garnets can be classified into three types: i) magmatic garnets (Grt-1A) are intergrown with plagioclase, K-feldspar, and quartz, host both melt and mineral inclusions, and have high REE + Y contents (6488–19,215 ppm); ii) magmatic–hydrothermal garnets (Grt-1B) occur as overgrowths on Grt-1A, host both melt and fluid inclusions, and have intermediate REE + Y contents (2681–8683 ppm); and iii) hydrothermal garnets (Grt-2) are intergranular with quartz and altered biotite, host primary fluid inclusions, and have the lowest REE + Y contents (476–1247 ppm). The texture and composition of the three types of garnet indicate that the magma have undergone a transition from a volatile-undersaturated to a volatile-oversaturated aqueous system. The fluid, from which some REE minerals precipitated, present in the magma system was derived from the magma itself rather than from an external source, as evidenced by the similarity in Nd isotopic composition between the REE minerals and the whole-rock samples. During this transition, the presence of high-HREE garnet prevents the HREE partitioning into refractory minerals (e.g., zircon, REE-bearing phosphate) or extracting from the magma system by the fluid. Our findings show that granites containing high-HREE garnet have high potential for forming ion-absorption HREE deposits and that garnet can reliably record their magmatic evolution.

Preliminary Assessment of Environmentally Friendly Mining Options Based on Various Mineral Resources—A Case Study of the Clarion-Clipperton Fracture Zone in Pacific

Deep-sea polymetallic nodules are associated with rich rare substances, such as rare-earth elements (REEs), Mo, Ti, Te, Li, which are currently in demand and are used in various applications. Deep-sea sediments near nodules are another important source of REEs, which will increase the resource potential of polymetallic nodules. Given the similarity of the mining technologies for deep-sea REEs and polymetallic nodules, this study proposed environmentally friendly mining options and developed a technoeconomic evaluation model by combining deep-sea polymetallic nodules and REEs. Using the Clarion-Clipperton Fracture Zone as an example, this study revealed that the development of polymetallic nodules together with REEs of nearby sediments in the form of by-products will improve the economic and environmental benefits. In addition, the effects of discount rate, cost, and price on the economic benefits of nodule mining were discussed, and a technical development direction was proposed based on scientific and technological needs.

Sulfuric Acid Leaching of Carbonatite ore with High Calcite Content in Lugiin Gol under Ambient Condition

AbstractCarbonatite bearing rare earth elements are rich sources of rare earth elements and play a critical role in the global supply chain. While carbonatite deposits are less accessible compared to ion adsorption clays, their mineral composition makes them essential for rare earth element extraction. Extraction of rare earth elements from carbonatite ore involves acid leaching, a process that we aim to explore in this study using the carbonatite ore from Lugiin gol. Characterization of the raw material and solid residue post‐leaching was conducted using X‐ray diffractometry, inductively coupled plasma optical emission spectroscopy, and a zeta potential analyzer. These analytical techniques were utilized for kinetic modeling, assessing the influencing factors of leaching, and determining metal recovery in the pregnant solution. The results of the study highlight the significant role of surface charge formation on target particles during milling in the acidic leaching process. This finding shed light on the importance of understanding the surface properties of the particles in the extraction of rare earth elements from carbonatite ores. The surface of particles in the supernatant of rare earth elements’ ore was negatively charged, with the median zeta potential of the 0.025 mm fraction being at its minimum of −60.6 mV.

Assessing the Potential of Rare Earth Elements in Bottom Ash from Coal Combustion in Poland.

The aim of the research was to assess the potential of bottom ash from Polish coal-fired power plants as an alternative source of rare earth elements (REY). The potential of these ashes was compared with fly ash from the same coal combustion cycle. The phase and chemical composition, as well as REY, were determined using: X-ray diffraction and inductively coupled plasma mass spectrometry. The tested ashes were classified as inert-low pozzolanic and inert-medium pozzolanic, as well as sialic and ferrosialic, with enrichment in detrital material. The phase and chemical composition of bottom ash was similar to fly ash from the same fuel combustion cycle. The REY content in the ash was 199-286 ppm and was lower than the average for global deposits, and the threshold value was considered profitable for recovery from coal. Bottom ash's importance as a potential source of REY will increase by recovering these metals from separated amorphous glass and mullite and grains rich in Al, Mg, K, and P. The industrial value of bottom ash as an alternative source of REY was similar to fly ash from the same fuel combustion cycle.

Selective extraction and recovery of rare earth elements from coal fly ash by carboxylated mesoporous carbon

The separation of Rare Earth Elements (REEs) from non-conventional sources is very critical to maintain the supply-chain balance of REEs in the Western world. Despite Coal Fly Ash (CFA) being designated as a prominent non-conventional source of REEs and several studies have reported on the extraction of REEs from CFA, the selectivity of REEs with respect to non-REEs in the CFA has never been reported. In this work, for the time, we have reported the selectivity of REEs over non-REEs using carboxylated mesoporous carbon (CMC) as the sorbent. The CMC was produced by carboxylating the soft-templated mesoporous carbon and then it was characterized successfully for porosity, FTIR, and SEM-EDX. The leachate produced from REEs contains 16 REEs and 20 non-REEs from groups 1 through 3 and 6 through 15 of the modern periodic table. The REEs were extracted within 80–90% in the 3 cycles along with the elements from groups of 1,3, 5, 8, and 11. Although a few other elements were also extracted, the values of the distribution coefficient confirmed that the CMC has a much higher affinity towards REEs except the non-REEs from groups 1 and 3. In the recovery mode, the REEs were recovered in the range of 20–100%, and heavier REEs demonstrated a better recovery. The recovery percent of non-REEs was also much lower compared to that of REEs, except for the elements from groups 3, 8, and 11. The non-REEs from group 3 demonstrated the highest competition, which can be attributed to the fact the REEs also belong to the same group of the periodic table. The ratio of extracted and recovered REEs over non-REEs was always greater than unity, suggesting that the CMC was selective towards REEs over non-REEs in extraction and recovery. The overall results suggest that CMC can potentially be used for selective extraction and recovery of REEs from coal fly ash.

Rare Earth Element Speciation in Coal and Coal Combustion Byproducts: A XANES and EXAFS Study.

Transitioning to a low-carbon economy, necessary to mitigate the impacts of anthropogenic climate change, will lead to a significant increase in demand for critical minerals such as rare earth elements (REE). Meeting these raw materials requirements will be challenging, so there is increasing interest in new sources of REE including coal combustion byproducts (CCBs). Extraction of REE from CCBs can be advantageous as it involves reusing a waste product, thereby contributing to the circular economy. While a growing body of literature reports on the abundance of REE in CCBs globally, studies examining the key factors which control their recovery, including speciation and mode of occurrence, are lacking. This study employed synchrotron-based X-ray absorption spectroscopy to probe the speciation and local bonding environment of yttrium in coals and their associated CCBs. Linear Combination Fitting identified silicate and phosphate minerals as the dominant REE-bearing phases. Taken together with the results of extended X-ray absorption fine structure (EXAFS) curve fitting, we find there is minimal transformation in the REE host phase during combustion, indicating it is transferred in bulk from the coals to the CCBs. Accordingly, these findings can be incorporated into the development of an efficient, environmentally conscious recovery process.

Impact of particle size and associated minerals on rare earth desorption and incorporation mechanisms in a South American ion-adsorption clay

This research delves into the intricate nexus of particle size, mineralogical composition, surface attributes, elemental mapping, and rare earth element (REE) adsorption mechanisms within an ion-adsorption clay sample from South America. The investigation entails the fractionation of the ion-adsorption clay into three size categories: S1 (< 0.25 mm), S2 (0.25–0.5 mm), and S3 (0.5–2 mm). Each fraction undergoes meticulous characterization to unveil its elemental composition, mineralogical composition, surface area, morphological characteristics, elemental mapping, and the mechanisms governing REE incorporation. The results indicate that S1 has 31% physiosorbed, 8% chemisorbed, and 61% mineralized REEs, while S2 has 40% physiosorbed, 5% chemisorbed, and 55% mineralized REEs, and S3 has 24% physiosorbed, 5% chemisorbed, and 71% mineralized REEs. The physisorbed REEs are attributed to the presence of kaolinite, conducive to mostly physisorption. In terms of grain size and REE content/type relationship, the results show that REE content decreases with increasing grain size; however, there is not a clear trend in terms of REE occurrence modes with grain size. Heavy rare earth elements (HREEs) are discernibly favored in adsorption over light rare earth elements (LREEs). This preference is underpinned by the weathering processes that led to the formation of ion-adsorption clay, which facilitated the transport and accumulation of HREEs. Notably, the ion-adsorption clay encompasses a substantial content of mineralized REEs, necessitating more demanding extraction methodologies, such as acid baking followed by water leaching if complete extraction of all REEs is desired. Among the desorbable REEs, physisorption dominates, encompassing over 80% of the total. Chemisorbed REEs exhibit versatility in association with various minerals, encompassing kaolinite, quartz, and goethite. In essence, this study unveils the intricate interplay between particle dimensions, mineralogical constitution, surface attributes, and REE adsorption modes within this ion-adsorption clay sample. The ion-adsorption clay in this study contains a significant portion of mineralized REEs that cannot be extracted using the mild conditions typically employed for the desorption process. Additionally, the REE concentration in this ion-adsorption clay is notably higher than the average found in clay deposits worldwide, reaching levels comparable to those of regolith deposits in China, which are a major global source of REEs. This remarkable concentration of REEs, along with the unique modes of their occurrence in this deposit, presents a significant interest to the scientific community.