Research

11 pages, 1898 KiB

Open AccessArticle

Tetrafluoroboric Acid Digestion for Accurate Determination of Rare Earth Elements in Coal and Fly Ash by ICP-MS Analysis

by Zheng-Hua Li, Giday WoldeGabriel and Oana Marina

Minerals 2024, 14(1), 72; https://doi.org/10.3390/min14010072 - 07 Jan 2024

Viewed by 1110

Abstract

Coal and coal-related fly ash often contain rare earth elements (REEs) that have the potential to be utilized as valuable mineral resources. Accurately determining the REE content in coal and fly ash is crucial for resource evaluation. The conventional approach involves using hydrofluoric [...] Read more.

Coal and coal-related fly ash often contain rare earth elements (REEs) that have the potential to be utilized as valuable mineral resources. Accurately determining the REE content in coal and fly ash is crucial for resource evaluation. The conventional approach involves using hydrofluoric acid (HF) to dissolve silicates and release REEs, which, however, prolongs the digestion process due to the additional step of complexing fluoride ions (F⁻) with boric acid (H₃BO₃). Determining the correct amount of H₃BO₃ for neutralization can be challenging, and in some instances, the binding of fluoride ions with certain lanthanides (Lns) hampers the accurate determination of all 14 naturally occurring rare earth elements in a single digestion batch by inductively coupled plasma mass spectrometry (ICP-MS). In this study, we present an alternative method that achieves the accurate determination of all 14 naturally occurring REEs using tetrafluoroboric acid (HBF₄) followed by ICP-MS analysis. This approach eliminates the need for an F⁻ complexing step. We tested this method on certified REE reference materials, including NIST 1632e (coal) and NIST 1633c (fly ash), as well as the REE geological reference material USGS AGV-1 (andesite). Our results demonstrated excellent recovery rates (relative standard deviation, RSD < ±10%), with a correlation coefficient (r²) exceeding 0.99. Using this method, we investigated the concentrations of all 14 REEs in coal and fly ash samples collected from various locations in the southwestern USA. This improved digestion technique streamlines the analysis process and enhances the accuracy of REE determination, facilitating a more comprehensive evaluation of REE-rich coal and fly ash deposits for resource exploration. Full article

(This article belongs to the Special Issue Rare Earth Elements: Occurrence, Exploration, Alternate Resources, Extraction Techniques, Chemical Characterization and Recycling)

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14 pages, 11755 KiB

Open AccessArticle

Oxyfluorides of Rare-Earth Elements in the Rocks of the Shatak Formation (Southern Urals)

by Sergey G. Kovalev, Sergey S. Kovalev and Aysylu A. Sharipova

Minerals 2023, 13(7), 935; https://doi.org/10.3390/min13070935 - 13 Jul 2023

Cited by 1 | Viewed by 738

Abstract

The Shatak Formation, comprising a part of the Mashak Suite (RF₂), is located on the western slope of the Southern Urals. It consists of various rock types, including sedimentary rocks, such as conglomerates, polymictic sandstones, aleurolites, and carbonaceous clayey shales, as [...] Read more.

The Shatak Formation, comprising a part of the Mashak Suite (RF₂), is located on the western slope of the Southern Urals. It consists of various rock types, including sedimentary rocks, such as conglomerates, polymictic sandstones, aleurolites, and carbonaceous clayey shales, as well as igneous rocks, including picrites, basalts, dacites, rhyodacites, and rhyolites, and volcanogenic–sedimentary rocks, such as tuffs and tuff breccias. In this article, oxyfluoride (La, Ce) (O_nF_m)₃ mineralization, occurring in the contact zone between the metabasalts and quartz sandstones, is described for the first time in the literature. This is represented by compounds of variable compositions forming an isomorphic series: trifluoride, (La, Ce)F₃–oxyfluoride, (La, Ce)OF–oxide, and (La, Ce)₂O₃. By analyzing several binary phase diagrams, significant coordination between oxygen, fluorine, and cerium in the chemical composition of oxyfluorides has been highlighted. However, the behavior of lanthanum has been shown to exhibit some irregularity. The genesis of oxyfluoride mineralization is attributed to the regional metamorphism of rocks within the Shatak Formation. During the hydrothermal process, the decomposition of fluorapatite, which is unstable during both hydrothermal metamorphism and supergene processes, resulted in the release of fluorine, as well as potentially lanthanum and cerium. Variations in the chemical composition of oxyfluorides, which are formed in the presence of an excess of oxygen resulting from water dissociation, are determined by local differences in the content of the main components within the forming microfractures. Full article

(This article belongs to the Special Issue Rare Earth Elements: Occurrence, Exploration, Alternate Resources, Extraction Techniques, Chemical Characterization and Recycling)

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20 pages, 12069 KiB

Open AccessFeature PaperArticle

Rare Earth Elements Geochemistry and ²³⁴U/²³⁸U, ²³⁵U/²³⁸U Isotope Ratios of the Kanyakumari Beach Placer Deposits: Occurrence and Provenance

by Thennaarassan Natarajan, Kazumasa Inoue and Sarata Kumar Sahoo

Minerals 2023, 13(7), 886; https://doi.org/10.3390/min13070886 - 29 Jun 2023

Cited by 2 | Viewed by 1130

Abstract

Geochemical studies of rare earth elements (REEs) as well as major and trace elements were conducted on the beach placer sands from the Kanyakumari coastal region, a well-known high background natural radiation area (HBNRA). For the first time, uranium isotope ratios (²³⁴ [...] Read more.

Geochemical studies of rare earth elements (REEs) as well as major and trace elements were conducted on the beach placer sands from the Kanyakumari coastal region, a well-known high background natural radiation area (HBNRA). For the first time, uranium isotope ratios (²³⁴U/²³⁸U and ²³⁵U/²³⁸U) were determined in the study area to investigate the provenance and leaching of U from the beach sands. Inductively coupled plasma mass spectrometry was used for the measurement of REEs and trace elements whereas thermal ionization mass spectrometry (TIMS) was used for the measurement of U isotope ratios. ∑REEs were found to be in the range of 778.93 to 15,007. 54 µg/g, whereas ∑Light REEs were in the range of 770.58 to 14,860.80 µg/g and ∑Heavy REEs varied from 8.35 to 146.74 µg/g. The enrichment factor showed the LREEs Th and U were extremely enriched in the Kanyakumari beach placer sands. The ²³⁵U/²³⁸U isotope ratios were similar to the natural terrestrial ratio value. The ²³⁴U/²³⁸U activity ratio varied from 0.995 to 1.071, and showed the prevailing secular equilibrium among them. The δ²³⁸U results could, to some extent, explain the U fractionation and source. Full article

(This article belongs to the Special Issue Rare Earth Elements: Occurrence, Exploration, Alternate Resources, Extraction Techniques, Chemical Characterization and Recycling)

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22 pages, 6612 KiB

Open AccessArticle

Analysis of Rare Earth Ores Using Laser-Induced Breakdown Spectroscopy and Laser Ablation Time-of-Flight Mass Spectrometry

by Amir Fayyaz, Raheel Ali, Muhammad Waqas, Usman Liaqat, Rizwan Ahmad, Zeshan A. Umar and Muhammed A. Baig

Minerals 2023, 13(6), 787; https://doi.org/10.3390/min13060787 - 08 Jun 2023

Cited by 4 | Viewed by 2676

Abstract

Rare earth elements are gaining significant importance in the scientific and technological fields for their exciting physical properties and characteristics. The aim of the present study was to determine rare earth elements (REEs) in geological ores found in the Northern Areas of Pakistan. [...] Read more.

Rare earth elements are gaining significant importance in the scientific and technological fields for their exciting physical properties and characteristics. The aim of the present study was to determine rare earth elements (REEs) in geological ores found in the Northern Areas of Pakistan. We present the application of laser-induced breakdown spectroscopy (LIBS) and laser ablation time-of-flight mass spectrometry (LA-TOF-MS) for the elemental analysis of geological ore samples containing REEs. The laser-induced plasma plume exhibits a wide array of emission lines, including those of rare earth elements such as Ce, La, and Nd. Furthermore, the spectral range, from 220 nm to 970 nm, encompasses emission lines from C, Fe, Ti, Na, Mg, Si, and Ca. The qualitative analysis of the constituent elements in the samples was performed by comparing the LIBS spectrum of the unknown sample with that of the spectroscopically pure rare earth elements (La₂O₃, CeO₂, and Nd₂O₃, with 99.9% metals basis) recorded under the same experimental conditions. The quantitative analysis was performed using the calibration-free laser-induced breakdown spectroscopy (CF-LIBS), LA-TOF-MS, and energy-dispersive X-ray (EDX) techniques. The results obtained by CF-LIBS were found to be in good agreement with those obtained using the LA-TOF-MS and EDX analytical techniques. LIBS is demonstrated to yield a quick and reliable qualitative and quantitative analysis, of any unknown geological sample, comparable to that of the other analytical techniques. Full article

(This article belongs to the Special Issue Rare Earth Elements: Occurrence, Exploration, Alternate Resources, Extraction Techniques, Chemical Characterization and Recycling)

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14 pages, 4159 KiB

Open AccessArticle

Leaching Mechanism of Aluminum during Column Leaching of Ion-Adsorption Rare Earth Ore Using Magnesium Sulfate

by Qi Guo, Zheng Li, Jiaxin Pan, Bo Li, Longsheng Zhao, Depeng Liu, Xudong Zheng and Chunmei Wang

Minerals 2023, 13(3), 401; https://doi.org/10.3390/min13030401 - 14 Mar 2023

Cited by 4 | Viewed by 1600

Abstract

Aluminum is a significant impurity in the ion-adsorption rare earth ore. The changes in the occurrences of aluminum have a great influence on the leaching of the rare earth ore. In this paper, the column leaching method was employed using magnesium sulfate as [...] Read more.

Aluminum is a significant impurity in the ion-adsorption rare earth ore. The changes in the occurrences of aluminum have a great influence on the leaching of the rare earth ore. In this paper, the column leaching method was employed using magnesium sulfate as a leaching agent to investigate the effects of pH and magnesium sulfate concentration in the leaching agent on the leaching of aluminum and rare earths. The results show that at low magnesium sulfate concentrations, the leaching of rare earths is greatly enhanced, while the leaching of aluminum is not significantly affected by a decrease in the pH of leaching agent. At high magnesium sulfate concentrations, a slight increase in the leaching of rare earths is observed, accompanied by a significant increase in the leaching of aluminum upon decreasing the pH of the leaching agent. The leaching behavior of aluminum is related to the changes in the occurrences of aluminum during the leaching process. At low magnesium sulfate concentrations, low pH promotes the transition of Hy-Al to Sol-Al, but due to the low Mg²⁺ concentration in the leaching agent, Sol-Al is back-adsorbed onto the clays and transformed into Ex-Al, resulting in no significant increase in the aluminum content in the leach solution. However, at higher magnesium sulfate concentrations, aluminum in the leach solution comes mainly from the transformation of Ex-Al. Lowering the pH of the leaching agent can significantly promote the transition of Hy-Al to Sol-Al, thereby greatly increasing the aluminum content in the leach solution. The above results provide theoretical support for the optimization of the in situ leaching of ion-adsorption rare earth ore using magnesium sulfate. Full article

(This article belongs to the Special Issue Rare Earth Elements: Occurrence, Exploration, Alternate Resources, Extraction Techniques, Chemical Characterization and Recycling)

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17 pages, 4146 KiB

Open AccessArticle

Laser-Induced Breakdown Spectroscopy (LIBS) for the Detection of Rare Earth Elements (REEs) in Meteorites

by Surya Harikrishnan, Adarsh Ananthachar, Khoobaram S. Choudhari, Sajan Daniel George, Santhosh Chidangil and V. K. Unnikrishnan

Minerals 2023, 13(2), 182; https://doi.org/10.3390/min13020182 - 26 Jan 2023

Cited by 2 | Viewed by 3214

Abstract

The spectroscopic characterization of plasma generated in meteorite samples during Laser-Induced Breakdown Spectroscopy (LIBS) shows the emission spectrum of elements present and also allows one to rapidly identify the elemental composition without any sample preparation and with good accuracy compared to some other [...] Read more.

The spectroscopic characterization of plasma generated in meteorite samples during Laser-Induced Breakdown Spectroscopy (LIBS) shows the emission spectrum of elements present and also allows one to rapidly identify the elemental composition without any sample preparation and with good accuracy compared to some other methods. In addition, LIBS has other advantages, such as multi-elemental response, micro–nano gram level of destructiveness and portability of the instrument. Since the presence of Rare Earth Elements (REEs) in meteorites is usually in trace levels or not at all, LIBS can be used as a potential alternative method for the meteorite fragment analysis which, in turn, gives valuable clues on its origin as well as the origin of the solar system and its impact on life on Earth, particularly on the presence of REEs. The elemental analysis results for a few of the selected samples, such as iron meteorites, lunar meteorites, eucrites and impact glass, are presented and discussed. The LIBS analysis was supplemented by Principal Component Analysis (PCA) with which it was possible to classify the samples into different classes according to their chief constituents, structure and origin. Full article

(This article belongs to the Special Issue Rare Earth Elements: Occurrence, Exploration, Alternate Resources, Extraction Techniques, Chemical Characterization and Recycling)

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16 pages, 2439 KiB

Open AccessArticle

Recovery of Rare Earth Element from Acid Mine Drainage Using Organo-Phosphorus Extractants and Ionic Liquids

by Tommee Larochelle, Aaron Noble, Kris Strickland, Allie Ahn, Paul Ziemkiewicz, James Constant, David Hoffman and Caitlin Glascock

Minerals 2022, 12(11), 1337; https://doi.org/10.3390/min12111337 - 22 Oct 2022

Cited by 4 | Viewed by 2041

Abstract

Acid mine drainage is a legacy environmental issue and one of the largest pollutants in many mining districts throughout the world. In prior work, the authors have developed a process for the recovery of critical materials, including the rare earth elements, from acid [...] Read more.

Acid mine drainage is a legacy environmental issue and one of the largest pollutants in many mining districts throughout the world. In prior work, the authors have developed a process for the recovery of critical materials, including the rare earth elements, from acid mine drainage using a preconcentration step followed by solvent extraction as a concentration and purification technology. As part of the downstream technology development efforts, we have synthesized a suite of ionic liquid extractants that facilitate greater separation factors leading to lower capital costs and reduced environmental impacts. This article provides a comparison of the conventional extractants D2EHPA, EHEHPA and C572 with their respective ionic liquids [c101][D2EHP,c101][EHEHP] and [c101][C572] for the recovery of rare earth elements from acid mine drainage. In the study, laboratory-scale, multi-contact solvent extraction tests were conducted at high and low extractant/dosages. The results show that the ionic liquids varied in performance, with [c101][D2EHP] and [c101][EHEHP] performing poorer than their conventional counterparts and [c101][c572] performing better. Recommendations for further study on [c101][c572] include stripping tests, continuous pilot testing, and techno-economic analysis. Full article

(This article belongs to the Special Issue Rare Earth Elements: Occurrence, Exploration, Alternate Resources, Extraction Techniques, Chemical Characterization and Recycling)

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Review

Jump to: Research, Other

47 pages, 3821 KiB

Open AccessReview

Advances in Analytical Techniques and Applications in Exploration, Mining, Extraction, and Metallurgical Studies of Rare Earth Elements

by V. Balaram

Minerals 2023, 13(8), 1031; https://doi.org/10.3390/min13081031 - 31 Jul 2023

Cited by 4 | Viewed by 2913

Abstract

The use of analytical techniques is important and critical in all areas related to REE, such as basic fundamental research, exploration, mining, extraction, and metallurgical activities at different stages by different industries. At every stage of these activities, rock, ore, minerals, and other [...] Read more.

The use of analytical techniques is important and critical in all areas related to REE, such as basic fundamental research, exploration, mining, extraction, and metallurgical activities at different stages by different industries. At every stage of these activities, rock, ore, minerals, and other related materials have to be analyzed for their REE contents in terms of elemental, isotopic, and mineralogical concentrations using different analytical techniques. Spectacular developments have taken place in the area of analytical instrumentation during the last four decades, with some of them having shrunk in size and become handheld. Among laboratory-based techniques, F-AAS, GF-AAS, ICP-OES, and MP-AES have become very popular. Because of high sensitivity, fewer interference effects, and ease of use, ICP-MS techniques, such as quadrupole ICP-MS, ICP-MS/MS, ICP-TOF-MS, MH-ICP-MS, HR-ICP-MS, and MC-ICP-MS, with both solution nebulization as well as direct solid analysis using laser ablation sample introduction methods, have become more popular for REE analysis. For direct analysis of solids, INAA, XRF, and LIBS techniques, as well as LA-based ICP-MS techniques, are being extensively utilized. The LIBS technique in particular requires little to no sample preparation. TIMS, SIMS, and SHRIMP techniques are being used for isotopic as well as dating REE depots. Portable analytical techniques, such as pXRF, pLIBS, and Raman spectrometers are able to perform in situ analysis even in the field, helping to make fast decisions during exploration studies. At present, hyperspectral remote sensing techniques including handheld, drone, and satellite-based techniques have become very popular in REE exploration studies because of their ability to cover larger areas in a limited time and, thus, became very cost-effective. Deployment of microanalytical devices/sensors mounted in remotely operated vehicles (ROV) is being successfully utilized in detecting REE-rich deposits in the deep oceans. Providing updated in-depth information on all these important aspects with suitable examples, especially from the point of view of REE research studies is the focal point of this review article. Full article

(This article belongs to the Special Issue Rare Earth Elements: Occurrence, Exploration, Alternate Resources, Extraction Techniques, Chemical Characterization and Recycling)

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22 pages, 851 KiB

Open AccessReview

Potential Future Alternative Resources for Rare Earth Elements: Opportunities and Challenges

by Vysetti Balaram

Minerals 2023, 13(3), 425; https://doi.org/10.3390/min13030425 - 16 Mar 2023

Cited by 24 | Viewed by 8552

Abstract

Currently, there is an increasing industrial demand for rare earth elements (REE) as these elements are now integral to the manufacture of many carbon-neutral technologies. The depleting REE ores and increasing mining costs are prompting us to consider alternative sources for these valuable [...] Read more.

Currently, there is an increasing industrial demand for rare earth elements (REE) as these elements are now integral to the manufacture of many carbon-neutral technologies. The depleting REE ores and increasing mining costs are prompting us to consider alternative sources for these valuable metals, particularly from waste streams. Although REE concentrations in most of the alternative resources are lower than current REE ores, some sources including marine sediments, coal ash, and industrial wastes, such as red mud, are emerging as promising with significant concentrations of REE. This review focuses on the alternative resources for REE, such as ocean bottom sediments, continental shelf sediments, river sediments, stream sediments, lake sediments, phosphorite deposits, industrial waste products, such as red mud and phosphogypsum, coal, coal fly ash and related materials, waste rock sources from old and closed mines, acid mine drainage, and recycling of e-waste. Possible future Moon exploration and mining for REE and other valuable minerals are also discussed. It is evident that REE extractions from both primary and secondary ores alone are not adequate to meet the current demand, and sustainable REE recovery from the alternative resources described here is also necessary to meet the growing REE demand. An attempt is made to identify the potential of these alternative resources and sustainability challenges, benefits, and possible environmental hazards to meet the growing challenges of reaching the future REE requirements. Full article

(This article belongs to the Special Issue Rare Earth Elements: Occurrence, Exploration, Alternate Resources, Extraction Techniques, Chemical Characterization and Recycling)

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Other

Jump to: Research, Review

16 pages, 3642 KiB

Open AccessConcept Paper

Pretreatment of Bituminous Coal By-Products for the Hydrometallurgical Extraction of Rare Earth Elements

by Tushar Gupta, Ahmad Nawab and Rick Honaker

Minerals 2023, 13(5), 614; https://doi.org/10.3390/min13050614 - 28 Apr 2023

Cited by 4 | Viewed by 1160

Abstract

Low-temperature plasma (LTP) oxidation has been widely used to study the mineralogy of the mineral matter existing in coal sources. The current study investigated the potential of LTP oxidation as a pre-treatment method to improve rare earth element (REE) leachability from coal and [...] Read more.

Low-temperature plasma (LTP) oxidation has been widely used to study the mineralogy of the mineral matter existing in coal sources. The current study investigated the potential of LTP oxidation as a pre-treatment method to improve rare earth element (REE) leachability from coal and its by-products. Representative density-fractionated samples of Baker and Fire Clay coarse refuse seam materials were ground to a top size of 180 µm and subjected to low-temperature plasma oxidation. Subsequently, the treated samples were leached at 1% w/v solids concentration and 75 °C for 5 h using (i) de-ionized (DI) water, (ii) 0.1 mol/L of ammonium sulfate, and (iii) 1.2 mol/L of sulfuric acid. It was determined that LTP treatment improved REE leaching characteristics, especially the leaching of heavy REEs (HREE), existing in the lighter density fractions of the Baker seam coarse refuse material. For instance, the HREE recovery for the 1.6 specific gravity (SG) float fraction increased from 8% to 33% using 0.1 mol/L of ammonium sulfate solution after 32 h of LTP treatment. This finding indicated that HREEs associated with the organic matter were released by the LTP treatment and adsorbed onto the surfaces of highly negative charged mineral matter and was exchanged with ammonium to allow their recovery. Similarly, when using 1.2 mol/L of sulfuric acid, the HREE recovery increased from 23% to 53% for the 1.6 SG float fraction. Interestingly, LTP oxidation did not provide significant improvement in REE recovery from the 2.2 sink density fractions, which was likely due to its lower organic content. No significant benefits were observed when treating the Fire Clay coarse refuse material, which was likely due to the lack of organic affinity and the difficult-to-leach REE minerals associated with the coal source such as monazite, xenotime, and zircon. Conversely, high-temperature oxidation within a temperature range of 600–750 °C significantly improved REE leaching characteristics for both coal sources. Improvement in REE recovery was due to decarbonization of the material, clay dehydroxylation and subsequent conversion of liberated REE-bearing minerals into a more leachable form. However, increasing the temperature above 800 °C decreased REE recovery due to the conversion of meta-kaolinite into mullite, which is chemically stable. Full article

(This article belongs to the Special Issue Rare Earth Elements: Occurrence, Exploration, Alternate Resources, Extraction Techniques, Chemical Characterization and Recycling)

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19 pages, 7777 KiB

Open AccessConcept Paper

Removal of Iron from Pyrite-Rich Coal Refuse by Calcination and Magnetic Separation for Hydrometallurgical Extraction of Rare Earth Elements

by Tushar Gupta, Ahmad Nawab and Rick Honaker

Minerals 2023, 13(3), 327; https://doi.org/10.3390/min13030327 - 26 Feb 2023

Cited by 5 | Viewed by 1623

Abstract

In the metallurgical extraction of rare earth elements (REEs), the ratio of contaminant ions to REEs in the leachate dictates the cost and operational efficiency of the downstream processes. The current study investigated the potential iron contamination removal from the feed to the [...] Read more.

In the metallurgical extraction of rare earth elements (REEs), the ratio of contaminant ions to REEs in the leachate dictates the cost and operational efficiency of the downstream processes. The current study investigated the potential iron contamination removal from the feed to the hydrometallurgical process by calcination followed by magnetic separation. The 2.20 specific gravity sink fraction of Baker coal seam coarse refuse was pulverized to finer than 180 μm, calcined at various temperatures, and separated into magnetic and non-magnetic fractions using a wet high-intensity magnetic separator at different field strengths. The untreated feed, calcined products, and their subsequent magnetic and non-magnetic fractions were subjected to acid leaching tests with 1.2 M sulfuric acid at 75 °C and 1% w/v solids concentration. The recovery of light and heavy rare earth elements (LREEs and HREEs, respectively) along with the concentration of common contaminant ions (Al, Ca, and Fe) were measured as output variables. The weight percent of magnetic material was maximized at approximately 29% by calcination at a temperature of 400 °C. Magnetic removal of this fraction using a field strength of 1.15 Tesla resulted in the rejection of 81% of the iron. Leaching of the magnetic fraction provided significantly higher Fe recovery relative to untreated feed material and the non-magnetic fraction. The non-magnetic fraction was subsequently calcined at 600 °C to dehydroxylate the clays and released the REE minerals in the same manner as the treatment of the original coarse refuse material. A comparison of the leachate elemental concentrations resulting from the leaching of both the calcined non-magnetic and original coarse refuse showed only a slight reduction in the iron content from the non-magnetic material. This finding combined with the REE loss in the magnetic fraction resulted in the conclusion that the magnetic removal step was unfavorable. Full article

(This article belongs to the Special Issue Rare Earth Elements: Occurrence, Exploration, Alternate Resources, Extraction Techniques, Chemical Characterization and Recycling)

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