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Leaching and Solution Treatments of Rare Earth Elements from Various Sources, Volume II

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A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Processing and Extractive Metallurgy".

Deadline for manuscript submissions: closed (17 February 2023) | Viewed by 25812

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Special Issue Editors

Prof. Dr. Kenneth N. Han

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Guest Editor

Department of Materials and Metallurgical Engineering, South Dakota School of Mines and Technology, Rapid City, SD 57701, USA
Interests: hydrometallurgy; metallurgical kinetics; solution chemistry; interfacial phenomena; electrometallurgy; nano/colloidal particles synthesis and applications
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Kwadwo Osseo-Asare

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Guest Editor

Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802, USA
Interests: hydrometallurgy; separation science & technology; environmental systems; materials synthesis & processing; wet processing in semiconductor fabrication; surface cleaning & finishing; interfacial and colloidal phenomena; surfactant science; semiconductor electrochemistry; thermodynamic modeling

Special Issue Information

Dear Colleagues,

Rare earth elements (REEs) have become an important group of metals used in many high-tech industries, especially in efficient green energy industries. The principal concentrations of REEs are associated with uncommon varieties of igneous rocks, alkaline rocks, and carbonatites. The major minerals containing REEs include monazite, bastnaesite, xenotime, and allanite. As there is a fast-growing demand for REEs to fuel the high-tech industries and the relatively REE-rich ore deposits are depleting, there have been considerable efforts in identifying low-grade ores and recovering REEs from recycling resources such as used magnets and other recycling streams. Additional sources also include clay minerals, coal and coal byproducts, especially in the eastern United States.

There is also an urgent need to identify new and innovative technologies to extract these valuable metals effectively and economically from low-grade ores and, at the same time, in an environmentally friendly manner. To meet this challenge, we had called a first issue on “Leaching of Rare Earth Elements from Various Sources” in 2020. We are pleased to note the result of this call was highly successful with the first issue consisting of high-quality papers in the field.

To continue the success of this attempt, we would like to announce the second round of the endeavor with an expanded scope of coverage. The purpose of this Special Issue is to provide important works currently being conducted in the field of leaching REEs from various sources. The key areas of focus include the leaching behavior of REEs from various sources before and after prior treatments; salient analysis of thermodynamic and kinetic aspects of leaching behaviors; the characteristics of the chemical precipitation of REEs in various solutions provided by the associated mineral matters included in the original sources and the effect on the secondary leaching process; solution treatments after leaching but excluding solvent extraction.

Prof. Dr. Kenneth N. Han
Prof. Dr. Kwadwo Osseo-Asare
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Minerals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

direct leaching
leaching after heat treatment
precipitation
complexation
thermodynamics
kinetics
selectivity
recycling
leach liquor treatments (SX excluded)

Related Special Issue

Leaching of Rare Earth Elements from Various Sources in Minerals (10 articles)

Published Papers (7 papers)

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Research

19 pages, 11248 KiB

Open AccessArticle

The Effect of Iron- and Calcium-Rich Waste Rock’s Acid Baking Conditions on the Rare-Earth Extraction

by Vitor L. Gontijo, Leandro Augusto Viana Teixeira and Virgínia Sampaio Teixeira Ciminelli

Minerals 2023, 13(2), 217; https://doi.org/10.3390/min13020217 - 02 Feb 2023

Cited by 2 | Viewed by 2661

Abstract

The work investigates the effect of sulfuric acid baking on rare earth element (REE) extraction from two waste rock samples from a phosphate mine. The role of different mineralogical assemblages and the degree of alteration (i.e., weathering), and the behavior of the main impurities–iron, phosphorus, and calcium–on REE extraction are emphasized. For both samples, the sulfuric acid baking at 25 °C, during 15 min, H₂SO₄:sample (w/w) mass ratio of 0.45:1 is the best condition for achieving the selective leaching of REE. For the iron rich-sample, the increase in temperature reduces REE extraction and increases iron dissolution. The corresponding sulfuric acid consumed by goethite (α-FeOOH) from 25 °C to 160 °C acid baking is ten times higher than that required for the monazite (REEPO₄) reaction. Conversely, higher REE and lower iron extraction are observed by increasing (sulfuric acid/sample) mass ratio (0.95:1). Due to the high sulfuric concentration during dissolution, a local saturation zone close to the dissolution front caused the precipitation of iron oxyhydroxides. The calcium-rich sample shows lower REE extraction by leaching (63% maximum) mainly due to the entrapment of REE-bearing minerals by a gypsum layer, and lanthanide’s uptake by calcium sulfate compounds formed during leaching. The results were discussed with the help of a detailed characterization of the residues. Full article

(This article belongs to the Special Issue Leaching and Solution Treatments of Rare Earth Elements from Various Sources, Volume II)

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20 pages, 5195 KiB

Open AccessEditor’s ChoiceArticle

Recovery of Rare Earth Elements from Mining Tailings: A Case Study for Generating Wealth from Waste

by Luver Echeverry-Vargas and Luz Marina Ocampo-Carmona

Minerals 2022, 12(8), 948; https://doi.org/10.3390/min12080948 - 28 Jul 2022

Cited by 16 | Viewed by 4639

Abstract

The growing demand for rare earth elements (REE) driven by their applications in modern technologies has caused the need to search for alternative sources of these elements as their extraction from traditional deposits is limited. A potential source of light rare earth elements (LREE) may be the monazite present in the mining waste generated in the Bagre-Nechí mining district in Colombia due to the processing of sands containing alluvial gold. Consequently, in this research, a systematic evaluation has been carried out for the extraction of

C e

L a

, and

N d

from a leach liquor obtained from monazite present in alluvial gold mining tailings. The leaching process carried out with

H C l

indicated the recovery of approximately 90% of

L a

and

N d

and

\sim 60 %

C e

; the solvent extraction tests of these elements showed that increasing the contact time and pH of the leaching liquor positively affects the extraction of lanthanum, cerium, and neodymium, achieving extractions close to 100% with

D 2 E H P A

and to a lesser extent with

C y a n e x 572

. McCabe–Thiele diagrams for extraction with

D 2 E H P A

indicated the requirement of three stages for the extraction of

C e

L a

and

N d

. Full article

(This article belongs to the Special Issue Leaching and Solution Treatments of Rare Earth Elements from Various Sources, Volume II)

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18 pages, 2527 KiB

Open AccessArticle

Leaching of Rare Earth Elements from NdFeB Magnets without Mechanical Pretreatment by Sulfuric (H₂SO₄) and Hydrochloric (HCl) Acids

by Anna Klemettinen, Andrzej Żak, Ida Chojnacka, Sabina Matuska, Anna Leśniewicz, Maja Wełna, Zbigniew Adamski, Lassi Klemettinen and Leszek Rycerz

Minerals 2021, 11(12), 1374; https://doi.org/10.3390/min11121374 - 06 Dec 2021

Cited by 12 | Viewed by 4604

Abstract

A simplified approach for rare earth elements leaching from NdFeB (neodymium-iron-boron) magnets was investigated. The possibility of simplifying the magnet recycling process by excluding grinding, milling and oxidative roasting unit operations was studied. Attempts to skip the demagnetization step were also conducted by using whole, non-demagnetized magnets in the leaching process. The presented experiments were conducted to optimize the operating conditions with respect to the leaching agent and its concentration, leaching time, leaching temperature and the form of the feed material. The use of hydrochloric and sulfuric acids as the leaching agents allowed selective leaching of NdFeB magnets to be achieved while leaving nickel, which is covering the magnets, in a solid state. The application of higher leaching temperatures (40 and 60 °C for sulfuric acid and 40 °C for hydrochloric acid) allowed us to shorten the leaching times. When using broken demagnetized magnets as the feed material, the resulting rare earth ion concentrations in the obtained solutions were significantly higher compared to using whole, non-demagnetized magnets. Full article

(This article belongs to the Special Issue Leaching and Solution Treatments of Rare Earth Elements from Various Sources, Volume II)

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Graphical abstract

11 pages, 8328 KiB

Open AccessArticle

Leaching the Unleachable Mineral: Rare Earth Dissolution from Monazite Ore in Condensed Phosphoric Acid

by Harry Watts and Tonya Fisher

Minerals 2021, 11(9), 931; https://doi.org/10.3390/min11090931 - 27 Aug 2021

Cited by 2 | Viewed by 3251

Abstract

Monazite is a poorly soluble mineral of rare earth phosphate. It is an ore of the rare earths which is difficult to break down; in industry either concentrated sulphuric acid or caustic soda is used to attack finely ground monazite at between 140 °C and 400 °C. In these processes, the rare earths are converted into different solid compounds, undergoing an incomplete conversion. Here we show a new process for a direct and much faster breakdown of monazite by simple dissolution under milder conditions. Condensed phosphoric acid was used to dissolve rare earths (up to 96 g/L) from unground monazite sand from four sources. Greater than 99% of light rare earths dissolved within 30 min at 260 °C. The cooled solution can be diluted to an extent with water to reduce viscosity for analysis or further processing. This method of dissolution avoids the use of strong acids/bases and reduces the risk of dusk exposure from fine grinding of particles. Full article

(This article belongs to the Special Issue Leaching and Solution Treatments of Rare Earth Elements from Various Sources, Volume II)

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17 pages, 3127 KiB

Open AccessArticle

Leaching Behaviors of Calcium and Aluminum from an Ionic Type Rare Earth Ore Using MgSO₄ as Leaching Agent

by Qiang He, Jiang Qiu, Minglu Rao and Yanfei Xiao

Minerals 2021, 11(7), 716; https://doi.org/10.3390/min11070716 - 02 Jul 2021

Cited by 8 | Viewed by 2521

Abstract

During the leaching process of ionic rare earth ore (ICREO), ion-exchangeable phase calcium (IEP-Ca) and ion-exchangeable phase aluminum (IEP-Al) are leached along with rare earth, which causes many problems in the enrichment process, such as increasing the precipitant agent consumption and rare earth loss, etc. The agitation leaching kinetics and the column leaching mass transfer process of IEP-Ca and IEP-Al were studied to understand the leaching behavior of impurity in ICREO, which provides guides for the adjustment of the leaching process and to limit the co-leaching of impurities. IEP-Ca and IEP-Al were leached by ion exchange, with the leaching agent cations and the leaching kinetics described by an internal diffusion-controlled shrinking core model with an apparent activation energy of 8.97 kJ/mol and 10.48 kJ/mol, respectively. In addition, a significant reduction in the leaching efficiency of aluminum was caused by the hydrolysis reaction reinforced by the increase in MgSO₄ concentration and temperature. The leaching kinetic data of IEP-Ca and IEP-Al was verified by the column leaching mass transfer process. There was a synchronous increase in the peak concentration of the outflow curve and leaching efficiency of calcium with the concentration of MgSO₄ since IEP-Ca was easily leached. Therefore, as the leaching efficiency of calcium was already very high in the 0.20 mol/L MgSO₄ leaching process, the leaching rate of calcium was limited by the leaching temperature and injection rate of MgSO₄. For aluminum, the hydrolysis of Al³⁺ was promoted by increasing the MgSO₄ concentration and the leaching temperature, thereby effectively reducing the content of aluminum in the leachate. Full article

(This article belongs to the Special Issue Leaching and Solution Treatments of Rare Earth Elements from Various Sources, Volume II)

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21 pages, 3268 KiB

Open AccessArticle

Thermodynamic Analysis of Precipitation Characteristics of Rare Earth Elements with Sulfate in Comparison with Other Common Precipitants

by Kenneth N. Han and Rina Kim

Minerals 2021, 11(7), 670; https://doi.org/10.3390/min11070670 - 23 Jun 2021

Cited by 10 | Viewed by 3352

Abstract

The selective precipitation of rare earth elements (REEs) in acidic media often plays a key role in the effective extraction of these elements from various sources such as ores and recycling streams. In this study, the precipitation characteristics of REEs with sulfate, a frequently used precipitant, were carefully examined, and the results were compared with those of other precipitants, such as phosphate, oxalate, and fluoride/carbonate systems. Emphasis is given on various forms of precipitates, such as anhydrous sulfate, octa-hydrated sulfate, and sodium double salt, in which the sodium double salt was compared with the anionic double salt precipitation of the fluoride-carbonate system. It was found that anions such as Cl⁻, NO₃⁻, and SO₄²⁻ play an important role in the precipitation behavior, particularly through complexation with the dissolved REEs. In general, the effectiveness of precipitation follows the order of sodium double salt, a hydrated form of sulfate, and anhydrous sulfate. In this study, it was observed that the synergistic role of a double salt precipitation, either cationic or anionic, is frequently as effective as that of oxalate and phosphate, even in a low pH range. Full article

(This article belongs to the Special Issue Leaching and Solution Treatments of Rare Earth Elements from Various Sources, Volume II)

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16 pages, 5748 KiB

Open AccessArticle

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

by Zongliang Zhang, Landon Allen, Prasenjit Podder, Michael L. Free and Prashant K. Sarswat

Minerals 2021, 11(5), 484; https://doi.org/10.3390/min11050484 - 01 May 2021

Cited by 12 | Viewed by 3380

Abstract

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

(This article belongs to the Special Issue Leaching and Solution Treatments of Rare Earth Elements from Various Sources, Volume II)

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