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Recovery of Rare Earth Elements (REEs) from Coal Ash
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Recovery of Rare Earth Elements (REEs) from Coal Ash

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 (31 December 2023) | Viewed by 4595

Special Issue Editor

Dr. Sudip Maity

E-Mail Website
Guest Editor
CSIR-Central Institute of Mining and Fuel Research (Digwadih), FRI, Dhanbad 828108, Jharkhand, India
Interests: rare earth elements in coal and coal ash; mineralogy and X-ray powder diffraction; molecular structure of coal; heterogeneous catalysis; Fischer–Tropsch synthesis; coal-to-liquid; non thermal plasma reformation for hydrogen generation

Special Issue Information

Dear Colleagues,

The demand for Rare Earth Elements (REEs) is increasing continuously in order to sustaining the need for synthesis of advanced materials utilized in a range of applications from quantum computing and materials science to medical applications; however, the conventional resources are not sufficient to meet the enhanced need of the present society. Coal ash (CA), a complex anthropogenic waste material, could be a secondary resource of REEs, as CA is known to have high concentrations of these elements. Annually billions of tons of CA are generated due to combustion of coal in thermal power stations. However, recovery of REEs from CA is a real challenge and intensive research work is going on in this area by several eminent researchers around the globe. Solvent extraction techniques are one the most effective and widely used methods for recovery. Recently, some new methods have also been studied, such as flash joule heating and biological methods. Solvent extraction process is usually preceded by physical beneficiation processes, such as size separation, magnetic separation, specific gravity separation, etc., followed by alkali pretreatment and then subjected to acid leaching. The most common reagent used for solvent extraction are di-(2-ethyl hexyl) phosphoric acid and tributyl phosphate. The problem is these processes or reagents are not economically viable. Due to environmental concerns, use of organic acids (Green chemicals) are becoming attractive. In this Special Issue, we are trying to bring together the cutting-edge research going on around the globe towards recovery of REEs from CA by different pathways. It is my great privilege to welcome authors to publish their target oriented research and comprehensive reviews for better understanding of recovery techniques towards secondary source of REEs.

Dr. Sudip Maity
Guest Editor

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Keywords

  • recovery of REEs from coal ash
  • green chemistry pathway for REEs
  • secondary resource for critical elements
  • solvent extraction
  • value addition to CA

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Published Papers (2 papers)

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Research

16 pages, 4924 KiB  
Article
Recovery of Rare Earth Elements from Coal Fly Ash with Betainium Bis(trifluoromethylsulfonyl)imide: Different Ash Types and Broad Elemental Survey
by Ting Liu, James C. Hower and Ching-Hua Huang
Minerals 2023, 13(7), 952; https://doi.org/10.3390/min13070952 - 17 Jul 2023
Cited by 4 | Viewed by 2246
Abstract
Previously, proof-of-concept studies have demonstrated that rare-earth elements (REEs) can be preferentially extracted from coal fly ash (CFA) solids using a recyclable ionic liquid (IL), betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf2N]). When the suspension of aqueous solution—IL-CFA—is heated above 65 °C, the majority of [...] Read more.
Previously, proof-of-concept studies have demonstrated that rare-earth elements (REEs) can be preferentially extracted from coal fly ash (CFA) solids using a recyclable ionic liquid (IL), betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf2N]). When the suspension of aqueous solution—IL-CFA—is heated above 65 °C, the majority of REEs will separate from the bulk elements in the solids and partition to the IL phase. Acid stripping of the IL removes REEs and regenerates the IL for reuse in additional extraction cycles. The objective of this study is to showcase the applicability and effectiveness of the optimized method to recover REEs from various CFAs. Six CFA samples with different characteristics (feed coal basins, coal beds, and ash collecting points) and classifications (Class C and Class F) were examined. The process performance was evaluated for a broad range of elements (33 total), including 15 REEs, two actinides, six bulk elements, and 10 trace metals. Results confirmed good recovery of total REEs (ranging from 44% to 66% among the CFA samples) and the recovery process’ high selectivity of REEs over other bulk and trace elements. Sc, Y, Nd, Sm, Gd, Dy, and Yb consistently showed high leaching and partitioning into the IL phase, with an average recovery efficiency ranging from 53.8% to 66.2%, while the other REEs showed greater variability among the different CFA samples. Some amounts of Al and Th were co-extracted into the IL phase, while Fe co-extraction was successfully limited by chloride complexation and ascorbic acid reduction. These results indicated that the IL-based REE-CFA recovery method can maintain a high REE recovery efficiency across various types of CFA, therefore providing a promising sustainable REE recovery strategy for various coal ash wastes. Full article
(This article belongs to the Special Issue Recovery of Rare Earth Elements (REEs) from Coal Ash)
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19 pages, 3389 KiB  
Article
Pilot Scale Testing of Lignite Adsorption Capability and the Benefits for the Recovery of Rare Earth Elements from Dilute Leach Solutions
by Ahmad Nawab and Rick Honaker
Minerals 2023, 13(7), 921; https://doi.org/10.3390/min13070921 - 8 Jul 2023
Cited by 2 | Viewed by 1690
Abstract
Naturally occurring organic materials containing humic acids show a strong affinity towards rare earth elements (REE) and other critical elements. Leaching experiments on lignite coal waste produced from construction sand production revealed that the contained REEs were associated with the organic matter. Furthermore, [...] Read more.
Naturally occurring organic materials containing humic acids show a strong affinity towards rare earth elements (REE) and other critical elements. Leaching experiments on lignite coal waste produced from construction sand production revealed that the contained REEs were associated with the organic matter. Furthermore, adsorption studies revealed that the lignite waste was capable of extracting REEs from a model solution and increased the REE content of the lignite waste by more than 100%. As such, this study aimed to utilize the lignite waste to adsorb REEs from pregnant leach solutions and acid mine drainage sources having low REE concentrations and subsequently leach the lignite material to produce pregnant leach solutions containing relatively high amounts of REEs, which benefits the performance and economic viability of downstream separation and purification processes. An integrated flowsheet was developed based on this concept and tested at a pilot scale. The pregnant leachate solution (PLS) was generated from a heap leach pad containing 2000 tons of Baker seam coarse refuse. The pilot scale circuit was comprised of aluminum precipitation, adsorption using the waste lignite, and rare earth-critical metal (RE-CM) precipitation stages in succession. The results indicated that the aluminum precipitation stage removed over 88% and 99% of the Al and Fe, respectively. The adsorption stage increased the REE content associated with the waste lignite from 457 ppm to 1065 ppm on a whole mass basis. Furthermore, the heavy REE (HREE) content in the feedstock increased by approximately 250%, which raised the percentage of HREE in the REE distribution by 19 absolute percentage points. In addition to the REEs, concentrations of other critical elements such as Mn, Ni, and Zn also improved by 75%, 37%, and 250%, respectively. Bench-scale tests revealed that increasing the solids concentration in the waste lignite and PLS mix from 1% to 20% by weight enhanced the adsorption efficiency from 32.0% to 99.5%, respectively. As such, a new flowsheet was proposed which provides significantly higher REE concentrations in the PLS that can be fed directly to solvent extraction and/or oxalic acid precipitation and, thereby, enhancing process efficiency and economics. Full article
(This article belongs to the Special Issue Recovery of Rare Earth Elements (REEs) from Coal Ash)
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