Rare earth minerals in a “no tonstein” section of the Dean (Fire Clay) coal, Knox County, Kentucky

Hower, James C.; Berti, Debora; Hochella, Michael F.; Mardon, Sarah M.

doi:10.1016/j.coal.2018.05.001

Cited by 55 publications

(23 citation statements)

References 25 publications

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“…It is difficult to differentiate them by SEM-EDX. REE phosphates have also been identified previously using TEM 17,34 and EPMA. 19 A lime (CaO) particle containing minor REEs (REE oxide content < 0.5 wt %) is shown in Figure 1c.…”

Section: Methodsmentioning

confidence: 70%

Comprehensive Understandings of Rare Earth Element (REE) Speciation in Coal Fly Ashes and Implication for REE Extractability

Liu

Huang

Tang

2019

Environ. Sci. Technol.

100

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In recent years, recovery of rare earth elements (REEs) from coal fly ashes (CFAs) has been considered as a promising resource recovery option. Yet, quantitative information on REE speciation in CFAs and its correlation with REE extractability are not well established. This study systematically investigated the REE speciation-extractability relationship in four representative CFA samples by employing multiple analytical and spectroscopic techniques across the micro to bulk scale and in combination with thermodynamic calculations. A range of REE-bearing phases are identified, such as REE oxides, REE phosphates, apatite, zircon, and REE-bearing glass phase. REEs can occur as discrete particles, as particles encapsulated in the glass phase, or distribute throughout the glass phase. Although certain discrepancies exist on the REE speciation quantified by X-ray adsorption spectroscopy and acid leaching due to intrinsic limitations of each method, both approaches show significant fractions of REE oxides, REE phosphates, apatite, and REE-bearing Fe oxides. This study contributes to an in-depth understanding of the REE speciation–distribution–extractability relationship in CFAs and can help identify uncertainties associated with the quantification of REE speciation. It also provides a general methodology for future studies on REE speciation in complex environmental samples and a knowledge basis for the development of effective REE recovery techniques.

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Section: Methodsmentioning

confidence: 70%

Comprehensive Understandings of Rare Earth Element (REE) Speciation in Coal Fly Ashes and Implication for REE Extractability

Liu

Huang

Tang

2019

Environ. Sci. Technol.

100

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“…12 The Fire Clay coal seam is well-known for its relatively high REE contents, which is mainly due to the tonstein layer (tuffaceous input) existing in the seam. 10,14,15 Leaching of the tonstein material (infiltrational input), detrital mineral input into the peat, and subtle hydrothermal fluid from the southeast side also caused the enrichment of REEs in the upper and lower benches of the coal seam. 10 Fractionation of the REEs in coal seams occurred due to the different genetic types and chemical natures of REEs.…”

Section: Introductionmentioning

confidence: 99%

Acid Leaching of Rare Earth Elements from Coal and Coal Ash: Implications for Using Fluidized Bed Combustion To Assist in the Recovery of Critical Materials

2019

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High temperature pretreatment of coal-based mineral matter in an oxidizing environment significantly enhances the leaching characteristics of rare earth elements (REEs). A research study has found that the temperatures used in fluidized-bed combustion (FBC) of coal to produce electricity are near optimum for pre-treating the associated mineral matter prior to leaching to maximize the recovery of critical materials. Tests were performed on representative samples collected from preparation plants treating West Kentucky No. 13, Illinois No. 6, and Fire Clay coal seam sources as well as fly ash and bed ash samples from two FBC power plants. Acid leaching tests using 1.2M HCl at 75℃ were performed on both the coal and the FBC ash samples. Prior to leaching, the coal samples were pretreated at temperatures of 600℃, 750℃, and 900℃ in an oxidizing environment to study the effect on leaching characteristics. The results showed that pretreatment at 600℃ for 2 hours resulted in a significant increase in REE recovery from a range of 20-40% to about 80% for all coal sources. The leaching kinetics are characterized by a quick release of rare earth elements within the first few minutes of the process. For the West Kentucky No. 13 coal source, about 75% of REEs were leached in the first 15 min from the 1.4-1.8 specific gravity (SG) fraction that was calcined at 600℃. Additionally, the leaching kinetics of the major contaminant, i.e., Fe, were much lower than the REEs, which significantly benefits the efficiency of leaching and the downstream upgrading processes. REE leaching characteristics of the FBC ash samples were similar to that of the calcined coals. Mineralogy characterization showed that the degree of crystallinity for both the calcined coal and FBC samples were similar to the original associated mineral matter, which provided evidence for the advantage of using the FBC byproducts as REE feedstocks over pulverized coal boilers that utilize temperatures greater than 1200℃. These findings were used to develop a conceptual flowsheet that incorporates FBC technology and its typical combustion environment to enhance the feasibility of recovering critical materials from coal-based sources.

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“…Overall, studies such as this, including our previous TEM investigations 8,9 and the work by Saikia et al 12 and Zhao et al, 14 illustrate the information to be gained through the fine-scale examination of coal structures. Elemental occurrences passed off as being in an organic association are seen to be truly associated with minerals.…”

Section: Discussionmentioning

confidence: 57%

Ultrafine Mineral Associations in Superhigh-Organic-Sulfur Kentucky Coals

2018

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Two high-organic-sulfur Kentucky coals, the eastern Kentucky River Gem coal and the western Kentucky Davis coal, are examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), both including elemental analysis by energy-dispersive spectroscopy (EDS). From the SEM–EDS analysis, it is observed that the western Kentucky coal had areas with Pb and Cd in addition to the expected Fe and S and the eastern Kentucky coal had individual Fe–S-rich areas with La and Ni and with Si, Al, Cr, Ni, and Ti. TEM and selected area electron diffraction (SAED) analyses demonstrate that anglesite with a rim of Pb-bearing amorphous Fe-oxide occurs in the western Kentucky coal. Melanterite, an Fe-sulfate, with minor Al, Si, and K EDS peaks, suggests that clay minerals may be in close association with the sulfate, is also detected in the coal. A polycrystalline metal in the eastern Kentucky sample with a composition similar to stainless steel is adjacent to an Al-rich shard. Euhedral pyrite grains surrounded by kaolinite and gibbsite are detected. Overall, it is noted that element associations should not be assumed to be organic just because minerals cannot be seen with optical microscopy or with standard bulk analytical techniques, such as X-ray diffraction (XRD).

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Rare earth minerals in a “no tonstein” section of the Dean (Fire Clay) coal, Knox County, Kentucky

Cited by 55 publications

References 25 publications

Comprehensive Understandings of Rare Earth Element (REE) Speciation in Coal Fly Ashes and Implication for REE Extractability

Comprehensive Understandings of Rare Earth Element (REE) Speciation in Coal Fly Ashes and Implication for REE Extractability

Acid Leaching of Rare Earth Elements from Coal and Coal Ash: Implications for Using Fluidized Bed Combustion To Assist in the Recovery of Critical Materials

Ultrafine Mineral Associations in Superhigh-Organic-Sulfur Kentucky Coals

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