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Title: Effects of roasting additives and leaching parameters on the extraction of rare earth elements from coal fly ash

Abstract

Coal fly ash is a promising alternative source for rare earth elements (REE), which are critical materials in many technologies. REEs are entrained in the aluminosilicate glass of the fly ash particles, hindering their ability to solubilize during acid leaching. The purpose of this research was to test the effectiveness of roasting techniques to improve extraction of REEs from fly ash, determine key parameters controlling REE extraction, and understand trade-offs in reagent use. Representative coal ash samples from major U.S. coal basins (Appalachian, Illinois, and Powder River basins) were roasted using a variety of chemical additives (Na 2O 2, NaOH, CaO, Na 2CO 3, CaSO 4, (NH 4) 2SO 4). Further experiments investigated the effects of additive:ash ratio, roasting temperature, and leachate pH on REE extraction. We found here that NaOH roasting often recovered >90% of total REE content, equivalent to the USGS-recommended method (Na 2O 2 sintering). Other additives tested recovered <50% of total REE content; the 450 °C sinter temperature, which was well below the melting points of these agents, may have been a contributing factor. Decreasing the NaOH-ash ratio did not significantly inhibit in REE recoveries, while increasing the leachate pH led to a sharp decline. Theremore » was a strong positive correlation between REE extraction and leachate H + molarity. Recoveries of ~100% were observed for the Powder River Basin ash sample regardless of the roasting agent and additive:ash ratio used. This suggests that acid leaching alone is sufficient for recovering REEs from more soluble Powder River Basin ashes. For Appalachian and Illinois Basin ashes, the recommended roasting conditions for >70% REE extraction are a 1:1 NaOH-ash ratio and leaching with 1–2 mol/L HNO 3.« less

Authors:
 [1];  [2]; ORCiD logo [1]
  1. Duke Univ., Durham, NC (United States). Dept. of Civil and Environmental Engineering
  2. Univ. of Kentucky, Lexington, KY (United States). Center for Applied Energy Research
Publication Date:
Research Org.:
Duke Univ., Durham, NC (United States)
Sponsoring Org.:
USDOE Office of Fossil Energy (FE); National Science Foundation (NSF)
OSTI Identifier:
1526009
Alternate Identifier(s):
OSTI ID: 1542510
Grant/Contract Number:  
FE0026952; CBET-1510965; CBET-1510861; OISE-1243433
Resource Type:
Accepted Manuscript
Journal Name:
International Journal of Coal Geology
Additional Journal Information:
Journal Volume: 196; Journal ID: ISSN 0166-5162
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
rare earth elements; coal fly ash; sinter; extraction; recovery

Citation Formats

Taggart, Ross K., Hower, James C., and Hsu-Kim, Heileen. Effects of roasting additives and leaching parameters on the extraction of rare earth elements from coal fly ash. United States: N. p., 2018. Web. doi:10.1016/j.coal.2018.06.021.
Taggart, Ross K., Hower, James C., & Hsu-Kim, Heileen. Effects of roasting additives and leaching parameters on the extraction of rare earth elements from coal fly ash. United States. doi:10.1016/j.coal.2018.06.021.
Taggart, Ross K., Hower, James C., and Hsu-Kim, Heileen. Sat . "Effects of roasting additives and leaching parameters on the extraction of rare earth elements from coal fly ash". United States. doi:10.1016/j.coal.2018.06.021. https://www.osti.gov/servlets/purl/1526009.
@article{osti_1526009,
title = {Effects of roasting additives and leaching parameters on the extraction of rare earth elements from coal fly ash},
author = {Taggart, Ross K. and Hower, James C. and Hsu-Kim, Heileen},
abstractNote = {Coal fly ash is a promising alternative source for rare earth elements (REE), which are critical materials in many technologies. REEs are entrained in the aluminosilicate glass of the fly ash particles, hindering their ability to solubilize during acid leaching. The purpose of this research was to test the effectiveness of roasting techniques to improve extraction of REEs from fly ash, determine key parameters controlling REE extraction, and understand trade-offs in reagent use. Representative coal ash samples from major U.S. coal basins (Appalachian, Illinois, and Powder River basins) were roasted using a variety of chemical additives (Na2O2, NaOH, CaO, Na2CO3, CaSO4, (NH4)2SO4). Further experiments investigated the effects of additive:ash ratio, roasting temperature, and leachate pH on REE extraction. We found here that NaOH roasting often recovered >90% of total REE content, equivalent to the USGS-recommended method (Na2O2 sintering). Other additives tested recovered <50% of total REE content; the 450 °C sinter temperature, which was well below the melting points of these agents, may have been a contributing factor. Decreasing the NaOH-ash ratio did not significantly inhibit in REE recoveries, while increasing the leachate pH led to a sharp decline. There was a strong positive correlation between REE extraction and leachate H+ molarity. Recoveries of ~100% were observed for the Powder River Basin ash sample regardless of the roasting agent and additive:ash ratio used. This suggests that acid leaching alone is sufficient for recovering REEs from more soluble Powder River Basin ashes. For Appalachian and Illinois Basin ashes, the recommended roasting conditions for >70% REE extraction are a 1:1 NaOH-ash ratio and leaching with 1–2 mol/L HNO3.},
doi = {10.1016/j.coal.2018.06.021},
journal = {International Journal of Coal Geology},
number = ,
volume = 196,
place = {United States},
year = {2018},
month = {6}
}

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