MODES OF EMPLACEMENT OF RARE EARTH ELEMENTS IN COALS: EXAMPLES FROM THE FIRE CLAY COAL, EASTERN KENTUCKY

Fly ash from the combustion of eastern Kentucky Fire Clay coal in a southeastern United States pulverized-coal power plant was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). TEM combined with elemental analysis via energy dispersive X-ray spectroscopy (EDS) showed that rare earth elements (REE; specifically, La, Ce, Nd, Pr, and Sm) were distributed within glassy particles. In certain cases, the REE were accompanied by phosphorous, suggesting a monazite or similar mineral form. However, the electron diffraction patterns of apparent phosphate minerals were not definitive, and P-lean regions of the glass consisted of amorphous phases. Therefore, the distribution of the REE in the fly ash seemed to be in the form of TEM-visible nano-scale crystalline minerals, with additional distributions corresponding to overlapping ultra-fine minerals and even true atomic dispersion within the fly ash glass.

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Distribution of rare earth elements in eastern Kentucky coals: Indicators of multiple modes of enrichment?

International Journal of Coal Geology ◽

10.1016/j.coal.2016.04.009 ◽

2016 ◽

Vol 160-161 ◽

pp. 73-81 ◽

Cited By ~ 79

Author(s):

James C. Hower ◽

Cortland F. Eble ◽

Shifeng Dai ◽

Harvey E. Belkin

Keyword(s):

Rare Earth ◽

Rare Earth Elements ◽

Eastern Kentucky ◽

Multiple Modes

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Leaching Kinetics of Rare Earth Elements from Fire Clay Seam Coal

Minerals ◽

10.3390/min10060491 ◽

2020 ◽

Vol 10 (6) ◽

pp. 491

Author(s):

Xinbo Yang ◽

Rick Q. Honaker

Keyword(s):

Activation Energy ◽

Rare Earth ◽

Sulfuric Acid ◽

Rare Earth Elements ◽

Froth Flotation ◽

Mineral Acid ◽

Product Layer ◽

Major Mechanism ◽

Mixed Control ◽

Fire Clay

Recovery of rare earth elements (REEs) from coal samples collected from the Fire Clay coal seam using diluted mineral acid solutions was investigated. The initial processing step was coal recovery using conventional froth flotation which concentrated the REEs in tailing material resulting in an upgrade to values around 700 ppm on a dry whole mass basis. Leaching experiments were performed on the flotation tailings material using a 1.2 M sulfuric acid solution adjusted to a temperature of 75 °C to study the extractability of REEs from coal material. The effect of particle size, leaching time, leaching temperature, and solid concentration on REE leaching recovery were evaluated. The kinetic data obtained from leaching over a range of temperatures suggested that the leaching process follows the shrinking core model with possibly a mixed control mechanism that may be a result of several heterogenous materials leaching simultaneously. Leaching recovery increased rapidly at the beginning of the reaction then slowed as the system reached equilibrium. The apparent activation energy determined from test data obtained over a range of temperatures using 1 M sulfuric acid was 36 kJ/mol for the first 20 min of reaction time and 27 kJ/mol for the leaching period between 20 and 120 min. The leaching of light REEs during the initial stage was determined to be driven by a chemical reaction, followed by the formation of a product layer, which required lower activation energy in the later stage of leaching. In regards to the heavy REEs, the major mechanism for leaching is desorption and the product layer formation does not affect the heavy REEs significantly.

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