Abstract
Certain Central Appalachian coals, most notably the Fire Clay coal with a REY-enriched volcanic ash fall tonstein, are known to be enriched in rare earth elements. The Fire Clay tonstein has a greater contribution to the total coal + parting REY than would be inferred from its thickness, accounting for about 20%–35% of the REY in the coal + parting sequence. Underground mining, in particular, might include roof and floor rock and the within-seam partings in the mined product. Beneficiation, necessary to meet utility specifications, will remove some of the REY from the delivered product. In at least one previously published example, even though the tonstein was not present in the Fire Clay coal, the coal was enriched in REY. In this case, as well as mines that ship run-of-mine products to the utility, the shipped REY content should be virtually the same as for the mined coal. At the power plant, however, the delivered coal will be pulverized, generally accompanied by the elimination of some of the harder rock, before it is fired into the boiler. Overall, there are a wide range of variables between the geologic sample at the mine and the power plant, any or all of which could impact the concentration of REY or other critical materials in the coal combustion products.
Highlights
Central Appalachian coals, in particular the Middle Pennsylvanian Fire Clay coal in EasternKentucky and Southern West Virginia, are known to be relatively enriched in rare earth elements (REE); or rare earth + yttrium (REY) if Yttrium is included
The study was originally planned as a single-seam, single-mine investigation of the partitioning of mercury; the added focus on rare earth elements was serendipitous, a function of the use of a Fire Clay coal correlative as the source coal
There are unique features of the study which need to be considered when comparing the results with REY concentrations in fly ash from other power plants
Summary
Kentucky and Southern West Virginia, are known to be relatively enriched in rare earth elements (REE); or rare earth + yttrium (REY) if Yttrium is included. The Fire Clay coal stands out because it includes a volcanic ash-derived parting or tonstein [1], which has a high REY content [2,3]. Portions of the coal above and, in particular, below the tonstein are enriched in REY [2]. In some cases where the tonstein is not present, the coal is still enriched in REY [3]. Comparing average ash-basis REYs from five major coals (Table 1, after Bragg et al [4]), it can be seen that the Fire Clay coal and its correlatives have a higher total REY than the other coals.
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