Energy Sources, Vol.17, No.1, 41-55, 1995
ENRICHMENT AND DEPLETION OF ELEMENTS IN A SUBBITUMINOUS COAL AND IN ITS 120-DEGREES-C, 400-DEGREES-C, AND 800-DEGREES-C ASHES
This study reports on the enrichment and depletion of elements in selected suites of subbituminous coals from the Highvale Mine, Alberta, Canada, and in their 120-degrees-C, 400-degrees-C, and 800-degrees-C ashes. All elements analyzed in the raw coal are within the world range for coals, and some small variations in elemental concentration were noted due to variations in ash content of the samples. Ashing at 120-degrees-C resulted in an enrichment of all elements by a factor of 1.5 x to 6.5 x in one suite of samples and by a factor of 5 x to 11 x in the other suite. Generally, the elements Br and Se are enriched by a lower factor than other elements, Mo is absent in all 120-degrees-C ashed samples, and the samples with the higher ash content show a smaller elemental enrichment than samples with lower ash content (cleaner coals). All elements in the 400-degrees-C ashed samples are enriched by a factor of 1.5 x to 6.5 x in one suite of samples and by 1.5 x to 9.5 x in the other. Surprisingly, the elements Br, Cl, and Se are enriched two- to sixfold, pointing to the possibility of formation of salts (i.e., bromide salts), a process taking place due to the reactions of anions with cations during ashing. By 800-degrees-C, the elements Br, Cl, and Mo are completely volatilized. Most elements are enriched by a factor of 5 x to 8 x in the lower-ash sample and by 2.5 x to 3.5 x in the higher-ash sample of the first suite, while the enrichment is between 3.5 x and 6 x in the samples of the second suite. Enrichment factors (EFs) are calculated using the ratio of elemental concentration versus Al concentration in air/crust (method A), and the concentration in ash (method B). EFs are consistently higher when calculated using method B. This indicates that it is method B which should be used when calculating enrichment factors, because method A is used for environmental studies in general (i.e., water, soil, coal), whereas method B is used specifically for coal.
Keywords:TRACE-ELEMENTS;COMBUSTION