Environ. Scl. Technol. 1994, 18, 12-18
Elemental Partitioning in Ash Depositories and Material Balances for a Coal Burning Facility by Spark Source Mass Spectrometry Robert J. Conzemlus," Tlmothy D. Welcomer, and Harry J. Svec Ames Laboratory-U.S. Department of Energy and Department of Chemistry, Iowa State University, Ames, Iowa 5001 1
W Spark source mass spectrometry
(SSMS) is shown to
be an excellent analytical tool for determining enrichment factors and a useful tool for measuring material balances for a coal burning facility. Enrichment and material balance are measured for 62 elements in an Iowa and a Colorado coal by using SSMS as the sole analytical technique. Copper was used as an internal reference. The elements As, Cd, Ga, Ge, Pb, Sn, T1, and Zn were found to be highly partitioned in the various ash depositories and Bi, Cs, Cu, I, Mo, Na, Se, Ta, and W were partially partitioned. The halogens, Hg, S, and Se were found to be lost to the stack. One-third of the elements studied for material balance gave an influent/effluent ratio agreeing within 30% of unity. Systematic errors are noted in relative sensitivity coefficients, used for instrument calibration, for some of the elements and between coal and ash samples.
Introduction Certain elements are known to concentrate in various ash depositories in coal burning facilities (1-3). The current trend toward the burning of coal containing significant levels of inorganic constituents presents the opportunity for using these ash depositories as sources of some strategically important elements. In searching for such opportunities an analytical technique is needed which possesses high sensitivity and broad elemental coverage. Spark source mass spectrometry (SSMS) possesses both of these attributes. However, it has reputed limited reproducibility and accuracy (3-6) unless combined with isotope dilution (7) which also limits its elemental range and complicates sample preparation. When special sample fusion techniques are used to improve homogeneity (8), spectral inferferences increase, contamination of the samples is likely, and the time required for the analysis increases. When electrical means for recording SSMS results (9) are used to reduce the measuring uncertainties, the mass resolution is limited. Measurements of elemental material balances (MB) at coal burning facilities are made usually by using a combination of analytical techniques (1,10, 11). Here, MB as well as elemental partitioning were studied solely by SSMS by using minimal sample preparation, but with legitimate sampling, for a broad array of elements. The purpose of the MB measurements were to study sources of random variations such as sample inhomogeneity and to identify systematic errors due to instrument calibration by using coal and ash reference standards. Results cited summarize work from a more detailed study (12).
Experimental Section The coal burning facility used in this study is located on the Iowa State University campus. It produces power and steam for operating the university and normally burns a blend of high sulfur Iowa coal and low sulfur Colorado coal in order to meet environmental sulfur emission standards. A schematic illustration of the ash recovery 12
Environ. Scl. Technol., Vol. 18, No. 1, 1984
sites and distribution of ash from the particular boiler used in this study is given in Figure 1. The boiler is a spreader-stoker unit where -60% af the ash falls below the boiler grates as bottom ash (BA), -34% is recovered in a primary mechanical collector (PMC) which is -85% efficient, and the remaining ash is collected in an electrostatic precipitator (ESP) which is -97% efficient. For this study the plant burned only the Iowa coal mined near Lovilla, IA, during August of 1979 and only the Colorado coal mined near Craig, CO, during September of 1979 in this particular boiler. In mid-August and -September 12 samples of the influent coal and 12 samples at each of the ash recovery sites were collected during a 3-day period by using American Society for Testing and Materials (ASTM) standard methods (12,13). These samples were crushed, mixed, riffled, and then low-temperature ashed (LTA) (12) prior to analysis by spark mass spectrometry. All of the samples (coal, ash, and reference standards) were subjected to identical LTA (
