COMPARISON OF TRACE-ELEMENT CONTENTS OF RAW AND CLEAN COMMERCIAL COALS

The airborne emission of some of the inorganic trace elements found in coal is subject to potential regulation as air toxic substances under the 1990 Clean Air Act Amendments (CAAA). Therefore, reliable information about the concentrations of these elements in coals is important for assessing the necessity and impact of possible regulations. However, much of the published data on trace elements in coals was obtained on geological samples. These data are not pertinent to all commercial coals, particularly the majority of midwestern and eastern bituminous coals, which are cleaned to remove mineral matter and increase heating value prior to use. The purpose of this paper is to present trace element data for eastern and midwestern bituminous coals, provide an estimate of their temporal and geographic variability, and quantify the impact of coal cleaning on the reduction in trace element concentrations. Trace element data are provided for commercial (i.e., as shipped) coals from the Pittsburgh and Illinois #6 seams, and the Central Appalachia region. An analysis of a historical data base (1981-present) shows that the typical trace element concentration variability (percent relative standard deviation (PRSD)) for commercial coal from a single mine was 10-20% over that period. Across a broader geographical region in a single seam, the PRSD increased to 20-50%. A comparison of paired samples of raw and clean coals from eight preparation plants demonstrates that conventional coal cleaning is an effective means to reduce the concentrations of most trace elements. The total concentration of the 11 trace elements listed in the CAAA was reduced in approximately the same proportion as the ash by conventional coal cleaning (about 80% reduction on a mg/MM Btu basis). Trace element reductions are uniform for coals produced from different mines in the same seam.