A preliminary method for determining acceptable trace element levels in coal

A preliminary method for determining acceptable trace element levels in coal was established. In addition to the conventional coal quality parameters ash and sulfur, potentially hazardous trace elements As, Be, Cd, Cl, Cr, F, Hg, Mn, Ni, Pb and Se were selected for the evaluation, and their environmentally acceptable concentrations in coal were quantified at 5 and 0.5 weight %, and 6.5, 1, 0.8, 400, 15, 120, 0.15, 80, 30, 15 and 2.5 mg/kg, respectively. A pollution index (I) is proposed, by which coal is ranked into four classes: acceptable (I ≤ 0.252), marginal (0.252 < I ≤ 0.514), unacceptable (0.514 < I ≤ 0.751), and ultra-unacceptable coal (I > 0.751). 36 coal samples collected from the north of Ordos basin and Shanxi Province, China were classified with the method. Most of the cleaned coals were rated as acceptable or marginal, while the run-in-mine coals, feed coals, middlings and coal slimes were generally ranked as unacceptable or ultra-unacceptable coal. The evaluation results reflect the degree of cleanliness of these coal samples.