Distribution Of Mercury In A Gulf Coast Lignite Mine

摘要

Evaluation of mercury distribution throughout a coal seam allows for evaluation of alternatives to reduce mercury emissions from coal-burning electric utilities, such as selective mining. Mercury concentrations in coal samples from 31 cores of a 3-10 ft thick lignite seam in a 475 acre study area within Rusk County, TX, were measured. Detailed samples (0.1 ft sections) were collected from three of the cores, and 6-12 samples (including samples of over- and underburden) were collected from each of the other cores. ASTM method 6414-01 showed erroneously high mercury concentrations for three low-rank coal standards (NIST SRM 2682b, EPRI ES-5, and CANSPEX2003-1) using the Perkin-Elmer AAnalyst FIAS system. Accordingly, a modified assay method to measure the mercury concentration in Texas lignite was developed that recovered 97-108% of the mercury in the low-rank coal standards. Mercury results for the three detailed cores showed substantial vertical variation, with adjacent sections often differing by over 200 μg of Hg/kg of dry coal. Pyritic sulfur and total organic carbon were positively correlated with the mercury concentration. Mercury concentrations did not correlate with vertical or lateral position within the lignite seam within the study area. Consequently, selective mining to produce a lower Hg product is likely not feasible in this area.