Arsenic and Selenium in Texas Lignite

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Abstract
Texas lignite samples were analyzed for arsenic and selenium utilizing hydride generation-dc helium emission spectrometry and gas chromatography-microwave plasma emission spectrometry. Arsenic and selenium were present in the samples at levels ranging from 1.0 to 5.5ppm and 3.9 to 22.9 ppm, respectively. The arsenic concentrations vary slightly whereas the selenium levels fluctuate strongly as a function of depth in the lignite deposit. Analysis of specific gravity fractions of mined lignite indicated that arsenic and selenium are primarily associated with the lower density fractions and therefore probably in organic combination. Knowledge of the chemical nature of the arsenic and selenium in coals is necessary in order to select the most appropriate chemical and physical treatment methods to control emission of these toxic elements to the atmosphere during direct combustion and to prevent catalyst deactivation during fuel conversion processes. Elements associated with the heavier mineral fractions can be partially removed by washing techniques. However, elements chemically bound to the organic fraction can be separated only during or after combustion. during chemical conversion processes, or possibly by chemical extraction processes. Limited success was achieved in arsenic and selenium removal from raw lignite utilizing non-aqueous solvent extraction with dimethyl sulfoxide.