Mercury in Western Canadian subbituminous coal - a weighted average study to evaluate potential mercury reduction by selective mining

Western Canadian subbituminous coal is mined using strip-mining methods. The coal is used to feed coal-fired power plants for electricity generation. Parameters that influence the mercury content of these coals include the occurrence and frequency of partings in the seam, weathering, and epigenetic mineralization. Most partings have higher mercury content than the coal layers in the same seam, with the single bentonite bed having the highest Hg content. However, some high ash components, such as sandy siltstone, do not follow this trend. The incorporation of the high mercury partings into the as-mined coal may increase the Hg content in the feed coal. Epigenetic mineralization may also increase the mercury content of coal, depending on the nature of the mineralization. Calculation of the weighted mean of mercury content for various combination of lithological components of a seam illustrates how these components influence the total mercury content of the seam. This approach also suggests how selective mining might be used to reduce mercury in "as-mined" coal. Results of weighted average calculations of mercury indicate that the thin lithological units with moderate mercury may not necessarily influence that overall weighted average of Hg for a seam. However, there can be exception, such as presence of thin (3.5 cm) bentonite parting with high mercury in a 94.5 cm seam that increased the mercury content of seam by 83.4%. (C) 2004 Elsevier B.V. All rights reserved.