PrintPreparation
Coal mining employs basically the same traditional mining techniques used in hard rock mining - underground and surface ("strip") mining. One of the more efficient but environmentally destructive methods for mining coal involves "strip" mining. This technique is analogous to the open pit mining techniques used in hard rock mining whereby the soil and rock above the coal seam are removed to expose the seam. The seam is then blasted and the coal is scooped up by huge front end loaders or electric shovels and transported to a coal processing plant. These coal preparation plants use a variety of physical (e.g., screening) and chemical (e.g., flotation using high gravity liquids) methods to separate the raw coal from all of the non-combustible waste rock and minerals (e.g., pyrite). The coarser waste rock is piled up adjacent to the mined out area and the finer coal tailings coming from the preparation plant are discharged as a thick slurry into a man-made impoundment. After coal mining operations have ceased, the mine is reclaimed by dumping the waste rock into the pit, regrading the area to approximate the original contours of the land and then replanting the area using native grasses and trees. Source for this para, direct quote from US EPA glossary, here http://cfpub.epa.gov/npdes/glossary.cfm term, "Mining (Coal)"
An impoundment is "The entire structure used for coal slurry waste disposal, including the embankment, basin, beach, pool, and slurry." (source: National Research Council, 2002 this book: Coal waste impoundments: risks, responses, and alternatives, by National Research Council (U.S.). Committee on Coal Waste Impoundments) See http://www.nap.edu/openbook.php?isbn=030908251X&page=213
During the process of mining and cleaning coal, waste is created and must be permanently disposed of in an impoundment. Preparation of coal, also called washing, is how non-combustible materials are removed from the mine. As the coal is washed, waste is created and classified as either course refuse or fine refuse. Larger materials such as rocks and pieces of coal are defined as course refuse. Slurry, a combination of silt, dust, water, bits of coal and clay particles is considered fine refuse, and is the most commonly disposed of material held in an impoundment. Between 20 to 50 percent of the material received at a coal preparation plant may be rejected and housed in impoundments (National Research Council, 2002). The coarse refuse is used to construct the impoundment dam, which then holds the fine refuse or slurry, along with any chemicals used to wash and treat the coal at the coal preparation plant. Directly from http://www.coalimpoundment.org/aboutimpoundments/facts.asp What is an Impoundment?
Coal preparation, or “washing,” also causes water pollution when chemicals and water are used to separate impurities from mined coal. Up to 90 million gallons of coal preparation slurry are produced every year in the U.S., most of which are stored in large waste pits known as impoundments. Impoundments leak into local water supplies and can even burst dramatically, sending millions of gallons of wastes barreling down in mudflows and destroying property and lives. (The SIerra Club description: www.sierraclub.org/coal/downloads/0508-coal-report-fact-sheet.pdf)
Notes and possible exercises:
Coal preparation/processing and related topics (slurry, impoundments) not mentioned on pro-coal sites that I can find. Except here, http://www.mine-engineer.com/mining/coalprep.htm. Activist group here http://www.sludgesafety.org/coal_sludge.html
http://www.coalimpoundment.org/aboutimpoundments/facts.asp