Coal slurry or sludge is a waste fluid produced by washing coal with water and chemicals prior to shipping the coal to market. When coal is mined underground or by highwall or auger miners, there are significant amounts of rocks and clays mixed in. These materials must be removed before the coal can be sold to power plants or steel mills. In Appalachia and the Illinois Basin, coal companies use a process called "wet washing" to reduce the amount of non-combustible material. There are other methods of separating coal and non-coal used in other places, primarily where mining occurs in arid areas with limited water supplies.
In a wet washing plant, or coal preparation plant, the raw coal is crushed and mixed with a large amount of water, magnetite, and organic chemicals. The chemicals are primarily patented surfactants, designed to separate clays from the coal, and flocculants, designed to make small particle clump together. In massive "flotation columns", most of the coal floats to the surface and most of the other material (called "coarse refuse") sinks to the bottom. The huge volume of waste water left over is coal slurry. In the slurry are particles of rock, clay and coal too small to float or sink as well as all the chemicals used to wash the coal. While the coal industry likes to claim that the particles of "natural rock strata" and chemicals are perfectly safe, testing has shown coal slurry to be highly toxic.
Chronic exposure to the metals found in coal slurry can damage virtually every part of the body. Health problems caused by these metals include intestinal lesions, neuropathy, kidney and liver failure, cancer, high blood pressure, brittle bones, miscarriages and birth defects among others. Studies of the effects of coal slurry on human cell tissues have found evidence that coal slurry causes cancerous proliferation, cell death and damage to kidney cells.
Impoundments and slurry cells
Every preparation plant produces many thousands of gallons of coal slurry each day, requiring massive disposal areas. Most slurry is disposed of above ground either in massive toxic lakes called impoundments (made by damming up a hollow) or in smaller pits constructed of coarse refuse called slurry cells. Not only do these facilities often leach toxins and cause black water spills, there have been several catastrophic failures resulting to toxic floods, massive property destruction and death.
Slurry not stored above ground is pumped, or "injected," into abandoned underground mines. Once underground it can migrate into the groundwater contaminating local well water, especially when blasting from surface mining occurs in the area. Several communities have had their water supply contaminated by underground injection causing widespread, often life-threatening illnesses.
Technologies exist to remove and reuse the water in slurry, resulting in a dry waste product that can be more safely and easily contained. While some of these technologies were in widespread use in Appalachia in the early 1980s, today few plants use them due to the increased costs.