Coal slurry impoundment

Coal slurry consists of solid and liquid product of a coal preparation plant. As a slurry, coal is separated from non-combustable components (ash) and can be fractionated by particle size as well. Coal slurry can be transferred by pipeline or with specialised pumps such as a progressive cavity pump to pump the highly abrasive, corrosive and viscous coal slurry.

The scale of water usage and hence potential costs and problems is large. More than 7 billion tons of coal are mined per year (2010), using approximately 200 litres of water per ton.

Ideally, coal slurry consists only of crushed coal and water, which can be separated perfectly at low cost. In practice, the separation is significantly costly. Furthermore, the slurry consists also of very fine coal dust that results in a waste called blackwater, which is stored in large impoundment ponds, often together with coal ash. Such ponds are susceptible to disastrous releases, such as the Buffalo Creek flood of 1972. This impounded liquid waste can sometimes total billions of gallons in a single facility.

...
Wikipedia