To transform the coal ash into a slurry , coal is separated from non-combustable components and can be fractionated by particle size as well . Coal slurry can be transferred by pipeline or with specialized pumps such as a progressive cavity pump to pump the highly abrasive , corrosive and viscous coal slurry . More than 7 billion tons of coal are mined per year ( 2010 ) , using approximately 200 litres of water per ton . However , the amount of water required hinges on the surface characteristics of the coal being used . Most coal slurrys require the addition of a surfactant to reduce the viscosity , ergo reduce the stress on pipelines and pumps . Recent studies have employed new methods of slurry preparation , like using ultrasonic irradiation and a mixture of natural and synthetic surfactants to improve the stability and rheological properties of coal slurry . Ideally , coal slurry consists only of crushed coal and water , which can be efficiently separated . In practice , the separation is significantly costly due to the large amounts of water needed and wastewater generated by the process . Furthermore , the slurry consists also of very fine coal dust that results in a waste called blackwater . As blackwater can not be purified by a water treatment plant , it is stored in large impoundment ponds . Such ponds are susceptible to disastrous releases , such as the Buffalo Creek flood of 1972 or the Martin County coal slurry spill of 2000 , which released over 250 million gallons of coal slurry . Coal slurry can contain hazardous chemicals such as arsenic and mercury and can kill aquatic wildlife , as was the case in the Martin County spill . This impounded liquid waste can sometimes total billions of gallons in a single facility .
Buffalo Creek flood
Buffalo Creek flood
Coal slurry