Coal slurry is a waste product of coal mining and processing, and contains both liquid and solid constituents. Particles of coal, water and chemicals used to prepare coal for market make up the slurry. Suitable methods of processing coal slurry for reuse or return to the environment have not been implemented, so the waste is held in storage in above ground ponds or pumped into worked-out underground mines. Failures of surface slurry impoundments and pipelines have caused damage to the environment and property, raising concerns about their safety. Potential contamination of ground water is an issue with underground disposal methods.
Components in slurry come from the coal and the chemicals used in processing it. The washing or purifying process reduces pollution-causing contaminants in the coal, but these impurities then become part of the slurry. The composition of coal slurry varies depending on the coal and the processing methods. Waste products from coal mining and preparation contain potentially toxic organic and inorganic compounds, sulfates, ammonium and heavy metals. Alternative methods of processing, including dry processing techniques, could reduce the quantity of coal slurry generated.
Impoundment ponds are created as part of the mining process, using the solid rock left after coal extraction. Dams are constructed using the rock and soil, and are generally located at the head of a valley near the coal preparation plant. Some impoundment ponds contain billions of gallons of slurry. Under certain circumstances a tailing dam might be prone to failure, resulting in the release of large quantities of coal slurry.
Underground injection is another method of disposing of coal slurry. The slurry is pumped into abandoned coal mines. Initially thought to be a safer method of disposal, there have been reports of leakage into ground water. This has caused contamination of wells near the abandoned mines, and users of the wells claim their many health problems are related to the tainted water.
Coal slurry pipelines are a method of transporting usable coal to power plants or shipping ports when the availability of preferred modes of transport are unavailable. This type of slurry contains pulverized coal mixed with an equal portion of water. It flows from the mine to its final destination through specially engineered pipelines and must be dried before it can be used. Waste slurry pipelines are used to move the material left after processing to a disposal site.