Leaching coal mining waste

Derivation (1) Leaching of bauxite with caustic soda followed by precipitation of a hydrated aluminum oxide by hydrolysis and seeding of the solution. The alumina hydrate is then washed, filtered, and calcined to remove water and obtain the anhydrous oxide. (2) Aluminum sulfate from coal mine waste-waters is reduced to alumina. 

Atmospheric oxidation of iron pyrites (FeS2) in coal and associated rocks and rapid dissolution of the resultant sulfur oxides and iron sulfates in percolating waters produce very acidic effluents (acid mine drainage) (Berkowitz, 1985). The extent and toxicity of the waste streams depend on coal characteristics, local rainfall patterns, topography, and site drainage features. Leaching of such waste could lead to an unacceptable level of contamination of surface and groundwater. 

The source of the problem, highly contamined acid drainages from disposal of mineral wastes from coal extraction, has been thoroughly documented. Tables 1, 2, and 3 show the mineralogy, trace element content, and leaching concentrations of the trace elements for a typical coal waste derived from mining high-sulfur Appalachian coal in western Pennsylvania. 

Surface strip mining of coal destroys the native vegetation at the mine site. The topsoil is sufficiently disturbed that it is difficult to rehabilitate the site and re-start the native growth pattern. Oxidation of waste coal and mine residues produces sulfuric acid and releases toxic materials such as arsenic, selenium and beryllium. These leach into the ground water and drain into streams and lakes. At a minimum, these materials strongly alter the types of plant and animal life able to survive in their presence. At the worst, they kill all life near the mine. 

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