Pyrite in UK coals: its environmental significance

• Published in: Fuel (Guildford) 1994-07, Vol.73 (7), p.1051-1055
• Main Authors: Spears, D.Alan, Martinez Tarazona, M.Rosa, Lee, S.
• Format: Article
• Language: English
• Subjects: Applied sciences; Coal and derived products; Energy; environmental impact; Exact sciences and technology; Fuels; pyrite; Structure, chemical and physical properties; trace elements
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/0016-2361(94)90236-4

The geochemistry of pyrite formation in coals is considered. Sulfate availability in pore-solutions has long been recognized as an important control, but also important are the iron-bearing minerals. Pyrite formation takes place over a long period. Trace elements are incorporated into the pyrite from solutions derived from within the enclosing sedimentary system in concentrations apparently unrelated to the time of formation. Pyrite is an important location of trace elements in the coal, including Ni, Cu, Zn, As, Se, Mo, Ag, Tl and Pb. These elements are volatile at the operating temperatures in coal-fired power stations; fractionation between furnace bottom ash and fly ash is demonstrated for Eggborough power station. Condensation at cooler temperatures leads to a surface association and fine-particle enrichment. Particulates and gaseous emissions are of environmental concern, but also the disposal of fly ash may lead to contamination of groundwater, particularly as the trace elements are readily accessible for reaction. In a study of fresh fly ash rapid release of trace elements into solution was noted, but fly ash weathered for 17 years still continues to release elements into solution, albeit at a slower rate, presumably from dissolution of the glass. Improved, cost-effective separation of pyrite from coal before combustion, would not only reduce S emissions but also lessen the environmental impact of a number of toxic trace elements.