PYRITE IN UK COALS - ITS ENVIRONMENTAL SIGNIFICANCE

The geochemistry of pyrite formation in coals is considered. Sulfate a vailability in pore-solutions has long been recognized as an important control, but also important are the iron-bearing minerals. Pyrite for mation takes place over a long period. Trace elements are incorporated into the pyrite from solutions derived from within the enclosing sedi mentary system in concentrations apparently unrelated to time of forma tion. Pyrite is an important location of trace elements in the coal, i ncluding Ni, Cu, Zn, As, Se, Mo, Ag, Tl and Pb. These elements are vol atile at the operating temperatures in coal-fired power stations; frac tionation between furnace bottom ash and fly ash is demonstrated for E ggborough power station. Condensation at cooler temperatures leads to a surface association and fine-particle enrichment. Particulates and g aseous emissions are of environmental concern, but also the disposal o f fly ash may lead to contamination of groundwater, particularly as th e trace elements are readily accessible for reaction. In a study of fr esh fly ash rapid release of trace elements into solution was noted, b ut 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 be fore combustion, would not only reduce S emissions but also lessen the environmental impact of a number of toxic trace elements.