Environmental aspects of power plants fly ash utilization in deep coal mine workings

Powerplant fly ash (EA) utilization is still far from being satisfactory in the most developed countries, and almost none in the developing ones that use coal as a main source of power generation. iia attractive field of high-volume FA utilization is use in deep mines iu the form of low-ratio mine water: FA mixtures for subsidence, methane, and fire control and prevention. Utilization of 57.5% of the annual generation of 16.2 million tons of coal combustion wastes (CCW) places Poland at the top of the countries, which produce comparably high amounts of CCW. Of this, 3.5 million tons/a is routinely utilized underground. In total, in deep coal mines by the end of 1996 were used 24.2 million tons of FA. This chapter is focused on the environmental aspects of "pure" FA use in deep mine workings. Environmental evaluation of a large-scale FA utilization underground has been based on the extensive studies carried out for 24 coal mines of the Upper Silesia coal basin (USCB) in Poland on the background of technological flowsheets of the process, load-based criteria developed for the environmental impact assessment (EIA) and ground water protection requirements. Pure FA has originated from two power plants of firm power 1,600 MW and 1,520 MW. Besides the direct application purposes, utilization of Fh in the form of low-ratio saline mine water (slurry): FA mixture in dry mine workings insulated frost the dynamic resources of ground water was shown to be the most environmentally beneficial option. Due to the partial chemical binding, but mainly as a result of permanent physical and physiochemical retention in the mixture, reduction of considerable loads of macro-constituents and trace elements in mine drainage discharged to the recipients call be attained. Mode and extent of binding/release of these constituents in the stage of dewatering/solidification and their leachability from the solidified mixture highly depend upon the characteristics and interaction of FA and mine water, in particular upon the salinity of input mine water, as well as the input and resultant alkalinity of mine water and mixture. Generally, susceptibility of trace elements to mobilization from I-nine water: FA mixture is low due to the equilibria constraints. Elevated leachability ill all the systems invariably show Cr(VI) and Mo. Solidified FA mixtures display very good sealing properties against air penetration, but are permeable to the vertical infiltration and susceptible to further release of macro-constituents (Cl, SO4, Na, Ca, NH4-N, COD) and trace elements Cr-t, Cr(VI), and Mo. Therefore, utilization of mine water: FA mixtures in the feeding areas of recoverable ground water resources should be restricted.