Environmental Aspects of Power Plants Fly Ash Utilization in Deep Coal Mine Workings

Abstract

Powerplant fly ash (EA) utilization is still far from being satisfactoryin the most developed countries, and almost none in the developing onesthat use coal as a main source of power generation. iia attractive fieldof high-volume FA utilization is use in deep mines iu the form oflow-ratio mine water: FA mixtures for subsidence, methane, and firecontrol and prevention. Utilization of 57.5% of the annual generationof 16.2 million tons of coal combustion wastes (CCW) places Poland atthe 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{''} FAuse in deep mine workings. Environmental evaluation of a large-scale FAutilization underground has been based on the extensive studies carriedout for 24 coal mines of the Upper Silesia coal basin (USCB) in Polandon the background of technological flowsheets of the process, load-basedcriteria developed for the environmental impact assessment (EIA) andground water protection requirements. Pure FA has originated from twopower plants of firm power 1,600 MW and 1,520 MW. Besides the directapplication purposes, utilization of Fh in the form of low-ratio salinemine water (slurry): FA mixture in dry mine workings insulated frost thedynamic resources of ground water was shown to be the mostenvironmentally beneficial option. Due to the partial chemical binding,but mainly as a result of permanent physical and physiochemicalretention in the mixture, reduction of considerable loads ofmacro-constituents and trace elements in mine drainage discharged to therecipients call be attained. Mode and extent of binding/release of theseconstituents in the stage of dewatering/solidification and theirleachability from the solidified mixture highly depend upon thecharacteristics and interaction of FA and mine water, in particular uponthe salinity of input mine water, as well as the input and resultantalkalinity of mine water and mixture. Generally, susceptibility of traceelements to mobilization from I-nine water: FA mixture is low due to theequilibria constraints. Elevated leachability ill all the systemsinvariably show Cr(VI) and Mo. Solidified FA mixtures display very goodsealing properties against air penetration, but are permeable to thevertical infiltration and susceptible to further release ofmacro-constituents (Cl, SO4, Na, Ca, NH4-N, COD) and trace elementsCr-t, Cr(VI), and Mo.Therefore, utilization of mine water: FA mixtures in the feeding areasof recoverable ground water resources should be restricted.