This report intends to summarize impacts of fly-ash disposal on soil-water environment with special reference to the behaviour of trace elements. Physico-chemical properties of fly-ash and trace elements release in environment are dependent on the geological origin of coal, form of the element in coal, combustion products, type of coal burning process, nature of emission control devices, methods of disposal and climatic conditions. Physical and biological transport of trace element, their bioaccumulation, transformation as well as interaction with ecosystem are discussed in terms of their importance in availability, mobility, persistence and ultimate toxicity. Needed research in the areas is identified.

Pulverised coal and corresponding fly-ash collected from the stack precipitator of thermal power plants were analysed for eight heavy metals. Fly-ash was separated into various sized fractions which were then chemically characterized. The fly-ash contained higher concentrations of heavy metals with respect to their coal. Except in the case of Pb, Cd and Co, the heavy metals were more concentrated in the <53 µm than in the >150 µm fraction. For the probable contribution of these metals to atmospheric emission and waste ash, it is necessary to estimate the enrichment factors from coal to fly-ash. INTRODUCTIONCoal is undoubtedly the prime source of energy in our country. At present, coal-fired power generating plants account for 55 percent of the total generating capacity. 1 The increased use of coal will produce additional quantities of fly-ash, one of the waste products of burning pulverised coal. India produces mostly poor quality coal with a 25-30 percent ash content. It is estimated that ten percent of the resultant fly-ash is released into the atmosphere, whereas the rest of solid fly-ash is available for disposal. 1 ' 2 The fly-ash generated by these plants is and will continue to be a disposal problem. Emission from thermal power stations is a major source of particulates and gaseous pollutants. Apart from gaseous pollutants thermal power plants add particulate matter to the air. Of all types of particulates the presence of toxic trace metal like, As, Cd, Cr, Cu, Co, Zn, Mn, Ni and Pb constitutes the greatest health hazard. Moreover, inhalation of metals is more harmful than ingestion by way of food or water.Analysis of heavy metals concentrations in pulverised coal, fly-ash and in different size fractions of the fly-ash produced from power plants was carried out to assess the probable contribution of these metals through coal burning to atmospheric emission and waste ash. MATERIALS AND METHODThe material used for the present investigation was pulverised coal from different mines and corresponding fly-ash collected from the stack precipitator of power plants. The coal, fly-ash and its component size fractions were analysed to characterise their chemical composition. The fly-ash (No. 1) was fractionated by mechanical sieving into the following particle sizes >150, 150-106, 106-75, 75-53 and <53 /im. Known volumes of all the samples were digested with hydrofluoric aqua regia, 3 and the digested samples were analysed for Cr, Mn, Ni, Pb, Cd, Cu, Co and Zn by the Perkin Elmer (703) Atomic Absorption Spectrophotometer. 4

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A column experiment study has been carried out in order to understand the phenomenon of leaching of selected trace elements like Cr, Mn, Ni and Pb by the action of acidic rain water on a fly-ash/soil bed in a water environment, fly-ash/soil such as in a landfill area of fly-ash disposal sites. Metals measured at depth of 8 , 16 and 24 of soils in columns showed variation in concentrations. However, a lower pH with lower total metals and higher available metals concentrations in a top layer soil than in subsequent lower layers of alluvial soils have been observed. pH has been found as one of the most important parameters in regulating the change in available and total metal content in layers of soils. Metals retention in soil and their release into leachate water were also found to be dependent on organic matter, cation exchange capacity, adsorption/precipitation and subsequent mobility of heavy metals in soil, in order of importance.The metals content in the leachate's water were not formed proportional to the amount of fly-ash applied to the soil bed. Mass balance calculations indicate the amounts of Cr, Mn, Ni and Pb that can possibly leach and percolate through a fly-ash/soil bed to ground water.

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