TO STUDY THE LEACHING BEHAVIOR OF COAL ASH

Abstract

Coal-based power generation produces over 750 Mt of coal ash per year globally, but under 50% of world
production is utilized. Large amounts of fly ash are either stored temporarily in stockpiles, disposed of in ash landfills or
lagooned. Coal ash is viewed as a major potential source of release of many environmentally sensitive elements to the
environment. This coal fly ash and demonstrates that a large number of elements are tightly bound to fly ash and may not
be easily released to the environment, regardless of the nature of the ash. This review provides an extensive look at the
extent to which major and trace elements are leached from coal fly ash. It also gives an insight into the factors
underlying the leach ability of elements and addresses the causes of the mobility. The mode of occurrence of a given
element in the parent coal was found to play an important role in the leaching behavior of fly ash. The amount of calcium
in fly ash exerts a dominant influence on the pH of the ash–water system. The mobility of most elements contained in ash
is markedly pH sensitive. The alkalinity of fly ash attenuates the release of a large number of elements of concern such as
Cd, Co, Cu, Hg, Ni, Pb, Sn or Zn among others, but at the same time, it enhances the release of oxyanionic species such
as As, B, Cr, Mo, Sb, Se, V and W. The precipitation of secondary phases such as ettringite may capture and bind several
pollutants such ash As, B, Cr, Sb, Se and V