Mitigation of Leaching of Major and Trace Elements from Pond Ash Deposits by Lime Column Treatment

Abstract

Fly ash generated from the coal fired thermal power plants is mostly sluiced into ash ponds by wet disposal method. Leachate emanating from the ash pond contaminates the ground water as well as surface water and poses a threat to the eco-system. Stabilization of ash is an effective means to mitigate the problem of leaching. This paper highlights the effect of lime column on the leachate characteristics of pond ash. For this purpose, large scale laboratory model of sedimented pond ash bed was prepared with a centrally installed lime column simulating a field condition. The samples were collected from various radial distances and depths after 30, 90, 180 and 365 days of installation of lime column and subjected to different tests for determination of pH value, hydraulic conductivity and concentration of different elements like Ca, Ni, Pb, Zn, Cu, Cr, Fe in the leachate sample. The leachability of different elements is expressed in terms of leachate load ratio. Further the leachate load ratio of different elements in the leachate sample is correlated to the hydration products, pH value and hydraulic conductivity. From the test results, it is found that lime column treatment is an effective means of reducing the concentration of metals in the leachate emanating from ash ponds.