Long-term leaching prediction of constituents in coal bottom ash used as a structural fill material

Abstract

This study is aimed to assess the long-term leaching of inorganic constituents from structural fills composed of reused coal bottom ash in Korea and identify key parameters that affect the amount of the constituents leached. A model for the prediction of long-term leaching by percolation of stormwater through a structural fill is adopted and used. The long-term leaching model is applied to five field sites in Korea using site-specific parameters obtained for each site and coal bottom ash specific parameters determined using column studies for two coal bottom ash samples collected from coal-fired power plants. The long-term leaching of trace inorganic constituents, As, Cu, Sb, and Zn, is variable among the sites primarily due to the variation in the total amount of leachable constituents and application depth of a structural fill. First-order leaching rate constant is also one of the key parameters when the leaching rate is relatively small. Because of the significant variability in the leaching rate constants and application depths, the time for the leachate constituent concentration to reach half the initial value, t (50%), ranges from less than a year to more than hundreds of years for the studied sites and constituents. The long-term leaching characteristics of the trace inorganic constituents are predicted to significantly vary by the type of reused bottom ash and the site conditions, suggesting the need to determine the model parameters in a case-specific manner.