Evaluation of Leaching Protocols for Testing of High-Carbon Coal Fly Ash–Soil Mixtures

Beneficial reuse of coal combustion byproducts, e.g., in highway construction, requires an evaluation of metal leaching potential. Metal leaching from high-carbon fly ash in soil mixes typical of highway embankment construction was evaluated using different soil-fly ash mixtures and three common leaching tests: the water leach test (WLT), the Toxicity Characteristic Leaching Procedure (TCLP), and the column leach test (CLT). The effect of test methodology and pH on Cu, As, and Cr leaching was examined. TCLP concentrations for Cu and As exceeded those from WLTs in the majority of mixtures due to lower pH conditions, while Cr was higher in the WLT for alkaline fly ash mixtures. Maximum CLT concentrations were higher than TCLP and WLT concentrations for the majority of mixtures, but usually decreased rapidly, suggesting that leachate concentrations might initially exceed regulatory limits, but only for a short time. A comparison of leaching results is discussed as a framework for the development of a flexible, integrated leaching protocol incorporating elements of batch and column leach tests to provide more accurate, site-specific leaching predictions given time and cost constraints.DOI: 10.1061/(ASCE)EE .1943-7870.0000668. © 2013 American Society of Civil Engineers. CE Database subject headings: Fly ash; Chromium; Copper; Arsenic; Coal; Soils; Mixtures; Recycling. Author keywords: Leaching; Fly ash; Batch leach test; Column leach test; Chromium; Arsenic; Copper.