Long-term leaching mechanisms of Portland cement-stabilized municipal solid waste fly ash in carbonated water

A leach test is described and applied to municipal incinerator fly ash (10%) stabilized in Portland cement. The test differs from previous tests mainly by bubbling CO2 through the leachant, which itself is periodically renewed. An advantage of the test is that pH remains nearly constant at 6.5 to 6.8 throughout the test duration. The results of leach tests are con-elated with microstructural studies of the leached layer, which reaches a depth of similar to 800 mu m in 214 days. Development of a complex zonal structure gives a semiprotective surface layer. If the initial slope of the leaching curve as a function of time(1/2) is prolonged, experimental results fall well below this extrapolated curve as leaching times increase beyond >100 to 200 h. Important changes occur in leach mechanisms at about this time, and the predictive accuracy of shea-term accelerated tests, particularly when pH is not stabilized, is questioned. (C) 1999 Elsevier Science Ltd. All rights reserved.