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 mainl y by bubbling CO2 through the leachant, which itself is periodically renewe d. 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 w ith 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 g ives a semiprotective surface layer. If the initial slope of the leaching c urve as a function of time(1/2) is prolonged, experimental results fall wel l below this extrapolated curve as leaching times increase beyond >100 to 2 00 h. Important changes occur in leach mechanisms at about this time, and t he predictive accuracy of shea-term accelerated tests, particularly when pH is not stabilized, is questioned. (C) 1999 Elsevier Science Ltd. All right s reserved.