Abstract :
The chemistry of the landfill environment is complex and dissolution rates may be higher than in natural systems. As will be shown in this paper, there are often great uncertainties in terms of leaching kinetics and long-term emissions of landfills in general. Leaching tests used in the laboratory may reflect a leaching behaviour not consistent with real landfill scenarios. Geochemical calculations for model systems provide an impression of the possible long-term behaviour of buffered, inorganic landfills. For a buffered carbonate-containing system (this system may be a mono-landfill of slag and/or ash after a few decades and/or centuries), maximums for the solubility of the elements Zn, Cd, Pb and Cu can be calculated while taking into account the presence of gypsum, the complexation in water (“speciation”) and other factors influencing solubility. We have made these calculations using the recent version of the geochemical code PHREEQC-2. Finally, we conclude that under most circumstances the total elemental content, or the so-called “total availability,” is a valuable assessment tool when combined with other criteria, such as leachable amounts and leachate test results. Exceptions may be carbonate-buffered monofill scenarios (e.g. monofill or quasi-monofill of MSWI residues), where setting limits on some elemental contents (Cu, Zn, Fe and Mn) does not seem to be very useful.
