Diffusion tests for assessing leaching from incineration residues

Abstract: Increasing amounts of incineration residues need to be disposed, reused or treated, which calls for reliable characterisation methods. Leaching tests are often used for an assessment of release of pollutants from wastes under a variety of leaching factors. Nevertheless, the prediction of the contaminants release in field is difficult due to the complexity of the processes occurring in field. This work aims at evaluating limitations and possibilities of making long- term leaching predictions for incineration residues using diffusion leaching tests. Also the effect of carbonation on the leaching of elements was evaluated. Leaching predictions for Cl and Pb based on diffusion test data were compared with leachate data from MSWI bottom ash reused in road construction as well as leachate data obtained using a two-step compliance test. For the first years, leaching of Cl from bottom ash in field could be predicted with an accuracy within one order of magnitude. This could be considered as a good fit. Good agreement was also found between leaching predictions based on the diffusion test and the compliance test for Pb. However, predictions based on a diffusion tests might be misleading for longer time periods as the stock of contaminants depletes. Longer time series of field data are needed for comparison. Field conditions such as wet/dry and freezing/thawing cycles were not considered in this work, but might affect the mobility of contaminants. The impact of such field factors deserves a thorough examination in future research. Carbonation was found to significantly affect leaching of some elements from MSWI bottom ash. Leaching of Pb and Zn was increased due to carbonation, while leaching of Cr, Mo, and Sb decreased. Leaching of Cu was increased by carbonation alone, but it was also observed that leaching could be decreased if carbonation is combined with water-solidification. With such effect on leaching it is necessary to take carbonation into account when leaching predictions are made.