Long Term Leaching Behavior of Antimony from MSWI Bottom Ash: Influence of Mineral Additives and of Organic Acids

The leaching of Sb in alkaline environment is known to be mainly governed by the precipitation of Ca- and Fe-antimonates. To reduce Sb leaching from MSWI bottom ash below the regulatory limit for recycling as construction material, Ca- and Fe-containing chemicals and industrial residues were added to this bottom ash. Short term and medium long term leaching tests were performed by lab batch tests and outdoor field tests. This confirmed that the tested chemicals and industrial residues reduce Sb leaching to below the regulatory limit. Carbonation tests with subsequent leaching were performed to provide information on the long term leaching behavior of Sb from MSWI bottom ash. Upon carbonation, Sb leaching from the bottom ash to which Fe-2(SO4)(3) or Ca- and Fe-containing industrial residues were added, increased over time, but did not exceed the regulatory limit value after full carbonation. When carbonation progressed, Sb leaching from the untreated bottom ash decreased, which could not be explained by the current state of the knowledge on mechanisms for Sb leaching in alkaline environments. As the leaching of Sb after carbonation was altered similarly as that of Cu, we experimentally checked if Sb leaching could also be influenced by the presence of organic acids,. As a result, we showed that Sb leaching from MSWI bottom ash in alkaline environments is indeed influenced by the presence of organic acids like humic and fulvic acids.