Substance flows of heavy metals in industrial-scale municipal solid waste incineration bottom ash treatment: A case study from Austria

Abstract

While standard municipal solid waste incineration bottom ash (IBA) treatment aims to recover only ferrous and non-ferrous metals, enhanced treatment of IBA also promotes a recovery of glass and the mineral fraction. In this study, an enhanced dry-wet IBA treatment plant consisting of commonly applied dry process units, including several screens, a crusher, magnetic and eddy current separators and rarely applied wet process units, including a wet jigger, falcon concentrators and a wet shaking table, was evaluated for its ability to treat IBA from grate (G) and fluidized bed (FB) incineration. The process was examined on a material and substance flow level with regard to Ag, Cd, Co, Cr, Cu, Mn, Ni, Pb, Sb and Zn. It was found that the wet process units separated 52% of the total substance load of the aforementioned substances from G-IBA, while only 28% were separated from FB-IBA. The dry process units separated 57% from FB-IBA, while only 21% from G-IBA. The balance was found to remain in the mineral fraction of G-IBA (27%) or to be split between glass (7%) and mineral fraction (7%) of FB-IBA. While FB-IBA treatment was described for the first time on a substance flow level, transfer coefficients of 57–73% into the mineral fraction were reported for other G-IBA treatment plants for the substances investigated. Gravity separation was found to be able to promote the conservation of metallic resources and to deplete the total contents of heavy metals in the mineral fraction, which is favorable in terms of utilization.