Treatment-oriented characterization of dry scrubber residue from municipal solid waste incineration

Dry scrubber residue from municipal solid waste incineration (MSWI) was characterized to identify critical inorganic pollutants and to suggest a conceptual treatment method. The key methods used were thermal analysis, including thermogravimetry (TG) and differential thermal analysis (DTA), pHstat titration, qualitative X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical equilibrium calculations, and statistics such as error propagation, principal component analysis (PCA), and empirical modeling based on factorial designs. Based on EU directives, the major inorganic pollutants Cd, Cr, Pb, and Zn were found. In addition, the pH was too high. With dry scrubber residue stabilization in mind, the impact of carbonation and hydration was assessed and judged to be encouraging. In particular, chemical equilibrium calculations showed that carbonation has considerable potential to lower the pH and the availability of Pb, Zn, and Cr. The impact of carbonation on the mobility of Cd was found to be small. During carbonation, a metal-trapping calcium aluminosilicate hydrate (C–A–S–H) phase is also formed. Both processes together have the potential to lead to a robust, reliable, and reasonable stabilization method for dry scrubber residue. However, to control these processes, the decisive factors need to be identified and their effects need to be quantified. Ca, Cl, Na, and K might be abundant components which would be mobile even after stabilization.