Abstract
Heavy metal removal from sewage sludge ash can be performed by mixing the ash with environmentally compatible chlorides (e.g. CaCl2 or MgCl2) and water, pelletizing the mixture and treating the pellets in a rotary reactor at about 1000 °C. Thermogravimetry–mass spectroscopy, muffle oven tests (500–1150 °C) and investigations in a laboratory-scale rotary reactor (950–1050 °C, residence time 1–25 min) were carried out. In the rotary reactor, up to 97% of Cu, 95% Pb and 95% Zn can be removed at 1050 °C. As Cl release starts from 400 °C (obtained from thermogravimetry–mass spectrometry experiments), heavy metals are already removed partially within the heating period. This heavy metal removal can be described as being similar to a first-order rate law. To meet the limit values specified in the Austrian and German fertilizer ordinances, residence times of the order of minutes are sufficient at 950 °C.
Acknowledgements
This research is part of the Vienna Centre of Excellence on Urban Mining which was co-funded by Zentrum für Innovation und Technologie GmbH (ZIT) of the City of Vienna and ASH DEC Umwelt AG, Vienna.
Notes
†This work is dedicated to the 60th birthday of Prof. Mikko Hupa from Abo Akademi University, Turku, Finland.