Chemical and mineralogical evaluation of slag products derived from the pyrolysis/melting treatment of MSW Amirhomayoun Saffarzadeh a, * , Takayuki Shimaoka b , Yoshinobu Motomura c , Koichiro Watanabe a a Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan b Institute of Environmental Systems, Department of Urban and Environmental Engineering, Faculty of Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan c Department of Earth and Planetary Sciences, Faculty of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan Accepted 2 December 2005 Available online 30 January 2006 Abstract This paper provides the results of studies on the characteristics of novel material derived from pyrolysis/melting treatment of muni- cipal solid waste in Japan. Slag products from pyrolysis/melting plants were sampled for the purpose of detailed phase analysis and char- acterization of heavy metal-containing phases using optical microscopy, electron probe microanalysis (EPMA), XRF and XRD. The study revealed that the slag material contains glass (over 95%), oxide and silicate minerals (spinel, melilite, pseudowollastonite), as well as individual metallic inclusions as the major constituents. A distinct chemical diversity was discovered in the interstitial glass in terms of silica content defined as low and high silica glass end members. Elevated concentrations of Zn, Cr, Cu, Pb and Ba were recorded in the bulk composition. Cu, Pb and Ba behave as incompatible elements since they have been markedly characterized as part of polymetallic alloys and insignificantly sulfides in the form of spherical metallic inclusions associated with tracer amounts of other elements such as Sb, Sn, Ni, Zn, Al, P and Si. In contrast, an appreciable amount of Zn is retained by zinc-rich end members of spinel and partially by melilite and silica glass. Chromium exhibits similar behav- ior, and is considerably held by Cr-rich spinel. The intense incorporation of Zn and Cr into spinel indicates the very effective enrichment of these two elements into phases more environmentally resistant than glass. There was no evidence, however, that Cu and Pb enter into the structure of the crystalline silicates or oxides that may lead to their easier leachability upon exposure to the environment. Ó 2005 Elsevier Ltd. All rights reserved. 1. Introduction Municipal solid waste (MSW) combustion residues have been largely taken into account as one of the potential sources of pollution to the surface environment including soil, water and atmosphere. These materials can be classi- fied in general as bottom ash (BA), air pollution control (APC) residues and molten slag. In Japan, thermal (melt- ing) and chemical treatment of BA and particularly APC residues are conducted on a large scale. Annually, 50 mil- lion tons of MSW are generated nationwide, of which over 75% is thermally processed (Katou et al., 2001; Sakai and Hiraoka, 2000). A state-of-the-art pyrolysis method has also been employed as a treatment technique. This technol- ogy adopts a continuous processing of waste stream from the raw state to the formation of the molten slag at two consecutive stages of pyrolysis and melting. Pyrolysis is the thermal degradation of waste in the absence of oxygen, which results in the production of char- coal, liquid, and gaseous products. This process maintains the thermal treatment of organic substances (in MSW) at a temperature range of 450–800 °C during which the drying of the waste and the release of volatile components of the carbonaceous material may occur (Livingston, 2002). The 0956-053X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.wasman.2005.12.005 * Corresponding author. Tel.: +81 92 642 3635; fax: +81 92 642 3614. E-mail addresses: a_saffarzadeh@yahoo.com, amir@mine.kyushu-u. ac.jp (A. Saffarzadeh). www.elsevier.com/locate/wasman Waste Management 26 (2006) 1443–1452