Municipal solid waste incineration (MSWI) is widely used in Japan, through which large amount of incineration residues are produced. The recycle/reuse of the incineration residues is troubled by many factors. This paper studied the MSWI bottom ash with the principal focus on Cl. Both bulk analysis and microanalysis methods have been carried out. The bulk analysis disclosed a particle-size dependent pattern of the Cl content in the bottom ash and the insoluble Cl is essentially in the form of Friedel's salt (3CaO center dot Al2O3 center dot CaCl2 center dot 10H(2)O). The microanalysis revealed that Cl preferentially exists in the quench phase of the individual bottom ash particle. Since Friedel's salt and the other quench products are thermally unstable, a series of thermal treatments were carried out to decompose such Cl-bearing phases. The experimental results showed the total Cl content in the MSWI bottom ash was reduced by 55.46% after a 4-h heating process at 1000 degrees C. The removal of the soluble Cl (originally as alkali salts) by the thermal process was found to be more effective. However, the insoluble Cl content in the heated sample was barely lowered owing to the formation of calcium chlorocalumite (11CaO center dot 7Al(2)O(3)center dot CaCl2) in the course of heating. (C) 2013 Elsevier B.V. All rights reserved.