Abstract. Trace chlorinated organic compounds are generated via thermal processes. Their formation is promoted by copper chloride in solid phase such as fly ash, especially in the post-combustion zone in municipal solid waste incineration. Previously, we reported the chemical state and change of copper chloride in a single model using the in situ quick scan x-ray absorption fine structure (QXAFS). However, a real solid phase, which is a complex system involving many elements, was not simulated. In this paper, we measured the Cu-K XAFS of a metal-mixture model upon heating to discuss the effect of mixing. The in situ QXAFS technique revealed that the reaction temperature of copper was lower, compared with the single model, when a mixture was measured. The result shows that the formation mechanism of chlorinated organic compounds derived from anthropogenic thermal sources can be described more correctly.