Recovery of metals occurring in significant amounts in municipal solid waste incineration fly ash, such as copper, could offer several advantages: a decreased amount of potentially mobile metal compounds going to landfill, saving of natural resources and a monetary value. A combination of leaching and solvent extraction may constitute a feasible recovery path for metals from municipal solid waste incineration fly ash. However, it has been shown that the initial dissolution and leaching is a limiting step in such a recovery process. The work described in this article was focused on elucidating physical and chemical differences between two ash samples with the aim of explaining the differences in copper release from these samples in two leaching methods. The results showed that the chemical speciation is an important factor affecting the release of copper. The occurrence of copper as phosphate or silicate will hinder leaching, while sulphate and chloride will facilitate leaching.

Copper is one of the most important trace elements in municipal solid waste (MSW) combustion. Knowledge of the speciation of copper is fundamental for the understanding of the effects of copper compounds on the combustion chemistry, the evaluation of the environmental effects of copper in ash leachates, and the development of methods to recover copper from the MSW combustion ash. In this work, an investigation of the speciation of copper in four ash flows from a bubbling fluidizedbed boiler using synchrotron-based X-ray absorption spectrometry is reported. The results showed that copper occurs in oxidation states 0, +1, and +2 in the bed ash and the cyclone ash, i.e., 10−20% Cu 0 , 25−35% Cu I , and 50−60% Cu II , whereas the filter ash contained copper only in oxidation state +2. The most common copper compounds in the bed ash are copper metal, Cu 2 O, CuO, and mixed oxides, such as CuCr 2 O 4 . The cyclone ash probably contained a mix of copper metal, Cu 2 O, CuCl, Cu(OH) 2 , and CuSO 4 ·5H 2 O, possibly also CuO. Copper sulfate was found as one of the major species in the filter ash together with a mix of hydroxides and chlorides.

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