Speciation of Copper in Ash from a Fluidized-Bed Boiler Fired with Municipal Solid Waste

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, for the evaluation of the environmental effects of copper in ash leachates and for 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 fluidized bed boiler using synchrotron based X-ray absorption spectrometry is reported. The results showed that copper occurs in oxidation states zero, +I and +II in the bed ash and the cyclone ash, i.e. 10-20 % Cu(0), 25-35 % Cu(I), 50-60 % Cu(II), whereas the filter ash contained copper only in oxidation state +II. The most common copper compounds in the bed ash are copper metal, Cu2O, CuO and mixed oxides, such as CuCr2O4. The cyclone ash probably contained a mix of copper metal, Cu2O, CuCl, Cu(OH)2 and CuSO4∙5H2O,