Characterization of fine fractions from the processing of municipal solid waste incinerator bottom ashes for potential recovery of valuable metals
Municipal waste incinerator bottom ashes contain copper contents comparable to those of low-grade ores in addition to other valuable metals. While the processing of coarse fractions (>2 mm) is state of the art, the fines with their residual metal content are landfilled. This paper presents the results from a mineralogical characterization of fine fractions from the processing of municipal solid waste incinerator bottom ashes. From the results, possible approaches for a recovery of copper from the fine fraction are derived. Spatially resolved phase analysis reveals that the material contains a very heterogenic mixture of naturally occurring compounds as well as particles of alloys, metals, artificial oxides, and sulfides. The most interesting element to recover is copper. Copper can be found in the form of alloys, simple sulfides (XS), and oxides (XO). During the incineration process, new phases are generated that differ from natural ones and therefore can be called artificial minerals. Additionally, several components are partially altered due to oxidation, especially after the prolonged outside storage of the bottom ash. Crystalline silicate and glass particles are only sporadically enriched in Cu. Based on these results, different processing techniques are discussed. Due to the small particle size distribution and the physical and physico-chemical properties of the particles, flotation seems to be the most promising technique for the enrichment of copper from municipal solid waste incineration bottom ash (MSWI-BA) fine fractions.