Mineralogical, geochemical, and petrological characterization of size-fractionated municipal solid waste incineration bottom ash (MSWIBA) from the perspective of precious and rare metal recovery

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Incinerated ash contains incombustible materials such as minerals and glass, base metals such as copper and zinc, and precious metals such as gold and silver. If these can be recovered and reused, incinerator ash can be economically valuable and environmentally safe. However, many issues still remain regarding the detailed characterization of incinerator ash. Therefore, this study focused on metal recovery from incinerator ash. To evaluate the potential for metal recovery, air-dried bottom ash samples were collected from three incinerators in Japan. Large non-combustible materials (metals, glass, stones, etc.) were removed manually, and the remaining residue was divided into five particle sizes using 4mm, 2mm, 1mm, and 0.5mm sieves, and multiple analyses were performed on each fraction. Experimental methods included X-ray fluorescence (XRF) analysis, X-ray diffraction (XRF) analysis, optical microscopy, scanning electron microscopy, and standard leaching tests on each fraction to identify each phase of incinerator bottom ash in each fraction and determine its physical and chemical properties. Dust ash contains a higher percentage of lead, zinc, and copper than the main ash. Therefore, it was considered desirable to separate and recover the dust ash in order to recover these three metals. However, due to the small percentage of dust ash generated, it was considered more profitable to recover lead from the separated dust ash and zinc and copper from the incinerator ash (dust ash and main ash) without separating and recovering the dust ash.