Heavy-metal reduction and solidification in municipal solid waste incineration (MSWI) fly ash using water, NaOH, KOH, and NH4OH in combination with CO2 uptake procedure

A new method for reducing heavy metals in municipal solid waste incineration (MSWI) fly ash was investigated. In many previous studies, acidic leaching was regarded as a standard method for metal-ion extraction. However, this process requires additional treatment of the wastewater containing heavy-metal components. Therefore, in this study, we used basic leaching solvents, i.e., 0.5 M aqueous NaOH, KOH, and NH4OH. The leachates and remaining solids were qualitatively and quantitatively analyzed. To facilitate the handling of the extracted heavy-metal components, the leached metal ions were fixed and precipitated using a CO2 uptake procedure. The solids were analyzed using X-ray fluorescence and X-ray diffraction, and scanning electron microscope images were obtained. The leachates were analyzed using inductively coupled plasma optical emission spectroscopy. In contrast to conventional acidic extraction, heavy-metal reduction and fixation, as well as the mass reduction of the waste, could be achieved with the proposed method.