A novel integrated method for ultrasonic-assisted MSWI fly ash decarbonization with PCDD/Fs detoxification and synergistic heavy metals stabilization

Abstract

A novel ultrasonic-assisted flotation method was developed to enhance the harmless treatment and resource utilization of municipal solid waste incineration fly ash (MSWI FA). This study examined ultrasound effects on collector (kerosene) and frother (2-octanol) emulsification and its role in flotation decarbonization. Additionally, the mechanism of PCDD/Fs detoxification and heavy metals migration and stabilization were revealed. The results indicated that ultrasonic emulsification significantly improved the collector dispersibility, while optimizing ultrasonic duration and power reduced emulsion droplets size and enhanced the collector adsorption capacity on carbon particles. Under optimal conditions (280 W_10 min), ultrasonic flotation effectively disintegrated agglomerated FA, increased carbon particle exposure, and enhanced decarbonization efficiency to 46.3 %. Meanwhile, ultrasound flotation enhanced NaCl and KCl dissolution, lowering Cl content in residue fly ash (ReFA) to below 2 %. PCDD/Fs were primarily enriched in activated carbon and transferred into the flotation FA (FFA), leading to a 48.9 % reduction in the toxic equivalent of PCDD/Fs in ReFA. Compared to FFA, ReFA exhibited a higher content of high-chlorinated PCDD/Fs, particularly 1,2,3,4,6,7,8-HpCDD, OCDD, 1,2,3,4,6,7,8-HpCDF, and OCDF. This distribution was likely attributed to the different selective adsorption behavior of activated carbon and calcium oxide (CaO). With the addition of 0.5 % Na₂S, the Pb leaching concentration was significantly reduced to 0.01 mg/L. In conclusion, this technology simultaneously achieved dechlorination, decarbonization, PCDD/Fs detoxification, and heavy metal stabilization, offering a low-carbon and energy-efficient FA treatment method.