Novel process utilizing alkalis assisted hydrothermal process to stabilize heavy metals both from municipal solid waste or medical waste incinerator fly ash and waste water

An alkalis assisted hydrothermal process was induced to stabilize heavy metals both from municipal solid waste or medical waste incinerator fly ash and waste water. The results showed that alkalis assisted hydrothermal process removed the heavy metals effectively from the waste water, and reduced leachability of fly ash after process. The heavy metal leachabilities of fly ash studied in this paper were Mn 17300 μg/L, Ni 1650 μg/L, Cu 2560 μg/L, Zn 189000 μg/L, Cd 1970 μg/L, Pb 1560 μg/L for medical waste incinerator fly ash; Mn 17.2 μg/L, Ni 8.32 μg/L, Cu 235.2 μg/L, Zn 668.3 μg/L, Cd 2.81 μg/L, Pb 7200 μg/L for municipal solid waste incinerator fly ash. After hydrothermal process with experimental condition [Na₂CO₃ dosage (5 g Na₂CO₃/50 g fly ash), reaction time = 10 h, L/S ratio = 10/1], the heavy metal removal efficiencies of medical waste incinerator fly ash were 86.2%-97.3%, and 94.7%-99.6% for municipal solid waste incinerator fly ash. The leachabilities of both two kinds of fly ash were lower than that of the Chinese national limit. The mechanism of heavy metal stabilization can be concluded to the chemisorption and physically encapsulation effects of aluminosilicates during its formation, crystallization and aging process, the high pH value has some contribution to the heavy metal removal and stabilization.