Detoxification of medical waste incinerator fly ash through successive flotation

Medical waste incinerator (MWI) fly ash is considered hazardous waste because it contains hypertoxic polychlorinated dibenzo-p-dioxins and dibenzofurans as well as heavy metals. To detoxify both substances, successive flotations of MWI fly ash were performed. The first step involved decarburization flotation, whereby 91.0% of the dioxins in MWI fly ash were transformed into a froth product. In the second step (ion flotation), the influence of ionic strength on heavy metals recovered from both raw and stimulated filtrates was explored. The results revealed that the optimal conditions were sodium dodecyl sulfate at 480 ppm, methyl isobutyl carbonyl at 150 ppm, impeller speed at 2000 rpm, and flotation time of 18 min for raw leachate, through which Zn (47.0%), Pb (56.5%), Cu (57.5%), and Cd (49.1%) were recovered. For the simulated filtrate, higher removal efficiencies were noted: 60.5%, 80.6%, 69.1%, and 64.1% for Zn, Pb, Cu, and Cd, respectively. The harmful effects of the coexisting ions in the raw filtrate on heavy metal recovery were observed.