抄録
With the increase in molten fly ashes emitted from waste incineration such as gasification and melting process, it is important to develop effective techniques to utilize these molten fly ashes. The molten fly ashes contain high concentration of toxic heavy metals such as Pb, Zn and Cu. Currently, molten fly ashes are landfilled after immobilization treatment such as by using a chelating agent. However, due to the shortage of dump yards and exhaustion of metal resources, it is necessary to recover the heavy metals from the molten fly ash, as well as to make the molten fly ashes harmless. The present study investigates the possibility of effective recovering of heavy metals from the molten fly ashes, by volatilization of the heavy metals converted to metal chlorides by heat treatment of the molten fly ashes in a vacuum in the presence of a chlorinating agent. Experiments were carried out using model fly ashes with hydrochloric acid as a chlorinating agent to study the formation behavior of heavy metal chlorides. Experiments were also carried out using two kinds of hydrochloric acid-soaked model fly ashes to investigate the volatilization behavior of Pb, Zn and Cu at 1123K, varying the pressure in a reactor (1013hPa and 13.3hPa). It was recognized that about 100% of Pb and Zn were enhanced to vaporize within 1 minute under 13.3hPa, compared to the time for complete volatilization of Pb and Zn (60 min) under 1013hPa. It was also found that Cu was, in particular, greatly enhanced in volatilization under a reduced pressure of 13.3hPa. Almost 100% of Cu was vaporized in 120min under 13.3hPa, although only 10% of volatilization of Cu was achieved under 1013hPa.
