Chromium behaviour during iron-bath melting separation process of MSW incineration fly ash

Fly ash from municipal solid waste (MSW) incineration is classified as a hazardous waste because it contains amounts of heavy metals and dioxins, which causes environmental pollution. The metal content from fly ash can be reduced by thermal treatment, which vaporizes the volatile metal compounds. It is easier to leach less heavy metal from thermally treated ash than from ash without thermal treatment. However, chromium (Cr) is an exception. To improve this method, a hypothesis based on phase diagram was proposed which was that the heavy metal can be removed from the slag phase into iron phase by using melted iron. So this study provided iron-bath melting experiment as a new pyrometallurgical route to test and verify this hypothesis. In this method, iron powder, which recovers the selected metals, was firstly fed into the furnace, and then pelletized fly ash was introduced in molten iron-bath atmosphere. This paper only focused on the behaviour of chromium. The results indicated over 50% Cr was retained in the slag phase and about 40% in the iron phase. Iron-bath melting promoted Cr transfer from the slag phase to the iron phase. Therefore, it was valid and could be an interesting alternative method for disposal of the fly ash.