Abstract

Fly ash generated from the ash-melting and gasification-melting plants of MSW, called Melting Furnace Fly Ash (MFFA), contains considerable amounts of heavy metals such as Pb and Zn. These metals can be recovered at smelting furnace after “pretreatment” for removal of unnecessary elements such as Cl, Sn and Si. Chemical pretreatment methods have been studied. However they have been discussed only the treatment cost and the content of Pb and Zn recovered, but neither applicability to various kinds of MFFA nor the environmental impact. In this study acid, alkaline and ammonia/chloride leaching methods were compared from the standpoints of (1) applicability to MFFA, (2) content of Pb and Zn recovered, (3) treatment cost and (4) environmental impact. 23 samples of MFFAs were gathered and classified into 4 types based on element contents, and Pb and Zn recovery experiment was conducted for the representative MFFA of those types. Consequently, 1) MFFA from gasification-melting plants cannot be treated by chemical methods. 2) The other MFFA can be treated to acceptable quality for Pb and Zn recovery at smelting furnace. 3) Only MFFA from the electric resistance ash-melting plants designed by N manufacturer can be treated easily by water washing method. 4) Alkaline and ammonia/chloride leaching method were more effective than acid leaching.

Key words : MFFA, ash-melting, gasification-melting, recovery of Pb and Zn