Recovery of metals from municipal solid waste incineration fly ash and red mud via a co-reduction process

Abstract

Extraction of heavy metals is the preferred option for municipal solid waste incineration (MSWI) fly ash (FA) stabilization and reutilization. In this paper, a co-reduction process for FA and red mud (RM) was proposed. The complementary compositions of FA and RM were favorable for the volatilization of volatile heavy metals and the alloy formation of siderophile heavy metals in the co-reduction system. The molten stage temperature of co-reduction FA and RM can be decreased significantly to 1100 °C – 1300 °C, compared with the molten stage temperature of direct melting FA above 1400 °C. The wastes were converted into three products: iron alloy containing Fe, Cu, Ni, and Cr; secondary FA containing Pb, Zn, and Cd; and vitrified slag. In the optimized co-reduction process, 76.06 % Fe, 74.53 % Cu, 83.40 % Ni, and 58.44 % Cr can be recovered by iron alloy, and 98.95 % Cd, 98.21 % Pb, and 86.78 % Zn can be recovered by secondary FA. The contents of heavy metals in the vitrified slag are much lower than those in traditional direct melting slag. Consequently, this co-reduction process could be a more environmentally sound solution for beneficial reutilization of FA and RM.