OPPORTUNITIES FOR ZN RECOVERY FROM SWEDISH MSWI FLY ASHES
Paper in proceedings, 2014
Large amounts of municipal solid waste incineration (MSWI) fly ash are generated annually. These ashes contain valuable metals like zinc (Zn) and copper (Cu) that could be recovered and re-used in the society. Moreover, extraction of metals would lead to cleaner ash residues that might be handled outside landfills. This paper investigates methods and potentials for recovery of Zn from Swedish MSWI fly ashes. The results show that by using acidic wastewater a maximum of 85% of the total Zn amount present in the original ash could be leached in a two-step process. The ash residues remaining after leaching contained reduced amounts of some toxic elements e.g. Cd, while others like Hg, Al, P, and Fe were enriched in the residue. There is a potential to return this ash residue to the furnace, which would destroy organic pollutants such as dioxins. Zinc was effectively recovered from the leachates using hydroxide precipitation or bio-electrochemical systems. The economic and climate effects from implementing the proposed method in full scale were evaluated based on several scenarios that were compared with the management method used today. In all scenarios the implementation of a Zn recovery process decreased the costs compared to the present handling. The most favourable option is to return the ash residue into the furnace.