Extraction of heavy metals from MSW incinerator fly ashes by chelating agents

An extraction process has been studied on a laboratory scale for the pretreatment of municipal solid waste (MSW) incinerator fly ash to remobilize Cr, Cu, Pb, and Zn. Five different types of fly ashes were treated with HCl, nitrilotriacetic acid (NTA), ethylendiaminetetraacetate (EDTA), or diethylenetriaminepentaacetate (DTPA) in a batch process in the pH range 2.5-10. The extraction of heavy metals by HCl was dependent on pH, increasing with increasing acid concentration. The efficiency of the chelating agents was independent of pH. By the treatment with 3.0% EDTA or DTPA, 20-50% of Cr, 60-95% of Cu, 60-100% of Pb, and 50-100% of Zn were extracted in the pH range 3-9. NTA was also effective in extracting Cr, Cu, and Zn. The maximum extraction of Cr, Cu, Pb, and Zn was obtained at 0.3-1.0% concentration of the chelating agents. NTA was effective in extracting Pb at a concentration as low as 0.1%. Extraction behavior of other elements during the treatment was also studied. The leaching test on the residues after the treatment with chelating agents showed that the fly ashes were successfully detoxified to meet the guideline for landfilling.