Speciation and leaching characteristics of heavy metals from municipal solid waste incineration fly ash

Abstract

• Characteristics of heavy metals in MSWI fly ash were investigated. • Coarse and fine particles MSWI fly ash can enrich more heavy metals. • Long-term environmental risk was low for As and Cr, but high for Pb and Hg. • CaO can effectively inhibit the leaching of As and Pb from MSWI fly ash. Fly ash from municipal solid waste incineration (MSWI) is classified as hazardous waste because it is rich in heavy metals (HMs), dioxins and other hazardous substances. In this paper, four kinds of MSWI fly ash were selected and tested to understand their physical and chemical properties, HM enrichment pattern, HM fugacity pattern and leaching toxicity. The results show that the main mineral components of MSWI fly ash are chlorine minerals and calcium minerals (NaCl, NaSO 4 , KCl, CaClOH, CaCO 3 , CaSO 4 , etc.), while only NaSO 4 and NaCl exist in MSWI fly ash without CaO injection. The HM contents in MSWI fly ash were As (25.8–922.0 μg/g), Cr (26.9–173.3 μg/g), Pb (988.8–1259.4 μg/g) and Hg (7.29–8.47 μg/g) and showed a trend of an initial decrease and later increase as the MSWI fly ash particle size decreased. The major species of As and Cr in the four MSWI fly ash samples were As(V) and Cr(III); Pb mainly existed as PbCl 2 and PbSO 4 . The injection of CaO could make the fly ash alkaline and promote the formation of Ca 3 (AsO 4 ) 2 , CaCrO 4 and PbCl 2 , which reduced the leaching rate of As and Pb to<10 % and 15 %, respectively. Hg exists mainly in the species of Hg 0 , Hg-OM, HgCl 2 , HgO and HgSO 4 , and its distribution is mainly influenced by the flue gas components. These results can provide a basis for studying the escape mode and leaching toxicity of HMs in MSWI fly ash.