Characterization of refuse-derived char from municipal solid waste: 2. Occurrence, abundance and source of trace elements

Abstract

The trace elements in refuse-derived char (RDC) generated by thermolysis of municipal solid waste (MSW) were studied to elucidate their occurrence, abundance and source. The content, enrichment factor, concentration trend, distribution, nature and modes of occurrence of major, minor and trace elements in RDC and RDC ash were characterized. It was found that a number of trace elements (Ag, Cd, Cl, Cr, Cu, Ho, I, Pb, Pr, Re, Sb, Sm, Sn, and Zn) in RDC have concentrations significantly higher (enrichment factor ≥10) than the respective Clarke (worldwide averaged) values for coals. The distribution of trace elements such as Cr, Cu, Mn, Ni, Pb, Sb, and Zn, is controlled mostly by the organic matter, clay minerals and Fe oxyhydroxides, and in some cases by carbonates, sulphates, phosphates, chlorides and alloys. Organics, heavier, magnetic, fine and especially accessory minerals and phases in RDC are concentrating phases for these trace elements. Trace elements in RDC may be present, in decreasing order of significance, as: element-organic compounds; impurities in the mineral matter; major components in the mineral matter; major and impurity components in the inorganic amorphous matter; and elements in the fluid constituents. This characterization also reveals those elements that have the greatest potential for environmental impacts or for possible resource recovery. The results show that the effective economic and environmental management of MSW and RDC requires a long-term strategy based on a detailed understanding of the source, formation, behaviour and fate of the modes of trace element occurrences in MSW, RDC and combustion waste residues.