ECN publication
Leaching behaviour of amorphous, mixed and crystalline vitrified MSWI fly ash
Published by: Publication date:
ECN 1997
ECN report number: Document type:
ECN-C--97-003 ECN publication
Number of pages: Full text:
104 Download PDF  

The leaching behaviour of vitrified Municipal Solid Waste Incinerator flyash, as produced by Electricite de France (EDF) in a plasma torch vitrification, has been investigated. Three slag configurations have been studied: amorphous, mixed and crystalline slag. The aggregation form is mainly a function of the cooling rate of the slag. The leaching behaviour of the three slag types as determined in a pH-stat leach test is remarkably different. In amorphous slag, Cr and S are more leachable than in mixed and crystalline slag. In crystalline and to a lesser extent in mixed slag the leachability of Ba, Cd, Cu, Ni, Pb, Sb, Sn, V and Zn is significantly higher than in amorphous slag. This is particularly true for Sb, which is leached in mg/l-concentrations from crystalline slag. In all tests, this general behaviour can be recognized. For several major elements the leaching behaviour is very consistent irrespective of slag type (e.g. Al, Si, Ca, P, Mg, B, Mn). Only for a few elements leachability appears to be controlled by dissolution of the glass matrix. The most relevant elements are controlled by solubility. The CEN two-step test is consistent with the pH-stat data. The identification of the release controlling mechanism is useful to decide if further action is needed. The geochemical modelling has been very useful in identifying relevant solubility controlling phases for different elements e.g. Al-gibbite; Ba-BaCaSO4; Cr-Cr(OH)3; Cu-tenorite; Fe-ferrohydrite; Mn-MnHPO4; Ni-Ni(OH)2; Pb-Pb(OH)2 (partly); Si-quartz; Zn-zinc silicates. The compacted granular leach test has provided release information under diffusion controlled conditions. The information generated has provided a basis of characterization of leaching behaviour from vitrified MSWI fly ash, that allows further conclusions on useful measures for changing process operating parameters as well as for management options in relation to utilization and disposal. 27 figs., 22 tabs., 30 refs.

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