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