Civil Engineering Reference
In-Depth Information
100
80
60
40
20
0
0.001
0.01
0.1
1
10
Particle size (mm)
12.7
Particle size distribution of MSWI fly ash. After Aubert et al.
(2004).
Volatile metals such as lead, zinc, tin cadmium and antimony, along with
group I metal halides (especially sodium and potassium chlorides) and, to
a lesser extent, sulphates, are concentrated in the fly ash. In terms of their
elemental composition, the fly ashes are dominated by calcium, aluminium
and silicon (mainly oxides) and by sodium and potassium halides (mainly
chlorides) along with sulphur, largely present as sulphate. youcai et al. (2002)
confirm, as might be expected, that the heavy metal content of the ash is a
function of the heavy metal content of the original waste. Much work has
been done on the elemental composition of MSW fly ash, amongst which
work by Fernandez et al. (1992), Greenberg et al. (1978) and Sawell and
Constable (1993) are very informative. readers are particularly referred to
the work of the International Ash Working Group (IAWG) reports, especially
'Municipal Solid Waste Incinerator residues' (Chandler et al. 1997). By
comparison with the bulk elemental composition, relatively little has been
done on the phase chemistry of fly ash. Eighmy et al. (1995) summarize
much previous work and go on to identify two principal particle types:
∑ 'An extremely fine grained, polycrystalline aggregated platelet material
containing many volatile elements such as Cl, K, Zn, Na S and Pb';
and
∑ 'spherical alumnosilicate particles'.
They describe the mineral phases associated with each; soluble salts such as
NaCl, K
2
ZnCl
4
and KClO
4
associated with the crystalline agglomorations
and in the remainder, a wide range of calcium, sodium and potassium
aluminosilicates, lead silicates and spinel phases. These observations are
