Civil Engineering Reference
In-Depth Information
6
S
TIBA8
S
TIBA7
5
S
TIBA6
4
S
TIBA8.8
3
2
1
0
0
50 100 150 200 250 300 350 400 450 500 550 600 650 700 750
Time (min)
12.18
Comparison of the aluminium metal remaining in the system
using Aubert's method following varying degrees of thermal pre-
treatment of MSWI bottom ash
After Qiao et al. (2008c).
much to recommend it and as it is a simple and robust technique, it may
become widely adopted.
Quantifying the glass content and its reactivity is more challenging.
Polarized light microscopy is well established and applicable to bottom
ash characterization, where the particle size is relatively coarse, but is less
attractive for very fine fly ash. The conventional method of point counting
the optically isotropic particles (in extinction under crossed polarized light)
would give a fair approximation of the glass content, but the results may be
erroneous where the glass fragments are strained or devitrified. Despite this
limitation, the method is robust and readily automated using image analysis.
The alternative method of Reitveld refinement of X-ray diffraction (XRD)
spectra in order to calculate the amorphous fraction seems too involved a
process to be widely adopted in practice.
Glass reactivity poses further difficulty in assessment. Practically, the
potential glass compositions may vary widely, depending on both the original
glass type and its thermal history during incineration. Once fused at high
temperature, the glasses are able to react with the materials near to them,
selectively dissolving some components but not others. Analytical electron
microscopy will quantify the range of glass chemistry within a sample, but
currently no adequate correlation is available which links composition to
reactivity. It seems likely that for the forseeable future, recourse must be
