Environmental Engineering Reference
In-Depth Information
FIGURE 9.13
XRD pattern of waste forms of synthetic waste (As, Cd, Cr, Pb, phenol).
source of silicon in this waste form. Figure 9.12D shows a significant amount of
chlorine. Since this was not present in the waste, it is coming from the binder.
EDX analyses of the waste show varied distribution of the waste elements.
Chromium was quite uniformly distributed in these waste forms, with some occasional
locally high concentrations. Arsenic and lead were rarely detected, but some areas
had high concentrations. These elements were possibly precipitated, whereas chro-
mium was adsorbed on the surface. The XRD patterns indicate a wide variation in
the presence of crystalline phases. (All these patterns include aluminum as an internal
standard.) Figure 9.13A has very few peaks and a broad hump. The pattern matches
that of granulated blast furnace slag. Melilite, typically found in slag, can be identified
in the pattern. No new peaks due to hydration could be identified in the pattern. Figure
9.13B also has a broad hump but several other peaks are present, suggesting a
significant amount of crystalline mineral content. Figure 9.13C has several broad
peaks, particularly at low two thetas. This is typical of clay minerals like smectite. A
clay was thus used in this waste form in binding the waste elements.
9.6.3
S
TRUCTURAL
C
HARACTERIZATION
OF
F
IELD
C
EMENT
-
S
OLIDIFIED
C
ONTAMINATED
S
OIL
The samples come from a site where the soil was contaminated from polynuclear
aromatic hydrocarbons, volatile organic compounds and cyanide, and was remedi-
ated by
in situ
solidification in 1992 by injection of a bentonite/portland cement
slurry using a rotating auger. A total of 16 samples were taken 10 years after the
solidification with the aim of examining long-term effectiveness of the remediation.
Several techniques, including XRD, SEM, DTG, DSC and FTIR, were used to
examine the structural characterization of these samples.
As shown by XRD in Figure 9.14A, the most dominant mineral in all XRD
patterns is quartz, which is the mineral form of sand. The amount of quartz in these
soils could be easily 60% or higher. All the major clay minerals, smectite, illite, and
kaolinite, are present in the soil samples. Sometimes all three are present in the same
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