Environmental Engineering Reference
In-Depth Information
processes that should cause a continuous increase in dissolved iron concentrations at the
near-neutral pH. However, no continuous increment of the dissolved iron concentration
in the solution and no iron corrosion products at the iron surface were found. They can
be attributed to the presence of aluminum that serves as an electron source for the
dissolved iron reduction. Aluminum was oxidized to dissolved aluminum ions that were
subsequently precipitated as aluminum hydroxide/oxyhydroxides.
OH
-
OH
-
CCl
4
+ H
+
+ H
2
O + 2e
-
CCl
4
+ H
+
+ H
2
O + 2e
-
Fe
2+
Fe
2+
Al
3+
Al
3+
Al(OH)
3
Al(OH)
3
CHCl
3
+ 0.5H
2
+ OH
-
CHCl
3
+ 0.5H
2
+ OH
-
Fe
0
Fe
0
Al
0
Al
0
Figure 7.4
Conceptual model accounting for the roles of aluminum and iron in the
reductive dechlorination of carbon tetrachloride.
7.2.2
Bimetallic Cu/Al Particles
7.2.2.1 Characterization
Figure 7.5 illustrates the XRD patterns of bimetallic Cu/Al particles. The
characteristic peaks of aluminum appear at 38.6, 44.8, 65.2, and 78.4°; the peaks
assigned to copper are at the positions at 43.4, 50.5, and 74.1
. The characteristic peaks
of aluminum hydroxide (bayerite, Al(OH)
3
) are assigned to 18.8, 20.4, 27.9, 36.6,
40.7, 53.3, 59.6, 64.0, 67.4, and 70.8°. The XRD pattern indicates that bimetallic
Cu/Al consisted of zero-valent forms of aluminum and copper, and aluminum hydroxide.
Aluminum hydroxide is a product from the redox reaction between Al and Cu
2+
during
the synthesis of bimetallic Cu/Al particles under alkaline conditions (Lien and Zhang,
2002):
°
3Cu
2
+
+
2Al
0
+
6OH
−
→
3Cu
0
+
2Al(OH)
(Eq. 7.6)
3
7.2.2.2 Dechlorination of Dichloromethane
Bimetallic Cu/Al particles have been shown to have enhanced reactivity toward
carbon tetrachloride. More importantly, they are capable of degrading dichloromethane
that is unable to be dechlorinated by most of zero-valent metals, iron nanoparticles and
bimetallic systems. An example is given in Figure 7.6. The batch bottle containing 20
g/L Cu/Al was spiked with 16 μmol dichloromethane four times. A fast initial process
followed by a slow subsequent process was found throughout the experiment while the
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