Environmental Engineering Reference
In-Depth Information
Control without nZVI
(
a
)
(
b
)
(
c
)
Enhanced transport
Difusion
ORP
(mv)
45
45
45
40
40
40
550
525
500
475
450
425
400
375
350
325
300
275
250
225
200
175
150
125
100
75
50
35
35
35
30
30
30
25
25
25
20
20
20
15
15
15
10
10
10
5
5
5
0
05
10
0
05
Distance from anode (cm)
0
15
20
10
15
20
0
5
10
15
20
Figure 2.35
Variation of ORP in the kaolin medium in
a)
EK assisted transport of
nZVI
b)
diffusion of nZVI and
c)
EK without nZVI; all using 1 mM NaCl as pore fluid
electrolyte (Gomes et al., 2013b).
variations for control tests of diffusion and electrokinetics without the
nano-iron are also presented. In these tests, the nZVI granules were placed
in the clay inside a transverse groove at about 8 cm from the anode end of
the clay bed and the tests were run under oxygen poor conditions using
5V across the working electrodes. As observed, the ORP reduced across
clay bed for the first 15 hours of transport and increased to above the origi-
nal values during the rest of the transport period. The ORP for the diffu-
sion only case remained mostly unchanged, and the EK only case showed
the typical pH dependent ORP variation expected with EK. Based on the
water chemistry of nano-iron (Sun et al., 2006), if the only contributor to
the ORP was nano-iron, the change in the ORP of the system would be
expected to vary within 50 mV between the pH units of 6.0 to 6.5. The ORP
changes for the diffusion tests did remain between
+50 and -50 mV
, over
the 48-hour duration without the electric field application. The EK assisted
transport of nZVI, on the other hand, displayed larger changes in ORP
across the clay bed indicating a synergistic effect of EK and nZVI activa-
tion within the first 15 hours of the process. The longer term ORP changes
showed the contribution of clay surface interactions with Fe(II) and Fe(III)
in presence of electrical potential as the ORP elevated over background
values at the average low pH value of 3.
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