Environmental Engineering Reference
In-Depth Information
In addition to mass transport processes, chemical reactions take place at
the electrodes. The principal electrode reaction observed is the electrolysis
of water. At the anode, water is oxidized and oxygen gas and hydrogen ions
are generated:
+
−
0
2H OO
→+
4H
+
4e E
= −
1 229V
.
(9.13)
2
2 gas
(
)
()
aq
At the cathode, water is reduced and hydrogen gas and hydroxide ions are
produced:
−
−
0
4H O e
+→ +
2H4OH
E=
−
0
.
828V
(9.14)
2
2 gas
(
)
()
aq
This means that acid is produced at the anode; thus, pH is reduced and
alkaline solution is produced at the cathode, that is, pH is increased. H
+
ions
leaving the anode and OH
−
ions leaving the cathode change pH of the soil
considerably (Acar and Alshawabkeh 1993).
9.4.2 Removal of Radionuclides
Improper handling of nuclear wastes and spent fuel, activities at nuclear fuel
production plants and nuclear waste processing plants, accidents involving
nuclear materials, especially those in nuclear reactors, and nuclear weapons
tests have caused severe contamination to the soil and groundwater on a
number of occasions (Korolev 2009). Radionuclides may enter the soil and/
or groundwater during storage, transport, and use of nuclear fuel and waste.
Before being abolished, nuclear tests were a major source of nuclear contami-
nation. The most serious contaminations have been caused by the isotopes
60
Co,
90
Sr,
90
Y,
106
Ru,
137
Cs,
144
Ce,
147
Pm,
238
Pu,
239
Pu,
240
Pu, and
226
Ra. The sever-
ity of contamination is largely determined by the toxicity of the radioactive
elements involved (Table 9.3).
Most soil decontamination technologies used are based on flushing soils
with various chemicals, chemical leaching, and selective extraction of radio-
nuclides. The main advantage of the new electrokinetic technique is that it
can be applied in situ to soils of low filtration ability.
Another advantage of electrokinetic techniques is that they easily can be
integrated (coupled) with other technologies promoting their advantageous
features by synergistic effects and suppressing their shortcomings. Such
integrated technologies include
• Electrokinetic biobarriers
• Electrolytic reactive barriers
• Electrokinetic-PRBs
• Electrokinetic-chemical oxidation/reduction
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