Fundamentals of electrokinetics - In-Situ Remediation of Arsenic-Contaminated Sites - page 86

operation and its potential applicability to a wide range of contaminants (Alshawabkeh et al ., 1999;
Kim and Kim, 2002; Pamukcu and Wittle, 1994; Reddy and Cameselle, 2009a). The electrokinetic
technology is envisioned for the removal/separation of organic and inorganic contaminants and
radionuclides. The potential of the technology for soil remediation has resulted in several field
implementations (DOE, 1998a; 1998b; Gent et al ., 2004; Ho et al ., 1999a; 1999b; Lageman,
1993; USEPA, 1998; 2003). Except for the applicability of electrokinetics to soil remediation,
the technology was originally used to consolidate low-permeability clayey soils for a long time
(Mitchell, 1991; 1993; Mitchell and Soga, 2005). In this chapter, the application of electrokinetics
for soil remediation is discussed.
The purpose of this chapter is to provide the fundamental concept of electrokinetics in soil
remediation. First, a variety of electrokinetic phenomena that occur in soils when an electric field
is applied are introduced. These are important because the electrokinetic technology is based on
naturally-occurring phenomena. Next, the fundamental principles and implementation system
of electrokinetics are detailed as well. In addition, the unique advantages and disadvantages of
electrokinetics over other remediation technologies are addressed. In the second part of the chapter,
the main considerations and operational parameters affecting the performance of electrokinetic
processing are detailed. In the third part, the researches and projects on electrokinetics that have
been conducted are presented and summarized with a focus on field applications. Finally, the
chapter closes with a brief consideration of prospects to improve the performance of electrokinetics
in soil remediation.

5.2 ELECTROKINETIC PHENOMENA

When electricity is supplied to a wet porous medium, such as soil, a variety of physico-chemical
phenomena occur, and they are called electrokinetic phenomena. In the early 19th century, these
electrokinetic phenomena were identified by Russian scientist Reuss (1809), who conducted
an experiment in which direct electricity was applied to wet clay soil (Acar and Alshawabkeh,
1993). However, it was in the early 20th century that the scientific phenomena became a basis
for engineering technologies. The electrokinetic phenomena accompany various physical and
chemical interactions and other related phenomena, and it is impossible to address all of them
in details here. Please refer to Mitchell (1991; 1993), Probstein (2003), and Mitchell and Soga
(2005) for an in-depth study.
In this section, representative electrokinetic phenomena that are directly related to the principles
of electrokinetic technology as well as the mechanisms of contaminant transport are discussed.
Electrolytic reaction of water is also addressed, because the reaction greatly affects the interac-
tions between soil particles and contaminants and finally controls transport of contaminants in
soil media. The electrokinetic phenomena related to contaminant transport are electromigration
(also termed ionic migration), electroosmosis (electroosmotic advection), electrophoresis, and
diffusion, and these are bases of electrokinetic technology by which contaminants are removed
from soils.

5.2.1 Electrokinetic transport phenomena
5.2.1.1 Electromigration or ionic migration
Under the influence of a direct current (DC) electric field, charged chemical species, such as
ions and polar molecules, move in pore water within soil media, and this transport phenomenon
is termed electromigration or ionic migration. On the basis of electromigration, cationic and
anionic contaminants are removed in the cathode (negative electrode) and anode (positive elec-
trode), respectively, during electromigration. Ionic mobility u i [m 2 s − 1 V − 1 ], defines the transport
velocity of the ionic species i under the effect of a unit electric field and can be theoretically esti-
mated by using the Nernst-Townsend-Einstein relation (Holmes, 1962) between the diffusion