Remediation and Management of Contaminated Soil - Sustainable Practices in Geoenvironmental Engineering - page 414

the electrodes, precipitation/co-precipitation, electroplating, or complexation with ion-
exchange resins (Reddy et al., 2001). This method is well suited for ine-grained soil and
dredged sediment.
Control of pH and electrolyte conditions within the electrode casings is essential in the
optimization of process eficiency. The process can be used to recover ions from soils,
muds, dredging, and other materials (Acar et al., 1993). Metals as soluble ions and bound
to soils as oxides, hydroxides, and carbonates are removed by this method. Other nonionic
components can also be transported with the low. Unlike soil washing, this process is
effective with clay soils.
Demonstrations of this technology have been performed but are limited in North
America (Mulligan et al., 2001). At pilot and full scale, the electrokinetic technology
has been tested for demonstration purposes at the following sites: (1) Louisiana State
University, (2) Electrokinetics, (3) Geokinetics International, and (4) Battelle Memorial
Institute. Geokinetics International has successfully demonstrated the in situ electro-
kinetic remediation process in ive ield sites in Europe for copper, zinc, lead, arsenic,
cadmium, chromium, and nickel. In the United Kingdom, it was evaluated for treatment
of highly contaminated mercury in canal sediments. Other ions such as cyanide, nitrate,
and radionuclides such as uranium and strontium can also be treated by electrokinetics.
Interferences include large metal objects, moisture content, temperature, and some other
contaminants. Metal recovery from highly contaminated soils could improve the process
economics.
Since soil and sediment particles have buffering capacity, release adsorbed substances
from the surfaces occurs when the value of pH decreases. Therefore, acidiication may be
a very effective method to solubilize the metal hydroxides and carbonates, other species
adsorbed onto sediment particles, as well as protonate organic functional groups (Yong et al.,
2006). Generally, in electrochemical remediation process, the development of an acidic front
is often coupled with a successful remediation (Nystroem et al., 2006). However, because of
the higher buffering capacity of sediments, acidiication of dredged materials may not be
an acceptable method. Surfactants can increase the solubility and mobility of heavy metals
during electrochemical remediation, depending on its function on decreasing the ζ poten-
tial of sediment and then reducing the Van der Waals interactions (Nystroem et al., 2006).
Therefore, using surfactants improves metal removal (Abidin and Yeliz, 2005). Direct costs
have been estimated at $15/m 3 with energy expenditure of $0.03/kW h. Addition of the cost
of enhancement could result in direct costs of $50/m 3 or more. Another study has estimated
full scale costs at $117/m 3 . For remediation of metal-contaminated ine-grained and hetero-
geneous soils, this technique could potentially be competitive (FRTR, 2007).
11.4.4 Solidification/Stabilization
The purpose of solidiication/stabilization (S/S) processes is to reduce the mobility of the
contaminants by addition of an agent that solidiies and then immobilizes the metals or
hydrocarbons. Binders include cement, ly ash, sodium silicates, lime, sulfur- and organic-
based binders, and pozzolans are added in situ or ex situ (USEPA, 2000). Other processes
or groups include bituminization, emulsiied asphalt, polyethylene extrusion, pozzolan/
Portland cement, and soluble phosphates. Ex situ S/S requires disposal of the stabilized
residue. Solidiication/stabilization is often utilized for metal contamination as there are
few destructive techniques available for metals. Some metals such as As, Cr(VI), Pb, Cu,
Ni, Zn, and Hg are suitable for this type of treatment. The metals are hydrolyzed to form
hydroxides, oxides, carbonates, sulfates, etc. that are of limited solubility. Liquid monomers