**1. Introduction**

Oil is the main source of energy in developed countries, its derivatives such as diesel, paraffin and liquefied gas are used for transport, heating and electricity production; in contrast, the pollution generated by the production processes required for the production, processing, transportation and distribution has generated a serious environmental problem affecting bodies of water, soil and air.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Polluted soil by hydrocarbons (HC) is importante in the environment, because the soil could be affected changing its physicochemical characteristics and lossing its ability to regenerate itself, or this regeneration takes a long time.

Because of this it is necessary to implement new techniques that allow the rehabilitation of soils in a shorter time and facilitate the process of restoration to the affected area.

There are plenty of available technologies to remediate soils contaminated with hydrocarbons, which are divided under three main headings: biological, physical, chemical and thermal treatments; however in the world most of the companies are dedicated to remediate soil using biological methods (bioremediation). Another important part of the mostly used technologies are soil washing, chemical oxidation and physical separation.

However, over the years a technique called physical chemistry electro‐remediation has been developed, which has proved its viability on the laboratory level and has been successfully applied in the field in some countries of Europe and the USA.

The electro‐remediation (ER) process, also called electrokinetic electrochemical treatment and/ or electro‐claim among others [1], is a technique within physicochemical treatments. ER has been considered to be a promising process addressing problems such as heterogeneous soils and low permeability, also can be applied *in situ* or *ex situ*, and is especially useful for reme‐ diation of inaccessible sites with minimal disruption to the surface, where other technologies fail. Besides it is also sensitive to a wide variety of contaminants.

The ER process is relatively safe, effective, easy to implement, economic and flexible from the points of applying on various types of soils and contaminants. Moreover, most of the *in situ* conventional methods present difficulties in treatment time in the case of fine‐grained soils with high water content and high organic or clay content; in contrast, the ER method is suitable for these types of soils too [2].

ER is a technology to restore contaminated soil based on the generation of an electric field from imposing direct current. For the application of potential difference or direct current, the use of electrodes (anode and cathode) placed in wells previously dug into the ground is required, usually the soil is wetted with an electrolyte to improve conditions driving the electric field. The action of the electrolyte makes the pollutant transport to the wells where it will be extracted. Unlike the fluid drag, this technique allows for a directed migration preventing contaminant dispersion outside the treatment zone [3].

The main mechanisms of the electric field leading the contaminants to the electrodes are electro‐migration, electro‐osmosis and electrophoresis. The first two processes have the greatest influence on contamination transport. These processes are described below [1]:

*Electro‐migration* is a phenomenon in which ions in solution and colloids having electric charge move through the electric field with a velocity that is proportional to the product of the strength of the electric field and mobility of the ion or particle.

The negatively charged ions (anions) will move toward the positively charged electrode and the positively charged ions (cations) will gravitate toward the negatively charged electrodes (cathode).This process is favored when the contaminations to be removed are metals with different oxidation states.

*Electro‐osmosis* is the transport process describing the movement of mass of fluid through the pores of the soil under the influence of a potential gradient. When a potential gradient is generated in presence of moist soil, a movement of ions appears toward the electrode polarized in order of their electric charge, generating a migration of them by movement of the water due to the hydration of these ions, and causing movement of fluid through the soil pores. The electro‐migration of species and the establishment of a double layer at the solid‐liquid interface generate an electro‐osmotic flow through the soil pores [4].

Electro‐osmosis is the most important transport mechanism for removal of compounds uncharged or weakly charged as organic pollutants. The electro‐osmotic component almost disappears in the cases of coarse sands and plastic clays wherein the electro‐migration is the most important contaminant removal mechanism. It becomes as important as the electro‐ migration in the cases of fine sand and silt with high amounts of water and low conductivity [4].

*Electrophoresis* is a mechanism observed when particles, colloids or micro‐surface electric charges that the contaminants bound to this material can be transported by the electric field [3].

Other mass transport phenomena occurring during ER are:

Polluted soil by hydrocarbons (HC) is importante in the environment, because the soil could be affected changing its physicochemical characteristics and lossing its ability to regenerate

Because of this it is necessary to implement new techniques that allow the rehabilitation of

There are plenty of available technologies to remediate soils contaminated with hydrocarbons, which are divided under three main headings: biological, physical, chemical and thermal treatments; however in the world most of the companies are dedicated to remediate soil using biological methods (bioremediation). Another important part of the mostly used technologies

However, over the years a technique called physical chemistry electro‐remediation has been developed, which has proved its viability on the laboratory level and has been successfully

The electro‐remediation (ER) process, also called electrokinetic electrochemical treatment and/ or electro‐claim among others [1], is a technique within physicochemical treatments. ER has been considered to be a promising process addressing problems such as heterogeneous soils and low permeability, also can be applied *in situ* or *ex situ*, and is especially useful for reme‐ diation of inaccessible sites with minimal disruption to the surface, where other technologies

The ER process is relatively safe, effective, easy to implement, economic and flexible from the points of applying on various types of soils and contaminants. Moreover, most of the *in situ* conventional methods present difficulties in treatment time in the case of fine‐grained soils with high water content and high organic or clay content; in contrast, the ER method is suitable

ER is a technology to restore contaminated soil based on the generation of an electric field from imposing direct current. For the application of potential difference or direct current, the use of electrodes (anode and cathode) placed in wells previously dug into the ground is required, usually the soil is wetted with an electrolyte to improve conditions driving the electric field. The action of the electrolyte makes the pollutant transport to the wells where it will be extracted. Unlike the fluid drag, this technique allows for a directed migration preventing

The main mechanisms of the electric field leading the contaminants to the electrodes are electro‐migration, electro‐osmosis and electrophoresis. The first two processes have the greatest influence on contamination transport. These processes are described below [1]:

*Electro‐migration* is a phenomenon in which ions in solution and colloids having electric charge move through the electric field with a velocity that is proportional to the product of the strength

The negatively charged ions (anions) will move toward the positively charged electrode and the positively charged ions (cations) will gravitate toward the negatively charged electrodes

soils in a shorter time and facilitate the process of restoration to the affected area.

are soil washing, chemical oxidation and physical separation.

applied in the field in some countries of Europe and the USA.

fail. Besides it is also sensitive to a wide variety of contaminants.

contaminant dispersion outside the treatment zone [3].

of the electric field and mobility of the ion or particle.

for these types of soils too [2].

itself, or this regeneration takes a long time.

290 Soil Contamination - Current Consequences and Further Solutions


At the anode: 2H2O‐4e− → O2(gas) + 4H+ (ac) *E*°= +1.229 V At the cathode: 2H2O + 2e− → H2(gas) + 2OH− *E*°= ‐0.828 V

It is noteworthy that electrolysis reactions depend on the type and arrangement of the electrodes [5] as well as the chemical species and electric potential applied during electro‐ remediation. Thus, protons generated at the anode move through the soil to the cathode by:


The alkaline medium developed at the cathode moves toward the anode by ion migration and diffusion of OH– , which is transport overshadowed by the electro‐osmotic flow and neutrali‐ zation of H+ , ranging to the cathode where the ions can recombine to form water [4].

In the last three decades, there have been several investigations at laboratory and pilot even applying electrokinetic basis to remove a variety of contaminants. The electro‐remediation has been successfully tested in the USA [1–7]. There are even companies offering it as an alternative remediation method within the portfolios of their services a large scale in soils with high clay content.

The ER method has demonstrated its ability to remove some organic contaminants in studies at laboratory, pilot or field [6], but its main application was on sites contaminated with metals in order to remove elements such as chromium, cadmium, mercury, lead, zinc, etc. [7].

In several studies, the application of the ER process has helped to achieve efficiencies close to 100% removal, particularly if the pollution is caused by a single metal (Pb). In *on‐site* applica‐ tions, the results depended on soil‐type variables and the type of pollutant [3].

One example is the consortium formed by Monsanto, DuPont and General Electric, where the applied technology was called LasagnaTM ER *in situ* to remove trichloroethylene, achieving removal of 98% [8].

Another practical example was developed by Sandia National Laboratories, for electrochem‐ ical *in situ* remediation of soil contaminated with chromium, where electrodes of Iridium/ Titanium were used with applying a power of 1572 kW/h; after 5 months of continuous treatment 64% efficiency was obtained [9].

Also, the ER was made at the Centro de Investigación y Desarrollo Tecnológico en Electroquí‐ mica, S. C. (CIDETEQ) at laboratory level in order to be able to apply it at pilot and on field level. For that reason, several investigations were developed that led to get familiar with different aspects of field application helping implementation of the technique in a petroleum industrial area. Meanwhile the Geological and Geophysical Institute of Hungary developed an analytical method for investigating the physical and chemical characteristics of soil.
