situ and in situ treatments obey different rules. However, the purpose of the
treatment should be to remove the mobilizable fraction of contaminant from the
contaminated material. Generally, the total contaminant concentration after washing
is not predictive of the leaching behavior of the residual contaminant (Tsang et al.
2013). The aim of leaching treatment is to reduce contaminant concentrations below
regulatory levels if any, but also to meet the criteria for contaminants leachability of
the treated materials considering the different exposure scenarios (Engelsen et al.
2010; van der Sloot and Kosson 2012). For SW, gravity and magnetic separations
are operated in order to eliminate macroscopic contaminants, whereas chemicals are
mainly involved for fine particles treatment (Dermont et al. 2008; Mann 1999). The
soil colloidal fraction, which is the most polluted one, is separated from the solid
phase using cheap molecules that adsorb strongly onto surfaces, like citrate or
surfactants. In contrast, in SF, the nonspecific adsorption of reagents is avoided
and they are used at low concentrations in order to prevent the decrease of the soil
hydraulic conductivity by pore clogging and the risk for secondary pollution
(Kedziorek and Bourg 2000; Hauser et al. 2005). The use of extracting agents at
low concentration requires selectivity and efficiency, which are obtained on the basis
of specific effects. They are due to a high molecular organization which favors the
formation of contaminant-rich mobile particles or water-soluble complexes.
1.3.2 Organic Contaminants Extraction
In spite of the high efficiency of organic solvents for the extraction of HOCs, they
were gradually banished from most of remediation processes for the benefit of the
water-based solutions, because of potential health risks and impacts on the environment (Birak et al. 2011; Gomes et al. 2013). Despite vegetal oils being used as
organic solvent substitutes, it is rather in the form of oil in water emulsions (von Lau
et al. 2014). Besides, supercritical carbon dioxide is used in dedicated extraction
units (Fu and Matthews 1999). The following discussion focuses on water-based
leaching approaches. Many natural molecules have been assessed, starting with HA
and FA, more especially dedicated to HOCs (Molson et al. 2002; van Stempvoort
et al. 2002) and their chemically modified parent compounds with enhanced
tensioactive properties and stability in aqueous solution (Garcia-Diaz et al. 2015).
Cyclodextrins (CDs) are pre-organized natural molecules which offer a hydrophobic
cavity. β-CD and its alkylated parent compounds, such as methyl-β-CD whose
performances have been improved through hemi-synthesis, show high capacities
to dissolve 3–4 rings PAHs in water (Rekharsky and Inoue 1998; Badr et al. 2004;
Viglianti et al. 2006). These molecules have low affinity for soil material and usually
they are stable for few weeks in saturated soils. Nevertheless, they are too selective
and too expensive to be used for soil remediation. The best suitability is obtained for
surfactants, which are much used for soil remediation (Paria 2008). They may be of
natural origin like for example Saponin. They can act either in the form of monomers
to mobilize NAPLs, micelles to dissolve them in water or emulsions when they are
22
N. Fatin-Rouge
treatment should be to remove the mobilizable fraction of contaminant from the
contaminated material. Generally, the total contaminant concentration after washing
is not predictive of the leaching behavior of the residual contaminant (Tsang et al.
2013). The aim of leaching treatment is to reduce contaminant concentrations below
regulatory levels if any, but also to meet the criteria for contaminants leachability of
the treated materials considering the different exposure scenarios (Engelsen et al.
2010; van der Sloot and Kosson 2012). For SW, gravity and magnetic separations
are operated in order to eliminate macroscopic contaminants, whereas chemicals are
mainly involved for fine particles treatment (Dermont et al. 2008; Mann 1999). The
soil colloidal fraction, which is the most polluted one, is separated from the solid
phase using cheap molecules that adsorb strongly onto surfaces, like citrate or
surfactants. In contrast, in SF, the nonspecific adsorption of reagents is avoided
and they are used at low concentrations in order to prevent the decrease of the soil
hydraulic conductivity by pore clogging and the risk for secondary pollution
(Kedziorek and Bourg 2000; Hauser et al. 2005). The use of extracting agents at
low concentration requires selectivity and efficiency, which are obtained on the basis
of specific effects. They are due to a high molecular organization which favors the
formation of contaminant-rich mobile particles or water-soluble complexes.
1.3.2 Organic Contaminants Extraction
In spite of the high efficiency of organic solvents for the extraction of HOCs, they
were gradually banished from most of remediation processes for the benefit of the
water-based solutions, because of potential health risks and impacts on the environment (Birak et al. 2011; Gomes et al. 2013). Despite vegetal oils being used as
organic solvent substitutes, it is rather in the form of oil in water emulsions (von Lau
et al. 2014). Besides, supercritical carbon dioxide is used in dedicated extraction
units (Fu and Matthews 1999). The following discussion focuses on water-based
leaching approaches. Many natural molecules have been assessed, starting with HA
and FA, more especially dedicated to HOCs (Molson et al. 2002; van Stempvoort
et al. 2002) and their chemically modified parent compounds with enhanced
tensioactive properties and stability in aqueous solution (Garcia-Diaz et al. 2015).
Cyclodextrins (CDs) are pre-organized natural molecules which offer a hydrophobic
cavity. β-CD and its alkylated parent compounds, such as methyl-β-CD whose
performances have been improved through hemi-synthesis, show high capacities
to dissolve 3–4 rings PAHs in water (Rekharsky and Inoue 1998; Badr et al. 2004;
Viglianti et al. 2006). These molecules have low affinity for soil material and usually
they are stable for few weeks in saturated soils. Nevertheless, they are too selective
and too expensive to be used for soil remediation. The best suitability is obtained for
surfactants, which are much used for soil remediation (Paria 2008). They may be of
natural origin like for example Saponin. They can act either in the form of monomers
to mobilize NAPLs, micelles to dissolve them in water or emulsions when they are
22
N. Fatin-Rouge