toxicity for the receiving medium, biodegradability and efficiency under the planned
conditions of application. The measurement of the efficiency includes the minimal
loss of ligand in the treated medium (e.g., due to adsorption and ion-exchange
interactions), the lowest concentration for which activity is observed, the selectivity
for leaching, and the effectiveness over the whole targeted population. As a general
rule, the higher the loss is, the higher the matters are (e.g., cost for reagents, pore
clogging, uncontrolled release with rebound effect).
Nevertheless, the enhanced solubilization of contaminants at field scale is ligand
intensive. A typical example of this is the HOCs mobilization with surfactants.
Typical SC values 0.27 for the dissolution of HOCs in micelles show that these
molecular structures contain much more surfactant than contaminant (Zhu and Feng
2003). Despite this ratio being inverted for emulsions, swollen micelles are favored
for many contaminant residuals because of both the limiting HOCs desorption
kinetics and the high value for the surfactant to HOC ratios usually used in SL
because of the mass transfer law. For this reason, it is desirable that the extracting
agents in soil leachates should be recovered for reuse.
1.4 State of Knowledge Regarding Soil Leachate Treatment
Technologies that Enable Their Reuse
In order to reuse washing solutions, contaminants present in soil leachates should be
removed selectively relative to chemical extractants. In the frame of environmental
pollution control, the removal of contaminants prevails over the recovery of chemical agents. The treatment of leachates usually involves a separative process in order
to remove and concentrate the mobilized contaminants. Usually, in many processes
(e.g., demetallation) ligands are just degraded (e.g., oxidation) to release contaminants which separate from the aqueous phase (Tucker et al. 1999; Finzgar and Lestan
2008; Huang et al. 2016). This chemical-intensive strategy is not sustainable and
may lead to secondary pollutions. At the exit of the treated zone, the soil leachate is
composed of free contaminant (C), free ligand (L), and their complexes written in the
simplified form C i L j . In order to recover and reuse the ligands while separating
contaminants from the aqueous phase, two strategies may be implemented:
• At least, the selective extraction of C and C i L j while keeping L in treated
leachates
• Or the selective extraction of C after the fast dissociation of the C i L j complexes
Separative treatments processes are classified into physical, physicochemical, and
chemical processes. Physical treatments are of special interest because of the absence
of added chemicals to the handled solution. The main drawbacks of chemical
treatments are the use of chemicals itself, the poor selectivity toward the targeted
contaminants, and the potential risks of chemical interferences within the whole
process.
1 Contaminant Mobilization from Polluted Soils: Behavior and Reuse of Leaching. . .
31
conditions of application. The measurement of the efficiency includes the minimal
loss of ligand in the treated medium (e.g., due to adsorption and ion-exchange
interactions), the lowest concentration for which activity is observed, the selectivity
for leaching, and the effectiveness over the whole targeted population. As a general
rule, the higher the loss is, the higher the matters are (e.g., cost for reagents, pore
clogging, uncontrolled release with rebound effect).
Nevertheless, the enhanced solubilization of contaminants at field scale is ligand
intensive. A typical example of this is the HOCs mobilization with surfactants.
Typical SC values 0.27 for the dissolution of HOCs in micelles show that these
molecular structures contain much more surfactant than contaminant (Zhu and Feng
2003). Despite this ratio being inverted for emulsions, swollen micelles are favored
for many contaminant residuals because of both the limiting HOCs desorption
kinetics and the high value for the surfactant to HOC ratios usually used in SL
because of the mass transfer law. For this reason, it is desirable that the extracting
agents in soil leachates should be recovered for reuse.
1.4 State of Knowledge Regarding Soil Leachate Treatment
Technologies that Enable Their Reuse
In order to reuse washing solutions, contaminants present in soil leachates should be
removed selectively relative to chemical extractants. In the frame of environmental
pollution control, the removal of contaminants prevails over the recovery of chemical agents. The treatment of leachates usually involves a separative process in order
to remove and concentrate the mobilized contaminants. Usually, in many processes
(e.g., demetallation) ligands are just degraded (e.g., oxidation) to release contaminants which separate from the aqueous phase (Tucker et al. 1999; Finzgar and Lestan
2008; Huang et al. 2016). This chemical-intensive strategy is not sustainable and
may lead to secondary pollutions. At the exit of the treated zone, the soil leachate is
composed of free contaminant (C), free ligand (L), and their complexes written in the
simplified form C i L j . In order to recover and reuse the ligands while separating
contaminants from the aqueous phase, two strategies may be implemented:
• At least, the selective extraction of C and C i L j while keeping L in treated
leachates
• Or the selective extraction of C after the fast dissociation of the C i L j complexes
Separative treatments processes are classified into physical, physicochemical, and
chemical processes. Physical treatments are of special interest because of the absence
of added chemicals to the handled solution. The main drawbacks of chemical
treatments are the use of chemicals itself, the poor selectivity toward the targeted
contaminants, and the potential risks of chemical interferences within the whole
process.
1 Contaminant Mobilization from Polluted Soils: Behavior and Reuse of Leaching. . .
31