1.4.3.3 Transmetallation
This is an organometallic reaction that involves the transfer of a ligand from one
metal to another. Lim (2005) reports the use of Fe(III) in excess to remove MTEs
divalent cations from their EDTA complexes, before EDTA regeneration in presence
of a large amount of phosphate in strong alkaline medium, in order to remove iron
(III) as solid FePO 4 .
1.4.4 Conclusion
A brief review of technology assessments for the reuse of soil leaching solutions is
presented in Table 1.2. Even if the regeneration of contaminated leaching solutions
has been demonstrated, its interest is not currently obvious since most of the
available treatment technologies suffer from selectivity, efficiency, and cost. The
process combining contaminant extraction and wastewater treatment must be considered as a whole. Its optimization for efficiency and selectivity with respect to
reactants, technologies, and process parameters is complex (Ahn et al. 2008b;
Hanafiah et al. 2018). The proper technology for leaching solution recovery should
follow the order of preference: physical > physicochemical > chemical, since risks
for operators, the natural environment, process disruption as well as waste management and recycling should be considered. Also one should bear in mind that
chemical reactions are never specific and that their efficiency and safety are limited
by interferences. Moreover, the number of steps and tools involved in treatment
trains should be lowered as much as possible in order to avoid complexity, fragility,
and costs. Currently, the most attractive technologies are:
• UF for the removal of HOCs, since it is robust (single step treatment) and
economic (approximately 1.25 € m
À3 of treated wastewater), but it is limited by
surfactant recovery from concentrated wastewater
• Pervaporation for the removal of VOCs (approximately 4.7 € m
À3 of treated
wastewater), but on diluted wastewater
• Sorption onto chelating resins such as Amberlite IRC 748 for the removal of
MTEs when leachable amounts of iron or nickel are low, since resins are easily
regenerated in acidic medium and may be advantageously coupled to electrolysis
for metal precipitation and purification
• Precipitation with sulfide ions for the removal of MTEs, but it may be dangerous
and the strategy for the soil treatment itself should be carefully designed.
Finally, it is a pity that most of the reported trials have been performed at the lab
scale, since field tests are required for validation and for full assessments. In the next
section, a field test assessing the feasibility of using UF for the reuse of soil leachates
in SF operations for the removal of petroleum hydrocarbons with PAHs as major
components is described.
1 Contaminant Mobilization from Polluted Soils: Behavior and Reuse of Leaching. . .
41
This is an organometallic reaction that involves the transfer of a ligand from one
metal to another. Lim (2005) reports the use of Fe(III) in excess to remove MTEs
divalent cations from their EDTA complexes, before EDTA regeneration in presence
of a large amount of phosphate in strong alkaline medium, in order to remove iron
(III) as solid FePO 4 .
1.4.4 Conclusion
A brief review of technology assessments for the reuse of soil leaching solutions is
presented in Table 1.2. Even if the regeneration of contaminated leaching solutions
has been demonstrated, its interest is not currently obvious since most of the
available treatment technologies suffer from selectivity, efficiency, and cost. The
process combining contaminant extraction and wastewater treatment must be considered as a whole. Its optimization for efficiency and selectivity with respect to
reactants, technologies, and process parameters is complex (Ahn et al. 2008b;
Hanafiah et al. 2018). The proper technology for leaching solution recovery should
follow the order of preference: physical > physicochemical > chemical, since risks
for operators, the natural environment, process disruption as well as waste management and recycling should be considered. Also one should bear in mind that
chemical reactions are never specific and that their efficiency and safety are limited
by interferences. Moreover, the number of steps and tools involved in treatment
trains should be lowered as much as possible in order to avoid complexity, fragility,
and costs. Currently, the most attractive technologies are:
• UF for the removal of HOCs, since it is robust (single step treatment) and
economic (approximately 1.25 € m
À3 of treated wastewater), but it is limited by
surfactant recovery from concentrated wastewater
• Pervaporation for the removal of VOCs (approximately 4.7 € m
À3 of treated
wastewater), but on diluted wastewater
• Sorption onto chelating resins such as Amberlite IRC 748 for the removal of
MTEs when leachable amounts of iron or nickel are low, since resins are easily
regenerated in acidic medium and may be advantageously coupled to electrolysis
for metal precipitation and purification
• Precipitation with sulfide ions for the removal of MTEs, but it may be dangerous
and the strategy for the soil treatment itself should be carefully designed.
Finally, it is a pity that most of the reported trials have been performed at the lab
scale, since field tests are required for validation and for full assessments. In the next
section, a field test assessing the feasibility of using UF for the reuse of soil leachates
in SF operations for the removal of petroleum hydrocarbons with PAHs as major
components is described.
1 Contaminant Mobilization from Polluted Soils: Behavior and Reuse of Leaching. . .
41