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Oxydation par les ferrates d’un sol contaminé par du DNAPL en condition saturée : conséquences sur les Composés Aromatiques Polycycliques (HAP et CAP Polaires) : Expérimentations en batch et colonne

Abstract : Soils encountered at former coking plant sites are often impacted by Polycyclic Aromatic Compounds (PAC) inherited from coal tar spillages. The remediation of the source zones is complex, particularly in the aquifer where Dense Non-Aqueous Phase Liquids (DNAPL) occur. This thesis is part of the BIOXYVAL project and focuses on the in situ chemical oxidation of residual tar, remaining in the saturated zone after pumping of the DNAPL. The objectives of this thesis were to study and compare the oxidative efficiency of ferrates with other oxidants to remediate a solid matrix spiked with DNAPL. This work aimed to (i) understand the global degradation mechanisms, (ii) evaluate the possible formation of hazardous oxygenated by-products (O-PAC) and (iii) identify the limitations for an in situ application. Two laboratory studies were conducted: batch experiments, ideal reactor and enclosed system, and column experiments under flow through conditions. Our works highlight (batches) the systematic production and accumulation of O-PAC ketones along oxidation with permanganate and ferrates (oxydo-reductive pathway), whereas oxidants following a radical mechanism do not show accumulation of those by-products. High degradation yields are measured with all oxidants tested (except the Fenton-like and the hydrogen peroxide). Permanganate and ferrates were then studied in column experiments. The limited reactivity of permanganate linked to the stability and low availability of the pollutants resulted on a poor efficiency of the oxidant under continuous flushing. The MnO2 precipitates did not have a high impact on porosity but seemed to reduce the availability of the pollutants during oxidation. Production of O-PAC were measured with lixiviated particles. In the contrary, ferrates injections induced a rapid clogging of the porous media, linked to the formation of ferric particles. Simultaneously, high remobilization of DNAPL drops was observed during the injections. Like permanganate, some O-PAC by-products were detected with lixiviated particles. The results demonstrate the ability of ferrates to degrade PACs from the DNAPL but show that their injection in situ is today impractical, as the technical and economic feasibility are not forthcoming. This work suggests considering the optimization of ferrates application and propose other solutions for the studied site.
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Clotilde Johansson. Oxydation par les ferrates d’un sol contaminé par du DNAPL en condition saturée : conséquences sur les Composés Aromatiques Polycycliques (HAP et CAP Polaires) : Expérimentations en batch et colonne. Géochimie. Université de Lorraine, 2019. Français. ⟨NNT : 2019LORR0244⟩. ⟨tel-02555896⟩

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