Abstract
The contamination by chlorinated organic solvents is a worldwide problem as they can deeply penetrate aquifers, accumulating in the sub-surface as lenses of highly hazardous pollutants. In recent years, so called in situ oxidation processes have been developed to remediate chlorinated organic solvents from groundwater and soil by injecting solutions of oxidising agents such as permanganate or peroxydisulphate. We here present modified layered double hydroxides (LDHs) with intercalated oxidising agents that might serve as new reactants for these remediation strategies. LDHs might serve as support and stabiliser materials for selected oxidising agents during injection, as the uncontrolled reaction and consumption might be inhibited, and guarantee that the selected oxidants persist in the subsurface after injection. In this study, LDHs with hydrotalcite- and hydrocalumite-like structures intercalated with permanganate and peroxydisulphate anions were synthesised and their efficiency was tested in batch experiments using trichloroethene or 1,1,2-trichloroethane as the target contaminants. All samples were characterised using powder X-ray diffraction, thermal analysis coupled with mass spectrometry to directly analyse evolving gases, and Fourier-transform infrared spectroscopy. Additionally, particle size distribution measurements were carried out on the synthesised materials. Results of the batch experiments confirmed the hypothesis that oxidising agents keep their properties after intercalation. Permanganate intercalated LDHs proved to be most efficient at degrading trichloroethene while peroxydisulphate intercalated Ca,Al-LDHs were the most promising studied reactants degrading 1,1,2-trichloroethane. The detection of dichloroethene as well as the transformation of the studied reactants into new LDH phases confirmed the successful degradation of the target contaminant by oxidation processes generated from the intercalated oxidising agent.
Highlights
Decontamination of groundwater and soils from chlorinated organic solvents, formerly used as degreasing agents, cleaning solutions, paint thinners, or even pesticides, has become a major issue due to the increasing concern about the negative effect of these chemicals on health worldwide [1,2].Minerals 2020, 10, 462; doi:10.3390/min10050462 www.mdpi.com/journal/mineralsChlorinated organic solvents belong to the group of dense non-aqueous phase liquids (DNAPLs), which deeply penetrate aquifers, accumulating in the sub-surface [2,3] and forming lenses of recalcitrant, highly hazardous pollutants [4]
Total reaction times, estimated by comparing the curve progression of the experimental solution with that of the blank solution, varied regarding the amount of layered double hydroxides (LDHs) used in each experiment; the reaction seemed to be finished after 6 h using 2 g LDH and after 24 h using 1 g LDH
Contrary to the Ca,Al-LDHs, intercalated Ca,Al-LDH may have a large potential to be used for in situ chemical oxidation processes no significant degradation of 1,1,2-TCA was observed for the magnesium containing counterpart addressing 1,1,2-TCA
Summary
Decontamination of groundwater and soils from chlorinated organic solvents, formerly used as degreasing agents, cleaning solutions, paint thinners, or even pesticides, has become a major issue due to the increasing concern about the negative effect of these chemicals on health worldwide [1,2].Minerals 2020, 10, 462; doi:10.3390/min10050462 www.mdpi.com/journal/mineralsChlorinated organic solvents belong to the group of dense non-aqueous phase liquids (DNAPLs), which deeply penetrate aquifers, accumulating in the sub-surface [2,3] and forming lenses of recalcitrant, highly hazardous pollutants [4]. Decontamination of groundwater and soils from chlorinated organic solvents, formerly used as degreasing agents, cleaning solutions, paint thinners, or even pesticides, has become a major issue due to the increasing concern about the negative effect of these chemicals on health worldwide [1,2]. It needs to be considered that the reactants degrading contaminants are not fixed in the soil, but can be moved and transported by water flow [9,10,11]. The physical or chemical properties might be different in different soils, further reaction of the selected reactants under the new conditions needs to be taken into account. The retention procedures could be insufficient if such a further reaction takes place as the retained contaminant could be released under the new conditions and so the final fact would (and ) be to transfer the problem from one point to another
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