Layered Double Hydroxides with Intercalated Permanganate and Peroxydisulphate Anions for Oxidative Removal of Chlorinated Organic Solvents Contaminated Water

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.

Fluorescing Layered Double Hydroxides as Tracer Materials for Particle Injection during Subsurface Water Remediation

“…Calculations were based the on Frauenhofer and Mie theory [41,42]. All used methods are described in detail in previously published studies by the authors [8,14].…”

“…After completing the addition, the samples were aged in the parent solution for 1 day (Mg,Al-LDH) or six days (Ca,Al-LDHs) at room temperature under constant magnetic stirring. Based on the literature [32][33][34][35][36] and our previous results about the synthesis of the materials studied here [8,14,[37][38][39], different aging times were selected to optimize the procedure. The literature confirms the successful synthesis of rather well-formed hydrotalcite-like structures using aging times shorter than 24 h [8,32,33].…”

“…In recent years, the removal of chlorinated organic solvents, which can deeply penetrate aquifers, accumulating in the sub-surface as lenses of highly hazardous and toxic pollutants [1,2] from groundwater and soil, has become a major problem. Many laboratory-as well as field-scale studies exist considering different reaction pathways between reactants and the target contaminant, such as immobilization of contaminants [3][4][5][6][7][8][9] or in situ degradation of target contaminants into less hazardous or even non-hazardous substances [10][11][12][13][14][15][16][17][18]. Thereby, a major difficulty is the monitoring of reactants during the injection and after secondary mobilisation by groundwater flow.…”

“…The study presented here is focussed on the development of traceable particles by combining fluorescein, a commonly used, cheap, non-toxic, and non-harmful fluorescent dye, with hydrotalciteand hydrocalumite-like Layered Double Hydroxides. Please refer to previously published studies of the authors for a detailed description of the structure of the materials used here [8,14]. In recent years, Layered Double Hydroxides (LDHs) with intercalated fluorescent dyes have been widely studied and commonly synthesised via ion exchange [27][28][29] and reaction-diffusion [30] routes.…”

“…Further studies were carried out to compare the fluorescent LDHs presented here with previously studied reactive LDHs, which proved to be able to absorb and thus immobilize [8] or degrade [14] chlorinated organic solvents from aqueous solutions. To assess the potential traceability of the synthesised fluorescent LDHs in the subsurface, tests were carried out using an OIP-G system (Geoprobe Systems ® ), which is a novel tool developed for inducing fluorescence on contaminations caused by large polyaromatic hydrocarbon like creosote, coal tars, oils and fuels [26].…”