Abstract
In the present PhD project, novel synthesis and modifications of layered Fe(II)-Fe(III) hydroxides (green rusts, GRs) were investigated with focus on improved dehalogenation of carbon tetrachloride by using modified green rusts and/or altered reaction conditions. The Ph.D. project has comprised:
1. New strategy for synthesis of green rusts that enables upscaling. Larger scale application of GRs requires upscaling, including fast and reproducible production of GRs. In this study, we have adopted a homogenous precipitation approach where glycine is used as a buffering and complexing agent during sulphate green rust formation by aerial oxidation of FeII or co-precipitation by adding Fe(III) salt to Fe(II). In comparison with traditional green rust synthesis, pure GRs were synthesized in minutes.
2. Enhanced dehalogenation of CT by GR in presence of selected amino acids. In presence of glycine, chloroform (CF) formation is effectively suppressed: less than 10% of CT is transformed to CF, and more than 90% of dehalogenation products are found to be formic acid and carbon monoxide in presence of 60 mM glycine; while a 80% of CF recovery was obtained without amino acids addition.
3. A “switch” mechanism for GR reactivity. As GR easily become oxidized by oxygen and nitrate in the subsurface it may be useful to be able to block the oxidation. In order to preserve the reactivity of GR for target contaminated zone area, a reactivity control of GR is necessary until these reactive solids disperse in the target area. With this perspective, the concept of a switch for GR reactivity is proposed. The adsorption of silica on GR surface is able to slow down and even stop nitrate reduction and CT dehalogenation by GR since silica bind to the reactive sites, and thus the GR reactivity is switched off. Then, by introducing glycine to turn on the CT dehalogenation by GR.
1. New strategy for synthesis of green rusts that enables upscaling. Larger scale application of GRs requires upscaling, including fast and reproducible production of GRs. In this study, we have adopted a homogenous precipitation approach where glycine is used as a buffering and complexing agent during sulphate green rust formation by aerial oxidation of FeII or co-precipitation by adding Fe(III) salt to Fe(II). In comparison with traditional green rust synthesis, pure GRs were synthesized in minutes.
2. Enhanced dehalogenation of CT by GR in presence of selected amino acids. In presence of glycine, chloroform (CF) formation is effectively suppressed: less than 10% of CT is transformed to CF, and more than 90% of dehalogenation products are found to be formic acid and carbon monoxide in presence of 60 mM glycine; while a 80% of CF recovery was obtained without amino acids addition.
3. A “switch” mechanism for GR reactivity. As GR easily become oxidized by oxygen and nitrate in the subsurface it may be useful to be able to block the oxidation. In order to preserve the reactivity of GR for target contaminated zone area, a reactivity control of GR is necessary until these reactive solids disperse in the target area. With this perspective, the concept of a switch for GR reactivity is proposed. The adsorption of silica on GR surface is able to slow down and even stop nitrate reduction and CT dehalogenation by GR since silica bind to the reactive sites, and thus the GR reactivity is switched off. Then, by introducing glycine to turn on the CT dehalogenation by GR.
| Original language | English |
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| Publisher | Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen |
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| Publication status | Published - 2016 |