Detection and behavior of iron-cyanide complexes in soils of a former Manufactured Gas Plant site

  • Soils and groundwater on sites of the former Manufactured Gas Plants (MGPs) are contaminated with various complex iron-cyanides (Fe-CN). The aim of this thesis was to evaluate a new method for the CN detection and to investigate the stability and retardation of Fe-CN complexes in soils. This study seeks for enhancing the efficiency of phytoremediation as a proper approach to decontaminate Fe-CN complexes and thus tries to make a contribution to environmental protection. Feasibility of Field Portable Near Infrared (FP NIR) Spectrometry to determine CN concentrations in soil was evaluated in order to develop a rapid and non-destructive in-situ method. The study revealed that FP NIR could be a reliable device for detecting CN concentrations >2400 mg kg−1 in the field and >1750 mg kg−1 after sample preparation in the laboratory, however the limits of detection are too high to replace the traditional methods. The applicability of neutral solution extraction to determine the water soluble CN fraction and the stability of Prussian BlueSoils and groundwater on sites of the former Manufactured Gas Plants (MGPs) are contaminated with various complex iron-cyanides (Fe-CN). The aim of this thesis was to evaluate a new method for the CN detection and to investigate the stability and retardation of Fe-CN complexes in soils. This study seeks for enhancing the efficiency of phytoremediation as a proper approach to decontaminate Fe-CN complexes and thus tries to make a contribution to environmental protection. Feasibility of Field Portable Near Infrared (FP NIR) Spectrometry to determine CN concentrations in soil was evaluated in order to develop a rapid and non-destructive in-situ method. The study revealed that FP NIR could be a reliable device for detecting CN concentrations >2400 mg kg−1 in the field and >1750 mg kg−1 after sample preparation in the laboratory, however the limits of detection are too high to replace the traditional methods. The applicability of neutral solution extraction to determine the water soluble CN fraction and the stability of Prussian Blue under saturated and unsaturated water conditions was studied in a column and batch experiments. Study revealed continuous solubility of Prussian Blue, in acidic and slightly alkaline MGP soils. Dissolution of ferric ferrocyanide under circum-neutral pH and oxic water conditions was proposed to be a function of time, where the released amount is dependent on the soil pH and total CN content. Modeling the long-term release of Fe-CN complexes from the MGP soils revealed two-phase-process. The fast released phase was attributed to the transport process of readily dissolved hexacyanoferrats that is taking place in the liquid phase combined with desorption of CN bound to heterogeneous surfaces that are in direct contact with aqueous phase (outer-sphere complexation). The CN release rates increased with increasing pH, decreased with low initial CN concentration and were retarded by the increase in OM content. The retardation of Fe-CN in soil was investigated in batch and column experiments. Experiments revealed that the excess of the available iron, which induced the formation of the Prussian Blue colloids despite the circum-neutral pH, was a very important factor in decreasing the CN concentration. Additionally, despite the chemical factors influencing the potential reaction with manganese oxides, the physical factors like pore size distribution, variation in the grain size etc. can reduce the CN concentration due to mechanical retention of the vertical colloidal ferric ferrocyanide movement. This study proposes colloidal vertical transport of the solid Fr-CN complexes as a potential alternative process influencing the CN mobility in the circum-neutral pH and under the excess of available iron conditions. The results presented in this thesis revealed limitations of the FP, but advancing the sample pretreatment procedures can improve the feasibility of the spectrometer in detecting CN signal. Long-term extraction with the distilled water provides reliable assessment of the potential environmental hazard due to continuous dissolution of the solid Fe-CN complexes. Inconsistency of the Prussian Blue stability reported in the literature to the one obtained in this study imply usage of the CN contaminated MGP soils, instead of synthetic solutions, to advance the knowledge concerning the solid Fe-CN dissolution behavior. Furthermore, in the non-acidic soils the CN solubility might be influenced by the equilibrium with manganese Fe-CN mineral.show moreshow less

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Metadaten
Author: Sut, Magdalena Maria
URN:urn:nbn:de:kobv:co1-opus4-40631
ISSN:2196-4122
Series (Serial Number):Geopedology and Landscape Development Research Series (4)
Place of publication:Cottbus
Referee / Advisor:Prof. Dr. Raab, Thomas, PD. Dr. habil. Fischer, Thomas, Prof. Dr. Naeth, Anne M.
Document Type:Doctoral Thesis
Language:English
Year of Completion:2014
Date of final exam:2014/05/27
Release Date:2017/01/04
Tag:Cyanide; FIA; NIR; Phytoremediation; Remediation; Soil contamination
GND Keyword:Altlastsanierung; Fließinjektionsanalyse; NIR-Spektroskopie; Phytoremediation; Übergangsmetallcyanide
Institutes:Fakultät 2 Umwelt und Naturwissenschaften / FG Geopedologie und Landschaftsentwicklung
Licence (German):Keine Lizenz vergeben. Es gilt das deutsche Urheberrecht.