Investigation on the Behaviour of Iron, Manganese, and Phosphate at the Sediment/Water Interface Influenced by an Electric Field
✍ Scribed by Wolf, Claudia ;Fischer, Roland ;Köster, Rainer ;Weidler, Peter
- Publisher
- John Wiley and Sons
- Year
- 2002
- Tongue
- English
- Weight
- 460 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0323-4320
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✦ Synopsis
This study presents laboratory experiments for the development of a new, innovative technology for the fixation of iron, manganese, and phosphate in sediments of stagnant waters. The method is intended for the use in lakes and reservoirs, in which high concentrations of iron and manganese in the hypolimnion lead e. g. to a limitation of utilization of raw water for the drinking water production. High phosphate contents released from the sediment can cause eutrophication. Due to the positioning of an electrode system at the sediment/water interface, a pH and redox barrier is established through electrochemical initiated reactions for the immobilization of iron, manganese, and phosphate. This reaction mechanisms are studied and discussed in a laboratory scale, based on investigations of the sediment, the pore and the overlying water. It is shown that in the process of the electrochemical polarization first iron and manganese are mobilized from the sediment through anodic proton formation. The dissolved species migrate in the electric field to the sediment/water interface with simultaneous oxidation through anodically produced oxygen (redoxbarrier) and are hydrolyzed there. They are accumulated in the pH-barrier as hydroxides/oxyhydroxides/ oxides. Cathodically produced hydroxide ions, which migrate into the opposite direction, form a pH-barrier and prevent the migration of the dissolved iron and manganese ions into the overlying water. Eventually, these reaction processes will generate the accumulation of iron and manganese in sediment layer direct over the anode. After remediation of the sediment for a period of 3 years it was possible to demonstrate the transformation of amorphous ferric hydroxide phases (Fe(OH) 3 ) to crystalline goethite (α-FeOOH) as well as hematite (α-Fe 2 O 3 ). Parallel to the iron and manganese oxidation or precipitation respectively, phosphate from the interstitial, from the water, and from the layer close to the sediment is chemically bound to the iron or aluminium phases.