Processes leading to reduced and oxidised carbon compounds during corrosion of zero-valent iron in alkaline anoxic conditions

• Published in: Chemosphere (Oxford) Vol. 250; p. 126230
• Main Authors: Guillemot, Typhaine, Cvetković, Benjamin Z., Kunz, Dominik, Wieland, Erich
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.07.2020
• Subjects: aerobic conditions; alkanes; alkenes; anaerobic conditions; Carbon - chemistry; carbon 14; Carbon Radioisotopes; Carboxylic acids; Corrosion; exposure duration; Fischer-Tropsch mechanism; gases; Hydrocarbons; iron; Iron - chemistry; Iron corrosion; irradiation; liquids; Organic Chemicals; Oxidation-Reduction; powders; radioactive waste; Radioactive waste management; sodium hydroxide; steel; Steel - chemistry; Water Pollutants, Chemical - chemistry; Hydrocarbons; Iron corrosion; Carboxylic acids; Fischer-Tropsch mechanism; Radioactive waste management
• DOI: 10.1016/j.chemosphere.2020.126230
• ISSN: 0045-6535; 1879-1298

The Swiss disposal concept foresees that carbon-14 (14C) is predominantly released from irradiated steel disposed of in a cement-based repository for low- and intermediate-level radioactive waste. To predict how 14C migrates in the cementitious environment of the repository near field and subsequently in the host rock, knowledge about the carbon speciation during anoxic steel corrosion in alkaline conditions is therefore essential. To this end, batch-type corrosion experiments with carbon-containing zero-valent iron (ZVI) powders subject to oxidative pre-treatments were carried out in NaOH solution at pH 11 and 12.5. Alkanes and alkenes (C1–C7) were identified in the gas phase and produced on the iron surface by a Fischer-Tropsch type mechanism. The kind of oxidative pre-treatment has an effect on the production rate of hydrocarbons (HCs). In the liquid phase, carboxylic acids were identified and produced during the oxidative pre-treatment of the ZVI powders. They are released instantaneously from the oxide layer upon contact with the alkaline solution. The kind of oxidative treatment and the exposure time to oxic conditions directly influence the amount of carboxylic acids accommodated in the oxide layer. •Carbon speciation is determined during iron corrosion in alkaline conditions.•Hydrocarbons (gaseous) and carboxylic acids (aqueous) are the main carbon species.•Hydrocarbons are formed by a Fischer-Tropsch process.•Carboxylic acids are generated due to exposure of iron to oxidative treatment.