In situ identification of carbonate-containing green rust on iron electrodes in solutions simulating groundwater

Open-circuit potential-time and spectral measurements were performed on iron electrodes in aqueous solutions containing calcium carbonate to simulate groundwater, to which an amount of carbon tetrachloride was added. In the case of a preoxidized iron electrode, the injection of the chlorinated aliphatic hydrocarbon resulted in the formation of carbonate-containing green rust. In situ identification, performed by Raman spectroscopy, was based on bands at ca. 433, 509, and 1053 cm(-1), which were assigned, respectively, to the Fe2+-OH stretching mode of green rust, the Fe3+-OH stretching mode of green rust, and the stretching vibrations of carbonate ions in the interlayer regions of the green rust. The assignment of the Fe2+-OH and Fe3+-OH stretching mode bands was confirmed by parallel experiments using D2O solution. The results of the open-circuit potential-time experiments are in good agreement with literature thermodynamic data for iron in carbonate-containing aqueous solutions.