In Situ Identification of Carbonate-Containing Green Rust on Iron Electrodes in Solutions Simulating Groundwater

Abstract

Open-circuit potential-time and spectral measurements were performed on ironelectrodes in aqueous solutions containing calcium carbonate to simulateground-water, to which an amount of carbon tetrachloride was added. In the case of apreoxidized iron electrode, the injection of the chlorinated aliphatic hydrocarbonresulted in the formation of carbonate-containing green rust. In situ identification,performed by Raman spectroscopy, was based on bands at ca. 433, 509, and1053 cm−1, which were assigned, respectively, to the Fe2+—OH stretching modeof green rust, the Fe3+—OH stretching mode of green rust, and the stretchingvibrations of carbonate ions in the interlayer regions of the green rust. Theassignment of the Fe2+—OH and Fe3+−OH stretching mode bands was confirmedby parallel experiments using D2O solution. The results of the open-circuitpotential-time experiments are in good agreement with literature thermodynamic datafor iron in carbonate-containing aqueous solutions.