Quantification of secondary Fe-phases formed during sorption experiments on chlorites


Quantification of secondary Fe-phases formed during sorption experiments on chlorites

Reuther, H.; Arnold, T.; Krawczyk-Bärsch, E.

During batch sorption experiments of heavy metals on chlorite not only sorption reactions take place, but also reactions of chemical weathering leading to mineral dissolution and the formation of secondary phases, in particular the Fe-oxy-hydroxide ferrihydrite. Despite of its minor mass, ferrihydrite plays a major role in removing aqueous uranium(VI) from solution, because of its large specific surface area which it introduces into the system. To accurately model the sorption and transport on or through geological materials it is necessary to precisely determine the mass of the newly-formed Fe-phase. As the relative mass of the ferrihydrite within the geological matrix was too small, it proved impossible to use powder X-ray diffraction or some other spectroscopic technique, e.g. Raman spectroscopy, for its identification and quantification.
Because of the ability to discriminate different sites and oxidation states of iron, Mössbauer spectroscopy was the method of choice. At first spectra of pure chlorite and pure ferrihydrite were measured. In a second step, simulated spectra were compared with spectra from powders with known chlorite/ ferrihydrite ratios. There was a good agreement between the predicted values and those obtained by the spectrum fit. Finally, the calibration spectra were used to investigate real geological material and to estimate the fraction of the secondary Fe-phase, which has formed during the sorption experiments. Changes of less than 2 % (absolute) could be detected. It should be noted that there is a strong overlap between the different subspectra and that a good counting statistics is required.

  • Hyperfine Interactions 156/157(2004), 439-443
  • Poster
    Int. Conference on the Applications of the Mössbauer Effect, 21.-25.09.2003, Muscat, Oman

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Publ.-Id: 5762