Regensburg 2010 – wissenschaftliches Programm
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KR: Fachverband Kristallographie
KR 2: Crystallography in nanoscience
KR 2.11: Vortrag
Dienstag, 23. März 2010, 12:45–13:00, H9
Confocal Raman investigation of the zoning in synthetic Ca(CO3,CrO4) crystals — •Alexander M. Gigler1,2, Nuria Sanchez-Pastor1, Guntram Jordan1, and Wolfgang W. Schmahl1,2 — 1Section Crystallography, LMU-München, D-80333 München — 2CeNS, LMU-München, D-80799 München
Due to its high mobility and toxic effects even in very low concentrations, hexavalent chromium (Cr6+) is known as one of the most common environmental contaminants resulting from its widespread use in industrial applications.[1] Here, we present data on the crystallization of CaCO3 in a silica hydrogel medium in the presence of different concentrations of Cr6+.[2,3] Morphological changes in calcite correlate with chromium incorporation in its structure. This incorporation is evidenced by the appearance of new vibrational bands in the Raman spectrum, which are consistent with the substitution of carbonate groups by chromate groups. Therefore, chromium incorporation into calcite could be described as an anionic solid solution with a very limited maximum chromate concentration. By means of Raman microscopy, we observed a zoning of the crystals. The central region was chromium-rich, while pure calcite was present in the outer region due to a depletion of chromium in the gel. Incorporation of chromium into calcite may solve a major environmental problem, since toxic chromium can be rendered harmless.
[1] Katz, Salem: The Biological and Environmental Chemistry of Chromium, VCH, 1994. [2] Henisch: Crystal growth in gels, Dover Publ., 1996. [3] Cruz et al. Geochim. Cosmochim. Acta 73, A252, 2009.