Mössbauer study of illitic clays containing iron-rich impurities

Abstract

The iron mineralogy of nineteen illitic clays from eastern Bavaria was studied by Mossbauer spectroscopy and X-ray powder diffraction. Mossbauer spectra of the <2 μm fraction were taken at RT, 120 K and 4.2 K. The clays contain both paramagnetic Fe3+ and Fe2+. Superparamagnetic oxides are frequently present. The Fe2+ quadrupole splitting and the ratio of Fe3+ at 4.2 K to Fe2+ at 120 K are correlated and define two groups distinguished by their mineral content. The samples were heated systematically for 48 h up to 1250°C in steps of 50°C. One clay which is rich in chlorite and Fe(II) was studied in detail after firing in air and following a reduction for 3 h at 800°C with charcoal. The transformations of the mineral phases with temperature as shown by X-ray diffraction are also evident in the Mossbauer spectra.