57Fe Mössbauer, XRD, FT-IR, FE SEM Analyses of Natural Goethite, Hematite and Siderite

Abstract

Natural goethite, hematite and siderite were analysed with 57 Fe Mössbauer, XRD and FT-IR. FE SEM images of samples were also taken. The Mössbauer spectra of limonite (α-FeOOH · nH2O) from Budapest (Hungary), Ljubija (Bosnia and Herzegovina) and Korçё (Albania) showed the same type of spectrum, indicating low crystallinity and broad particle size distribution. All goethite particles from these three locations were one-dimensional (1D), but with different nano/microstructures. A very early precursor of limonite from Budapest and Ljubija locations was assigned to FeS2 (pyrite and/or marcasite) which oxidised upon ventilation (oxygenation) under hydrogeothermal conditions, thus producing FeSO4 and Fe2(SO4)3. In the next step limonite deposits were formed. The similarity between this limonite formation under hydrogeothermal conditions and the chemical precipitation of goethite from FeSO4 or Fe2(SO4)3 solutions at laboratory level was briefly discussed. The deposition of lateritic goethite at the Korçë location is presumed to be due to the chemical weathering (tropical conditions) of ultramafic rocks. Under the same conditions and a proper pH the transformation of goethite to hematite is possible. Alternatively, the oxidation of Fe 2+ in magnetite and its transformation to hematite via maghemite (γ-Fe2O3) as an intermediate could have taken place. The Mössbauer spectrum of siderite from the Ljubija location showed a quadrupole doublet with asymmetric spectral lines. This asymmetry could be assigned to the Goldanskii-Karyagin effect, however, the contribution of the crystallite texture to this asymmetry cannot be excluded. Hematite and a small fraction of siderite at the Vareš location (Bosnia-Herzegovina) are of metasomatic origin deposited in limestone that now form a series of greatly metamorphosed sedimentary rocks. Hematite particles were deposited in the form of laminates (2D).

Goethite (α‐FeOOH) photocatalytic activity at natural concentrations by the addition of H2O2 at neutral pH and the simultaneous presence of fluoride and bicarbonate

“…Goethite was synthesized in the laboratory to be used to simulate the iron (hydr)oxide often present in groundwater and was characterized by several techniques to confirm its structure. The XRD pattern of synthesized goethite (Figure 1a) exhibited peaks at Mössbauer measurements (Figure 3a) showed an asymmetric sextet with broadened lines, a hyperfine magnetic field (B hf ) around 33 T, and a quadrupole splitting (QS) of 0.45 mm s −1 matching very well goethite structure [25][26][27]. Broadened lines and asymmetry could be related to poor crystallinity, as was confirmed by XRD patterns and the presence of Fe(II) [28], respectively, the latter coming from synthesis precursor FeSO 4 .…”

“…Mössbauer measurements (Figure 3a) showed an asymmetric sextet with broadened lines, a hyperfine magnetic field (B hf ) around 33 T, and a quadrupole splitting (QS) of 0.45 mm s −1 matching very well goethite structure [25–27]. Broadened lines and asymmetry could be related to poor crystallinity, as was confirmed by XRD patterns and the presence of Fe(II) [28], respectively, the latter coming from synthesis precursor FeSO 4 .…”

“…Goethite was synthesized in the laboratory to be used to simulate the iron (hydr)oxide often present in groundwater and was characterized by several techniques to confirm its structure. The XRD pattern of synthesized goethite (Figure 1a) exhibited peaks at 21.22°, 33.16°, 34.71°, 36.67°, 41.27°, 53.29°, and 59.09° ascribed to the presence of α‐FeOOH (JCPDS‐29‐0713) [24–27].…”

The Characterization and SCR Performance of Mn-Containing α-Fe2O3 Derived from the Decomposition of Siderite

“…The SEM images of the natural siderite and thermally treated samples are displayed in Figure 4. The bulk siderite with a relatively even and smooth surface can be observed in Figure 4a [46]. Moreover, there were much fewer siderite aggregated particles with irregular shape on the surface of the bulk siderite [47].…”

Natural and engineered clays and clay minerals for the removal of poly- and perfluoroalkyl substances from water: State-of-the-art and future perspectives

“…Classification of soil clays and clay minerals (adapted from [66] and [67]). Images of chlorite and allophane, and hematite are reproduced from the 'Images of Clay Archive' of the [68] and [69], and [70], respectively). Variable charge under varying pH values in oxides and phyllosilicates;…”