The thermal stability of sideronatrite and its decomposition products in the system Na2O–Fe2O3–SO2–H2O

摘要: The thermal stability of sideronatrite, ideally Na2Fe3+(SO4)2(OH)·3(H2O), and its decomposition products were investigated by combining thermogravimetric differential analysis, in situ high-temperature X-ray powder diffraction (HT-XRPD) Fourier transform infrared spectroscopy (HT-FTIR). data show that for increasing temperature there are four main dehydration/transformation steps sideronatrite: (a) between 30 40 °C sideronatrite transforms into metasideronatrite after the loss two water molecules; both XRD FTIR suggest this transformation occurs via minor adjustments building block. (b) 120 300 II, a still poorly characterized phase with possible orthorhombic symmetry, consequently to an additional molecule; disappears from assemblage above 175 °C. (c) 315 415 II anhydrous Na3Fe(SO4)3 compound. This step hydroxyl groups involves breakdown [Fe3+(SO4)2(OH)]∞2− chains formation intermediate transient amorphous precursor Na3Fe(SO4)3. (d) T > 500 °C, compound is replaced Na-sulfate thenardite, Na2SO4, plus Fe-oxides, according Na3Fe3+(SO4)3 → 3/2 Na2(SO4) + 1/2 Fe2O3 SOx reaction products. Na–Fe sulfate around 540 For higher temperatures, Na-sulfates decomposes only hematite survives final product. understanding behavior minerals such as related sulfates important environmental point view, due presence these phases evaporitic deposits, soils sediments including extraterrestrial occurrences, technological use materials many industrial applications.