The thermal behavior of melanterite from the Fornovolasco mine (Tuscany, Italy) has been investigated via differential thermal analysis (DTA), thermogravimetry (TG), in situ high-temperature X-ray powder diffraction (XRPD) and Fourier-transform infrared spectroscopy (FTIR). The DTA curve showed endothermic peaks at 70, 100, 260, 500–560 and 660◦C whereas the TG curve evidenced a total mass decrease of ~68%, in keeping with the loss of all H2O and SO4 groups. Rietveld refinements were performed for all the collected patterns in the 25–775◦C range and converged at 1.57 ≤ R (%) ≤ 2.75 and 1.98 ≤ Rwp (%) ≤ 3.74. The decomposition steps FeSO4·7H2O → FeSO4·4H2O (25 ≤ T ≤ 50◦C) → FeSO4·H2O (50 < T ≤ 100◦C) → FeOHSO4 (75 < T ≤ 200◦C) → Fe2(SO4)3 (400 < T ≤ 500◦C) → Fe2O3 (500 < T ≤ 775◦C) were obtained. The high-temperature infrared analysis confirmed that melanterite undergoes a three-step dehydration in the 25–300◦C temperature range. The FeOHSO4 phase is stable over a wide range of temperature and transforms partially to Fe2 (SO4)3 without the formation of Fe2O(SO4)2. The findings highlight a different behavior of the studied sample with respect to the synthetic salt.

In situ high-temperature x-ray powder diffraction and infrared spectroscopic study of melanterite, feso4·7h2o

Lacalamita M.;Ventruti G.;Schingaro E.
2021-01-01

Abstract

The thermal behavior of melanterite from the Fornovolasco mine (Tuscany, Italy) has been investigated via differential thermal analysis (DTA), thermogravimetry (TG), in situ high-temperature X-ray powder diffraction (XRPD) and Fourier-transform infrared spectroscopy (FTIR). The DTA curve showed endothermic peaks at 70, 100, 260, 500–560 and 660◦C whereas the TG curve evidenced a total mass decrease of ~68%, in keeping with the loss of all H2O and SO4 groups. Rietveld refinements were performed for all the collected patterns in the 25–775◦C range and converged at 1.57 ≤ R (%) ≤ 2.75 and 1.98 ≤ Rwp (%) ≤ 3.74. The decomposition steps FeSO4·7H2O → FeSO4·4H2O (25 ≤ T ≤ 50◦C) → FeSO4·H2O (50 < T ≤ 100◦C) → FeOHSO4 (75 < T ≤ 200◦C) → Fe2(SO4)3 (400 < T ≤ 500◦C) → Fe2O3 (500 < T ≤ 775◦C) were obtained. The high-temperature infrared analysis confirmed that melanterite undergoes a three-step dehydration in the 25–300◦C temperature range. The FeOHSO4 phase is stable over a wide range of temperature and transforms partially to Fe2 (SO4)3 without the formation of Fe2O(SO4)2. The findings highlight a different behavior of the studied sample with respect to the synthetic salt.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11586/392873
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