THERMOCHEMISTRY OF YAVAPAIITE KFE(SO4)2: FORMATION AND DECOMPOSITION
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dc.contributor.author | Forray F.L. | |
dc.contributor.author | Drouet C. | |
dc.contributor.author | Navrotsky A. | |
dc.date.accessioned | 2023-11-26T02:22:39Z | |
dc.date.available | 2023-11-26T02:22:39Z | |
dc.date.issued | 2005 | |
dc.identifier | https://www.elibrary.ru/item.asp?id=14581372 | |
dc.identifier.citation | Geochimica et Cosmochimica Acta, 2005, 69, 8, 2133-2140 | |
dc.identifier.issn | 0016-7037 | |
dc.identifier.uri | https://repository.geologyscience.ru/handle/123456789/41995 | |
dc.description.abstract | Yavapaiite, KFe(SO4)2, is a rare mineral in nature, but its structure is considered as a reference for many synthetic compounds in the alum supergroup. Several authors mention the formation of yavapaiite by heating potassium jarosite above ca. 400°C. To understand the thermal decomposition of jarosite, thermodynamic data for phases in the K-Fe-S-O-(H) system, including yavapaiite, are needed. A synthetic sample of yavapaiite was characterized in this work by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermal analysis. Based on X-ray diffraction pattern refinement, the unit cell dimensions for this sample were found to be a = 8.152 ± 0.001 Å, b = 5.151 ± 0.001 Å, c = 7.875 ± 0.001 Å, and β = 94.80°. Thermal decomposition indicates that the final breakdown of the yavapaiite structure takes place at 700°C (first major endothermic peak), but the decomposition starts earlier, around 500°C. The enthalpy of formation from the elements of yavapaiite, KFe(SO4)2, ΔH°f = −2042.8 ± 6.2 kJ/mol, was determined by high-temperature oxide melt solution calorimetry. Using literature data for hematite, corundum, and Fe/Al sulfates, the standard entropy and Gibbs free energy of formation of yavapaiite at 25°C (298 K) were calculated as S°(yavapaiite) = 224.7 ± 2.0 J.mol−1.K−1 and ΔG°f = −1818.8 ± 6.4 kJ/mol. The equilibrium decomposition curve for the reaction jarosite = yavapaiite + Fe2O3 + H2O has been calculated, at pH2O = 1 atm, the phase boundary lies at 219 ± 2°C. | |
dc.title | THERMOCHEMISTRY OF YAVAPAIITE KFE(SO4)2: FORMATION AND DECOMPOSITION | |
dc.type | Статья | |
dc.identifier.doi | 10.1016/j.gca.2004.10.018 |
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