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THERMAL DEHYDRATION OF NATURAL HYDROUS FERRIC SULFATE Fe(SO4)(OH)?2H2O
Abstract
Thermal dehydration of a natural hydrous ferric sulfate Fe(SO4)(OH)?2H2O was studied using x-ray-phase and thermal analyses. This mineral was found in the hypergenesis zone of the Khangalas gold deposit, Eastern Yakutia, Russia. A comparative analysis of the sample with known hypergenic hydrous ferric sulfates with a similar Fe2O3:SO3 ratio close to 1:1 was performed. The dissimilarities between the founded mineral and its possible polymorphs ? butlerite and parabutlerite are identified. The mineral is less stable and begins to break down at 60 °C. Water loss in the first two endothermic peaks (120 and 255 °C) is about 16%, which is close to the loss of two H2O molecules. At 120 °C a new previously unknown phase X is formed, which persists to temperatures of ~255-280 °C. No analogs to the X ray pattern of this phase could be found. The interplanar distances and intensities of its main lines are as follows: d (I) -9.3(100), 4.66(25), 3.53(42), 3.32(10), 2.144(8) A. It is likely that this phase is a hydrous sulfate Fe(SO4)(OH)·0.5H2O, that has not yet been identified in nature. Completely water and OH group disappear by 450 °C, while the mass loss is ~24 %. For temperatures of ~300 °C and higher, the dehydration processes for all the minerals of the studied group are almost identical. When further heating occurs, the mineral is completely dehydrated and anhydrous ferrous sulfates are formed. The final stage of the decomposition of anhydrous ferrous sulfate after heating the sample to 700 °C ? hematite formation.
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References11
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