Dehydration processes in the meta-autunite group minerals meta-autunite, metasaléeite, and metatorbernite
Dehydration processes in the meta-autunite group minerals meta-autunite, metasaléeite, and metatorbernite
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偏赤铁矿族矿物偏赤铁矿、偏钠铁矿和偏红铁矿的脱水过程
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发表时间：
2005
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通讯作者：
T. Murakami
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作者：
Yohey Suzuki;Tsutomu Sato;H. Isobe;T. Kogure;T. Murakami
摘要我们研究了变奥陶石族铀酰磷酸盐矿物的脱水过程，该矿物由铀酰磷酸盐片层和层间阳离子以及水分子组成。本研究选用了变奥陶石[Ca(UO_2PO_4)_2⋅_6H_2O]、变钠铝石[Mg(U_2PO_4)_2⋅_8H_2O]和变辉石[Cu(U_2PO_4)_2⋅_8H_2O]作为研究对象。通过室温至300℃温控X射线衍射分析，研究了相邻的两个磷酸铀酰晶片之间的层间距随温度的变化，以确定结构不同的脱水相。热重和差热分析(TG/DTA)也在类似于X射线分析的条件下进行，以澄清脱水相的水化状态。透射电子显微镜证实，在相当于300°C的高真空下，铀酰磷酸盐薄片的结构保持不变。变奥陶石、变铝榴石和变辉石通过失去水分子而减小了它们的基面间距。TG/DTA和X射线衍射结果的比较表明，脱水相的基本间距随温度的变化如下：在RT时为8.32ä(单位摩尔比6 H2O)，在RT时为7.31(？H2O)和6.68？(？75°C、120°C和300°C时分别为6.34？(2H2O)和5.81？(1H2O)；水)，40°C时为6.62ä(可能为2 H2O)，160°C时为6.54ä(2 H2O)，300°C时为5.52ä(1 H2O)；变辉岩在RT时为8.61ä(8 H2O)，100℃时为8.07ä(4 H2O)，200°C时为6.58ä(2 H2O)，300°C时为5.60ä(1 H2O)。在相同的实验条件下，X射线衍射仪和TG/DTA显示的脱水过程与前人的研究结果略有不同。我们的结果清楚地证明了变奥陶石族矿物中先前未知的脱水相的存在，它们的基本间距小于6ä，可能具有不同的热力学性质
Abstract We investigated dehydration processes in uranyl phosphate minerals of the meta-autunite group that consist of uranyl phosphate sheets and interlayer cations, and water molecules. Meta-autunite [Ca(UO2PO4)2⋅6H2O], metasaléeite [Mg(UO2PO4)2⋅8H2O], and metatorbernite [Cu(UO2PO4)2⋅8H2O] were selected for our study. The change in basal spacing between two adjacent uranyl phosphate sheets with temperature was examined by temperature-controlled X-ray diffraction (XRD) analysis from room temperature (RT) to 300 °C to determine structurally distinct, dehydrated phases. Thermogravimetric and differential thermal analyses (TG/DTA) were also performed under conditions similar to those used for the XRD analysis to clarify the hydration states of the dehydrated phases. Retention of the structure of the uranyl phosphate sheets under a high vacuum, equivalent to 300 °C, was confirmed by transmission electron microscopy. Meta-autunite, metasaléeite, and metatorbernite decreased their basal spacings by losing water molecules. Comparison of the TG/DTA and XRD results indicates that the changes in basal spacings of the dehydrated phases with temperature are as follows: 8.32 Å (6 H2O per unit formula) at RT, 7.31 (? H2O) and 6.68 Å (? H2O) at 75 °C, 6.34 Å (2 H2O) at 120°C, and 5.81 Å (1 H2O) at 300°C for meta-autunite; 8.29 (8 H2O) and 7.73 Å (? H2O) at RT, 6.62 Å (probably, 2 H2O) at 40 °C, 6.54 Å (2 H2O) at 160 °C, and 5.52 Å (1 H2O) at 300 °C for metasaléeite; and 8.61 Å (8 H2O) at RT, 8.07 Å (4 H2O) at 100 °C, 6.58 Å (2 H2O) at 200 °C, and 5.60 Å (1 H2O) at 300 °C for metatorbernite. The dehydration processes revealed by XRD and TG/DTA under similar experimental conditions are slightly different from those obtained by previous studies. Our results clearly demonstrate the presence of previously unknown dehydrated phases of the meta-autunite group minerals with basal spacings less than 6Å that may have distinct thermodynamic properties