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Thermodynamic studies of zippeite, a uranyl sulfate common in mine wastes

机译：矿山废料中常见的硫酸铀酰zippeite的热力学研究

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Zippeite is a potassium uranyl sulfate mineral that forms on uranium mine wastes and that may be important in nuclear waste disposal. Little is known about its thermodynamic properties. In this study, we synthesized zippeite, K-3(H2O)(3.3)[(UO2)(4)(SO4)(2)O-3(OH)], and measured its thermodynamic properties. The standard enthalpy of formation of zippeite from the elements, -8655,97 +/- 12.55 kJ/mol, was calculated from the measured enthalpy of dissolution in a high-temperature oxide melt solution calorimeter. Solubility measurements were conducted from both undersaturation and supersaturation in order to constrain the equilibrium state. Using the solubility product (K-sp) obtained from the solubility data, the standard Gibbs free energy of formation of zippeite at 298 K was calculated to be -7783.44 +/- 6.87 kJ/mol. This value, coupled with the standard enthalpy of formation value determined from the calorimetric data, was then used to calculate the standard entropy of formation, - 2926.49 +/- 45.64 J/mol. Our studies yield the first complete set of thermodynamic properties of zippeite, and the results allow us to predict the conditions under which its formation is favorable relative to other uranyl minerals under a wide range of conditions of geologic and engineering interest. (C) 2016 Elsevier B.V. All rights reserved.
机译：Zippeite是一种铀铀酰硫酸钾矿物，形成于铀矿废物上，在核废料处置中可能很重要。对其热力学性质知之甚少。在这项研究中，我们合成了zippeite，K-3（H2O）（3.3）[（UO2）（4）（SO4）（2）O-3（OH）]，并测量了其热力学性质。根据元素在高温氧化物熔体溶液量热仪中测得的溶解焓，可以计算出由元素形成的锆石的标准焓-8655,97 +/- 12.55 kJ / mol。从不饱和和过饱和两个方面进行了溶解度测量，以限制平衡状态。使用从溶解度数据获得的溶解度乘积（K-sp），计算出在298 K时形成的标准吉布斯自由能为-7783.44 +/- 6.87 kJ / mol。然后将该值与根据量热数据确定的标准形成焓值结合起来，用于计算形成的标准熵-2926.49 +/- 45.64 J / mol。我们的研究产生了锆石的第一个完整的热力学性质，结果使我们能够预测在广泛的地质和工程条件下，其形成相对于其他铀酰矿物有利的条件。 （C）2016 Elsevier B.V.保留所有权利。

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