TY - JOUR
T1 - Thermodynamic studies of zippeite, a uranyl sulfate common in mine wastes
AU - Sharifironizi, Melika
AU - Szymanowski, Jennifer E.S.
AU - Sigmon, Ginger E.
AU - Navrotsky, Alexandra
AU - Fein, Jeremy B.
AU - Burns, Peter C.
N1 - Publisher Copyright:
© 2016 Elsevier B.V.
PY - 2016/12/30
Y1 - 2016/12/30
N2 - 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, K3(H2O)3.3[(UO2)4(SO4)2O3(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 (Ksp) 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.
AB - 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, K3(H2O)3.3[(UO2)4(SO4)2O3(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 (Ksp) 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.
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U2 - 10.1016/j.chemgeo.2016.10.022
DO - 10.1016/j.chemgeo.2016.10.022
M3 - Article
AN - SCOPUS:84999711603
SN - 0009-2541
VL - 447
SP - 54
EP - 58
JO - Chemical Geology
JF - Chemical Geology
ER -