Stability of Peroxide-Containing Uranyl Minerals

Abstract

Minerals containing peroxide are limited to studtite, (UO 2 )O 2 (H 2 O) 4 , and metastudtite, (UO 2 )O 2 (H 2 O) 2 . High-temperature oxide-melt solution calorimetry and solubility measurements for studtite (standard enthalpy of formation at 298 kelvin is –2344.7 ± 4.0 kilojoules per mole from the elements) establishes that these phases are stable in peroxide-bearing environments, even at low H 2 O 2 concentrations. Natural radioactivity in a uranium deposit, or the radioactivity of nuclear waste, can create sufficient H 2 O 2 by alpha radiolysis of water for studtite formation. Studtite and metastudtite may be important alteration phases of nuclear waste in a geological repository and of spent fuel under any long-term storage, possibly at the expense of the commonly expected uranyl oxide hydrates and uranyl silicates.