Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original Paper

Jakub Plášil

Oxidation-hydration weathering of uraninite: the current state-of-knowledge

Journal of Geosciences, volume 59 (2014), issue 2, 99 - 114

DOI: http://doi.org/10.3190/jgeosci.163

Oxidation-hydration weathering of uraninite, the most common U-bearing mineral in nature, comprises various physical and chemical processes that lead to the destruction of the fluorite-type structure of uraninite where U is present as tetravalent. This results in replacement of uraninite by weathering products containing U in hexavalent form, i.e. as uranyl ion, UO₂²⁺. The final assemblage of the weathering products, uranyl minerals, and their compositions depend on the various factors, namely the composition of the primary minerals and percolating oxidizing fluids that cause the alteration. The knowledge of such processes and stabilities of the uranium minerals is of the great interest namely due to demand for U as the energy source. During the past decade there has been substantial progress in understanding the mineralogy, crystallography and thermodynamics of uranyl minerals and thus a substantially improved understanding of the weathering processes themselves. This review aims to summarize the state-of-art of the current knowledge on uranium-related topics as well and identify some of the important questions that remain unanswered.
The text is dedicated to Jiří Čejka on occasion of his 85^th birthday anniversary. Jiří greatly contributed not only to the spectroscopy and mineralogy of uranyl minerals, but also to the questions pertaining their origin and stability. Many important issues were addressed, even if briefly, in the pioneering book “Secondary Uranium Minerals” by Čejka and Urbanec (1990) which has served, for a long-time, as a guide for beginning uranium mineralogists.