New Mineralogical Data on Uranophane and β-Uranophane; Synthesis of Uranophane

Fabien Cesbron, Philippe Ildefonse and Marie-Claude Sichere
LEMI-ESEM, Université d'Orléans, B.P. 6747, 45069 Orléans Cedex 2—LPCE-CNRS, Orléans, France
Laboratoire de Minéralogie-Cristallographie, associé au CNRS, Université P. et M. Curie, Tour 16, 4 place Jussicu, 75252 Paris Cédex 05, France

Abstract: Uranyl-silicates are widespread minerals in oxidised parts of various uranium deposits, and they frequently contain associations of the polymorphic forms of uranophane. In several recent works devoted to the study of uranium deposits as natural analogues of high-level nuclear waste repository (HLNWR), uranophane is frequently mentioned but without determination of the exact polymorphic species. The existence of two polymorphs presenting different stabilities has to be taken into account when considering the long-term behaviour of these minerals and the use of thermodynamic models for predicting the radionuclide migration in HLNWR. We present here new crystallographic data on beta-uranophane, and preliminary results of synthesis experiments of uranyl silicates. XRD patterns and calculated parameters of beta-uranophane from a Mexican U-deposit are presented. Synthesis experiments succeeded in crystallising uranophane (alpha form) at different pH, Si-, Ca- and Na activities, but beta-uranophane was never obtained. The controlling physico-chemical parameters responsible for the occurrence of these two polymorphic forms are still unknown.

Keywords: uranophane • β-uranophane • synthesis • Mexico

Mineralogical Magazine; June 1993 v. 57; no. 387; p. 301-308; DOI: 10.1180/minmag.1993.057.387.12
© 1993, The Mineralogical Society
Mineralogical Society (