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Formation, Oxidation and Alteration of Ianthinite

Published online by Cambridge University Press:  25 February 2011

Robert J. Finch  and
Rodney C. Ewing
Robert J. Finch
Affiliation:
Department of Earth and Planetary Sciences, University of New Mexico Albuquerque, New Mexico 87131 U.S.A.
Rodney C. Ewing
Affiliation:
Department of Earth and Planetary Sciences, University of New Mexico Albuquerque, New Mexico 87131 U.S.A.
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Abstract

Ianthinite, UO2.86·1.5H2O, is a weathering product of uraninite, UO2+x, and has been reported as a corrosion product of UO2. Ianthinite alters to schoepite, UO3·2H2O, or studtite, UO4·2-4H2O, in water. The structures of ianthinite, schoepite and studtite are unknown, but their unit cell parameters differ significantly, and transformations are likely reconstructive.

XRD powder data for ianthinite and becquerelite are similar, and they are probably iso-structural; U4+, as U(OH)22+, replaces Ca2+ in the interlayer. The proposed formula is

U(OH)22+[(UO2)6O4(OH)6]·6H2O.

Oxidation in air, has been reported to form schoepite; however, in the absence of water, the oxidation of ianthinite,

U(OH)22+[(UO2)6O4(OH)6]·6H2O + 1/2 O2 => (UO2)2+[(UO2)6O4(OH)6]·7H2O ,

shows that epi-ianthinite is structurally distinct from schoepite. The oxidation of fine-grained material is rapid, and the color change — from dark purple to yellow — is dramatic. The acicular habit of ianthinite is preserved during oxidation, and acicular “schoepite” is observed in nature, as well as in leaching experiments on spent fuel. Possible substitution of Pu4+ for U4+ suggests that Pu-ianthinite may control Pu solubility in oxidizing, U-saturated solutions.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 333: Symposium V – Scientific Basis for Nuclear Waste Management XVII , 1993 , 625
Copyright
Copyright © Materials Research Society 1994

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