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Stability of Rare‐Earth Disilicates: Ionic Radius Effect
Author(s) -
Galunin Evgeny,
Alba María D.,
Vidal Miquel
Publication year - 2011
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2010.04272.x
Subject(s) - ionic radius , leaching (pedology) , amorphous solid , actinide , chemical stability , ionic bonding , mineralogy , materials science , chemistry , chemical engineering , ion , inorganic chemistry , crystallography , geology , soil water , organic chemistry , soil science , engineering
Rare‐earth (RE) disilicates, of general formula RE 2 Si 2 O 7 , are one of the products of the chemical reaction between RE (elements), which are actinide simulators, and the silicates used in the engineered barrier systems of deep geological repositories (DGPs). The aim of this paper is to establish the stability range of the disilicate phase as function of the nature of the RE (RE=Sc, Lu, or Y) and examine whether this phase would permit RE leaching under experimental conditions simulating those of the DGP. The β‐polymorphs of the RE disilicates were synthesized by the sol–gel method and subsequently submitted to a pH stat leaching test. The rates of RE and Si leaching were measured and the transformation of the crystalline and amorphous phases was examined by X‐ray powder diffraction and nuclear magnetic resonance techniques. The results indicate that the disilicate phases were stable within a wide range of pH, their stability being related to the hydrated ratio of the RE. Disilicate stability increased with the ionic radius of the RE. As a result, the Sc disilicate was stable throughout the pH range tested, whereas Y and Lu disilicate leaching was only observed at pH<4. Thus, it was confirmed that the formation of the disilicate phases could contribute to the confinement of radioactive wastes in engineered barriers.