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Leaching of neptunium from garnet- and murataite-based ceramics
-
S. Perevalov
Published/Copyright:
September 25, 2009
Leach resistance of neptunium-doped garnet- and murataite-based ceramics with calculated compositions (in wt.%: 38 Fe2O3, 21 Gd2O3, 16 NpO2, 15 ZrO2, 10 CaO and 55 TiO2, 10 Mn2O3, 10 CaO, 10 NpO2, 5 ZrO2, 5 Al2O3, 5 Fe2O3 respectively was studied. The samples were prepared from pre-activated oxide mixtures by sintering/melting in platinum ampules at 1450 °C. The murataite ceramic is composed of predominant murataite structure phases with five- (5C) and eight-fold (8C) elementary fluorite unit cell and minor rutile (≤5% of total bulk). The garnet-based sample is a polyphase ceramic and consists of major garnet phase, interstitial Fe2O3 and Ca-Fe-phase, and rare grains of (Ca,Zr,Np)O2-phase (cubic solid solution) included in the larger garnet grains. The edge of the garnet grains is enriched with Np as compared with their rim by approximately 1.5−2 times. Np leach-rates were measured using an ANS_16.1 test. Np leach rate from the murataite-based ceramic reduced significantly from 2.44×10-6 g/(cm2 day) within the first 2 hours of leaching to 3.41×10-9 g/(cm2 day) at 672 hours of leaching. At the same time for the garnet-based ceramic corresponding values were 1.49×10-5 g/(cm2 day) and 1.77×10-6 g/(cm2 day), respectively. Higher leach rates at early periods are due to the dissolution of trace phases and Np release from defect surfaces. Leach rate values at later periods of leaching are characteristic of the “equilibrium” leach rate of the element (Np). Much higher Np leaching from the garnet ceramic may be due to 1) higher concentration of Np at the edge of the garnet grains with a relatively low chemical durability; 2) leaching of Np traces from highly soluble minor Np-Zr-rich phase.
Received: 2005-8-15
Accepted: 2006-3-26
Published Online: 2009-9-25
Published in Print: 2006-11-1
© Oldenbourg Wissenschaftsverlag
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