Zirconolites from Sri Lanka, South Africa and Brazil
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ZIRCONOLITES FROM SRI LANKA,
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SOUTH AFRICA AND BRAZIL
RODNEY C. EWING AND RICHARD F. HAAKER Department of Geology, University of New Mexico, Albuquerque, NM 87131 THOMAS J. HEADLEY AND PAUL Fi HLAVA Sandia National Laboratories , Albuquerque, NM 87185 ABSTRACT Zirconolites, CaZrTi 2 O7 , from Sri Lanka and Pala Bora, South Africa, and a calzirtite, CaZr 3 TiO9 , from Jacupiranga, Brazil, were examined using the electron microprobe, x-ray (annealing study), transmission electron diffraction electron microscopy and optical microscopy, scanning all three microscopy. The x-ray data indicate that zirconolites are metamict. Both Sri Lanka zirconolites are amorphous to the limits of resolution of the electron microscope (%lO A). The Pala Bora zirconolite is largely isolated domains (50-200 A) of amorphous but contains crystalline material which may be the result of post-metamict recrystallization and alteration. The only other significant evidence for chemical alteration was the lower Th concentration (1-2 weight percent) and slightly lower analytic totals for the rims of the Sri Lanka zirconolites. Upon annealing at 11300C for 5 hours, all three zirconolites recrystallized as microcrystalline aggregates. Refined unit cell parameters and volumes are consistent with published data for synthetic zirconolites. Both Sri Lanka zirconolites contain microvoids, spherical in shape, and 200 Angstroms to 2 microns in size. This porosity may be the result of helium arising from the decay of U and Th. The accumulation calzirtite was highly crystalline, exhibited no porosity, and was unchanged by the annealing treatment. INTRODUCTION Zirconolite, CaZrTiO. , is the principal host for actinide and rare earth ceramic, elements in SYNROC and the Sandia Titanate, proposed titanate, high-level radioactive waste forms (1,2,3). A critical concern has been the evaluation of the long-term stability of radioactive waste forms, particularly as a function of radiation and alteration effects in the presence of water. leaching expeygnents, doping experiments in which Accelerated hydrothermal , and neutron irradiations have been highly active radionuclides, such as Pu used to simulate long-term effects (4,5). Recent work has concentrated on using naturally occurring analogues to phases in SYNROC as benchmarks for comparison to the results of accelerated laboratory experiments (6,7). This study presents the results of detailed electron microprobe and x-ray diffraction analysis, as well as careful characterization using transmission electron microscopy (TEM) of three samples of zirconolite and a and scanning electron microscopy (SEM), single specimen of calzirtite, CaZr 3 TiO9 , a mineral species closely related to zirconolite. The zirconolite samples were obtained from the following sources: Paris (#111.35 from Sri Museum National D'Histoire Naturelle Mineralogie, Lanka); United States National Museum, Washington D. C. (#B20392 from Walawada, This work was support~gd by the U.S. Department DE-AC-04-76-D P00789. A U.S. DOE facility.
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