Leaching of Natural and Synthetic Sphene and Perovskite
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LEACHING OF NATURAL AND SYNTHETIC SPHENE AND PEROVSKITE
J.B. METSON, G.M. BANCROFT, S.M. KANETKAR, H.W. NESBITT, W.S. FYFE, Centre for Chemical Physics and Department of Geology, University of Western Ontario, London, Canada N6A 5B7 and P.J. HAYWARD, Atomic Energy of Canada Ltd., Pinawa, Manitoba ROE ILO.
INTRODUCTION Titanates and titanate-based ceramics are being considered as possible hosts for fuel reprocessing wastes in several waste management programs,
being examined, tion process' However,
largely
A variety of titanate based wasteforms is
because of their low leach rates.
including the hot-pressed product of the rutile microencapsula2
and the titanate-based SYNROC assemblage .
for relatively low waste loadings,
and for waste vaults sited in
formations characterised by silica-rich groundwaters, titanosilicate sphene
a wasteform based on the
(CaTiSiO5 ) may offer a number of advantages.
Reference
to the H -H 2 0-CaO-TiO2 -SiO2 activity diagram3 shows sphene to be in,
or close
to, thermodynamic equilibrium with a range of natural groundwaters.
Analysis
of natural sphene samples show the structure has considerable ability to tolerate a wide range of multivalent cations, which can substitute for Ca and Ti in
the lattice.
Rare earth substitutions are particularly common and have 4
been reported at levels of 46 wt% Re 2 03 . Atomic Energy of Canada Limited (AECL)
is
currently investigating the use of
sphene-based glass ceramics to host the wastes produced from possible repro5
cessing of irradiated CANDU* fuels .
We report here on the leaching behaviour
of natural and synthetic sphenes and a CaTiSiOs glass, in
deionized water,
with varying pH and with Ca2+ and silica additions to the leachant. studies on natural and synthetic perovskite in
Leaching
deionized water are also
reported.
EXPERIMENTAL Crystalline sphene samples were obtained from two locations in Ontario, North Crosby township and Lake Clear, Renfrew County. prepared by grinding,
Sphene ceramics were
cold pressing and sintering a crystallised CaTiSiO5
*CANada Deuterium Uranium.
330
frit.
CaTiSiO5 glasses were prepared by melting well mixed silica and titania
with calcium carbonate. 1 hour, then cast in
After loss of C0 2 , the melt was held at 1450WC for
stainless steel molds.
The cast cylinders were annealed
0
at 750 C before cutting and polishing into 3 mm thickness,
10 mm diameter
discs. Perovskite leach results were obtained from a 120 mg single crystal from Magnet Cove Arkansas and a 100 mg synthetic,
flux-grown single crystal
(98%
theoretical density). In all cases, samples were leached in Teflon bottles at a temperature of 900C. Limited sample quantities made the MCC-1 leach test method6 impractical for all but the sphene glass samples, 7
IAEA method
so alternative methods were used.
The
was used for all perovskite leach testing as small surface areas
are involved and solution replacement is sufficient leachant for analysis.
the only practical way of assuring
The method also provides conveni
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