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ORNL-2749.txt
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—~
G
3 4Y45kL 03L1L388 2
ORNL-2749
Reactors-Power
TID-4500 (14th ed.)
SOLUBILITY RELATIONS AMONG RARE-EARTH FLUORIDES
IN SELECTED MOLTEN FLUORIDE SOLVENTS
DOCUME‘NT COLLECTION g
,, I.IBRARY LOAN COPY
DO NOT TRANSFER TO ANOTHER PERSON
If you wish someone else ATy thns A
LT TY TS R LR s L3
" _cm_d__ Ty hbr_c_ry IR Tede Lol
OAK RIDGE NATIONAL LABORATORY
operated by
UNION CARBIDE CORPORATION
for the
U.S. ATOMIC ENERGY COMMISSION
o
e St
e ST
Off[cg of Techmcol Servu:es .
Deporfmenf of. Commerce_, S
Woshlngfon 25 ‘D.C.
.
_LE(;AL 'N'oflcs =
This report was prepared asan occount of Government sponsored ‘work. Neliher fhe Umfed Sfofes, ‘
nor the Commission, nor: any person. uchng on behul! of the Cammlss:on. . -
A. Makes any warranty. or represenfohon expressed or lmplled wflh respeci to 1|'le accurucy, .
completeness, or usefulness of the.. |nformahon contained. m fl'ns report, B thuf the use ‘of
any information, apparafus,, mafhod Jor process dlsclosed |n thls report moy not. lnfrlnge'
privately owned rights; or
B. Assumes any liabilities with respecf to the use of or for dumages resu[h'ng from 1'|'|e use of
any |nformahon, apparatus, methed, of process dusclosed in this report.
As used in the above, "person octing on behalf of the Commission"’ |no|ud_fes .un;y em.p'lo)'ree or
contractor of the Commission, or employee of such contractor, to the extent that such employee’
or contractor of 1|1e Commission, or employee of such contractor . prepares, diseeminotes, or
- provides access to, any information’ pursuanf to his employment or. contract with the Commcssmn,
or his employment with such contractor.
e
i
B
Troe AN T
T it Ty B Bt ewisfins Db WS tTP BTG
St ok e
ORNL-2749
Reactors-Power
TID-4500 (14th ed.)
Contract No. W-7405-eng-26
REACTOR CHEMISTRY DIVISION
SOLUBILITY RELATIONS AMONG RARE-EARTH FLUORIDES
IN SELECTED MOLTEN FLUORIDE SOLYENTS
-DATE ISSUED
0CT 131959
OAK RiDGE NATIONAL LABORATORY
Ook Ridge, Tennessee
operated by :
UNION CARBIDE CORPORATION s
for the [
U.S. ATOMIC ENERGY COMMISSION ' MARTIN MAR
(R
T . C e - . . . - e
Y T R A T e T - : .
.
.
+
vt
. .t
: a
o
’ .
.
4
1
.
'
. .
CONTENTS
.....................................................................................................................................................
..............................................................................................................................................
Results
----------------------------------------------------------------------------------------------------------------------------------------------------
Solubilify of Single Rare-Earth Fluorides
------------------------------------------------------------------------------------
Solubility of Rare-Earth Fluorides as Functions of Composition .......c.uienenmnenincninnns
Solubilities of Mixed Rare-Earth Fluorides in Lil:-Ber-UI:4 (62.8-36.4-0.8
Mole %)
..........................................................................................................................................
Additional Data Pertinent to a Solid-Solvent Extraction of Rare-Earth Poisons.....cccceuuunnne.
Appendix —~ Solubility Data for Cel:3 in Yarious Solvents
--------------------------------------------------------------
SOLUBILITY RELATIONS AMONG RARE-EARTH FLUORIDES IN SELECTED
MOLTEN FLUORIDE SOLVENTS
W. T. Ward R. A. Strehlow
W. R. Grimes G. M. Watson
ABSTRACT
Solubility measurements of rare-earth and yttrium fluorides have been made in various solvents
containing zirconium or beryllium fluoride with certain alkali-metal fluorides, and in some cases
uranium fluoride, present.
Tests have been performed which pertain to the development af a
method of removal of rare earth fluoride nuclear poisons from certain mixtures of interest to the
Molten Salt Power Reactor Program. The method is shown to be effective in several concentration
ranges.
INTRODUCTION
Rare-earth fission products formed in a reactor
fueled with a circulating molten fluoride solution
may be expected to account for significant neutron
loss. Appreciation of this fact has motivated
studies of solubilities which would be pertinent
to the design and operation of such a reactor.
The feasibility of several processes in which
rare earths could be extracted from molten fluoride
solutions depends substantially on the solubility
relations among the rare-earth fluorides. This same
information also is of interest with regard to the
maintenance of homogeneity of the fuel, since
precipitation of a rare-earth fluoride in the fuel
circuit of the reactor might interfere with its satis-
factory operation.
This report presents some of the data obtained
on the solubilities of LaF,, CeF,;, SmF,, and
YF, in solvents containing sodium fluoride and
zirconium fluoride and in others containing beryl-
lium fluoride with lithium or sodium fluoride.
Two.. specific uranium-containing compositions
which -are potentially useful in a molten-fluoride-
fueled reactor have been selected. In addition,
a sufficient variety of non-uranium-containing
solvents have been chosen to assure that the
solubility relations among this selection of rare-
earth fluorides would be adequately known. This
is a continuation of work reported earlier! con-
cerning a solvent of composition NaF-ZrF ,-UF,
"W. T. Ward e al., Solubility Relations Among Some
Fission Product Fluorides in NaF-ZrF4-UF4 (50-46-4
mole %), ORNL-2421 (Jan. 15, 1958).
(50-46-4 mole %). The same radiotracer technique
was used for the present work.
RESULTS
Solubility of Single Rare-Earth Fluorides
The solubilities of CeF,, LaF,, and SmF; meas-
ured in the solvent, LiF-BeF,-UF, (62.8-36.4-0.8
mole %), are shown in Fig. 1 along with the cor-
responding results from the earlier work. Although
the solubility levels of these solutes in the LiF-
BeF,-UF , solvent mixture are considerably lower
than in the NaF-ZrF ,-UF, composition, they are
still adequate to assure that precipitation of the
rare-earth fluorides would not be inimical to re-
actor operation at probable burnup rates for about
four or five years.? A second feature of the data
is the closer approximation of the data for the
beryllium-containing solvents to a straight line
on the plot of log solubility vs T~!, which may
be interpreted as implying a lower degree of in-
teraction in the solution between solute and
solvent cations. This approach to ideality of the
solute in the beryllium system would not be ex-
pected to affect the feasibility of a solid solvent
extraction process, since both the substituting ion
[presumably Ce(lll)] and the extracted ions [e.g.,
Sm(I11)] would behave similarly.
For comparison, the solubility of YF,, along
with that of CeF, is shown in Fig. 2 for a single
NaF-BeF, composition (61-39 mole %). From these
results it may be inferred that the same qualitative
2Molten Salt Reactor P}ogram Status Report, ORNL-
2634, p 234 (Nov. 12, 1958).
UNCLASSIFIED
ORNL-LR-DWG 31423R
| IN NaF-2rR,-UF,
(50-46~4 mole %)
l I
PROBABLY UNSATURATED
SmF. ‘
3
YFy
Sm F3
CeF3
La F3
SOLUBILITY {mole %)
IN LiF-BeFp-UF,
(62.B-36.4-
0.8 mole %}
9 0+ N 12 13 14 15 16
10,000/ 7 (°K)
Fig. 1. Solub‘llity of Some Fission-Product Tri-
fluorides In Molten Fluoride Fuels.
order of solubilities exists for the rare-earth fluo-
rides in these solvents as was observed in the
NaF-ZrF ,-UF, (50-46-4 mole %) and LiF-BeF,-
UF, (62.8-36.4-0.8 mole %) solvents. This de-
crease in solubility with increase in the size of
the trivalent solute cation is probably related to
an as yet unmeasured trend of the heats of fusion
of the trifluorides. "
Solubility of Rare-Earth Fluorides as
Functions of Composition
Figure 3 shows that the presence of UF, in
small amounts does not affect the rare-earth solu-
bility greatly. The proportion of alkali-metal fluo-
ride to BeF, or ZrF ,, however, has a considerable
effect. : o
Several experiments were performed to determine
the solubility of a typical rare-earth fluoride,
CeF, in various solvents in each of the systems
UNCLASSIFIED
ORNL-LR-DWG 39655
0.8
c6
0.4
0.2
<
RARE-EARTH FLUCRIDE IN FILTRATE (mole %)
04
0.08
0.086
0.04
9 10 1 12 13 14 15
10,000/ 7 (°K}) '
Filg. 2. Solubllity (mole %) of YF3 and of CeF, in
NaF-Ber (61-39 mole %).
NaF-ZrF ,, LiF-BeF,, NaF-BeF,, and LiF-NaF-
BeF,. Figures 4 to 6 show the graphically inter-
polated solubilities in the selected compositions
in the four systems for several temperatures. Data
from which these curves were obtained are listed
in the Appendix. Figure 7 displays the 600°C
isotherm for the solubility of CeF, in the three
solvent systems containing beryllium. These curves
indicate the magnitude of the solvent interaction,
which is apparently less in the LiF-BeF, system
than in those containing NaF. The solubilities
exhibit minima in each case at compositions near
37 mole % BeF,. These minima appear to occur
at slightly higher BeF, concentrations at higher
temperatures (Figs. 5 and 6). '
Solubilities of Mixed Rare-Earth Fluo_rides in
LiF-Ber-UF4 (62.8-36.4-0.8 Mole %)
Rare-earth fluorides form solid solutions with
each other. However, they apparently do not form
solid solutions with the fuel solvent components.
These facts, coupled with the strong temperature
dependence of their solubilities, suggest that a
solid-solvent extraction might be a feasible method
UNCLASSIFIED
ORNL- LR-DWG 39656
4
.
2
v ' X
o
£ o\
E o8 X
{0
& 06 @,
5 R
T
z ‘%
m
5 04 ‘%
\Y
0.2
SOLVENT COMPOSITION {mole o}
© 61.6 LiF, 38.4 BeF,, O UF,
® 60.45 LiF, 38.3 BeF,, .25 UF,
- A 61.5LiF, 36.6 BeF,, 1.9 UF,
0.4 | | |
8 9 10 1" 12 13 14
10,000/7 (°K})
Fig. 3. Effect of UF, on Solubllity of CeF; in LIF-
Ber (62-38 mole %). Solvent composition calculated
from filtrate analyses (average values).
for substituting a low-cross-section rare earth
(e.g., Ce) for the high-cross-section ones (e.g.,
Sm). For a thermal reactor the differences in
poisoning between Ce and, say, Sm are large.
The advantages from the standpoint of neutron
economy of such a scheme are, consequently,
great. The advantage of this type of extraction for
an intermediate- or fast-neutron reactor is con-
siderably less. In the consideration of any of
the extraction schemes which are based on the
substitution of an innocuous rare-earth fluoride for
a high-cross-section one, the required data include
the solubility behavior of mixed rare-earth fluo-
rides. Such information will allow the single-stage
equilibrium distribution to be calculated.
The solubilities of selected pairs of rare-earth
fluorides in LiF-BeF ,-UF , (62.8-36.4-0.8 mole %)
have been determined, with substantially the same
techniques as those reported earlier.! In the
earlier work it was shown that the pairs LoFs-
UNCLASSIFIED
ORNL-LR-DWG 39657
i
10 |
9
!
8 !
7
5 \
E s 1
E \\ 800°C
. \
= \ 675°C
T
\
| /
\
\ .
A \\‘ ] 4550
\ / /.
\\ /
| \\; /‘ / /
/8
2
o
0 10 20 30 40 . 50 60
Zrf, IN SOLVENT (mole 7o) '
Flg.‘ 4. Solubllity of CeFa_ in NuF-ZrF4 Solvents.
CeF, and CeF,-SmF, form solid solutions and
behave in fairly predictable ways.
The equation representing a single equilibrium
stage for the extraction of a poison (e.g., SmF,)
from the solvent by a solid (e.g., CeF,) is
CeF3(ss) + SmFa(d‘) = Ce.FB(d) + SmF3(.'ss') ,
where (d) indicates that the rare-earth fluoride
is dissolved in the solvent, and (ss) that it is
in solid solution. With suitable restrictive con-
ditions the equilibrium constant for this reaction
can be shown to be approximately equal to .a
UNCLASSIFIED
ORNL-LR-DWG 39658
" BeF, IN SOLVENT (mole %)
.
2.4 H
LiF - BeF, SOLVENT | NaF -BeF, SOLVENT
2.2
2.0
700°C
1.8
700°C
1.6
\ /
° °
52 44 — o — 7 o
® o
o
g /
O o9 /
5 1.2
a
5
z /
.2 ®
"
8 1.0 //
/o
0.8 e
. \soo°c ‘\ o
A o' /
0.6 / \ /
: \«/L 600°C /
0.4
' A/{A /c/
X D,fi O/ »
02 w0~ 500°C p}x{ ‘
o7 500°C
0 .
20 30 40 50 20 30 40 50
BeF, IN SOLVENT (mole %)
Fig. 5. Comparison of CeF3 Solubllity (mole %) In LIF-BeF2 and In NaF-Ber.'
60
UNCLASSIFIED
ORNL-LR-DWG 39659
GREATER THAN 4%
mole %o AT 650°C
0.5
0.2
CeF3 IN FILTRATE (mole %)
0.05
0.02
‘NaF ~LiF
0.01
0 10 20 30 40 50 60
8eF, IN SOLVENT (mole To)
Fig. 6. Solubility (mole %) of CeF, In NaF-LIF-BeF,
Solvents.
simple solubility ratio:!
NeoF (d) VsmF Seor
ceF ,(d) "SmF4(ss) " CeFg4
K: = ;
NSmF3(d) NCeFa(.ss) ng
F3
where N is the mole fraction of the given species
in the specified phase and $° is the mole fraction
of the given species_ in a saturated solution in
the absence of the other rare-earth fluoride, all
at the same temperature.
The results of equilibrating CeF3-LaF3-so|ven'r
of several different compositions are
shown in Fig. 8. For the three relative com-
positions of CeF3-LaF used as solutes, the total
rare-earth solubility in virtually every case fell
between the solubilities of the pure rare-earth
fluorides. Figure 9 shows the corresponding re-
sults with one mixed composition in the CeF -
mixtures
UNCLASSIFIED
ORNL-LR-DWG 39660
® LiF-BeF, -
O Lif — NaF -BeF,
A NoF-BeF,
2 N\ea p
3 o8 N - /
£ r
l}"_J \ \‘ ./ /A
3 \ 4 pai
H os e, e
T \\\ .
= \ e A
< \ Ne~” o,
s A //
S oa \ '/
\,_+
A
0.2 . :
20 30 40 50 60
BeF, IN SOLVENT {male %)
Fig. 7. Comparison of CeF, Solubility {mole %) in
'LiF-BeF,, In LIF-NaF-BeF,, and in NaF-BeF, at
600°C. ‘
SmF ;-solvent system. These results are con-
“sistent with those observed for the NaF-Zer-UFd
(50-46-4 mole %) solvent.! Table 1 shows the
calculated extraction coefficients along with those
based on the experimental results for the CeF .-
LaF, system. Although the estimated values are
somewhat poorer than in the earlier work, the
present data appear' to be entirely adequate for
practical purposes.
A possibility existed that AIF, might offer some
advantage as the solid extractant in view of its
lower cost and neutron cross section. Solubility
measurements of AIF, in the same LiF-BeF ,-UF,
solvent indicated that the solubility increases with
the amount of AIF, added. The data presented in
Fig. 10 show also that the addition of CeF, de-
creases the AIF_ solubility somewhat. The pre-
cipitating phase is probably 3LiF-AlF, (ref 3).
Figure 11 shows that the solubility of CeF, is
somewhat higher in the presence of AlF, than in
3P, P. Fedotieff and K. Timofeeff, Z. anorg. w allgem.
Chem. 206, 266 (1932).
UNCL ASSIFIED ' UNCLASSIFIED
4 ORNL—-LR- DWG 39664 ORNL—~LR—-DWG 39662
I I { 4 -
CALCULATED TOTAL COMPOSITION {mole %)
© 1.80 CeFy, NO LaFy
1.82 CeFy, 0.78 LaFy
A 185 Cefy, 2.27 LaFy , \
183 CeFy, 330 LaFz \
® NO Cefy, 2.20 LoFz ~ > \
»
”
o
™
rd
v
o
™
L~
L~
&
7
-
vd
/ .
\\ \
TOTAL RARE-EARTH FLUORIDE IN FILTRATE {mole %)
o
N
A
TOTAL RARE-EARTH FLUORIDE IN FILTRATE {(mole %)
o
N
©
Ny
.
7
Z
SmFy ONLY (NO CeF3 PRESENT) N
CeFy ONLY (NO SmFy PRESENT)
SUM OF SOLUBILITIES WHEN BOTH ARE PRESENT
(TOTAL COMPOSITION: 2.83 mole % Cefy,
01 . . - 2.22 mole %o SmFz)
9 10 1 12 13 . 14 0.1 : : . L
10.000 / 7 (°K) 9 10 11 12 13 14
’ 10,000/7 (°K)
-
[ 2 = v]