838
C. C. TEMPLETON, B. F. ROTHSCHILD AND N. F. HALL
THORIUM NITRATE. 111’ THE DISTRIBUTION O F THORIUM K I T R A T E BETWEEN W r i T E R AKD CERTAIN ESTERS AND THE r\TA4TURE O F T H E DISTRIBUTION EQUILIBRIUM CHARLES C. TEMPLETON:
BILL F. ROTHSCHILD?
AND
NORRIS F. HALL
Department of Chemistry, University of W i s c o n s i n , M a d i s o n , W i s c o n s i n Received September 1.6, 1948
Esters will probably not have large-scale practical use as extractants for thorium because of the greater instability of their solutions (6) than that of alcohols and ketones. However, in other respects esters have about as desirable solvent properties as alcohols and ketones. Thus we are presenting here a brief study of the solvent properties of ethyl acetate and ethyl butyrate. EXPERIMENTAL
Leaching with ethyl butyrate The solubility of Th(N03)4-4Hz0in ethyl butyrate reaches about 40-60 per cent before there is appreciable evolution of gas from the solution (6); that of mixed rare earth nitrates ( 5 ) in ethyl butyrate is about 1-2 per cent of anhydrous nitrates. After 7 days of agitation, the weight of total oxides per 100 g. of solution was found to be 18.5 g., the weight of thorium nitrate per 100 g. of solution was 30.5 g., and the weight ratio of thorium dioxide t o the rare earth oxides was 10.1. This thorium enrichment of 91.0 per cent is about that predicted from the solubility values. Thorium nitrateurater-ethyl acetate and thorium nitratewater-ethyl
butyrate
The distribution of thorium nitrate between water and ethyl acetate and between water and ethyl butyrate was investigated in the same way as in the previous study ( 5 ) . The data for the ethyl butyrate systems are recorded in table 1; those for the ethyl acetate systems are listed in table 2. Both solvents \yere of Eastman Kodak Company “practical” grade. A11 observations were made a t room temperature. Figure 1 shows the usual plot of the logarithm of the mole fraction of thorium nitrate in the ester phase against the logarithm of that in the aqueous phase. Except for the most concentrated end, the points approximate to a straight line, which shows the existence of a relation of the form: (Mole fraction of Th(NO& in ester phase) (Mole fraction of Th(K03)d in aqueous phase)” The best value of n-that
=
determined graphically from the slope of the line in
For previous papers in this series see references 5 and 6 . Present address : Chemistry Department, Cniversity of Michigan, Ann Arbor, Michigan. * Present address : Chemistry Department, University of Chicago, Chicago, Illinois.
DISTRIBUTION
OF THORILX
NITRATE BETTTEES TATER
839
AXD ESTERS
figure 1-was 8.5. The values of R for n = 8.5 are listed in the last column of table 1. The average value of li is 5.0 x lo8. The arerage deviation of the individual values of I< is 18 per cent. This is fair constancy in view of the fact that the individual points are slightly off the line from x-hich is calculated TrlBLE 1 E t h y l butyrate-thorium nitrate-water systems
S*UPLE S O
Saturated Ester
X'ater
mi.
ml.
Ester
+jFG;,
,
phase
VALUES O F E: X 10-9 FOR
Aqueous phase
phase
Ester
Aqueous phase
n = 8.5
0.02241 0.01733 0.008S2 0.00360 0.00099 0.00029
0.06219 0.06806 0.05249 0.04831 0.04397 0.03653
4.0 5.6
solution ~
nil
I
0.0 , 0.2 0.4
3.0 3.0 3.0 3.0 3.0 3.0
0.6 0.8 1.o
3 0 2 s 2.6 2.4 2.2 2.0
~
' 1
1
4.76 3.74 1.96 0.81 1 0.23 0.07
34 31 33.41 32 .OS 31.02 20.6s 28.81
6.7 5.3 3.1 4.8
TABLE 2 Ethyl acetate-thoriiirn nitrate-water systems '
TOTAL COllPOSITION
l
SAXPLE NO.
Ester , Water
__ m
t
8
9
I
-_
Saturated
$
~
I -
~
I
AFTER F I R S T 2-1 H R . OF AGITATIOX
~, ~
~
3
~
,
AFTER 24 HR. OF STANDISG
solution
mz
ml.
mi.
3.0 3.0 30
0.0 0.2 0.4
3.0 2.8 2.6
I
1
10
3 0
0.6
2.4
11
3.0
0.8
2.2
12
3.0
1.0
2.0
Xiscihle AIisciLile Indistinct phnse sepnrn t ion Indistinct phase sep3rnt ion TKOdistinct phnsrs T w o distinct piloses
lliscible AIiscible Indistinct plinse sepRI'B t ion Indistinct phase sepiirnt ion Ind is t iric t phase separation Tn-o distinct plinses
Miscible Miscible Miscible
Miscible
, 1
lliscible Miscible Miscible
Miscible
Miscible
Miscible
Miscible
hIis c i b 1e
>wing t o the ordinary analytical errors for each value). Thus ethyl butyrate ehar-es very niuch the same as the higher alcohols and ketones v i t h respect to ater and thorium nitrate. Ethyl acetate n-as found t o be unsuitable as an extractant and the distribuon expression could not he determined by the procedure used. The solutions ' thorium nitrate, water, and ethyl acetate w r e mixed and agitated for 24 hr.
840
C. C. TENPLETOS, B. F. ROTHSCHILD A S D N. F. HSLL
The solutions n-ith the highest thorium nitrate concentrations \\-ere completely miscible. Those of low concentration formed tn-o distinct phases, while those of
i
.10
MOLE FRACTIONS Th(N03)4 IN AQUEOUS PHASE FIG.1. Distribution of thorium nitrate between rrater and ethyl butyrate
intermediate concentration showed some indistinct tendency tou-ard separation. Even after an additional 24 hr. of standing, only the solutions of lovi thorium
DISTRIBUTIOS O F THORIUM XITR-ITE BETWEEX TVATER ASD ESTERS
8.11
nitrate concentration shon-ed any definite separation of aqueous and organic phases. -After 24 hr. more of agitation all the solutions exhibited only one phase, which failed to separate into tn-o phases even after GO days of standing. From the data it appears that ethyl acetate is more soluble in an aqueous solution of thorium nitrate than in Ii-ater alone. and would only be useful as an extractant under very special circumstances. This is a different situation from that in TI-hich microscopic amounts of material are extracted from aqueous solution n-ith ethyl acetate (1). Ethyl butyrate, hov-ever, may find use as an extraction solvent at appreciable concentrations of thorium nitrate. S-ITURE O F THE DISTRIBL-TIOS REACTIOS
The distribution of thorium nitrate betn-een water and three types of organic solvents has been shown ( 5 , 6) to be described by a relation of the form: (Mole fraction of Th(S03)4in organic phase) (Mole fraction of Th(SO3)4 in aqueous phase)"
=
k'
where Th(SOa)?was regarded as a single molecular species. On this empirical basis, the exponent a \\-as between -1.8 and 5.5 for certain alcohols, and between 7 and 8 for methyl ketones. Obviously the value of a is mainly determined by the state of aggregation of thorium nitrate in both the aqueous and the organic phases. There is direct evidence from the n-ork of Robinson and Levien (4) on vapor pressures by the isopiestic method, and from the cryoscopic measurements of Misciattelli (2), that thorium nitrate is a strong electrolyte which yields one Th4+ and four SOa- ions in aqueous solution. On the other hand, specific evidence on the state of thorium nitrate in the organic phase is almost completely lacking. We previously correlated ( 5 ) the high solubility of thorium nitrate in certain organic solvents n-ith the oxygen-containing groups in such solvents. Since increased steric hindrance around such a group appreciably ion-ers the solubility, Dther factors being constant, n-e attributed the solubility specifically to some interaction betn-een these oxygen atoms in the solvent molecule and the solute nolecule as a \\-hole. Hon-ever, there is as yet no evidence indicating hon- many jolvent molecules are thus coordinated by the solute. -Although no electrical .onductivity data exist for these systems, the most reasonable assumption seems o be that the solute molecule in the organic phase is basically an unionized iposibly polymerized) Th(SOJ), unit, whatever the degree of its solvation. We lesire to shoir below that such a postulation is strongly supported by the comnon-ion effect of added nitric acid on the distribution. On this premise the distribution reaction ~ r o u l dessentially be:
+
Th't 4SOa(aqueous phase)
a
[Th(S03)4] (organic phase)
muming activity coefficients of unity, the relation for this equilibrium ~rouldbe: orgX[Th(SOJa] =I( aqsTh4-.aqx4 SOY
(3)
842
C . C . TEXPLETON, B. F. ROTHSCHILD A S D K. F. HALL
TABLE 3 Calcitlations for predzcling changes in dastrzbution c u r i e s d u e to added nztric acid y l i i ~ ( 4 ~ b)4 log (y/ki) = log 5 4 log ( 4 ~ b )
+
+
+
I
0.03 0.035 0.04 0.045 0.05
I I
0.177 0.544 0.602 0.653 0.699
-2 -2 -2 -2 -2
I
, I I
0.793 0.128 0.418 0.673 0.903
-6 -5 -5 -5 -5
b = 0.02 X
0.03 0.035 0.04 0.045
0.05
I
LOG (42
+ b)
I
0.146 0.204 0.255 0.301 0.342
-1 -1 -1 -1 -1
I I
LOG
I
(rlki)
0.061 0.360 0.622 0.857 1.067
-5
-5 -5
-5 -5
b = 0.10 X
0.03 0.035 0.04 0,045 0.05
I I I I
LOG (4x
+ b)
0.342 0.380 0.115 0,447 0 477
-1 -1 -1 -1 -1
LOG (y/kd
0.845 1.064 1.262 1.441 1.607
-5 -5
-5 -5 -5
For solutions with no additional SO,, aqXSOg = 4aqXTh4+,and therefore: orgx [Th(S03)4] = K‘ aqxsTh4+
In systems that are sufficiently dilute so that the water molecules account for almost all the molecules in the aqueous phase, orgx [Th(NO3)4] N ]
