Extraction of Uranyl Butyrate b y Organic Solvents. Distribution and Rate of Transfer in Continuous Countercurrent Spray Extraction Column R.
K.
S. GHOSAL and D. DUTT C o l l e g e of Engineering and Technology, Jadavpur University, Calcutta
T
h e solvent extraction h a s been widely used for commercial purification of uranium compounds for production of high purity uranouranic o x i d e (U,O,) and uranium metal. T h e distribution of uranyl nitrate between water and various organic s o l v e n t s and i t s continuous countercurrent extraction i n spray, packed, wetted-wall, and p u l s e columns h a v e been studied by many workers (1-8). T h e distribution study for t h i s s a l t s h o w s that t h e extraction c a p a c i t y of s o l v e n t s rapidly f a l l s off with d e c r e a s e i n concentration and and is very poor at the dilute end. It h a s b e e n found by experiment t h a t uranyl butyrate g i v e s favorable distribution with a number of organic s o l v e n t s , even at t h e dilute end. An investigation h a s been carried out (1) t o find t h e equilibrium distribution of uranyl butyrate between water and s e v e r a l organic s o l v e n t s and (2) t o study t h e r a t e of transfer i n continuous countercurrent spray extraction column with some s u i t a b l e solvent s e l e c t e d for t h e purpose, s u c h a s isoamyl alcohol.
32,
India
After s e t t l i n g of t h e precipitate, t h e c l e a r supernatant solvent layer w a s decanted off before t h e a c t u a l filtration. Results o f Distribution Study. T h e d a t a for uranyl butyrate distribution between water a n d four different s o l v e n t s a r e shown i n F i g u r e s 1 to 4. T h e pH v a l u e s of t h e different s t o c k s o l u t i o n s u s e d were adjusted by regulating t h e concentration of f r e e butyric acid. No attempt w a s made t o regulate t h e pH of t h e equilibrated aqueous phase. B e s i d e s t h e above four solvents, extraction properties of s o l v e n t s l i k e benzene, toluene, carbon tetrachloride, ethyl-
::[
DISTRIBUTION O F URANYL BUTYRATE BETWEEN WATER AND ORGANIC SOLVENTS Preparation of Uranyl Butyrate Stock Solution. Uranyl butyrate w a s prepared from uranyl n i t r a t e (hexahydrate, Mallinkcrodt, analytical reagent quality). An o u n c e of t h e s a l t w a s d i s s o l v e d i n about 500 yl. of water and ammonium diuranate, (NH,), U,O, w a s precipitated by t h e addition of sufficient quantity of liquid ammonia. T h e precipitate w a s filtered, and washed free of ammonium nitrate, and then mixed with an e x c e s s of butyric a c i d (pure, E. Merck) t o form a slurry. T h e slurry w a s d i s s o l v e d in sufficient quantity of distilled water, and t h e solution obtained w a s carefully evaporated t o saturation and then cooled overnight t o c r y s t a l l i z e t h e uranyl butyrate. T h r e e c r o p s of c r y s t a l s were collected. T h e crystallized product w a s washed with a small amount of water and then d i s s o l v e d i n warm water. T h e pH of t h e solution obtained w a s a d j u s t e d by further addition of butyric acid and t h e solution w a s preserved i n a dark p l a c e for equilibrium distribution study. Solvents Used. T h e s o l v e n t s used were methyl isobutyl ketone (supplied by Burmah-Shell, t h e fraction distilled a t 117-18'C. w a s used for t h e distribution study); ethyl a c e t a t e (pure, boiling point, 77.15'C.); isoamyl alcohol (boiling range 128' t o 132OC.k cyclohexanone (boiling range 1.54' to 156'C.). Equilibrium Procedure. Aqueous uranyl butyrate s o l u t i o n s with different concentrations of uranium a n d equal volumes of t h e appropriate solvent were brought t o equilibrium by periodically shaking for about 5 minutes, every 15 minutes for 1.5 hours, and were left overnight for separation of t h e phases. T h e temperatures of t h e s a m p l e s were noted, and 10 ml. of each of t h e separated p h a s e s were t h e n pipetted for a n a l y s i s . Analysis. T h e samples of aqueous p h a s e s were precipit a t e d hot by addition of liquid ammonia with stirring and t h e p r e c i p i t a t e s of ammonium diuranate were filtered, dried, and ignited t o U,O, at about 85OoC. T h e s a m p l e s of t h e solvent p h a s e were t r e a t e d similarly. In t h i s c a s e , sufficient distilled water w a s added and t h e mixture w a s boiled before precipitation with liquid ammonia.
258
INDUSTRIAL AND ENGINEERING CHEMISTRY
C.,Groms
Uranium per Liter,Woter Phase
Figure 1. Uranyl butyrate distribution between water and mothy isobutyl ketone
pH of Stock Solution
A
x
3.435 3.24 2.96 2.64 22-4'C.
e n e dichloride, trichloroethylene, isoamyl acetate, hexyl alcohol, butyl alcohol, ethyl ether, a n d nitromethane were determined colorimetrically. Of t h e s e solvents, butyl alcohol h a s fairly good extraction power. Ethyl ether and nitromethane a l s o h a v e some extraction power, and t h e r e s t a r e quite unsuitable. T h e effect of ammonium butyrate a s a s a l t i n g out agent with a number of t h e s o l v e n t s w a s a l s o studied qualitatively. Isoamyl alcohol, cyclohexanone, and methyl isobutyl ketone extract uranium butyrate almost completely from a n aqueous p h a s e i n t h e p r e s e n c e of sufficient ammonium butyrate. Solvents l i k e nitromethane and ethyl a c e t a t e g i v e a multifold i n c r e a s e i n t h e distribution r a t i o of uranyl butyrate in t h e p r e s e n c e of ammonium butyrate. T h e extraction power of t o l u e n e and isoamyl a c e t a t e is negligible e v e n i n t h e p r e s e n c e of sufficient ammonium butyrate. VOL. 3, NO. 2
extraction power of t h e s o l v e n t s i n c r e a s e s with fall of pH i n t h e original aqueous phase-i.e., t h e i n c r e a s e i n t h e free butyric acid concentration. T h e distribution r a t i o s , C,/C,, for t h e four s o l v e n t s s t u d i e d a t approximately e q u a l a q u e o u s p h a s e concentrat i o n s after equilibrium and a t nearly e q u a l pH v a l u e s of t h e s t o c k solution may b e compared a s shown i n T a b l e 1. T h e s e v a l u e s h a v e been taken from F i g u r e s 1 t o 4. Cyclohexanone w a s found t o b e t h e most s u i t a b l e solvent of t h o s e studied, on t h e b a s i s of extraction power. However, considering availability, c o s t , and solubility in water, isoamyl w a s s e l e c t e d for study of t h e r a t e of extraction of uranyl butyrate i n a continuous spray tower. RATE OF EXTRACTION OF URANYL BUTYRATE BY ISOAMYL. ALCOHOL IN CONTINUOUS C O U N T E R C U R R E N T S P R A Y TOWER
A solution of uranyl butyrate containing an equimolar quantity of ammonium butyrate w a s prepared by adding C.,Groms
Figure 2.
Uranium per Liter,Woter Phose
Uranyl butyrate distribution between water and ethyl acetate
pH of Stock Solution 3.43s A 3.04 2.59 X 2.24 24-7 O C .
-++ L i t e r , W a t e r Phase
Figure 4.
Uranyl butyrate distribution between water and cyclohexanone
. A
1 I I ] 0 1 2 3 4 5 6 7 8 I
I
I
]
Cr, Grams Uranium p e r Liter,Water Phase Figure 3. Uranyl butyrate distribution between water and isoamyl alcohol
A
'
+
X
pH of Stock Solution 3.58 3.16 2.80 2.61 2.22 27-31 C.
DISCUSSION OF RESULTS
T h e d a t a i n F i g u r e s 1 t o 4 i n d i c a t e t h a t a l c o h o l s and k e t o n e s h a v e fairly good extraction power. T h e s e r e s u l t s are, i n general, confirmed b y more qualitative s t u d i e s . T h e s e l a t t e r s t u d i e s also i n d i c a t e d t h a t hydrocarbons and chlorinated hydrocarbons h a v e negligible extraction power. Further, t h e d a t a i n t h e f i g u r e s s h o w that, i n general, t h e 1958
pH of Stock Solution 2.80 2.61 2.21 30-3 O C .
butyric a c i d , in e x c e s s , t o t h e filtered and w a s h e d prec i p i t a t e of ammonium diuranate which w a s obtained by t h e addition of liquid ammonia t o a uranyl nitrate solution. No attempt w a s made t o s e p a r a t e t h e uranyl butyrate from ammonium butyrate by crystallization, a s w a s done during
Table
Solvent Used Methyl isobutyl ketone
I.
Comparison of Distribution R a t i o s for Four D i f f e r e n t Solvents
pH of Stock S o h .
Concn. in Equilibrated Aqueous P h a s e of Uranium, Grams per Liter, C w
Distribution Ratio, C J C w
2.64
5.0
0.68
Ethyl acetate Isoamyl alcohol
2.59
5.0
0.90
2.61
4. so
3.33
Cyclohexanone
2.61
5.0
5.0
CHEMICAL AND ENGlNEERiNG DATA SERIES
259
t h e distribution study. B e c a u s e t h e p r e s e n c e of a small amount of ammonium butyrate (equimolar with r e s p e c t t o uranyl butyrate) will h a v e some effect on t h e distribution ratio of uranyl butyrate, s e p a r a t e s e r i e s of equilibrium d a t a were determined with e a c h different solution of uranyl butyrate u s e d i n t h e m a s s transfer study. T h e pH v a l u e s of t h e aqueous s o l u t i o n s were a d j u s t e d with free butyric acid. T h e distribution data a r e shown i n F i g u r e 5. T h e p r e s e n c e of a small amount of ammonium butyrate actually improves t h e extraction power of t h e solvent a s shown in T a b l e 11.
EXPERIMENTAL PROCEDURE
About 5 gallons of uranyl butyrate solution in a q u e o u s p h a s e containing about 10 grams of uranium per l i t e r with equimolar amount of ammonium butyrate were prepared. T h e pH of t h e solution w a s a d j u s t e d by t h e addition of f r e e butyric acid. T h i s solution w a s fed in a f e e d v e s s e l , C,, whence it w a s pumped into t h e overhead tank, D,. About 5 gallons of isoamyl alcohol were similarly fed into t h e other v e s s e l , C,, and t h e n c e into t h e overhead tank, D,, through t h e a c t i o n of compressed nitrogen. T h e p h a s e t o b e main-
a .c 0
a
: -:: 5 u
L
-
c J
zn 3-
c?
&,Grams Uranium per Liter,Water Phase
Figure 5. Distribution of uranyl butyrate between water and isoamyl alcohol in presence o f ammonium butyrate
pH of Stock Solution
*
3.35 3.08 31-32 C.
E X T R A C T I O N EQUIPMENT
A diagrammatic sketch of t h e a p p a r a t u s u s e d is shown in F i g u r e 6. T h e tower w a s constructed of borosilicate g l a s s 1.5 i n c h e s i n i n s i d e diameter and 5 feet high. It w a s built
Table
II.
-7
E f f e c t of Ammonium Butyrate on Extraction
C o n c n of Ammonium Butyrate, Gram Mole/ Gram Mole Uranyl Butyrate in Original Aqueous Phase
C o n c n of Uranium Grams/Liter, in Equilibrated Aqueous P h a s e
Distribution Ratio, Read from Figures 3 and 5
Temp., O C.
pH of Stock Soln
28
3.16
Nil
1.0
28
Nil
2.0
2.45 2.25
32
3.16 3.08
1.0
1.0
3.25
32
3.08
1.0
2.0
31
3.35
1.0
3.10 3.05
31
3.35
1.0
1.0 2.0
2.85 Figure 6.
of f i v e individual g l a s s s e c t i o n s joined together by stainl e s s s t e e l flanges. T h e 5-gallon feed v e s s e l s , receiving tanks, 10-gallon overhead tanks, p i p e lines, and regulating c o c k s were a l l made of s t a i n l e s s s t e e l . T w o g l a s s rotameters were u s e d t o meter t h e flow of liquids into t h e column proper. T h e liquids entered t h e column through two s t a i n l e s s s t e e l distributors, e a c h having 22 perforations 1/16 inch i n diameter.
260
INDUSTRIAL AND ENGINEERING CHEMISTRY
Extraction equipment
A. B.
Tower Flanges C,,C,. F e e d v e s s e l s D,,D,. Overhead tanks E. Rotameters F. Regulating cocks G. Gas cylinder H. Distributors P. Pump R. Receiving tanks VOL. 3, NO. 2
T o b l e 111. System: Isoamyl Alcohol-Uranyl Butyrate-Water Temperature = 30" to 32" C. Column diameter = 1.5 inches, i n s i d e diameter Column height I5 f e e t E f f e c t i v e column volume = 1566 ml. (54 inches of column),
Flow Rates, Cm.
Series
A
pH of Original Aqueous Phase
Phase Dispersed
3.35
Isoamyl alcohol
3.08
Water
2.25 4.05 8.00 12.50 10.35 10.35 10.35 10.35
N = Grams Uranium/ Minute, Transferred, B a s e d on
Aqueous Solvent Aqueous Solvent
Aqueous
Solvent
Phase
Phase
Grams Uranium/ Min.
Outlet*
LS
4.55 12.5 7.67 12.5 11.05 12.5 16.00 12.5 4.55 12.5 7.67 12.5 11.05 12.5 14.72 12.5 18.70 12.5 11.05 21.1
Water
B
W'
Uranium Concentration, Grams/Liter
12.5 12.5 12.5 12.5 12.5 24.3 17.9 17.9
C
w2
s,
9.64 9.64 9.64 9.64 9.64 9.64 9.64 9.64 9.64 9.64 10.40 10.40 10.40 10.40 10.40 10.40 10.40 10.40
Outlet'
C
inlet' C
'VPV,
KOV,W'
1/Mh
Wl
s1
3.54 5.13 7.30 12.92 2.19 5.44 7.03 9.40 12.30 4.25
2.46 2.89 3.08 3.90 2.58 2.80 2.90 2.98 3.40 2.40
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
5.372 0.59 0 0.826 1.042 0.367 0.598 0.848 1.116 1.330 0.910
0.505 0.731 1.038 1.840 0.312 0.774 1.000 1.332 1.745 1,020
0.439 0.661 0.932 1.441 0.340 0.686 0.924 1.224 1.538 0.965
0.0579 0.0840 0.1210 0.1930 0.0424 0.0893 0.1220 0.1720 0.2205 0.1300
78.6 91.3 91.5 83.0 107.5 86.0 90.6 85.6 84.8 85.0
2.00 2.96 6.24 10.95 9.00 4.50 6.02 6.20
2.10 2.12 2.66 3.36 3.28 1.75 2.51 2.55
0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
0.212 0.382 0.705 1.000 0.838 1.018 0.930 0.925
0.284 0.420 0.889 1.560 1.278 1.245 1.228 1.262
0.248 0.401 0.797 1.280 1.058 1.132 1.079 1.094
0.0319 0.0524 0.1020 0.1675 0.1320 0.1640 0.1405 0.1425
70.7 77.3 78.5 74.5 78.5 63.0 73.6 72.6
0.3r 0.3-
then changed regularly, keeping t h a t of t h e other p h a s e c o n s t a n t , and in t h i s W a f , s e v e r a l r u n s were made. T h e s a m p l e s were then analyzed for uranium content.
0.2 -
RESULTS
T h e over-all r a t e coefficient Kqv,wa, b a s e d o n water p h a s e was c a l c u l a t e d from t h e equation, KO",Wa
=
PV
where
0.020.02k
grams of uranium transferred between p h a s e s
0.01L 2
I I H I ' I
3 4 5 L.,
IO
20
1
=
minut e
30
CmIMinute, W a t e r Phase
Figure 7. Rate coefficient vs. water phase velocity for both water and solvent phases dispersed, at varying p H values of stock solutions
Phase pH of Stock Dispersed Solution Alcohol 3.35 A Water 3.35 Water 3.08 Alcohol phase rate 12.5 cm./minute
tained continuous w a s then allowed t o enter t h e column a t a predetermined r a t e with t h e s o l v e n t p h a s e outlet cock open (to drive out t h e a i r i n s i d e t h e column) and t h e water p h a s e outlet c o c k c l o s e d . When t h e column w a s almost full of t h e continuous phase, t h e d i s p e r s e d p h a s e w a s run into t h e column a t t h e d e s i r e d rate. T h e outlet c o c k s were t h e n regulated t o maintain t h e s o l v e n t water i n t e r f a c e a t a fixed position very n e a r t o t h e continuous p h a s e inlet distributor. When t h e continuous p h a s e i n t h e column had changed by about 2 t o 2.5 times, s a m p l e s of outlet s o l v e n t and a q u e o u s p h a s e s were taken. T h e flow r a t e of o n e of t h e p h a s e s w a s 1958
N."
average v a l u e
V
= effective column volume, l i t e r s
A C, = l o g mean driving force, (Cw,- CwT)-(Cwl - CwT) CW,
In
- cw;
cWl - c Wl*
K O V , W e= over-all r a t e coefficient b a s e d on water p h a s e ,
1 minute
Height of an over-all transfer unit (H.T.UoV,w) w a s calc u l a t e d by t h e equation H.T.UOv,,
-~ LW KOV,Wa
CHEMICAL AND ENGINEERING DATA SERIES
261
where
L, = velocity of water flow, b a s e d on column c r o s s section, cm./minute T h e r e s u l t s a r e tabulated i n T a b l e I11 and plotted in F i g u r e s 7 t o 9. From F i g u r e 7, i t is s e e n that for both t h e water and t h e solvent p h a s e s d i s p e r s e d a n d with t h e different pH v a l u e s of t h e s t o c k solution, t h e r a t e coefficient, is directly proportional t o t h e water p h a s e velocity, L i e o .
+4
ied-the v a l u e s of H.T.Uov , e t h e r for t h e spray tower were found t o lie within 47.2 t o 344 cm., depending on t h e p h a s e dispersed and t h e flow conditions. From qualitative experiments with thorium nitrate solution, i t w a s found that t h e thorium hydroxide formed by t h e addition of liquid ammonia is practically insoluble i n butyric a c i d solution, unlike uranium under t h e same conditions. Similar experiments with cerrous nitrate show that t h e precipitate obtained after addition of ammonia,
0.02
0.01
> 0.005t-
L 4+
0.4
0.2
0
0.8 1.0 Flow Ratio
0.6 L./L.
1.2
1.4
1.6
Figure 9. H.T.O.gy,w values VI. flaw ratio, at varying p H values, for both water and solvent phases dispersed
X
t
0.002
3
io
5
L,,cm.per
20 30 min.,Aicohol Phase
50
Figure 8. Rate coefficient VI. water phase velocity for both water and solvent phases dispersed, at varying pH values of stock solutions
when treated with butyric acid, is d i s s o l v e d i n t h e form of butyrate, which is but slightly extracted by isoamyl alcohol for very low concentration of uranium in t h e aqueous phase. T h e s e qualitative experiments may s u g g e s t a method of separation or uranium from thorium and cerium s a l t s . T h e r e s u l t s of t h e distribution study show that isoamyl alcohol h a s fairly good extraction power for uranyl butyrate. NOMENCLATURE
A pH 3.35 pH 3.08 1 = mean of 5 points 2 = mean of 9 points
From F i g u r e 8, t h e r e s u l t s may b e represented by t h e following approximate relationship for both t h e p h a s e s dispersed KOV,,'
= 0.007 Lw"o Ls0*p2'
,
= concentration of uranium, grams per liter .in equilibrated aqueous phase C, = concentration of uranium, grams per liter, in equilibrated organic phase C.$ = concentration of uranium, grams per liter, of an aqueous phase in equilibrium with solvent phase KOv,,' = over-all rate coefficient, based on water phase, l/minute N,, = grams of uranium transferred between p h a s e s per minute, average value V = effective column volume, liters h C m = log mean driving force, expressed mathematically a s C
Again, for both t h e p h a s e s d i s p e r s e d , H.T.U.,,,, was found t o b e slightly influenced by t h e pH v a l u e s of t h e stock solution a n d practically independent of t h e flow ratio a s shown i n F i g u r e 9.
- c,:
(CW*
In
)
- (CWl - c,;)
c w 2 - cw: CWI- c
Wl
DISCUSSION
Lw = superficial velocity of water flow based on column
From t h e material balance, i t is found that a l l of t h e deviations between t h e v a l u e s of t h e N, calculated from t h e two p h a s e s a s shown in T a b l e 111, differ in t h e same direction except for one run. Rather high deviation on t h e material b a l a n c e may b e d u e t o nonattainment of a perfectly s t e a d y condition i n t h e column and t o slight c h a n g e s i n t h e volume of p h a s e s due t o mutual saturation and t o s o l u t e transfer, for which no allowance h a s been made. For t h i s deviation, a n a v e r a g e v a l u e of N, b a s e d on both t h e p h a s e s , h a s b e e n used t o c a l c u l a t e t h e r a t e coefficients and t h e H.T.U. values. From t h e study i t a p p e a r s that major r e s i s t a n c e t o m a s s transfer in t h e system lies i n t h e aqueous p h a s e and t h e r e fore for efficient extraction of uranyl butyrate t h e water p h a s e should b e dispersed. T h e H.T.U.,, values, obtained h e r e (63 t o 1 0 7 cm.) may b e compared'with H.T.Uo, e t h e r for t h e uranyl nitratediethyl ether-water s y s t e m a s &ported by Jodra, Luina, and Oroz (3). In their system, where t h e distribution is favora b l e for the water phase-unlike t h e present s y s t e m stud-
Ls = superficial velocity of solvent flow, based on col-
cross section, cm. per minute
262
INDUSTRIAL AND ENGINEERING CHEMISTRY
umn c r o s s section, cm. per minute =height of over-all transfer unit, based on water phase, cm. Subscripts 1 and 2 refer to the bottom and top sections of the tower, respectively
H.T.U,,,,
LIT E RATU R E C I T E D (1) Glueckauf, E., McKay, H. A. C., Mathieson, A. R., Trans. Faraday SOC. 47, 4 3 7 4 9 (1951).
(2) Jenkins, I. L., McKay, H. A. C., Ibid., 50, 107-19 (1954). (3) Jodra, G., Luina, A. P., Oroz, A,, Nuclear Engineering, Part II, pp. 127-43; Chem. Eng. Progr. Symposium Set. 50, No, 12 (19.54). (4) Katzin, L. I., Sullivan, J. C., J. Phys. & Colloid Chem. 55, 346-74 (1951). (5) Murdoch, R., Pratt, H. R. C., Trans. Inst. Chem. Engrs. (London) 31, NO. 4, 307-26 (1953). (6) Warner, R. K., Australian J. Appf. Sci. 3, No. 2, 156-72 (1952). (7) Ibid. 4, No. 3, 427-43 (1953). (8) Woodfield, F. W., Sege, G., Nuclear Engineering, Part III, pp. 14-17; Chem. Eng. Prog. Symposium Ser. 50, No. 1 3 (1954). Received for review February 18, 1957. Accepted January 3, 1958. .
I
.
I
VQL. 3, NO. 2
