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Separation of zirconium from hafnium in nitric acid solutions by solvent extraction using dibutyl butylphosphonate
Hydrometallurgy, 3 (1978) 275--282 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
275
SEPARATION OF ZIRCONIUM FROM HAFNIUM IN NITRIC ACID S O L U T I O N S BY S O L V E N T E X T R A C T I O N U S I N G D I B U T Y L B U T Y L PHOSPHONATE P A R T 2. M I X E R - S E T T L E R R U N S
A.E.P. BROWN* and A.G. WAIN Atomic Energy Research Establishment, Harwell, Didcot, Oxon (U.K.)
(Received January 24th, 1977; in revised form December 5th, 1977)
ABSTRACT Brown, A.E.P. and Wain, A.G., 1978. Separation of zirconium from hafnium in nitric acid solutions by solvent extraction using dibutyl butylphosphonate. Part 2. Mixersettler runs. Hydrometallurgy, 3: 275--282. A process for zirconium/hafnium separation based on the distribution data given in Part 1 (Brown and Healy, 1978) has been successfully tested in a 10-stage Croda mixersettler. The hafnium content of the zirconium could be reduced below the specification for nuclear grade zirconium. Purification of the zirconium from uranium could be achieved, and the hafnium could be recovered if desired. A flowsheet is presented.
INTRODUCTION F l o w s h e e t s (Mukherji, 1 9 7 0 ) f o r t h e p r e p a r a t i o n o f n u c l e a r grade z i r c o n i u m f r o m ores c o n t a i n i n g h a f n i u m , b y s o l v e n t e x t r a c t i o n i n t o t r i b u t y l p h o s p h a t e (TBP) dissolved in an i n e r t d i l u e n t f r o m nitric acid s o l u t i o n , a n d i n t o m e t h y l isobutyl ketone from thiocyanate solutions have been tested and operated w i t h e i t h e r m i x e r - s e t t l e r s or p u l s e d c o l u m n s . In t h e T B P process high ( > 4 0 % ) T B P c o n c e n t r a t i o n s at high acidities (8 M HNO3) are r e q u i r e d , a n d in t h e t h i o c y a n a t e p r o c e s s o n e is l e f t w i t h an a q u e o u s r a f f i n a t e c o n t a i n i n g thioc y a n a t e w h i c h c o u l d lead to possible disposal p r o b l e m s . T h e p r o c e s s d e s c r i b e d a n d t e s t e d in this p a p e r is b a s e d on t h e results given in Part 1 ( B r o w n a n d Healy, 1978). In outline, t h e z i r c o n i u m is e x t r a c t e d b y 20% wt./vol, d i b u t y l b u t y l p h o s p h o n a t e / S o l v e s s o 150 f r o m 5 M HNO3, a n d t h e organic e x t r a c t is s c r u b b e d w i t h 3 M HNO3 to r e m o v e residual h a f n i u m . T h e z i r c o n i u m is t h e n b a c k w a s h e d w i t h water. U r a n i u m s t a y s m a i n l y in t h e organic p h a s e o n b a c k w a s h i n g , a n d a n y residual u r a n i u m a c c o m p a n y i n g t h e z i r c o n i u m c o u l d b e s c r u b b e d o u t again w i t h a small s o l v e n t stream. T h e *Present address: Instituto de Energia AtSmica, Calxa Postal 11049, Sao Paulo, S.P. (Brazil).
276
solvent is washed with dilute NaOH and water before recycling. The process yields nuclear grade zirconium (< 100 ppm Hf). The requirement to remove uranium from the zirconium is an unusual one, arising from the high uranium c o n t e n t of the type of ore found in Brazil. EXPERIMENTAL
Reagen ts
All reagents used with the exception of the zirconium feedstock for runs 1, 2 and 3 are described in Part 1 (Brown and Healy, 1978). The zirconium nitrate feedstock solution was prepared from zircosil granular (a zirconium silicate ore) supplied b y Associated Lead Manufactureres Ltd., containing approximately 66% Zr, 33% SiO2 and 1.5--2.0% Hr. The ore was treated by an alkali fusion with sodium hydroxide (1.4 g NaOH/g ore) at 700°C for one hour. The fused mass was washed and digested for two hours with water at 80°C. The solution was filtered, and the precipitate was further washed with cold water and then digested with concentrated nitric acid for two hours at 80°C to dissolve the zirconium. Acidified gelatine was added to flocculate silica which appeared in colloidal form in the zirconium liquor. After the silica had been filtered off, the acidity of the solution was adjusted to be 5 M in HNO3 and uranium as the nitrate at a concentration of 0.4 g/1 U was added to simulate the particular t y p e of ore already mentioned. Analysis
Zirconium was analysed by precipitation as the oxalate, ignition to the oxide, and weighing or directly on the solution by X-ray fluorescence. Feed solutions were spiked with radioactive ~TSHf tracer and analysed either by gammacounting using sodium iodide detector or by X-ray fluorescence. Uranium was determined b y the delayed neutron counting technique, nitric acid as described in Part 1 and silica by emission spectrography. Mixer-settler runs
Equilibrium data for zirconium and hafnium (see Part 1) were used to construct McCabe-Thiele diagrams to define solvent and aqueous flows to separate zirconium and hafnium. Three runs were carried out, as indicated in Table 1. The residence time in the mixer-settlers was sufficiently long to anticipate near 100% stage efficiencies and the performance of a given number of stages agreed well with the McCabe-Thiele Diagrams. A ten-stage Croda Scientific Equipment Ltd., mixer-settler was used using the modified larger t y p e of glass tube (Hanson et al., personal communication). Feeds were metered with Watson-Marlow peristaltic pumps, the aqueous phase by direct metering and the organic phase by displacement, to prevent
277
TABLE 1 Principal features of runs Feed: Zr, 24 g/l; Hf, 0.5 g/l; U, 0.4 g/l; silica, 0.031 g/1 Run 1
Run 2
Run 3
Flow rates (ml/min)
Aq. feed Scrub Solvent Backwash
3 1.5 9 9
3 1.5 9 9
3 1.5 9 9
Acidities (M)
Aq. feed Scrub
5 5
5 5
5 3
No. of stages
Extraction Scrub
5 4
4 6
3 7
Organic phase from extraction (g/l)
Zr Hf U
11.3 0.012 --
8.5 0.044 0.14
6.9 0.006 0.14
Raffinate
Zr (g]l) Zr lost (%)
0.012 0.05
0.03 0.18
0.16 1.2
Zr product (ppm)
Hf U
1060 --
5200 100
87 220
a t t a c k o f t h e silicone t u b i n g b y the solvent. T h e e q u i p m e n t o p e r a t e d with a c e n t r e feed and solvent and scrub were fed f r o m either end o f t h e mixer-settler bank. E a c h r u n lasted a b o u t seven hours, giving a b o u t eight t h r o u g h p u t s o f solvent and f o u r o f a q u e o u s phase, sufficient for a s t e a d y state t o be reached. E q u i l i b r i u m c o n d i t i o n s were r e a c h e d in a b o u t one h o u r s o p e r a t i o n . T h e solvent was n o t p r e - e q u i l i b r a t e d with nitric acid as m a n u a l pre-equilibration w o u l d have been necessary. T h e z i r c o n i u m nitrate was b a c k w a s h e d i n t o an equal v o l u m e o f w a t e r using the same e q u i p m e n t . A f t e r each r u n t h e solvent was cleaned u p with three 0.1 M N a O H washes f o l l o w e d b y three w a t e r washes b e f o r e re-use. N o p r o b l e m s with c r u d f o r m a t i o n o c c u r r e d after t r e a t m e n t o f the feed w i t h gelatin p r i o r t o a run. RESULTS
Zirconium~hafnium separation All runs were s t o p p e d at s t e a d y state o p e r a t i o n and samples t a k e n o f b o t h the a q u e o u s a n d solvent phases f r o m the d i f f e r e n t stages. T h e s e samples were a n a l y s e d f o r z i r c o n i u m and h a f n i u m with t h e results given in Figs. 1--3 and
278
I ..×--×-bx \
1.~--
6 4 2
/
/6
/
\\
X/ CONC g/I
6 .,,,,X"
41
/ OC
\"X Hf ( AQ ) X, \ " XHf (OROJ- -
\ -
\ \
\ k
\
X/ ./
\
\ \ \
X"
~Zr(AQ)
OOOl 8 I
B
o.ooo,
\TRACT(
2 ~ ,~ ~ ~ ~ ~ STAGE N U M B E R
Fig. 1. Zirconium and hafnium profiles for run 1. Table 1. The extracti(tn of zirconium was as expect ed virtually complete; the slight loss in run 3 was due to the use of only 3 extraction stages. For nuclear grade material < 1 0 0 ppm of hafnium is per mi t t ed in the zirconium product. As this was n o t achieved in run 1, additional scrub stages were added in run 2. However, the hafnium c o n c e n t r a t i o n in the zirconium was even higher perhaps because the solvent was less loaded with zirconium. It was then realised that DHf in the scrub section was high, varying from 0.1 to 0.2, in relation to the solvent to aqueous flow ratio used. For run 3, therefore, the nitric acid scrub c o n c e n t r a t i o n was reduced from 5 M to 3 M. This decreased the nitric acid level in the extraction section (the aqueous raffinate was found to be 4.2 M
279 10
6 ~0~ 2
0"
~ /×/ .....
x
', \x
I/
~
x/
X .... ~
El-~__[3 ._~B~.~"~ - -
CONC g/t
S
XOZr(ORG )
\.
,~ ..-,X \.,
/x"
.7"
--~
-\ 'k.,
\
'\X "\XHf(AOJ \
',
x-"
o....
\
"\
\
"oZr (AQ) \
oo~ -8 4
2
\ \
6
./J::L,.,
\
\ \
~'E~
O"
\
,,-, 'xHf (ORG)
oooi ~
"",ElU(0 RG.) ~'~
8
UB
---ou (AQ)
EXTRACT1
2 I
STAGE
NUMBER
Fig. 2. Z i r c o n i u m , h a f n i u m and u r a n i u m profiles for run 2.
in acid) w i t h o u t seriously affecting the extraction of zirconium. The Hf(org) profile in Fig. 3 shows t h a t zirconium of nuclear grade is produced with 4--5 scrub stages. In all runs the zirconium nitrate was backwashed into an equal volume of water. The silica c o n t e n t of the zirconium product was ca. 400 ppm. Separation factors may be estimated from the concentration profiles in Figs. 2 and 3 and the data in Table 1.
280
4 2
6 4 2
/ X [] ~
. _EF--- ~
I
~ .iZ O . -
\
/ 6 CONC
g/l
/
4
6 Zr (AO)
\
I
x\
:/\ \
,,x
/
Zr {ORG.) Hf (AQI
~
/
X,.. ,...X/
/ \\
X
0.01
\\ )~
i
i',,
/ 'x Hf [ORG.~
//-K. \/ /
--u~ -r U
"
\.
~uUCORG~ ~u IAa~
×
O"O'
8
X _ . _,~_.. _X . ~ .. - y ~
2 0.0001
1
2
3
4
5 6 7 8 9 STAGE NUMBER
10
Fig. 3. Zirconium, hafnium and uranium profiles for run 3.
Zirconium/uranium separation The extraction of uranium into DBBP is high at all ranges of acidity, the distribution coefficient at trace levels varying between 40 for 0.4 M HNO3 and 150 for 5 M HNO3. The uranium is therefore extracted with the zirconium but during backwashing it remains largely in the organic phase. The behaviour of uranium during extraction, scrub and backwash Was investigated in runs 2 and 3. Profiles are given in Figs. 2 and 3. More than 99% of the uranium was extracted with the zirconium. During backwashing of the zirconium, a small proportion of the uranium accompanied the zirconium. The level of uranium
281
in the zirconium product would not indeed be acceptable, but the uranium could readily be eliminated by a small volume organic scrub in the zirconium backwash contactor. Flowsheet
The recommended flowsheet, giving nuclear grade zirconium, is shown in Fig. 4.
SCRUB 1 HN03 3M VOL. 0.5
I.
FEEO Zr 23 Hf 0.5
[ SOLVENT
1
u
/ 2 ~ /
/
o.~
HNO3 5M VOL. 1
SCRUB (? STAGES)
ISOLVESSO150] | VOL. 3 |
EXTRACTION (3 STAGES) RAFFINATE Zr 0,,16 Hf 0,33 U 0.0013 HNO3~Z.M VOL. 15
EXTRACT Zr 7.4 Hf 0,0006 U 0,13 HN03-0.2M VOL. 3
BACKWASH I WATER VOL 3 BACKWASH (10STAGES) SOLVENT
--~--r o.~ U 0.13 HNO3 LOW VOL 3
PROOUCT Zr 7.4 Hf~lOOppm U ~200 ppm HN03~0.2 M VOL 3
NaOH and water washes and re-use Fig. 4. Flowsheet for zirconium/hafnium separation. Concentrations in g/1 unless stated otherwise.
282
Hafnium recovery Hafnium is a valuable product, and could be recovered from the aqueous raffinate after zirconium extraction. The distribution data in Part 1 show that sufficiently high DH~ values with 20% DBBP/Solvesso 150 could be obtained by operating at 6 M HNO3 or by raising the temperature to 60°C. Probably, too, raising the DBBP concentration to 40% would give the desired result. Backwashing with water should give a pure hafnium product. ACKNOWLEDGEMENTS The authors would like to thank Mr. F. Birks of Applied Chemistry Division, AERE for carrying out some of the analyses, and one of the authors (A.E.P. Brown) the British Council for a research grant.
REFERENCES 1 Brown, A.E.P. and Healy, T.V., 1978. Hydrometallurgy, 3: 265--274. 2 Mukherji, A.K., 1970. Analytical Chemistry of Zirconium and Hafnium, Pergamon, Oxford pp. 157--197, and further references given there.
275
SEPARATION OF ZIRCONIUM FROM HAFNIUM IN NITRIC ACID S O L U T I O N S BY S O L V E N T E X T R A C T I O N U S I N G D I B U T Y L B U T Y L PHOSPHONATE P A R T 2. M I X E R - S E T T L E R R U N S
A.E.P. BROWN* and A.G. WAIN Atomic Energy Research Establishment, Harwell, Didcot, Oxon (U.K.)
(Received January 24th, 1977; in revised form December 5th, 1977)
ABSTRACT Brown, A.E.P. and Wain, A.G., 1978. Separation of zirconium from hafnium in nitric acid solutions by solvent extraction using dibutyl butylphosphonate. Part 2. Mixersettler runs. Hydrometallurgy, 3: 275--282. A process for zirconium/hafnium separation based on the distribution data given in Part 1 (Brown and Healy, 1978) has been successfully tested in a 10-stage Croda mixersettler. The hafnium content of the zirconium could be reduced below the specification for nuclear grade zirconium. Purification of the zirconium from uranium could be achieved, and the hafnium could be recovered if desired. A flowsheet is presented.
INTRODUCTION F l o w s h e e t s (Mukherji, 1 9 7 0 ) f o r t h e p r e p a r a t i o n o f n u c l e a r grade z i r c o n i u m f r o m ores c o n t a i n i n g h a f n i u m , b y s o l v e n t e x t r a c t i o n i n t o t r i b u t y l p h o s p h a t e (TBP) dissolved in an i n e r t d i l u e n t f r o m nitric acid s o l u t i o n , a n d i n t o m e t h y l isobutyl ketone from thiocyanate solutions have been tested and operated w i t h e i t h e r m i x e r - s e t t l e r s or p u l s e d c o l u m n s . In t h e T B P process high ( > 4 0 % ) T B P c o n c e n t r a t i o n s at high acidities (8 M HNO3) are r e q u i r e d , a n d in t h e t h i o c y a n a t e p r o c e s s o n e is l e f t w i t h an a q u e o u s r a f f i n a t e c o n t a i n i n g thioc y a n a t e w h i c h c o u l d lead to possible disposal p r o b l e m s . T h e p r o c e s s d e s c r i b e d a n d t e s t e d in this p a p e r is b a s e d on t h e results given in Part 1 ( B r o w n a n d Healy, 1978). In outline, t h e z i r c o n i u m is e x t r a c t e d b y 20% wt./vol, d i b u t y l b u t y l p h o s p h o n a t e / S o l v e s s o 150 f r o m 5 M HNO3, a n d t h e organic e x t r a c t is s c r u b b e d w i t h 3 M HNO3 to r e m o v e residual h a f n i u m . T h e z i r c o n i u m is t h e n b a c k w a s h e d w i t h water. U r a n i u m s t a y s m a i n l y in t h e organic p h a s e o n b a c k w a s h i n g , a n d a n y residual u r a n i u m a c c o m p a n y i n g t h e z i r c o n i u m c o u l d b e s c r u b b e d o u t again w i t h a small s o l v e n t stream. T h e *Present address: Instituto de Energia AtSmica, Calxa Postal 11049, Sao Paulo, S.P. (Brazil).
276
solvent is washed with dilute NaOH and water before recycling. The process yields nuclear grade zirconium (< 100 ppm Hf). The requirement to remove uranium from the zirconium is an unusual one, arising from the high uranium c o n t e n t of the type of ore found in Brazil. EXPERIMENTAL
Reagen ts
All reagents used with the exception of the zirconium feedstock for runs 1, 2 and 3 are described in Part 1 (Brown and Healy, 1978). The zirconium nitrate feedstock solution was prepared from zircosil granular (a zirconium silicate ore) supplied b y Associated Lead Manufactureres Ltd., containing approximately 66% Zr, 33% SiO2 and 1.5--2.0% Hr. The ore was treated by an alkali fusion with sodium hydroxide (1.4 g NaOH/g ore) at 700°C for one hour. The fused mass was washed and digested for two hours with water at 80°C. The solution was filtered, and the precipitate was further washed with cold water and then digested with concentrated nitric acid for two hours at 80°C to dissolve the zirconium. Acidified gelatine was added to flocculate silica which appeared in colloidal form in the zirconium liquor. After the silica had been filtered off, the acidity of the solution was adjusted to be 5 M in HNO3 and uranium as the nitrate at a concentration of 0.4 g/1 U was added to simulate the particular t y p e of ore already mentioned. Analysis
Zirconium was analysed by precipitation as the oxalate, ignition to the oxide, and weighing or directly on the solution by X-ray fluorescence. Feed solutions were spiked with radioactive ~TSHf tracer and analysed either by gammacounting using sodium iodide detector or by X-ray fluorescence. Uranium was determined b y the delayed neutron counting technique, nitric acid as described in Part 1 and silica by emission spectrography. Mixer-settler runs
Equilibrium data for zirconium and hafnium (see Part 1) were used to construct McCabe-Thiele diagrams to define solvent and aqueous flows to separate zirconium and hafnium. Three runs were carried out, as indicated in Table 1. The residence time in the mixer-settlers was sufficiently long to anticipate near 100% stage efficiencies and the performance of a given number of stages agreed well with the McCabe-Thiele Diagrams. A ten-stage Croda Scientific Equipment Ltd., mixer-settler was used using the modified larger t y p e of glass tube (Hanson et al., personal communication). Feeds were metered with Watson-Marlow peristaltic pumps, the aqueous phase by direct metering and the organic phase by displacement, to prevent
277
TABLE 1 Principal features of runs Feed: Zr, 24 g/l; Hf, 0.5 g/l; U, 0.4 g/l; silica, 0.031 g/1 Run 1
Run 2
Run 3
Flow rates (ml/min)
Aq. feed Scrub Solvent Backwash
3 1.5 9 9
3 1.5 9 9
3 1.5 9 9
Acidities (M)
Aq. feed Scrub
5 5
5 5
5 3
No. of stages
Extraction Scrub
5 4
4 6
3 7
Organic phase from extraction (g/l)
Zr Hf U
11.3 0.012 --
8.5 0.044 0.14
6.9 0.006 0.14
Raffinate
Zr (g]l) Zr lost (%)
0.012 0.05
0.03 0.18
0.16 1.2
Zr product (ppm)
Hf U
1060 --
5200 100
87 220
a t t a c k o f t h e silicone t u b i n g b y the solvent. T h e e q u i p m e n t o p e r a t e d with a c e n t r e feed and solvent and scrub were fed f r o m either end o f t h e mixer-settler bank. E a c h r u n lasted a b o u t seven hours, giving a b o u t eight t h r o u g h p u t s o f solvent and f o u r o f a q u e o u s phase, sufficient for a s t e a d y state t o be reached. E q u i l i b r i u m c o n d i t i o n s were r e a c h e d in a b o u t one h o u r s o p e r a t i o n . T h e solvent was n o t p r e - e q u i l i b r a t e d with nitric acid as m a n u a l pre-equilibration w o u l d have been necessary. T h e z i r c o n i u m nitrate was b a c k w a s h e d i n t o an equal v o l u m e o f w a t e r using the same e q u i p m e n t . A f t e r each r u n t h e solvent was cleaned u p with three 0.1 M N a O H washes f o l l o w e d b y three w a t e r washes b e f o r e re-use. N o p r o b l e m s with c r u d f o r m a t i o n o c c u r r e d after t r e a t m e n t o f the feed w i t h gelatin p r i o r t o a run. RESULTS
Zirconium~hafnium separation All runs were s t o p p e d at s t e a d y state o p e r a t i o n and samples t a k e n o f b o t h the a q u e o u s a n d solvent phases f r o m the d i f f e r e n t stages. T h e s e samples were a n a l y s e d f o r z i r c o n i u m and h a f n i u m with t h e results given in Figs. 1--3 and
278
I ..×--×-bx \
1.~--
6 4 2
/
/6
/
\\
X/ CONC g/I
6 .,,,,X"
41
/ OC
\"X Hf ( AQ ) X, \ " XHf (OROJ- -
\ -
\ \
\ k
\
X/ ./
\
\ \ \
X"
~Zr(AQ)
OOOl 8 I
B
o.ooo,
\TRACT(
2 ~ ,~ ~ ~ ~ ~ STAGE N U M B E R
Fig. 1. Zirconium and hafnium profiles for run 1. Table 1. The extracti(tn of zirconium was as expect ed virtually complete; the slight loss in run 3 was due to the use of only 3 extraction stages. For nuclear grade material < 1 0 0 ppm of hafnium is per mi t t ed in the zirconium product. As this was n o t achieved in run 1, additional scrub stages were added in run 2. However, the hafnium c o n c e n t r a t i o n in the zirconium was even higher perhaps because the solvent was less loaded with zirconium. It was then realised that DHf in the scrub section was high, varying from 0.1 to 0.2, in relation to the solvent to aqueous flow ratio used. For run 3, therefore, the nitric acid scrub c o n c e n t r a t i o n was reduced from 5 M to 3 M. This decreased the nitric acid level in the extraction section (the aqueous raffinate was found to be 4.2 M
279 10
6 ~0~ 2
0"
~ /×/ .....
x
', \x
I/
~
x/
X .... ~
El-~__[3 ._~B~.~"~ - -
CONC g/t
S
XOZr(ORG )
\.
,~ ..-,X \.,
/x"
.7"
--~
-\ 'k.,
\
'\X "\XHf(AOJ \
',
x-"
o....
\
"\
\
"oZr (AQ) \
oo~ -8 4
2
\ \
6
./J::L,.,
\
\ \
~'E~
O"
\
,,-, 'xHf (ORG)
oooi ~
"",ElU(0 RG.) ~'~
8
UB
---ou (AQ)
EXTRACT1
2 I
STAGE
NUMBER
Fig. 2. Z i r c o n i u m , h a f n i u m and u r a n i u m profiles for run 2.
in acid) w i t h o u t seriously affecting the extraction of zirconium. The Hf(org) profile in Fig. 3 shows t h a t zirconium of nuclear grade is produced with 4--5 scrub stages. In all runs the zirconium nitrate was backwashed into an equal volume of water. The silica c o n t e n t of the zirconium product was ca. 400 ppm. Separation factors may be estimated from the concentration profiles in Figs. 2 and 3 and the data in Table 1.
280
4 2
6 4 2
/ X [] ~
. _EF--- ~
I
~ .iZ O . -
\
/ 6 CONC
g/l
/
4
6 Zr (AO)
\
I
x\
:/\ \
,,x
/
Zr {ORG.) Hf (AQI
~
/
X,.. ,...X/
/ \\
X
0.01
\\ )~
i
i',,
/ 'x Hf [ORG.~
//-K. \/ /
--u~ -r U
"
\.
~uUCORG~ ~u IAa~
×
O"O'
8
X _ . _,~_.. _X . ~ .. - y ~
2 0.0001
1
2
3
4
5 6 7 8 9 STAGE NUMBER
10
Fig. 3. Zirconium, hafnium and uranium profiles for run 3.
Zirconium/uranium separation The extraction of uranium into DBBP is high at all ranges of acidity, the distribution coefficient at trace levels varying between 40 for 0.4 M HNO3 and 150 for 5 M HNO3. The uranium is therefore extracted with the zirconium but during backwashing it remains largely in the organic phase. The behaviour of uranium during extraction, scrub and backwash Was investigated in runs 2 and 3. Profiles are given in Figs. 2 and 3. More than 99% of the uranium was extracted with the zirconium. During backwashing of the zirconium, a small proportion of the uranium accompanied the zirconium. The level of uranium
281
in the zirconium product would not indeed be acceptable, but the uranium could readily be eliminated by a small volume organic scrub in the zirconium backwash contactor. Flowsheet
The recommended flowsheet, giving nuclear grade zirconium, is shown in Fig. 4.
SCRUB 1 HN03 3M VOL. 0.5
I.
FEEO Zr 23 Hf 0.5
[ SOLVENT
1
u
/ 2 ~ /
/
o.~
HNO3 5M VOL. 1
SCRUB (? STAGES)
ISOLVESSO150] | VOL. 3 |
EXTRACTION (3 STAGES) RAFFINATE Zr 0,,16 Hf 0,33 U 0.0013 HNO3~Z.M VOL. 15
EXTRACT Zr 7.4 Hf 0,0006 U 0,13 HN03-0.2M VOL. 3
BACKWASH I WATER VOL 3 BACKWASH (10STAGES) SOLVENT
--~--r o.~ U 0.13 HNO3 LOW VOL 3
PROOUCT Zr 7.4 Hf~lOOppm U ~200 ppm HN03~0.2 M VOL 3
NaOH and water washes and re-use Fig. 4. Flowsheet for zirconium/hafnium separation. Concentrations in g/1 unless stated otherwise.
282
Hafnium recovery Hafnium is a valuable product, and could be recovered from the aqueous raffinate after zirconium extraction. The distribution data in Part 1 show that sufficiently high DH~ values with 20% DBBP/Solvesso 150 could be obtained by operating at 6 M HNO3 or by raising the temperature to 60°C. Probably, too, raising the DBBP concentration to 40% would give the desired result. Backwashing with water should give a pure hafnium product. ACKNOWLEDGEMENTS The authors would like to thank Mr. F. Birks of Applied Chemistry Division, AERE for carrying out some of the analyses, and one of the authors (A.E.P. Brown) the British Council for a research grant.
REFERENCES 1 Brown, A.E.P. and Healy, T.V., 1978. Hydrometallurgy, 3: 265--274. 2 Mukherji, A.K., 1970. Analytical Chemistry of Zirconium and Hafnium, Pergamon, Oxford pp. 157--197, and further references given there.