THIRD PHASE FORMATION IN THE EXTRACTION

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135
I s s ue no. 285 Oct ober 2007
FOUNDER’ S DAY
S P E C I A L I S S U E
THIRD PHASE FORMATION IN THE EXTRACTION
OF U (VI), Th (IV) AND Pu (IV) BY N,
N-DIALKYL ALIPHATIC AMIDES
R.K. Jha, K.K.Gupta, P.G. Kulkarni, P.B. Gurba, P. Janardan, R.D. Changarani and P.K.Dey
PREFRE Plant, Nuclear Recycle Group
Bhabha Atomic Research Centre, Tarapur
and
P.N. Pathak and V.K.Manchanda
Radiochemistry Division
Bhabha Atomic Research Centre
This paper was awarded the Best Award in the poster category at the DAE-BRNS Symposium on
“Emerging Trends in Separation Science and Technology (SESTEC-2006)
held at BARC, Mumbai, during September 29-October 1, 2006
I
n recent years, dialkyl aliphatic amides are being
explored as potential alternate extractants to tri-n-butyl
phosphate (TBP), for the reprocessing of uranium,
plutonium and thorium-based fuels. This is due to the
fact, that these ligands possess certain distinct
advantages like poor extraction of fission products,
benign nature of their degradation products, complete
incinerability of the spent solvent and easy synthesis. In
this regard, several dialkyl aliphatic amides have been
synthesized and investigated in our laboratory, under
the conditions prevailing in the PUREX process [1,2].
Among the amides studied, N, N- dihexyl derivatives of
n-hexanamide (DHHA), n-octanamide (DHOA) and n-
decanamide (DHDA) are identified as suitable candidates
for actinide extraction [1,2].
Third phase formation in nuclear solvent extraction
system is observed at high metal and / or mineral acid
loading of the organic phase. Under certain conditions,
the organic phase splits into two layers, the light layer
containing most of the diluent, little extractant and metal;
and a heavy or third phase containing high concentration
of extractant, metal and little diluent. The phenomenon
of third phase formation is mainly caused by the limited
solubility of the metal-ligand complex in the non-polar
organic phase [3].
During the reprocessing of spent nuclear fuel by solvent
extraction, the occurrence of third phase in the extraction
system is undesirable and hence should be avoided.
Apart from posing operational problems and limiting
the throughput of the plant, the third phase formation
during the extraction of fissile elements like plutonium,
constitutes criticality hazard. This is particularly
relevant to fast reactor fuel reprocessing, where the
plutonium concentration is fairly high. Third phase
formation in the TBP extraction of Th (IV), U (IV) and
Pu (IV) is well known [4]. In our earlier publication,
we reported the third phase formation in
the extraction of uranyl nitrate by DHHA and
DHOA [5]. The present work reports the Limiting
Organic Concentrations (LOC), above which third
136
I s s ue no. 285 Oc t ober 2007
FOUNDER’ S DAY
S P E C I A L I S S U E
Table 1 : LOC of Pu (IV) and U (VI) as a function of nitric acid
concentration at 25
O
C
@ Third phase in the form of crud
phase formation occurs during extraction of Pu (IV) with
1.1M DHOA in n-dodecane; U (VI) with1.1M DHDA in
n-dodecane; and Th (IV) with 1.1M DHOA and 1.1M
DHDA in n-dodecane(n-DD) and normal paraffin
hydrocarbon (NPH) as a function of nitric acid
concentration at 25° C. In the case of Th (IV), LOCs
were also measured with 1.1M TBP in n-DD/NPH for
comparison.
The LOC determination was carried out as follows : A
stock solution of 100 mg/ml of Pu (IV) was prepared in
2M HNO
3
by purifying Pu (IV) nitrate

solution by anion
exchange separation method. Stock solutions of U (VI)
& Th (IV) of 300-350 g/l were prepared by dissolving
nuclear grade U
3
O
8
and Th (NO
3
)
4
in 0.5 M nitric acid.
Suitable aliquots of the stock solution were evaporated
and dissolved in the desired concentration of nitric acid.
In the case of plutonium, the oxidation state was adjusted
to Pu (IV) by passing N
2
O
4
gas
through the solution at room
temperature and was
confirmed analytically by TTA
extraction method.
Equal volumes (2ml) of the
aqueous phase containing Pu
(IV) (100- 300 mg/ml)/ U(VI)
( 300-350 mg/ml )/ Th(IV)
(300-350 mg/ml) at the
desired concentration of
nitric acid ( 1-7 M) and
pre-equilibrated organic
phase ( 1.1 M DHOA/DHDA/
TBP in n-DD/NPH) were
equilibrated by magnetic
stirring for 30 minutes in
thermostated water bath
adjusted to 25°C. The third
phase so formed in the
system was redissolved by
diluting the aqueous phase
with nitric acid solution of the
required concentration. After
equilibration, the two phases were allowed to settle for
one hour. The organic phase was assayed for metal
concentration to compute the LOC. Plutonium assay was
carried out by ICP-AES employing 300.057 nm emission
line. Prior to estimation, Pu from the organic phase was
quantitatively stripped in to the aqueous phase (0.5 M
HNO
3
), using 0.5 M solution of tertiary butyl
hydroquinone in 1.1 M TBP/NPH as an organic soluble
reductant. Uranium was determined by redox titrimetry
(Davis & Gray method). Thorium estimation was carried
out by complexometric titration at pH 1-2 with 0.01 M
EDTA using Xylenol Orange as indicator. Nitric acid
concentration of the aqueous phase at equilibrium was
determined by potentiometry, using standard NaOH
solution after complexing metal ions with saturated
solution of potassium oxalate. The LOC data obtained
for Pu (IV) & U (VI) are given in Table 1 and that for Th
(IV) in Table 2.
137
I s s ue no. 285 Oct ober 2007
FOUNDER’ S DAY
S P E C I A L I S S U E
Table 2 : LOC of Th (IV) as a function of nitric acid concentration at 25
O
C
(LOC values are in g/l)
The LOC value of Pu (IV) in DHOA-n-DD system,
increases from 29.49 g/l (at 1 M HNO
3
) to 49.30 g/l (at
3.3 M HNO
3
); thereafter it decreases gradually to 13.15
g/l at 7M HNO
3
. This variation in the trend can be due
to the change in the proportions of the extractable species
like Pu(NO
3
)
4
.2DHOA, HNO
3
.DHOA and [Pu(NO
3
)
6
]
2-
[ HDHOA]
+
2
with varying aqueous phase nitric acid
concentration [2,5]. At lower nitric acid concentrations
(0.5-1 M), the third phase appeared in the form of crud,
that can be attributed to the extensive aggregation of
the extractable species in the organic phase [6]. The LOC
data in U (VI)-DHDA-n-DD system indicates no definite
trend from 0.5 to 5 M HNO
3
(25.41 – 55.4 g/l). Third
phase appeared in the form of crud which redissolved
on diluting the aqueous phase with the respective
concentration of nitric acid. However, at higher nitric
acid concentration (from 5.5 to 8 M), the crud formation
was not observed and the LOC values decreased from
68.5 g/l (at 5.6 M HNO
3
) to 39.1 g/l at 8 M HNO
3
.
The data from Table 2 indicates that the LOC of Th(IV)
with DHOA are lower than that of TBP & DHDA at all
the nitric acid concentrations studied( 1- 7 M) and for
DHDA-n-DD/ NPH is the highest. In all the cases, LOC
decreases with increasing nitric acid concentration. This
may be due to increasing polarity of the organic phase
due to increased extraction of nitric acid resulting in
decreased solubility of Th solvated species. The LOC varies
from 39.55 g/l to 14.15 g/l for DHOA-n-DD
system,38.56 g/l to 13.25 g/l for DHOA-NPH
system,64.96 g/l to 19.92 g/l for DHDA-n-DD
system,59.35 g/l to 18.21 g/l for DHDA-NPH system,
45.15 g/l to 15.16 g/l for TBP-n-DD system and 44.25
g/l to 12.99 g/l for TBP-NPH system from 1 to 7 M
HNO
3
. It is significant to note that the LOC values for all
the extractants are marginally higher in n-dodecane as
compared to NPH, unlike the Pu(IV) and U(VI) , which
exhibit higher solubility in relatively polar diluents like
NPH[5].
138
I s s ue no. 285 Oc t ober 2007
FOUNDER’ S DAY
S P E C I A L I S S U E
Ab o u t t h e Au t h o r sAb o u t t h e Au t h o r s
Ab o u t t h e Au t h o r sAb o u t t h e Au t h o r s
Ab o u t t h e Au t h o r s
The study is part of the extensive work taken up in our
laboratory for evaluating the usefulness of the commonly
used amides in various spent fuel reprocessing schemes.
References
1.P.B. Ruikar, PhD Thesis, Bhabha Atomic Research
Centre, Bombay University (1992).
2.K.K.Gupta, PhD Thesis, Bhabha Atomic Research
Centre, Mumbai University (1997).
3.Y.Marcus, A.S. Kertes, Ion Exchange & solvent
extraction of Metal complexes; Wiley Interscience:
New York, p.715 (1969).
4.P.R.Vasudeva Rao, Z.Kolarik, Solvent Extr. Ion
Exch., 14,955 (1996).
5.K.K.Gupta, V.K. Manchanda, S.Sriram, G.Thomas,
P.G.Kulkarni and R.K.Singh, Solvent Extr. Ion
Exch.,18, 1,421 (2000).
R.Chiariza, M.P.jensen, M.Borkowski, J.R.Ferraro,
P.Thiyagarajan and K.C.Littrel, Solvent Extr. Ion
Exch., 21, 1, 1-27, (2003).
Mr. P.K. Jha joined Plutonium
Plant Trombay in 2000 after
completing his B.Sc. in Chemistry
(Hons.) from L.N.Mithila University,
Darbhanga. He is currently working
as a Chemist in PREFRE, Tarapur.
He has registered for M.Sc. from the University of
Mumbai. His topic for research is “Evaluation of N,
N-dialkyl amide as thorium-based fuel”.
Dr K.K.Gupta (B.Sc. Chemistry
(Hons.), University of Delhi,
Ph.D., University of Mumbai,
1998) joined PREFRE Plant BARC,
Tarapur in 1977 and is currently
working in Spectroscopy
Laboratory of the Plant. His main
area of research is development of alternate
extractants to TBP in PUREX process and
Spectrochemical Analytical methods for the assay
of actinides in the various streams of the PUREX
process.
Mr P.G.Kulkarni


(Chemistry graduate, Karnataka
University, Dharwar 1971), joined Fuel Reprocess-
ing Division, BARC in 1972. He is currently working
in Quality Control analysis group of Laboratory
Section, PREFRE, Tarapur. His area of interest is char-
acterization of nuclear materials with respect to
trace elemental impurities employing ICP-AES. He
is also working on the development of analytical
technique using ICP-AES for process control in re-
processing plants and investigations on the
dialkyl amides as alternate extractants in PUREX
process.
Mr. P. Janardan
( (
( (
(B.Tech.,
Chemical Engineering from
Osmania University Hyderabad,
1
st
Class with distinction) Joined
PREFRE plant in 1975. He was
associated with the
commissioning trials of PREFRE
Plant and carried out required modifications based
on the commissioning trials experience. Presently
he is holding the post of Plant Superintendent of
PREFRE plant and is fully responsible for the
operation of the Plant. He was also involved in the
Spent Fuel Storage Facility Tarapur for
commissioning trials and later took charge of the
SFSF. He also attended the international training
course on Implementation of State System of
Accounting for the Control of Nuclear Material at
Moscow during Oct. 2004. He has also attended
the Technical meeting of IAEA to review and
develop a safety guide on classification of
radioactive wastes at Vienna during Nov.2006.
139
I s s ue no. 285 Oct ober 2007
FOUNDER’ S DAY
S P E C I A L I S S U E
Mr R.D.Changrani graduated in
Chemical Engineering in 1974
from M.S. University Baroda,
joined BARC, Tarapur in 1975
from 18
th
batch of BARC Training
School. He was associated with
commissioning of PREFRE plant
and completed several campaigns of reprocessing
of PHWR fuel from different reactors. He was elevated
to the post of Chief Superintendent of NRG facilities
since 2003 and is responsible for the continuous
operation of the reprocessing and waste
management plants. He has been involved in
commissioning of AVS, resin fixation facility and
Spent Fuel Storage Facility. He has participated in
many International Conferences. He was an active
member of a committee formed by Crisis
Management Group, DAE to provide guidelines for
the transport of spent fuel by road.
Mr P.K. Dey is a graduate in
chemical Engineering from
Jadavpur University, Kolkata. He
joined BARC in the year 1971
and is associated with the
activities of spent fuel
reprocessing of the
Department. He has vast experience in construction,
commissioning and operation of reprocessing
plants. He has carried out extensive R&D studies to
improve the reprocessing technology for better
recovery and minimization of radioactive waste
generation. He has more than 120 papers to his
credit in various international journals and
symposia. Presently he is Head of Fuel Reprocessing
Division of BARC and is responsible for the
operation of all the reprocessing plants in the
country.
Dr P.N. Pathak joined
Radiochemistry Division in
1995 after completing the 38th
batch of Chemistry training
course. He has contributed
towards the basic studies
Dr V.K. Manchanda


joined
the Radiochemistry Division,
B.A.R.C. in 1969 after
graduating from Delhi University
and from B.A.R.C. Training
School . He was awarded Ph.D.
by Bombay University in 1975
and carried out Post-Doctoral work at UTEP, Texas,
U.S.A. as a Fulbright Scholar (1985-87). His research
interests include; thermodynamics and kinetics of
complexes of macrocyclic ligands with lanthanides
and actinides, design and synthesis of novel
extractants of actinides relevant in the back end of
the fuel cycle, chemical quality control of Pu-based
fuels and speciation of actinides in aquatic
environment. He is a Ph.D. guide for Chemistry at
the University of Mumbai and HBNI. He has about
150 publications in international journals and
about 400 conference / symposium papers. He is
currently on the Advisory Board of an internationally
reputed journal “Radiochimica Acta” and is a
member of Board of Studies in Chemical Sciences
of HBNI (Deemed University). He is the President of
IANCAS and is founder President of Indian
Association of Separation Scientists and
Technologists (INASAT). He currently heads the
Radiochemistry Division of BARC.
dealing with reprocessing of thorium-based fuels
using branched dialkyl amides and the use of
macrocyclic ligands for 90Sr / 90Y separation. He
has worked as a post-doctoral research fellow in
Prof. G.R. Choppin’s laboratory at the Florida State
University, Tallahassee, Florida, USA. He has studied
the interaction of actinides, fission products and
structural elements with different forms of silica.
He is the recipient of Tarun Dutta Memorial Award
instituted by Indian Association of Nuclear Chemists
and Allied Scientists (IANCAS). He has 53
publications in international journals and 90
conference / symposium papers.