IBN AL- HAITHAM J. FOR PURE & APPL. SCI VOL. 23 (1) 2010

Continuous Extraction and Stripping of Neptunium By

Fresh and Degradated Tributyle Phosphate Using Co-60
Cell

H. H. Al-Taweel , A. H. Al-jibori
Department of Chemistry, College of Education Ibn- Al Haitham ,
University of Baghdad.

Abstract
The behaviour of Np-239 during the Continuous extraction and stripping was followed .
Three Continuous extraction experiments were carried out . In the first experiment the
extraction and stripping were carried out by using Tributyl Phosphate / treated odorless
kerosene as the organic phase , while the aqueous phase was uranium and neptunium-239
dissolved in 3M HNO3 . In the second experiment irradiation of organic phase up to 30 M rad
were carried out , while keeping the aqueous phase as it is in the first experiment. In the third
experiment , the acidity of the aqueous phase was 1.5M instead of 3M and keeping the
organic phase as it is in experiment 1. The results obtained in tables 1-3 show the possibility
of rejection Np-239 according to the conditions of run 1. The degradation product of the
tributyl phosphate namely di and monobutyl phosphate plays an important role in the
difficulty of Np stripping. The third experiment conditions were the best.

Introduction
In hot nitric acid solution neptunium can be existed in three valence states ( IV, V, VI )
depending on the acidity, oxidation potential of the solution , nitrous acid concentration and
nitrate ion concentration. So the neptunium behaviour appears very complicated while the
trivalent state can not be observed in nitric medium except as transient species . the
hexavalent state is the stable form in high concentrations of nitric acid ( > 5M) while the
pentavalent state is the most stable form in lower nitric acid solution < 2M [1-4] . The
pentavalent state exists as NpO2+ ion which disproportionates at higher acid concentration to
Np IV and Np VI. This disproportionation reaction can be represented by the following
equation which is strongly dependent on acidity .

2NpO2+ +4H+ Np4+ + NpO22+ + 2H2O

Since the reduction to Np4+ involves the breaking of the strong Np-O bond of the NpO2+ ,
the oxidation to NpO22+ is favored in this reaction because it takes place with a simple
electron transfer [4-7]
It is desirable that neptunium would be rejected to the high activity waste , preferably in the
first extraction cycle , but it is not clear that the necessary extent of rejection could be
accomplished in one cycle . The following reaction might occur and it is not possible to
control precisely the position of equilibrium

NpO2 + 1/2 HNO2 + 1/2 H2O NpO2 + 2/3 H + 1/2 NO3
2+ + + -

The oxidation of NpO2+ by NO3- is favored by high acidity and low nitrous acid
concentration in the 10-3 M range [4] , while even at high acidities , nitrous acid (10-2M)
reduces NpO22+ to NpO2+.

IBN AL- HAITHAM J. FOR PURE & APPL. SCI VOL. 23 (1) 2010

Thus maintenance of the desired inextractable pentavalent state , depends on maintaining
the nitrous acid concentration in the proper range.
Published work on Neptunium distribution ratios of tetra and hexavalent by TBP in xylene
from 3M HNO3 shows that the distribution ratio of the hexavalent is much higher than
tetravalent state [3].
It is well known that radiolysis is by far the greatest contributor to solvent degradation and
that the main products from radiolysis of TBP are H2MBP and HDBP , and it is reported that
HDBP is produced in a greater yield than H2MBP [2,4].
The presence of nitric acid increases the yield of HDBP and H2MBP.
The aim of the present work is to investigate the continuous extraction and stripping
behaviour of neptunium by carrying out 3 continuous extraction runs to follow the Neptunium
behaviour:

1- In the first run , fresh 20% TBP/kerosene/3M HNO3 system was used.
2- In the second run , irradiated 20% TBP/kerosene/3M HNO3 system was used.
3- In the third run , fresh 20% TBP/kerosene/1.5M HNO3 system was used.

Experimental
Three samples of U3O8 of about 20,15 and 10 mgs were irradiated separately for 72 hours
in the research reactor. The neutron flux was 0.5×1013 n/cm2 .Sec. and the reactor power was
(5MW). The Np-239 resulting from the uranium irradiation was used after a short cooling
time of about two days.
Each sample was dissolved in 6M nitric acid and diluted with more than 20 mls of 6M
Nitric acid , the first two samples were refluxed for about 30 minutes , then added to the feed
solution .The third sample was heated until the brown fumes of nitric acid covered the whole
container.

Irradiation of the extractant
Five liters of the extractant (20%TBP/Kerosene/HNO3) were exposed to a γ -ray source of
Co-60 for 105 hours up to 30 Mrad to study the effect of organic degradation products namely
monobutyl phosphate and dibutyl phosphate that could be formed due to γ – rays emitters that
are actually present in such a process. i.e a simulation of real conditions . This irradiated
extractant was by used in the second run.
The estimation of the degradation product , resulting from the above irradiation of the TBP
, was analysed using HPLC and found to be 0.56%.
Continuous extraction experiments
The feed solution for the continuous extraction and then stripping run was prepared from
the following constituents:
- A portion of the dissolved irradiated uranium sample containing Np-239.
- 35g/l uranium as UO2.
- 7g/l aluminium as Al(NO3)3.9H2O.
- 7g/l magnesium as Mg(NO3)2.6H2O.
- 0.02M sodium nitrite.
- 3M nitric acid.
Hydraulic equilibrium was carried out for both extraction and stripping batteries (fig-1)
according to the following parameters:
Aqueous phase:
- Strip solution , 0.1M HNO3 , 0.6 l/hr.
- Scrub solution , 3M HNO3 , 0.12l/hr.
- Feed solution , 35g/l uranium in 3M HNO3 , 0.36 l/hr , 7g/l aluminum and 7g/l Mg
As nitrate , and 0.02M NaNO2.
Organic phase.

IBN AL- HAITHAM J. FOR PURE & APPL. SCI VOL. 23 (1) 2010

- 20% TBP – Kerosene - 0.6 l/hr.
The above parameters were set for the first continuous extraction run.
For the second run the organic phase was irradiated by using Co-60- source up to 30M
Rad . In the third run , the same conditions and parameters as in the first continuous extraction
run except the acidity of the scrub and feed solutions were made 1.5M HNO3 instead of 3M.
Measurements
Np-239 activity were measured by using 277 keV γ energy with the aid of Ge detector of
(97) cm3 active volume and 4096 – multichannel analyser, camac ADC type 9060 linked with
HP-computer ( Princeton-Gamma Tech, W. Germany).

Result and Discusion
Continuous extraction- stripping run no.1
The result of the first Continuou extraction run table 1 shows ( at the steady state i.e. after 3
hours of operation) that neptunium is almost completely extracted by TBP.
Only 3- 3.9% of Neptunium follows the aqueous waste stream (A.W) . This behaviour
could be explained that the nitric acid morality of the extraction battery (3M HNO3) is quite
suitable to make Np in the extractable VI and IV valence state.
Stripping with 0.1 HNO3 is very efficient with 100% of Np being stripped (A.P in table.1)
and 0.2 - 0.7% of Np in organic waste , for a couple of samples only , the remaining , samples
gave undetectable activity , thus complete stripping was accomplished.
Continuous extraction- stripping run no.2
The effect of the degradation products of the organic solution (formation of HDBP and
H2MBP) was followed in this run ,the results were tabulated in table 2 , it can also be
concluded that all Neptunium is extracted to the organic phase , even more than the case of
the non-irradiated solvent. This is also evident from the very low percentages of Neptunium
in aqueous waste streams between 0.9-2.0% at the steady state ( i.e. after 3hr s of operation).
A major difference in results of the first continuous extraction run and the second is
observed in the stripping stages , were a poor stripping was clearly noticed , ranging between
61-75%.The remaining Neptunium not stripped ranging between 25-38% is left in the organic
waste stream (O.W). This poor stripping may be explained on the basis that certain
degradation products are forming with Neptunium , difficulty stripped complexes.
Continuous extraction- stripping run no.3
In table 3 were neptunium in the extraction stages is being separated among the aqueous
waste stream (58-60% after 4 hours of operation ) and the organic product (40-44% after 4
hours of operation ). This indicates that both extractable Np IV,VI valence state and non
extractable V valence state were formed in solution at such low acidity (1.5M HNO3) . A
complete stripping of Np is observed in the stripping stages.

Conclusion
1- Almost complete extraction of neptunium in the first run made us to conclude
that little amounts of the neptunium is in a pentavalent state.
2- Neptunium stripping is difficult when irradiated solvent is being used .
3- Lowering the acidity of nitric acid from 3M to 1.5M reduced greatly the percentage
of Neptunium coextracted with uranium.
Therefore to have better results in rejection of neptunium to the high activity waste , a
lower nitric acid conc.(1.5M) of the feed is recommended rather than 3M .Also, more than
one extraction cycle is required.

References
1-Siddall , T.H. ;Dukes , E.K.(1959) J.Am.Chem.,Soc.,81:790.
2-Wymer , R.G ; Vodra , B.L. (1981) Light Water Reactor Nuclear Fuel Cycle ,
CRC press:91.

IBN AL- HAITHAM J. FOR PURE & APPL. SCI VOL. 23 (1) 2010

3-Patil , S.K. (1973) J.Inorg.Nuc.Chem.,35:2357.
4-Schuls, W. ; Navartil , J.D.(1984) Science and Technology of Tributyl
Phosphate,CRC press :12 .
5-Rudisill, T. S. (2002) WSRC – TR report, Westinghouse Savannah River

Company ,72 Rev.1.
6-Gaubert , E.t.; Jobson , M ; Birkett , J. E ; Denniss , I.S. and I. May (2000)
Atalante 2 : 16.
7-May , I. ; Taylor , R.j. and Brown , G.(1998) J. alloys and compounds, 5:271

Table (1): Continuous extraction and stripping run using fresh 20%
TBP-kerosene as extractant , and feed solution 35 gU/l ,
7 gAl/l ,7 gMg/l in 3M HNO3 and 0.02M NaNO2, scrubbing
with 3M HMO3 and stripping with 0.1 HNO3.

Times in
hours

Extraction Stripping
%Np in A.W. %Np in O.P. %Np in A.P. %Np in O.W.

1 2.0 50
2 3.4 81.1 100 Nil
3 3.9 100.0 100 0.7
4 3.0 95.9 100 0.2
5 3.6 95.4 100 Nil

5.5 3.8 96.1 100 Nil

Table (2):Continuous extraction and stripping run using irradiated
20% TBP-kerosene as extractant , and the feed , scrub and
strip is the same as in table (1).

Times in
hours

Extraction Stripping
%Np in A.W. %Np in O.P. %Np in A.P. %Np in O.W.

1
2
3 2.0 100 75 25
4 1.5 93 62 38
5 0.9 100 73 31

5.5 0.9 100 61 36
Table(3): Continuous extraction and stripping run using fresh 20%
TBP-kerosene as extractant , and feed solution 35 gU/l ,
7 gAl/l ,7 gMg/l in 1.5M HNO3 and 0.02M NaNO2,
scrubbing with 1.5M HMO3 and stripping with 0.1 HNO3.

Times in
hours

Extraction Stripping
%Np in A.W. %Np in O.P. %Np in A.P. %Np in O.W.

2.5 43 57 100 Nil
3.0 48 52 100 Nil
4.0 58 42 100 Nil
5.0 60 40 100 Nil
5.5 56 44 100 Nil

Where
A.W. is aqueous waste stream
O.P. is organic product stream
A.P. is aqueous product stream
O.W. is organic waste stream

IBN AL- HAITHAM J. FOR PURE & APPL. SCI VOL. 23 (1) 2010

20%TBP
kerosene

Feed
solu.

Scrub
solu.

Strip
Solu.

Stripping battery

Extraction battery

A.P. O.W. A.W.

Table 1. Continuous extraction and stripping run using fresh 20%
TBP-kerosene as extractant , and feed solution 35 gU/l ,
7 gAl/l ,7 gMg/l in 3M HNO3 and 0.02M NaNO2, scrubbing
with 3M HMO3 and stripping with 0.1 HNO3.

Times in
hours

Extraction Stripping
%Np in A.W. %Np in O.P. %Np in A.P. %Np in O.W.

1 2.0 50
2 3.4 81.1 100 Nil
3 3.9 100.0 100 0.7
4 3.0 95.9 100 0.2
5 3.6 95.4 100 Nil

5.5 3.8 96.1 100 Nil

Table 2:Continuous extraction and stripping run using irradiated
20% TBP-kerosene as extractant , and the feed , scrub and
strip is the same as in table 1.

Times in
hours

Extraction Stripping
%Np in A.W. %Np in O.P. %Np in A.P. %Np in O.W.

1
2
3 2.0 100 75 25
4 1.5 93 62 38
5 0.9 100 73 31

5.5 0.9 100 61 36

Table 3. Continuous extraction and stripping run using fresh 20%
TBP-kerosene as extractant , and feed solution 35 gU/l ,
7 gAl/l ,7 gMg/l in 1.5M HNO3 and 0.02M NaNO2,
scrubbing with 1.5M HMO3 and stripping with 0.1 HNO3.

Times in
hours

Extraction Stripping
%Np in A.W. %Np in O.P. %Np in A.P. %Np in O.W.

2.5 43 57 100 Nil
3.0 48 52 100 Nil
4.0 58 42 100 Nil
5.0 60 40 100 Nil
5.5 56 44 100 Nil

Where
A.W. is aqueous waste stream
O.P. is organic product stream
A.P. is aqueous product stream
O.W. is organic waste stream

final report
مجلة ابن الهيثم للعلوم الصرفة والتطبيقية المجلد23 (1) 2010

Table 1