Journal of Nuclear and Radiochemical Sciences, Vol. 13, No.1, pp. 1-7, 2013

ArticlesExtraction of Europium(III) and Cobalt(II) by N,N,N’,N’-Tetraoctyldiglycolamide and
N,N,N’,N’-Tetrahexyldiglycolamide from Aqueous Acid Solutions
E. Metwally, A. Sh. Saleh*, and H. A. El-Naggar,
Nuclear Chemistry Department, Hot Laboratories Center, Atomic Energy Authority, Inshas, Cairo - 13759,
Egypt
Received: November 7, 2012; In Final Form: January 15, 2013
N,N,N’,N’-tetraoctyldiglycolamide (TODGA) and N,N,N’,N’-tetrahexyldiglycolamide (THDGA) were synthesized
and characterized in order to further evaluate them as extracting agents for Eu(III) and Co(II) from nitric andhydrochloric acid solutions. Analysis of the dependence of metal distribution ratio, DM, on concentrations ofr e a ge nt s i nd ic a t e d t h a t t h e d om i n a nt ex t r a c t e d c om plexe s a r e E u ( T OD GA) 3 ( NO 3 ) 3 ( H NO 3 ) ,Eu(THDGA)3 (NO3)3 (HNO3), Eu(THDGA)3 (NO3)3 (HNO3)2 and Co(TODGA)Cl2 (HCl). In addition, TODGA wasevaluated for partitioning of Eu(III). It was concluded that, with acidity adjustment, Eu(III) can be separated fromZr(IV), Nb(V), Co(II) and Cs(I) in nitric and hydrochloric acids.

1. Introduction
One of the main concerns related to the disposal of high–level radioactive liquid waste (HLLW) generated after reprocessing of spent nuclear fuel is related to the presence within
this waste of long-lived radionuclides (LLRNs). The LLRNs
in the spent nuclear fuels are mostly the so-called minor
actinides (neptunium (Np), americium (Am) and curium (Cm))
and certain fission products. Transmutation of LLRNs toshort-lived or stable isotopes represents a viable nuclear waste
management strategy to drastically reduce the time and spacerequirements for a geological repository of the remaining
waste. To be able to destroy LLRNs in a transmutation process
they must be separated from the rest of the HLLW. Therefore,
the concept of partitioning and transmutation (P&T) has been
proposed for treatment of HLLW.1-3 The P&T concept imposes
highly-set demands on recovery yields and decontamination
factors of the separated species. In this context, there has been
considerable interest in amide extractants for the extraction oftrivalent actinides and lanthanides from HLLW.4-9 The amide
reagents have the advantage that they can be completely
decomposed to gaseous products, thus minimizing any residues
for ultimate containment. Several studies have indicated that
diglycolamide-based extractants show unusually effective
extraction of actinides and lanthanides from nitric acid solutions.10-14 Among diglycolamides, N,N,N’,N’-tetraoctyldiglycolamide (TODGA) has shown the most favorable combination ofproperties.15,16 and has been the focus of further studies. Sasaki
and Choppin13 have shown that the diglycolamide group is tridentate in configuration complexing trivalent metal ionsthrough two carbonyl oxygen donors and an ether oxygen
donor. Another interesting behavior of diglycolamide extraction systems is the hyperstoichiometric acid dependency. Yaita
et al.17 attributed it to acid – driven aggregation of diglycolamide which was studied by several authors.18,19 On the other
hand, Shimada et al.20 and Sasaki et al.21 attributed the hyperstoichiometric acid dependency of diglycolamide extraction toassociation of nitric acid molecules in metal - diglycolamide
complexes.
In seek for partitioning of HLLW, Modolo et al.22,23 investigated the efficiency of TODGA for extraction of trivalent* C o r r e s p o n d i ng a u t h o r. E - m a i l : a . s a l e h @ e a e a .o r g.eg,
foralaa@hotmail.com Tel.: +20 244620776, Fax: +20 244620784

actinides and lanthanides from raffinate of the PUREX process. They have also evaluated an extractant mixture of
TODGA and tributylphosphate (TBP) for the separation ofactinides(III) and lanthanides(III).24-26 Extraction studies havedemonstrated the efficiency of the TODGA + TBP extractant
mixture for the recovery of minor actinides from genuine
PUREX raffinate. Very high recovery and decontamination
factors were obtained for Am and Cm. Ansari et al. 27 haveevaluated a mixture of TODGA and N,N-dihexyloctanamide(DHOA) for lanthanides partitioning from simulated HLLW.
Quantitative extraction (forward and backward) of trivalentlanthanides was achieved in four stages each.
In spite of the previous studies, the research continues forbetter understanding of the basic chemistry involved in diglycolamide extraction systems and for developing the process forpotential full-scale operation. Additionally, only few studies
have been reported on extraction of transition metal ions withdiglycolamides. Therefore, our purpose in this research is to(i) study the extraction behavior of Eu(III) with diglycolamides,(ii) further evaluate TODGA as extractant for lanthanides partitioning and (iii) study the extraction behavior of Co(II) withTODGA and primarily identify the structure of Co – TODGA
complexes.
2. Experimental
2.1. Synthesis of tetraalkyldiglycolamides. N,N,N’,N’tetraoctyldiglycolamide (TODGA) and N,N,N’,N’-tetrahexyldiglycolamide (THDGA) were synthesized by the reaction of
diglycolyl chloride with dialkylamines (dioctylamine or dihexylamine) and triethylamine.28 All chemicals were purchasedfrom Aldrich and used as received. The products of TODGA
and THDGA were characterized by elemental analysis andnuclear magnetic resonance. The elemental analysis was performed on a Vario EL Elementar analyzer and the 1H-NMR
characterization was performed on a Varian Gemini 200 MHz
NMR spectrometer. The chemical shift values are reported
relative to trimethylsilane (TMS) standard and using CDCl3 as
solvent.
N,N,N’,N’-tetraoctyldiglycolamide (TODGA) was obtained
as yellow oil in 57% yield. The % composition found: C(73.52), H (12.24), N (5.03); calcd for C36H72N2O3: C (74.43), H(12.49), N (4.82). The chemical shift values (ppm): 4.185 (s),3.175 (t), 3.069 (t), 1.153 (br) and 0.759 (br) are assigned to the© 2013 The Japan Society of Nuclear and Radiochemical Sciences
Published on Web 01/28/2013

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J. Nucl. Radiochem. Sci., Vol. 13, No. 1, 2013***

protons of O-CH 2-CO, N-CH 2-(CH2) 6 -CH3, N-CH 2-(CH2) 6 CH 3, N-CH 2 -(CH*2 ) 6 -CH 3 and N-(CH 2 ) 7-CH*3, respectively.
The structure of TODGA is presented in Figure 1(a).
N,N,N’,N’-tetrahexyldiglycolamide (THDGA) was obtained
as yellowish brown oil in 92% yield. The % composition
found: C (70.78), H (11.64), N (6.34); calcd for C28H56N2O3: C(71.74), H (12.04), N (5.98). The chemical shift values (ppm):
4.205 (s), 3.199 (t), 3.087 (t), 1.426 (br), 1.187 (br) and 0.786(m) are assigned to the protons of O-CH*2-CO, N-CH*2-(CH2) 4CH 3 , N-CH* 2 - (CH 2 ) 4 -CH 3 , N-CH 2 -CH* 2 - (CH 2 ) 3 -CH 3 , N(CH 2 ) 2 -(CH*2 ) 3 -CH 3 and N-(CH 2 ) 5 -CH*3, respectively. The
structure of THDGA is presented in Figure 1(b).
2.2. Reagents. All the chemicals were of analytical grade
and all water was bidistilled. The radionuclides 152+154Eu, 141Ce,
95
Zr, 181Hf, 95Nb, 60Co and 134Cs were used as tracers for Eu, Ce,Zr, Hf, Nb, Co and Cs, respectively. 152+154Eu, 141Ce, 95Zr, 181Hf,
60
Co and 134Cs were prepared by neutron irradiation of suitabletarget materials in the Egyptian research reactor ET-RR-2.
95
Nb was obtained as the daughter of 95Zr.
2.3. Extraction procedure. As an alkane diluent has usually been utilized in liquid – liquid extraction processes involving HLLW, the organic solutions were prepared by dissolving
certain quantities of TODGA or THDGA in n-hexane. The
organic solution was equilibrated with acid solution of desiredconcentration without metal ion. One mL of the pre-equilibrated organic solution was mixed with 1 mL of aqueous solution spiked with tracer amount(s) of radionuclide(s). The
mixture was shaken mechanically in 5 mL glass vial in a thermostated water bath at 25 ± 1 °C. Preliminary experiments
indicated that the reaction is fast and equilibrium is reachedwithin 5 minutes, which is consistent with kinetics datareported for TODGA extraction systems.21 The two phases
were separated by centrifugation and suitable aliquots of bothphases were withdrawn for activity measurement. The gamma
activities of the radionuclides were measured using a hyper
pure germanium (HPGe) detector connected to multi-channel
analyzer operating under Genie-2000 software (Canberra
Corp.). The distribution ratio, DM, was calculated according toequation 1:
DM = Aorg / Aaq

O

O
C8H17

O

N

N

(a)
O

O
C6H13

O

N

N

C6H13

C6H13

C6H13

(b)
Figure 1. Structures of TODGA (a) and THDGA (b).

10

4

10

3

10

2

10

1

10

0

0.10M TODGA/n-hexane
0.01M THDGA/n-hexane

slope ~ 4.4(1)

where Aorg and Aaq are the gamma activities of the radionuclide
in the organic and aqueous phases, respectively.

C8H17

C8H17

C8H17

DEu

2

slope ~ 6.6-1

10

3. Results and Discussion
3.1. Extraction of europium(III)Extraction equilibrium: The extraction of radiotracer
amount of 152+154Eu(III) was studied from nitric acid solutions.
The nitric acid dependence of europium distribution ratio, DEu,
was measured and the results are presented in Figure 2. The
DEu increases with increasing HNO3 concentration which indicates that NO-3 anion plays an important role in the extraction
reaction. Since the diglycolamides are neutral ligands, it was
expected that three NO-3 anions were associated in the extracted
Eu – complexes in order to neutralize the charge of Eu3+ cation.
However, the nitric acid dependency reaches the power of 4.4
and 6.6 for TODGA and THDGA, respectively. This hyperstoichiometric acid dependency has been observed in diglycolamide extraction systems and has been attributed to nitric acid- driven aggregation of diglycolamides 17 and/or participationof HNO3 molecules in the extraction reactions.20,21
In order to investigate the role of nitrate ion in the extraction
reaction more closely, the nitrate ion dependency of DEu wasmeasured at constant concentration of H+ ion. The concentration of NO-3 ion was adjusted with NaNO3. The data presented
in Figure 3 indicate that the relation between DEu and NO-3 ionconcentration is a straight line relationship with slope equal to

-2

10

0.1

1

10

[HNO3] / M
Figure 2. Effect of nitric acid concentration on distribution of radiotracer amount of Eu(III).

~ 3 for TODGA and THDGA. Therefore, three NO-3 anions
participate in the extraction reaction of Eu(III).
Also, the acid dependency of Eu(III) distribution ratio, DEu,
was measured at constant concentration of nitrate ion. The
results are presented in Figure 4 which indicates that the relation between DEu and HNO3 concentration is a straight line
relationship with slopes equal to 0.8 ± 0.1 and 1.6 ± 0.2 for
TODGA and THDGA, respectively. Therefore, one moleculeof HNO3 is associated in Eu - TODGA complexes, whereas Eu- THDGA complexes may contain one or two molecules of
HNO3. Sasaki et al.21 also suggested the presence of either one
or two HNO3 molecules in metal(III) - diglycolamide complexes.
In order to determine the stoichiometric number of extract-Extraction of Europium(III) and Cobalt(II) by N,N,N’,N’

1000

0.01M TODGA, 0.1M HNO3
0.01M THDGA, 0.1M HNO3
0.01M TODGA, 2M HNO3
0.01M THDGA, 2M HNO3

100

slope ~ 2.9
slope ~ 3.3

DEu

DEu

10

1
slope ~ 2.9

0.1

0.01

10

2

10

1

10

0

10

-1

10

-2

10

-3

2

-

3

4

[NO3 ] / M

5

6

10

7

Figure 3. Effect of nitrate ion concentration on distribution of radiotracer amount of Eu(III); [HNO3] = 0.1M.

100

10

-2

10

-1

[DGA] / M
Figure 5. Effect of diglycolamide concentration on distribution ofradiotracer amount of Eu(III).

slope ~ 0.8

K2 =
1

0.1

DEu =
0.01M TODGA/n-hexane
0.01M THDGA/n-hexane
0.1

1[Eu(TODGA)3(NO3)3(HNO3)][Eu3+]

Hence,
5

K2 =[HNO3] / M
Figure 4. Effect of nitric acid concentration on distribution of radiotracer amount of Eu(III); [(H,Na)NO3] = 3M.

ant molecules participating in the extraction reaction, thedependence of europium distribution ratio, DEu , on extractant
concentration was investigated. The values of DEu were plottedagainst extractant concentration ([TODGA] and [THDGA]) in
Figure 5. Straight lines were obtained with slopes equal to 2.8± 0.1. Therefore, three molecules of extractant (TODGA or
THDGA) participate in the extraction reaction. Based on theprevious results, the most predominant extraction reactions ofEu(III) could be represented by equations 2-4:
Eu3+ (aq) + 3 TODGA (org) + 3 NO-3 (aq) + HNO3 (aq)
Eu(TODGA)3(NO3)3(HNO3) (org)[Eu(TODGA)3(NO3) 3(HNO3)][Eu3+] [TODGA]3 [NO ]3 [HNO3]

The distribution ratio of Eu3+, DEu, is defined byslope ~ 1.6

0.01

-3

that some of these ligands reside in the outer coordination
sphere of Eu3+ cation.19-21
The equilibrium concentration constant of the extraction
reaction 2, K2, is expressed as follows:

10

DEu

TODGA, 1M HNO3THDGA, 3M HNO3

slope ~ 3.0

1

3

J. Nucl. Radiochem. Sci., Vol. 13, No. 1, 2013

DEu
[TODGA]3 [NO ]3 [HNO3](5)

Similarly, the equilibrium concentration constant of the extraction reaction 4, K4, is expressed as:
K4 =[Eu(THDGA)3(NO3) 3(HNO3)2][Eu3+] [THDGA]3 [NO ]3 [HNO3] 2

The distribution ratio of Eu3+, DEu, is defined byDEu =[Eu(THDGA)3(NO3)3(HNO3)2][Eu3+]

Hence,(2)

Eu3+ (aq) + 3 THDGA (org) + 3 NO-3 (aq) + HNO3 (aq)Eu(THDGA)3(NO3)3(HNO3) (org)(3)

Eu3+ (aq) + 3 THDGA (org) + 3 NO-3 (aq) + 2 HNO3 (aq)Eu(THDGA) 3 (NO3) 3 (HNO3)2 (org)(4)

As described above, the proposed Eu - complexes contain 3
molecules of tridentate diglycolamide, 3 NO-3 anions and 1 ~ 2molecules of HNO3. Since Eu3+ cation, with coordination number of 8 or 9, cannot accommodate all these ligands, it appears

K4 =

DEu
[THDGA]3 [NO ]3 [HNO3] 2(6)

Thermodynamic Parameters: The extraction of Eu(III)with TODGA and THDGA was studied at different temperatures (30 – 50 °C). The equilibrium constants of reactions 2
and 4 were calculated using equations 5 and 6. The obtained
values of ln K and the corresponding values of standard deviation (σ) are presented in Table 1. The values of lnK are plottedagainst 1/T in Figure 6. The data were fit with linear regres-4

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J. Nucl. Radiochem. Sci., Vol. 13, No. 1, 2013

TABLE 1: Equilibrium constants of Eu(III) extraction reactions and standard deviation values
Temperature(K)

Eu(III)–TODGA–HNO3
ln K2
σ
14.92
0.19
14.73
0.21
14.42
0.22
14.04
0.19
13.68
0.27

303
308
313
318
323
16

Eu(III)–THDGA–HNO3
ln K4
σ
12.01
0.30
11.53
0.29
11.26
0.34
10.45
0.40
10.63
0.37

10

12

1

DCo

ln K

14

10

8

0.10M TODGA, 1M HNO3
0.01M THDGA, 3M HNO3
0.00310.00320.1

slope ~ 2.8

0.0033-1

1/ T / K

Figure 6. Effect of temperature on distribution of radiotracer amountof Eu(III).

0.01
sion to calculate the enthalpy and entropy of the extraction process according to van’t Hoff equation 7:
ln K = –∆H ⎧ 1 ⎫ ∆S
⎪ ⎪+R ⎩T⎭ R(7)

where T is absolute temperature and R is the general gas constant.
The calculated values of the thermodynamic parameters are
given in Table 2. The obtained results indicate that the extraction processes are exothermic and driven by the relatively large
and negative enthalpy. On the other hand, the extraction processes are disfavored by the negative entropy, resulting fromcombining the metal ion with extractant molecules, associatedanions and acid molecules to form highly ordered extracted
complexes in the organic phase. These results are consistent
with those previously reported for diglycolamide extraction
systems.29,30
3.2. Extraction of cobalt(II)The extraction of radiotracer amount of 6 0 Co (II) withTODGA was studied from hydrochloric acid solutions. The
hydrochloric acid dependence of Co(II) distribution is shownin Figure 7. The distribution ratio of Co(II), DCo, is low anddoes not show much change up to 1M HCl. Beyond 1M HCl,
DCo increases with increasing HCl concentration up to 8M HCl.

0.1

1

[HCl] / M
Figure 7. Effect of hydrochloric acid concentration on distribution ofradiotracer amount of Co(II); [TODGA] = 0.1M.

The relation between DCo and HCl concentration could be represented in the later range by a straight line with slope equal to
2.8 ± 0.4. Therefore, it is suggested that three chloride anions
participate in the extraction reaction.
The chloride ion dependence of Co(II) distribution ratio wasmeasured at constant concentration of H+ ion. The concentration of chloride ion was adjusted with LiCl. The data are presented in Figure 8. The relation between DCo and chloride ion
concentration is a straight line relationship with slope equal to
3.1 ± 0.1, which confirms the suggestion that three chloride
anions participate in the extraction reaction.
Figure 9 represents the extraction of Co(II) from aqueous
solutions containing various concentrations of H + ion. The
concentration of chloride ion was kept constant using LiCl.
The distribution ratio of Co(II), DCo, increases with increasing
H + ion concentration. Beyond 2M H +, the relation could be
represented by a straight line with slope equal to 0.9 ± 0.1.
Therefore, one hydrogen ion participates in the extraction reaction of Co(II).
The distribution ratio of Co(II), D Co, was measured as a

TABLE 2: Thermodynamic parameters for extraction of Eu(III) with TODGA and THDGAΔH (kJ/mol)

ΔS (J/K.mol)

ΔG (kJ/mol)Eu(III)–TODGA–HNO3(4.6 ± 0.9) × 10

6

-49.6 ± 1.3-39.1 ± 4.3-38.0 ± 0.5

Eu(III)–THDGA–HNO3(2.5 ± 0.7) × 105-62.5 ± 2.1-106.6 ± 6.7-30.8 ± 0.8

SystemK (25 °C)

10

Extraction of Europium(III) and Cobalt(II) by N,N,N’,N’

J. Nucl. Radiochem. Sci., Vol. 13, No. 1, 2013

10

5

10
8
6

1

DCo

DCo

4
0.1

2
0.01

2

4

6

8

10

-

[Cl ] / M
1
0.005

Figure 8. Effect of chloride ion concentration on distribution ofradiotracer amount of Co(II); [HCl] = 0.2M, [TODGA] = 0.1M.

0.1[TODGA] / M

2Figure 10. Effect of TODGA concentration on distribution of radiotracer amount of Co(II); [HCl] = 8M.

10

1

2

10

1

10

0

Eu(III)
Ce(III)
Zr(IV)
Hf(IV)Nb(V)
Co(II)
Cs(I)

0.8

0.6

slope ~ 0.9

0.4
0.1

1

DM

DCo

0.01

10

-1

10

-2

10

+

[H ] / M
Figure 9. Effect of hydrogen ion concentration on distribution ofradiotracer amount of Co(II); [(H,Li)Cl] = 6M, [TODGA] = 0.1M.

function of TODGA concentration in the organic phase. Figure
10 shows that the relation between DCo and TODGA concentration is a straight line relationship with slope equal to 0.7 ± 0.1
which indicates that almost one molecule of TODGA participates in the extraction reaction. Therefore, the most predominant extraction reaction of Co(II) could be represented byequation 8:
2+

Co

(aq)

-

+

+ TODGA (org) + 3 Cl (aq) + H (aq)
Co(TODGA)Cl2 (HCl) (org)(8)

Finally, the extraction of Co(II) with TODGA was studied at
different temperatures (20 ~ 50 °C). It was found that theextraction reaction is nearly temperature independent in thestudied range of temperature.

0.1

1

10

[HNO3] / M
Figure 11. Effect of HNO3 concentration on distribution of radiotracer amounts of Eu(III), Ce(III), Zr(IV), Hf(IV), Nb(V), Co(II)and Cs(I) with 0.1M TODGA/n-hexane solution.

Separation of Eu3+ with TODGA: N,N,N’,N’-tetraoctyldiglycolamide (TODGA) has been examined for the separationof europium and some selected elements. Europium wasselected as a representative of trivalent f–elements. The otherselected elements are those that could be present in matrices ofnuclear waste. Figures 11 and 12 show the distribution ratiosof tracer amounts of 152+154Eu, 141Ce, 95Zr, 181Hf, 95Nb, 60Co and134
Cs with TODGA/n-hexane solution as a function of nitric6

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J. Nucl. Radiochem. Sci., Vol. 13, No. 1, 2013

10

TABLE 3: Separation factors of Eu(III) in the extraction
system: 0.1M TODGA/n-hexane – HNO3

2

1

10

0

[HNO3]
(M)
0.1
0.5
1
2
4
6
8

DM

10

Eu(III)
Ce(III)
Zr(IV)
Hf(IV)Nb(V)
Co(II)
Cs(I)

10

-1

10

-2

10

DEu /DZr

DEu /DNb

DEu /DCo

DEu /DCs

1.3
1.2
1.1
1.5
3.8
6.3
8.3

3.1
7.1
7.8
9.4
18
25
37

34
150
164
193
437
1002
2000

73
188
225
290
641
1670
4000

TABLE 4: Separation factors of Eu(III) in the extraction
system: 0.1M TODGA/n-hexane – HCl

-3

0.1

1

10

[HCl] / M
Figure 12. Effect of HCl concentration on distribution of radiotracer
amounts of Eu(III), Ce(III), Zr(IV), Hf(IV), Nb(V), Co(II) andCs(I) with 0.1M TODGA/n-hexane solution.

and hydrochloric acid concentrations, respectively. Figure 11
indicates that Eu(III) and Ce(III) are extracted quite well fromconcentrated nitric acid solutions. The extraction of Zr(IV),
Hf(IV) and Nb(V) is intermediate and that of Co(II) and Cs(I)is insignificant. Generally, the order of extractability at ≥ 3M
HNO3 is M(III) > M(IV) > M(V) >> M(II) ~ M(I). In addition, it can be observed that the values of DEu in Fig. 11 arelower than those in Fig. 2 which is probably due to competition
between Eu(III) ion and other metal ions for the extractant
molecules. This competition is more significant at higher
HNO3 concentrations where Ce(III), Zr(IV) and Hf(IV) arehighly extractable.
Figure 12 indicates that the extraction of Eu(III), Ce(III)and Co(II) from hydrochloric acid solutions is low till 2M HCl
and then increases drastically up to 8M HCl. Except for Co(II),the extraction of the studied metal ions from hydrochloric acidsolutions is generally lower than that from nitric acid solutions.
The separation factors of Eu(III) were calculated from nitricand hydrochloric acid media. The values are given in Tables 3
and 4. It is concluded that with adjustment of acid concentration, Eu(III) can be separated from Zr(IV), Nb(V), Co(II) andCs(I) in both HNO3 and HCl media.
4. Conclusion
N, N, N’, N’-t et r ao ct yld iglycola m ide ( TODGA) a nd
N,N,N’,N’-tetrahexyldiglycolamide (THDGA) show effective
extraction of Eu(III) from nitric acid solutions. However,TODGA is preferred to THDGA because TODGA has higher
lipophilicity than THDGA. The structures of the extracted Eucomplexes are suggested to be Eu(TODGA) 3 (NO3) 3 (HNO3),
Eu(THDGA)3(NO3)3(HNO3) and Eu(THDGA)3(NO3)3(HNO3)2.
The extraction reactions of Eu(III) are exothermic processes
driven by the relatively large and negative enthalpy and disfavored by the negative entropy. By acidity adjustment, TODGA
could potentially be used for separation of Eu(III) from Nb(V),

[HCl]
(M)
0.1
0.5
1
2
4
6
8

DEu /DZr

DEu /DNb

DEu /DCo

DEu /DCs

0.13
0.07
0.09
0.1
1.2
11.0
9.5

0.33
0.33
0.27
0.27
2.8
11.0
4.6

6.0
2.7
3.0
4.4
29
23
3.2

15
7.5
6.7
8.0
69
845
864

Zr(IV), Co(II) and Cs(I) in nitric and hydrochloric acid solutions. Generally, the order of metal ions extractability fromconcentrated nitric acid solution is M(III) > M(IV) > M(V) >>M(II) ~ M(I) and the extractabilities are generally higher from
nitric acid solutions than hydrochloric acid solutions. TODGA
also shows effective extraction of Co(II) from concentratedhydrochloric acid solutions and the structure of the extracted
complex is suggested to be Co(TODGA)Cl2 (HCl).
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