Short communication
Solvent Extraction of Barium into Nitrobenzene by Using Hydrogen Dicarbollylcobaltate in the Presence
of Slovafol 909
Emanuel Makrlik,1'* Petr Vanura2 and Pavel Selucky3
1 Faculty of Applied Sciences, University of West Bohemia, Husova 11, 306 14 Pilsen, Czech Republic
2 Institute of Chemical Technology, Prague, Faculty of Chemical Engineering, Department of Analytical Chemistry,
Technicka 5, 166 28 Prague 6, Czech Republic
3 Nuclear Research Institute, 250 68 Rez, Czech Republic
* Corresponding author: E-mail: makrlik@centrum.cz
Received: 14-01-2010
Abstract
Extraction of microamounts of barium by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-) in the presence of Slovafol 909 (L) has been investigated. The equilibrium data have been explained assuming that the species HL+, HL+, BaL2+ and BaL^ are extracted into the organic phase. The values of extraction and stability constants of the complex species in nitrobenzene saturated with water have been determined.
Keywords: Barium, Slovafol 909, hydrogen dicarbollylcobaltate, extraction and stability constants, water - nitrobenzene system
1. Introduction
Dicarbollylcobaltate anion1 and some of its halogen derivatives are very useful reagents for the extraction of various metal cations (especially Cs+, Sr2+, Ba2+, Eu3+ and Am3+) from aqueous solutions into a polar organic phase, both under laboratory conditions for purely theoretical or analytical purposes,2-30 and on the technological scale for the separation of some high-activity isotopes in the reprocessing of spent nuclear fuel and acidic radioactive waste. 31-33
Extraction of microamounts of Sr2+ and Ba2+ by a nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-)1 in the presence of polyethylene glycols PEG 200, PEG 300 and PEG 400 has been studied. It has been found that the extraction of the protonated polyethylene glycol molecule HL+ and the extraction of the complex ML2+ (M2+ = Sr2+, Ba2+; L = PEG 200, PEG 300, PEG 400) are predominant reactions in this water - nitrobenzene system. The respective equilibrium constants have been determined. The hydration numbers of the HL+ and ML2+ complex cations in the organic phase have been obtained.
The extraction and stability constants in the nitrobenzene phase increase in the order H+ < Sr2+ < Ba2+ and PEG 200 < PEG 300 < PEG 400, whereas the hydration numbers decrease in the same sequence.34
In the current work, the extraction of microamounts of barium by a synergistic mixture of hydrogen dicarbollylcobaltate (H+B-)1 and Slovafol 909 (L) in nitrobenzene was studied. We intended to find the composition of the species in the organic phase and to determine the corresponding equilibrium constants.
2. Experimental
Slovafol 909 (p-nonylphenylnonaethylene glycol) was supplied by Chemical Works, Novaky, Slovakia. Cesium dicarbollylcobaltate, Cs+B-, was synthesized in the Institute of Inorganic Chemistry, Rež, Czech Republic, by applying the method published by Hawthorne et al.35 A nitrobenzene solution of hydrogen dicarbollylcobaltate (H+B-)1 was prepared from Cs+B- by the procedure described elsewhere.36 The other chemicals used (Lachema,
Brno, Czech Republic) were of reagent grade purity. The radionuclide 133Ba2+ (Polatom, Poland) was of standard radiochemical purity.
The extraction experiments in the two-phase wa-ter-HCl-Ba2+ (microamounts)- Slovafol 909-nitrobenze-ne-H+B- system were performed in 10 cm3 glass test-tubes with polyethylene stoppers, using 2 cm3 of each phase. The test-tubes filled with the solutions were shaken for 2 hours at 25 ± 1 °C, using a laboratory shaker. Under these conditions, the equilibrium in the system under study was established after approximately 20 min of shaking. Then the phases were separated by centrifugation. Afterwards, 1 cm3 samples were taken from each phase and their y-activities were measured using a well-type NaI(T1) scintillation detector connected to a y-analyzer NK 350 (Gamma, Budapest, Hungary).
The equilibrium distribution ratios of barium, D, were determined as the ratios of the corresponding measured radioactivities of 133Ba2+ in the nitrobenzene and aqueous samples.
3. Results and Discussion
The dependence of the logarithm of the barium distribution ratio (log D) on the logarithm of the numerical value of the total (analytical) concentration of the ligand Slovafol 909 in the aqueous phase, log c(L), is given in Figure 1. The initial concentration of HCl in the aqueous phase, c(HCl) = 0.10 mol dm-3, and the initial concentration of hydrogen di-carbollylcobaltate in the organic phase, cB = 0.001 mol dm-3, are related to the volume of one phase.
With respect to the results of previous previous,1,3,20,34,37 the considered water-HCl-Ba2+(microa-mounts)- Slovafol 909 (L)-nitrobenzene-H+B- system
can be described by the set of reactions
Figure 1: Log D as a function of log c(L), where L is Slovafol 909, for the system water-HCl-Ba2+ (microamounts) - Slovafol 909 -nitrobenzene-H+B-; c(HCl = 0.10 mol dm-3, cB = 0.001 mol dm-3. The curve was calculated using the constants given in Table 2.
l^aq <"> ^ org
Horg + Lorg HLorg
H:rg+2Lorg<=>HUorg
Ball +2Horg«Ba;;+2Haq
Baa2q+ + nLorg + 2^ « BaL^rg + 2H;
(1) (2)
(3)
(4)
(5)
to which the following equilibrium constants correspond:
KD
[L0fg: [LJ

[HL+0fg]
°rS [Horg ][L org]
[HL
/?(HUorg) =
Kex(Ba;:) =
org -
[H^rg][Lorg]-[Ba;l][H:
2+ ÏÏH+ l2
2+ \ L*—"org J L aq J
org '	rD„2+-irTT+ -i2
[Ba2q ][H^rg
. j2+	[BaL;;orJ[H;q]2
K.CBaL,^)-	r 2
(6)
(7)
(8) (9)
(10)
The subscripts "aq" and "nb" denote the aqueous and organic phases, respectively.
A subroutine UBBE, based on the relations given above, the mass balance of the Slovafol 909 ligand and the electroneutrality conditions in both phases of the system under study, was formulated34,38 and introduced into a more general least-squares minimizing program LETAGROP39 used for determination of the "best" values of the extraction constants Kex(Bal2,+org). The minimum of the sum of errors in log D, i.e., the minimum of the expression
U = X(logDcalc - logD )2
(11)
was sought.
The values log KD = 1.38,37 log ß(HL+)= 5.64,
37
WD =	log ^(HL+rg
log £(HL+,org) = 8.2737 and log Kex(Baoo+g) = 0.934 were used for the respective calculations. The results are listed in Table 1. From this table it is evident that the extraction data can be best explained assuming the barium complex species BaL2+ and BaL22+ to be extracted into the nitrobenzene phase.
Knowing the value lok Kex(Bao+g) = 0.9,34 as well as the extraction constants log Kex(BaL2;+g) = 13.05 and
log K (BaL2+ ) = 16.65 determined here (Table 1), the
ex 2,org 2+ 2+
stability constants of the complexes BaL2o+g and BaL2+org in the nitrobenzene phase defined as
Table 1: Comparison of three different models of barium extraction from aqueous solution of HCl by nitrobenzene solution of H+B- in the presence of Slovafol 909.
Barium complexes	log	Kex "	U *
in the organic phase			
BaL2+	13.52	(14.09)	2.83
BaL2+	17.89	(18.48)	12.00
BaL2+, BaL2+	13.05 ± 0.22,	16.65 (16.87)	0.02
a The values of the extraction constants are given for each complex. The reliability interval of the constants is given as 3o(K), where o(K) is the standard deviation of the constant K.39 These values are given in the logarithmic scale using the approximate expression log K ± {log[K + 1.5o(K)] - log[K - 1.5o(K)]>. For o(K) > 0.2 K, the previous expression is not valid and then only the upper limit is given in the parentheses in the form of log K (log[K + 3o(k)]).39 b The error-square sum U =
= X(log Dcalc- log Dexp)2.

[BaL;
2+ _ _
ors ^ ~~ ra„ 2+
A(BaL^org) =
[Ba;+g][Lorg] [BaU;j
(12)
(13)
[Ba;;][Lorg]2
can be evaluated applying the following simple relations:
(14)
log/?(Ba ¿J = log Kex(BaL2+)-log Kex(Ba2+) (15)
The respective equilibrium constants are summarized in Table 2.
Table 2: Equilibrium constants in the water-HCl-Ba2+ (microa-mounts)-Slovafol 909-nitrobenzene - H+B- extraction system.
Equilibrium
log K
La
H+
« Lorg
+ L « HL+
~org org	org
H0 + 2L « HL+
org	org	2,org
Ba + 2H+ « Ba2+ + 2H+
aq	org	org	aq
Ba2+ + L + 2H+ « BaL2+ + 2H+
aq org	org	org	aq
Ba2+ + 2L + 2H+ « BaLf + 2H+
aq	org	org	2,org	aq
Ba2+ + L « BaL2"
org org	org
Ba2+ + 2L « BaL?+
org_org	2,org_
1.38a 5.64a 8.27a 0.9b 13.05 16.65 12.15 15.75
a Ref. 37. b Ref. 34.
Moreover, Figure 2 depicts the contributions of the species H
I+rg, HL+g and HL+org to the total hydrogen cation concentration in the equilibrium nitrobenzene phase, while Figure 3 shows the contributions of the cations Ba2o+rg, BaLo2r+g and BaL22,+org to the total barium concentration in the equilibrium organic phase. From both of these figures it follows that the complexes HL2+rg and BaL2+org are present in significant concentrations only at relatively high amounts of the Slovafol 909 ligand in the system under consideration.
Figure 2: Distribution diagram of hydrogen cation in the equilibrium nitrobenzene phase of the system water-HCl-Ba2+ (microa-mounts) -Slovafol 909-nitrobenzene-H+B- in the forms of H+, HL+ and HL+;
c(HCl) = 0.10 mol dm-3, cB = 0.001 mol dm-3
1	§[H+] = [H+rg]/c(H+)
2	8[HL+] = [HL+rg]/c(H+)org, 5 §[HL+] = [HL+,org]/c(H+)org, where c(H+)= [H+l + [HL+n
J + [HLW
The distribution curves were calculated using the constants given in Table 2.
Figure 3: Distribution diagram of barium in the equilibrium nitrobenzene phase of the system water-HCl-Ba2+ (microamounts) -Slovafol 909 -nitrobenzene-H+B- in the forms of Ba2+, BaL2+ and BaL2+;
c(HCl) = 0.01 mol dm-3, cB = 0.001 mol dm-3
1	8[Ba2+] = [Bao+g]/c(Ba2+)0rg,
2	8[BaL2+] = [BaLo+g]/c(Ba2+)org,
3	8[BaL2+] = [BaL2+org]/c(Ba2+)org,
where c(Ba2+)oIg = [Bao+g] + [BaLo+g] + [BaL^].
The distribution curves were calculated using the constants given in
Table 2.
Finally, it should be noted that the stability constants of the complex species ML2+g and ML2"org, where M2+ = Ca2+, Sr2+, Ba2+ and L is Slovafol 909, in nitrobenzene sa-
Table 3: Stability constants of the complexes ML2+ and ML^+ (M2+ = Ca2+, Sr2+, Ba2+; L = Slovafol 909) in nitrobenzene saturated with
water at 25 °C.		
m2+	log ß(ML^)	log ßtMLtrg)
Ca2+	9. 01a	12.79a
Sr2+	10.22b	14.52b
Ba2+	12.15c	15.75c
a Ref. 40. b Ref. 3.	c This work.	
turated with water are given in Table 3. Thus, in this medium, the stability of the considered complexes ML^g and ML2org increases in the series of Ca2+ < Sr2+ < Ba2+.
In conclusion, Table 4 summarizes stability constants of the complexes BaL2o+g and BaL2+org with fourteen oxyethylene ligands L, denoted by the symbols diglyme, triglyme, tetraglyme, PEG 200, PEG 300, PEG 400, Slovafol 909, 15C5, B15C5, 18C6, B18C6, DB18C6, DCH18C6 and DB21C7, in nitrobenzene saturated with water at 25 °C. From the data reviewed in this table it follows that in the mentioned nitrobenzene medium, the stability constants of the complexes BaL2o+rg increase in the order diglyme < triglyme < tetraglyme < DB18C6 < DB21C7 < B18C6 < PEG 200 < DCH18C6 < Slovafol 909 < PEG 300 < 18C6 < PEG 400, whereas the stability of the cationic complex species BaL22,+org increases in the following sequence: tetraglyme < triglyme < DB18C6 < DB21C7 < B15C5 < B18C6 < DCH18C6 < Slovafol 909 < 15C5 < 18C6.
Table 4: Stability constants of the complexes BaLo+ and BaL2+org [L = diglyme, triglyme, tetraglyme, PEG 200, PEG 300, PEG 400, Slovafol 909, 15-crown-5 (15C5), benzo-15-crown-5 (B15C5), 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dibenzo-18-crown-6 (DB18C6), dicyclohexano-18-crown-6 (DCH18C6), dibenzo-21-crown-7 (DB21C7)] in nitrobenzene saturated with water at 25 °C.
L	log ß(BaL^)	log ß(BaL22+org)	Ref.
Diglyme	3.37	-	41
Triglyme	5.18	8.03	41
Tetraglyme	6.23	7.35	41
PEG 200	10.93	-	34
PEG 300	12.17	-	34
PEG 400	12.80	-	34
Slovafol 909	12.15	15.75	This work
15C5	-	16.15	42
B15C5	-	13.3	43
18C6	12.47	17.78	38
B18C6	10.09	14.86	20
DB18C6	7.57	10.21	44
DCH18C6	11.75	15.43	45
DB21C7	8.86	12.26	46
4. Acknowledgements
This work was supported by the Czech Ministry of Education, Youth and Sports, Projects MSM 4977751303 and MSM 6046137307.
5. References
1.	E. Makrlik, P. Vanura, Talanta 1985, 32, 423-429.
2.	E. Makrlik, P. Vanura, P. Selucky, J. Solution Chem. 2009, 38, 1129-1138.
3.	Z. Valentova, E. Makrlik, Acta Chim. Slov. 2007, 54, 175178.
4.	E. Makrlik, P. Vanura, P. Selucky, Acta Chim. Slov. 2008, 55, 430-433.
5.	E. Makrlik, P. Vanura, P. Selucky, Acta Chim. Slov. 2008, 55, 223-227.
6.	E. Makrlik, J. Budka, P. Vanura, Acta Chim. Slov. 2009, 56, 278-281.
7.	E. Makrlik, P. Vanura, P. Selucky, V. A. Babain, I. V. Smir-nov, Acta Chim. Slov. 2009, 56, 718-722.
8.	E. Makrlik, P. Vanura, P. Selucky, Acta Chim. Slov. 2009, 56, 475-479.
9.	E. Makrlik, P. Vanura, P. Selucky, Acta Chim. Slov. 2009, 56, 973-976.
10.	E. Makrlik, P. Vanura, P. Selucky, Acta Chim. Slov. 2010, 57, 470-474.
11.	E. Makrlik, P. Vanura, P. Selucky, Acta Chim. Slov. 2010, 57, 485-492.
12.	E. Makrlik, P. Vanura, Z Phys. Chem. 2007, 227, 881- 886.
13.	E. Makrlik, P. Vanura, Z Phys. Chem. 2009, 223, 247-252.
14.	E. Makrlik, P. Vanura, P. Selucky, Z Phys. Chem. 2009, 223, 253-261.
15.	E. Makrlik, J. Dybal, P. Vanura, Z Phys. Chem. 2009, 223, 713-718.
16.	E. Makrlik, J. Budka, P. Vanura, J. Dybal, Monatsh. Chem.
2008,	139, 1349-1351.
17.	E. Makrlik, P. Vanura, P. Selucky, Monatsh. Chem. 2008, 139, 597-600.
18.	E. Makrlik, J. Budka, P. Vanura, P. Selucky, Monatsh. Chem.
2009,	140, 157-160.
19.	E. Makrlik, J. Dybal, P. Vanura, Monatsh. Chem. 2009, 140, 251-254.
20.	E. Makrlik, P. Vanura, P. Selucky, J. Halova, J. Radioanal. Nucl. Chem. 2007, 274, 625-629.
21.	E. Makrlik, P. Vanura, J. Radioanal. Nucl. Chem. 2008, 275, 217-220.
22.	E. Makrlik, P. Vanura, P. Selucky, J. Radioanal. Nucl. Chem. 2008, 275, 229-232.
23.	E. Makrlik, P. Vanura, J. Budka, J. Radioanal. Nucl. Chem. 2008, 275, 463-466.
24.	E. Makrlik, P. Vanura, P. Selucky, J. Radioanal. Nucl. Chem.
2008,	275, 309-312.
25.	E. Makrlik, P. Vanura, J. Radioanal. Nucl. Chem. 2008, 275, 673-675.
26.	E. Makrlik, P. Vanura, P. Selucky, J. Radioanal. Nucl. Chem.
2009,	279, 137-142.
27.	E. Makrlik, P. Vanura, P. Selucky, J. Radioanal. Nucl. Chem. 2009, 279, 287-291.
28.	J. Dybal, E. Makrlik, P. Vanura, J. Radioanal. Nucl. Chem. 2009, 279, 553-559.
29.	E. Makrlik, P. Vanura, P. Selucky, V. A. Babain, I. V. Smir-
nov, J. Radioanal. Nucl. Chem. 2009, 279, 743- 747.
30.	E. Makrlik, P. Vanura, Z. Sedláková, J. Radioanal. Nucl. Chem. 2009, 280, 607-611.
31.	J. D. Law, K. N. Brewer, R. S. Herbst, T. A. Todd, D. J. Wood, Waste Management 1999, 19, 27-37.
32.	V. N. Romanovskiy, I. V. Smirnov, V. A. Babain, T. A. Todd, R. S. Herbst, J. D. Law, K. N. Brewer, Solvent Extr. Ion Exch. 2001, 19, 1-21.
33.	J. D. Law, R. S. Herbst, T. A. Todd, V. N. Romanovskiy, V. A. Babain, V. M. Esimantovskiy, I. V. Smirnov, B. N. Zaitsev, Solvent Extr. Ion Exch. 2001, 19, 23-36.
34.	P. Vanura, E. Makrlík, J. Rais, M. Kyrs, Collect. Czech. Chem. Commun. 1982, 47, 1444-1464.
35.	M. F. Hawthorne, D. C. Young, T. D. Andrews, D. V. Howe, R. L. Pilling, A. D. Pitts, M. Reintjes, L. F. Warren, P. A. Wegner, J. Am. Chem. Soc. 1968, 90, 879-896.
36.	E. Makrlik, Collect. Czech. Chem. Commun. 1992, 57, 289295.
37.	P. Vanura, V. Jedinakova-Križova, P. Ivanova, J. Radioanal. Nucl. Chem. 1996, 208, 271-281.
38.	P. Vanura, E. Makrlik, Collect. Czech. Chem. Commun. 1993, 58, 1324-1336.
39.	L. G. Sillén, B. Warnqvist, Arkiv Kemi 1969, 31, 315- 339.
40.	E. Makrlik, P. Vanura, P. Selucky, J. Radioanal. Nucl. Chem. 2006, 269, 209-211.
41.	P. Vanura, E. Makrlik, Collect. Czech. Chem. Commun. 1985, 50, 581-599.
42.	Z. Valentova, E. Makrlik, J. Radioanal. Nucl. Chem. 2006, 267, 487-491.
43.	E. Makrlik, P. Vanura, J. Serb. Chem. Soc. 2006, 71, 11471151.
44.	E. Makrlik, P. Vanura, P. Selucky, J. Radioanal. Nucl. Chem.
2008,	277, 549-554.
45.	E. Makrlik, P. Vanura, P. Selucky, J. Radioanal. Nucl. Chem.
2009,	281, 633-638.
46.	E. Makrlik, P. Vanura, P. Selucky, J. Radioanal. Nucl. Chem. 2008, 275, 3-7.
Povzetek
Proučevali smo ekstrakcijo mikrokoličin barija z raztopino hidrogen dikarbolilkobaltata (H+B-) v nitrobenzenu v prisotnosti Slovafol 909 (L). Predpostavljamo, da so v ravnotežju v organski fazi prisotni kompleksi HL+, HL+, BaL2+ in BaL^+, za katere smo določili konstante ekstrakcije in konstante stabilnosti.