Short communication Extraction of Calcium and Strontium into Phenyltrifluoromethyl Sulfone by Using Synergistic Mixture of Hydrogen Dicarbollylcobaltate and "Classical" CMPO 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: 13-11-2009 Abstract Solvent extraction of microamounts of calcium and strontium by a phenyltrifluoromethyl sulfone (FS 13) solution of hydrogen dicarbollylcobaltate (H+B-) in the presence of octyl-phenyl-N,N-diisobutylcarbamoylmethyl phosphine oxide ("classical" CMPO, L) has been investigated. The equilibrium data have been explained assuming that the species HL+, HL+, ML2+, ML22+ and ML23+ (M2+ = Ca2+, Sr2+) are extracted into the organic phase. The values of extraction and stability constants of the cationic complex species in FS 13 saturated with water have been determined. In the considered FS 13 medium, it was found that the stability constants of the complex species CaL2+, where n = 1, 2, 3 and L is "classical" CMPO, are higher than those of the corresponding complexes SrL2+. Keywords: Calcium, strontium, hydrogen dicarbollylcobaltate, "classical" CMPO, phenyltrifluoromethyl sulfone, extraction and stability constants 1. Introduction Bidentate phosphonates, phosphine oxides and ma-lonamides have been intensively studied for the extraction of trivalent lanthanides and actinides from acidic media.1-3 A process using octyl-phenyl-N,N-diisobutyl-carbamoylmethyl phosphine oxide (i.e., "classical" CMPO) and called TRUEX was apparently used in the United States,1 whereas malonic diamides (RR'NCO)2CHR" (DIAMEX) were proposed in Fran-ce.2 Furthermore, a process involving chlorinated cobalt dicarbollide, polyethylene glycol (PEG 400), also called UNEX, has been reported for the simultaneous recovery of cesium, strontium, lanthanides and actinides from highly acidic media into phenyltrifluoromethyl sulfone (abbrev. FS 13).4'5 In this context it is necessary to emphasize that the mentioned FS 13 diluent was developed for the UNEX process as an alternative organic diluent to the highly polar nitrobenzene. Besides this, FS 13 has the advantage of low viscosity and very good solubility of the UNEX extractants and metal solvates.5 On the other hand, nitrobenzene derivatives have been successfully utilized as diluents for cobalt dicarbollide processes in Russia, however, they are deemed unsuitable for use in the United States due to the perceived hazards associated with nitrobenzene. Recently, extractive properties of synergistic mixture of hydrogen dicarbollylcobaltate (H+B-)6 and "classical" CMPO (see Scheme 1) toward Eu3+ and Am3+ has been investigated in the water-nitrobenzene system.7 On the other hand, in the current work, the solvent extraction of microamounts of calcium and strontium by a FS 13 solution of the mentioned synergistic mixture was studied. We intended to find the composition of the species in the organic phase and to determine the corresponding equilibrium constants. Scheme 1: Structural formula of octyl-phenyl-A,A-diisobutylcar-bamoylmethyl phosphine oxide (abbrev. "classical" CMPO or L, respectively). 2. Experimental Phenyltrifluoromethyl sulfone (FS 13) was kindly supplied by Khlopin Radium Institute, St. Petersburg, Russia. Octyl-phenyl-A,A-diisobutylcarbamoylmethyl phosphine oxide ("classical" CMPO) was purchased from Alpha - Ventron. Cesium dicarbollylcobaltate, Cs+B-, was synthesized in the Institute of Inorganic Chemistry, Rež, Czech Republic, using the method published by Hawthorne et al.8 A FS 13 solution of hydrogen dicarbollylcobaltate (H+B-)6 was prepared from Cs+B- by the procedure described elsewhere.9 The other chemicals used (Lachema, Brno, Czech Republic) were of reagent grade purity. The radionuclides 45Ca2+ and 85Sr2+ (DuPont, Belgium) were of standard radiochemical purity. The extraction experiments in the two-phase wa-ter-HCl-M2+(microamounts; M2+ = Ca2+, Sr2+)-FS 13-"classical" CMPO- H+B- systems 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 equilibria in the systems under study were established after 20 min of shaking. Then the phases were separated by centrifugation. In the case of the systems involving 45Ca2+, after evaporating aliquots (1 cm3) of the respective phases on Al plates, their ^-activities were measured by using the apparatus NRB-213 (Tesla PTemysleni, Czech Republic). On the other hand, in the case of the systems with 85Sr2+, 1 cm3 samples were taken from each phase and their y-activities were measured by means of a well-type NaI(T1) scintillation detector connected to a y-analyzer NK 350/A (Gamma, Budapest, Hungary). The equilibrium distribution ratios of calcium and strontium, D, were determined as the ratios of the corresponding measured radioactivities of 45Ca2+ and 85Sr2+ in the FS 13 and aqueous samples. 3. Results and Discussion The dependences of the logarithm of the calcium and strontium distribution ratios (log D) on the logarithm of the numerical value of the total (analytical) concentra- tion of the "classical" CMPO ligand in the initial FS 13 phase, log c(L), are given in Figures 1 and 2, respectively. The initial concentration of hydrogen dicarbolylcobaltate in the organic phase, ^ = 0.001 mol dm-3, as well as the initial concentrations of HCl in the aqueous phase, c(HCl) = 0.005 anf 0.01 mol dm-3, are always related to the volume of one phase. ■4 -3 -2 log c 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 + 3ct(K)]) .17 b The error-square sum U = 20og Dcalc - lOg DeIp)2. Table 2: Comparison of various models of strontium extraction from aqueous solutions of HCl by FS 13 solution of H+B- in the presence of "classical" CMPO. Strontium complexes in the organic phase log Kex a U b SrL2+ 9.73 (10.56) 50.60 SrL22+ 14.14 (14.60) 5.49 SrL3+ 17.86 (18.33) 3.28 SrL2+, SrL2+ Transformed to SrL22+ SrL22+, SrL223+ 13.35 (13.64), 17.53 (17.79) 0.35 SrL2+, SrL2+, SrL3+ 7.17 (7.45), 12.89 (13.29), 17.58 0.19 0.03 a See Table 1, footnote a. b See Table 1, footnote b. The values log KD = 3.2 (see Table 3, footnote a), log j6(HL+;rg) = 5.67 (see Table 3, footnote b), log ^(HL+2,org) = 20 and 8.64 (see Table 3, footnote b), log Kex(Cao+g) = -0.1 - 0.120 were used for the respective calcula- log Kex(Sr+g) : tions. The results are listed in Tables 1 and 2. From these tables it is evident that the extraction data can be best explained assuming the complexes ML2+, ML22+ and ML23+ (M2+ = Ca2+, Sr2+; L = "classical" CMPO) to be extracted into the FS 13 phase. Table 3: Equilibrium constants in the water-HCl-Ca2+ (microa-mounts)- FS 13-"classical" CMPO-H+B- system. Equilibrium log K Laq « Lorg H+rg + Lorg « HLOrg H+rg + 2Lorg « HL+,org Ca2; + 2Horg « Ca2o+g + 2HL+q Ca24 + Lorg + 2Horg « CaL2+g + 2H+q Ca2q + 2Lorg + 2Horg « CaLtrg + 2H+q Ca2+ + 3Lorg + 2Horg « CaL3;org + 2H+, ^ + Lorg « CaLog Ca2o+g + 2Lorg « CaL2+Org Ca2o+ + 3Lorg « CaL23^rg_ 3.2 a 5.67 b 8.64 b -0.1 c 7.35 14.01 18.45 7.45 14.11 18.55 ° Determined by the method of the concentration dependent distribution.18 b Determined by the method described in detail in Ref. 19. c Ref. 20. The respective equilibrium constants are summarized in Tables 3 and 4. Table 4: Equilibrium constants in the water-HCl-Sr2+ (microa-mounts)-FS 13-"classical" CMPO-H+B- system. Equilibrium log K Laq « Lorg H+rg+ Lorg « HLorg H+rg + 2Lorg « HI;+,org Sr2L"q + 2H+rg « Sr2+g + 2HL+q Sr2q + Lorg + 2Horg « ^2+, + 2H+q Sr2L"q + 2Lorg + 2H+rg « ^org + 2H+q Sr2q + 3Lorg + 2Horg « SrL2+org + 2H+q ^ + Lorg « SrLore ^ + 2Lorg « SrLtrg ^ + 3Lor, « SrLL,_ 3.2 a 5.67 b 8.64 b 0.1 c 7.17 12.89 17.58 7.07 12.79 17.48 a Determined by the method of the concentration dependent distri-bution.18 b Determined by the method described in detail in Ref. 19. c Ref. 20. Figure 3 depicts the contributions of the species H+rg, HL+rg and HL+ org to the total hydrogen cation concentration in the equilibrium FS 13 phase, whereas Figure Knowing the values log Kex(Ca2o+g) = -0.120 and log K„x(Sr2+g) = 0.1,20 as well as the extraction constants ex org log Kex (CaL^+g) = 7.35, log K^ (CaL^ ) = 14.01, log Kex (CaL23+org) = 18.45, log Kex (SrLo+g) = 7.17, log Kex (SrL22+org) = 12.89 and log Kex (SrL23+0rg) = 17.58 determined here (see Tables 1 and 2), the stability constants of the complexes ML2+, ML22+ and ML23+ (M2+ = Ca2+, Sr L = "classical" CMPO) in the organic phase defined as 2+ (12) (13) (14) can be evaluated applying the following simple relations: (15) (16) (17) Figure 3: Distribution diagram of hydrogen cation in the equilibrium organic phase of the water-HCl-Ca2+(microamounts) -FS 13-"classical" CMPO-H+B- extraction system in the forms of H+, HL+ and HL+; c(HCl) = 0.01 mol dm-3, cB = 0.001mol dm-3. 1 8(H) = [H+rg]/c(H+)org, 2 8(HL+) = [HL+rg]/c(H+)org, 3 8(HL+) = [HL+2,org]/c(H+)oig„ where c^^ = F+J + [HL+rg] + [H^- The distribution curves were calculated using the constants given in Table 3. Figure 4: Distribution diagram of calcium in the equilibrium organic phase of the water-HCl-Ca2+ (microamounts) -FS ^-"classical" CMPO - H+B- extraction system in the forms of Ca2+, CaL2+, CaLf+and CaL^+. c(HCl) = 0.01 mol dm-3, cB = 0.001 mol dm-3. 1 S(Ca2+) = [Ca2o++J/c(Ca2+)org, 2 8(CaL2+) = [CaL2o;]/c(Ca2+)olg, 3 8(CaL^+) = [CaL22+org]/c(Ca2+)org, 4 S(CaLf+) = [CaL23+org]/c(Ca2+)org, where c(Ca2+)0ig = [^ + [CaL2+J + [^L+J + [^L+J. The distribution curves were calculated using the constants given in Table 3. Figure 5: Distribution diagram of strontium in the equilibrium organic phase of the water-HCl-Sr2+ (microamounts) -FS 13-"clas-sical" CMPO - H+B- extraction system in the forms of Sr2+, SrL2+, SrLf+ and SrL23+. c(HCl) = 0.005 mol dm-3, cB = 0.001 mol dm-3. 1 8(Sr2+) = [Sr2o++,]/c(Sr2+)olg,, 2 8(SrL2+) = [SrL2oy/c(Sr2+)olg, 3 8(SrL|+) = [SrL^MSr2^, 4 8(SrL2+) = [SrL23+org]/c(Sr2+)olg, where c(Sr2+)0rg = [^/J + [SrL2+J + [M^ + [SrLtj. The distribution curves were calculated using the constants given in Table 4. 4 and 5 show the contributions of the cations M2+ , ML2+ , org org' ML2* and ML2* (M2+ = Ca2+, Sr2+; L = "classical" 2,org 3,org CMPO) to the total divalent metal cation concentrations in the corresponding equilibrium organic phase. From Figures 3, 4 and 5 it follows that the cationic complex species HL+2,org, CaL23+,org and SrL23+,org are present in significant concentrations only at relatively high amounts of the "classical" CMPO ligand in the systems under consideration. Moreover, it should be noted that the stability constants of the complex species ML2o+rg, ML22+,org and ML23+,org (M2+ = Ca2+, Sr2+; L = "classical" CCMTM^PO) in FS 13 saturated with water are log/ (CaL^) = 7.45, log/ (SrL;;+g) = 7.07, log/CaL^) = 14.11, log/(SrL^) = 12,79, log/ (CaL23+org) = 18.55 and log / (SrL23+org) = 17.48 as given in Tables 3 and 4. Thus, in the considered FS 13 medium, the stability constants of the complex species CaL;;+ where n = 1, 2, 3 and L is "classical" CMPO, are higher than those of the corresponding complexes SrL;;+. Finally, the stability constants of the complexes EuL3+ and AmL?+ in FS 13 saturated with water are 3,org 3,org log/ (EuL33+org) = 23.35 21 and log / (AmL33+org) = 23.69.21 It means that the stability of the complex cations CaL^+, SrL^+, EuL|+ and AmL|+, where L is "classical" CMPO, in the mentioned medium increases in the series of Sr2+ < Ca2+ << Eu3+ = Am3+. In conclusion, Table 5 summarizes stability constants of the cationic complexes ML2n+ (M2+ = Ca2+, Sr2+; L = "classical" CMPO; n = 2, 3) in water-saturated nitro- Table 5: Stability constants of the complexes ML2n+(M2+ = Ca2+, Sr2+; L = "classical" CMPO; n = 2,3) in nitrobenzene saturated with water (I) and in FS 13 saturated with water (II) at 25 °C. Medium log ß(CaL22+org ) log ß(CaL23org) log ß(SrL|+org) log ß(SrL23org) I a I b 14.46 14.11 19.52 18.55 13.09 12.79 17.31 17,48 a Ref. 14. b This work. benzene and in FS 13 saturated with water. From the data reviewed in this table it follows that the stabilities of considered complexes ML2n+ in both media are comparable. 4. Acknowledgements The present work was supported by the Czech Ministry of Education, Youth and Sports, Projects MSM 4977751303 and MSM 6046137307. 5. References 1. W. W. Schulz, E. P. Horwitz, Separ. Sci. Technol. 1988, 23, 1191-1210. 2. C. Cuillerdier, C. Musikas, P. Hoel, L. Nigond, X. Vitart, Separ. Sci. Technol. 1991, 26, 1229-1244. 3. G. R. Mahajan, D. R. Prabhu, V. K. Manchanda, L. P. Badhe-ka, Waste Management 1998, 18, 125-133. 4. 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. 5. J. D. Law, R. S. Herbst, T. A. Todd, V. N. Romanovskiy, V. A. Babain, V. M. 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Commun. 1993, 58, 1324-1336. 17. L. G. Sillen, B. Warnqvist, Arkiv Kemi 1969, 31, 315-339. 18. J. Rais, E. Sebestova, P. Selucky, M. Kyrs, J. Inorg. Nucl. Chem. 1976, 38, 1742-1744. 19. P. Vanura, Solvent Extr. Ion Exch. 1994, 10, 145-153. 20. P. Selucky, E. Makrlik, P. Vanura, unpublished results. 21. E. Makrlik, P. Vanura, P. Selucky, J. Radioanal. Nucl. Chem. 2010, 283, 571-575. Povzetek Proučevali smo extrakcijo mikrokoličin kalcijevih in stroncijevih ionov z raztopino hydrogendikarbolilkobaltata (H+B-) v prisotnosti oktil-fenil-_V,_V-diisobutilkarbamoilmetil karbamoilmetilfosfin oksida (CMPO, L) v feniltrifluorometilsul-fonu (FS 13). Dobljene podatke za ravnotežja smo razložili s predpostavko ekstrakcije kompleksov HL+, HL+, ML2+, ML2+ in ML23+ (M2+ = Ca2+, Sr2+) v organsko fazo. Določili smo konstante nastanka kompleksov v FS13 nasičenem z vodo. Ugotovili smo, da so konstante stabilnosti kompleksov CaL2+ (n = 1, 2, 3) višje od konstant kompleksov s stroncijem.