Solvent Extraction and Ion Exchange Behavior of Actinium, Alkaline ...

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Behavior of Actinium, Alkaline, and Rare Earth Elements in Sr-Resin/Mineral Acid Systems a

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a

Dmitry V. Filosofov , Nikolai A. Lebedev , Valery Radchenko , ab

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Alimardon V. Rakhimov , Steffen Happel & Frank Roesch a

Dzhelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna, Russian Federation b

Institute of Nuclear Physics of Uzbek Academy of Sciences, Tashkent, Republic of Uzbekistan c

Triskem International, Parc de Lormandiére, Campus de Ker Lann, Bruz, France

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d

Institute of Nuclear Chemistry, Johannes Gutenberg-University Mainz, Mainz, Germany Published online: 15 Jun 2015.

To cite this article: Dmitry V. Filosofov, Nikolai A. Lebedev, Valery Radchenko, Alimardon V. Rakhimov, Steffen Happel & Frank Roesch (2015): Behavior of Actinium, Alkaline, and Rare Earth Elements in Sr-Resin/Mineral Acid Systems, Solvent Extraction and Ion Exchange, DOI: 10.1080/07366299.2015.1046293 To link to this article: http://dx.doi.org/10.1080/07366299.2015.1046293

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Solvent Extraction and Ion Exchange, 00: 1–14, 2015 Copyright © Taylor & Francis Group, LLC ISSN: 0736-6299 print / 1532-2262 online DOI: 10.1080/07366299.2015.1046293

BEHAVIOR OF ACTINIUM, ALKALINE, AND RARE EARTH ELEMENTS IN SR-RESIN/MINERAL ACID SYSTEMS Dmitry V. Filosofov1 , Nikolai A. Lebedev1 , Valery Radchenko1 , Alimardon V. Rakhimov1,2 , Steffen Happel3 , and Frank Roesch4 Downloaded by [the LANL Research Library] at 08:58 15 July 2015

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Dzhelepov Laboratory of Nuclear Problems, Joint Institute for Nuclear Research, Dubna, Russian Federation 2 Institute of Nuclear Physics of Uzbek Academy of Sciences, Tashkent, Republic of Uzbekistan 3 Triskem International, Parc de Lormandiére, Campus de Ker Lann, Bruz, France 4 Institute of Nuclear Chemistry, Johannes Gutenberg-University Mainz, Mainz, Germany In this work, the interactions between the divalent alkaline earth elements (AEE) (Sr, Ba, Ra), the trivalent rare earth elements (REE) (Ce-Lu, Y), and Ac(III) with Sr-resin were investigated in the presence of HNO3 , HCl, HBr, HClO4 , and HPF6 . Distribution coefficients of these ions on the Sr-resin were determined under batch-loading conditions. Lastly, online column separations were performed to demonstrate the utility of these systems. Substantial differences in the behavior of the ions in solutions comprised of the five different acids were observed. These differences can partly be explained by a combination of ion exchange (primary) and extraction (solvation) mechanisms. From a practical point of view, the Srresin/HClO4 or Sr-resin/HPF6 systems were demonstrated to be effective for the separation and purification of the different groups of the elements. Keywords: alkaline earth elements, rare earth elements, actinium, Sr-resin, super acid, extraction, ion exchange

INTRODUCTION The separation of elements and metal ions is an important objective in many fields of chemistry. However, elements that possess similar chemical properties are difficult to separate, often requiring non-standard conditions for their separation. Therefore, the need for new and more selective separation systems drives further research in this area. In most cases the separation is performed by distribution of elements between two heterogeneous phases; in this work we explore liquid-solid phase extractions. For these types of extractions the most frequently used methods are extraction and ion exchange chromatography.[1−5] Nevertheless, practical combinations of ion exchange and solvent extraction have been used for many years, usually in sequence. Particular features are, for example, liquid ion exchangers, methods based on ion pair behavior,[6−10] and ionic liquids.[11,12] In addition, Address correspondence to Valery Radchenko, Chemistry Division, Los Alamos National Laboratory, Los Alamos, NM 87545. E-mail: [email protected]

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D. V. FILOSOFOV ET AL.

crown ether (CE) ligands are applied for the extraction of cations from aqueous media into conventional organic solvents as well as in ionic liquids.[13−15] Moreover, super acids such as HClO4 or HPF6 provide unique extraction selectivity as compared with typical mineral acids.[16−19] In this work the behavior of alkaline earth elements, the rare earth elements, and actinium was studied in systems comprised of Sr-resin and mineral (super) acids. The Srresin was selected for investigation because it is based on a crown ether for which the selectivity of complex formation correlates to the size of the cation. The individual elements studied are listed in Table 1, organized by their location on the Periodic Table and by their ionic radii. Based on the experimental determination of a systematic set of individual distribution coefficients, several effective separation strategies were developed using the Sr-resin/HClO4 system. These were tested for the effective separation among the groups of the elements and between the various individual elements.

EXPERIMENTAL Chemical Reagents and Materials The following reagents, materials, and equipment were used: bidistilled water, hydrochloric acid (HCl) (“chemical pure,” TU 6-09-2878-84), bought from Sigma-Tec, Ltd. (Russian Federation), perchloric acid (HClO4 ) (“osch 20-4,” GOST 14261-77), and hydrobromic acid (HBr) (“pure,” GOST 2062-77), bought from Reachim (Russian Federation), nitric acid (“osch 18- 4,” GOST 11125 - 84) purchased from Chimmed (Russian Federation), super acid hexafluorophosphoric acid (HPF6 ) - 65% bought from Sigma-Aldrich (Russian Federation). Sr-resin (1.0 M 4,4’(5’)-di-t-butylcyclohexano 18crown-6 (crown ether) in 1-octanol), was supplied by Triskem International (France). Perchloric acid (HClO4 ) is a strong oxidizer and close attention should be paid when working with high concentrations. Interaction with organic materials and heating may cause explosion and thus should be avoided.

Radionuclides for Distribution Coefficients and Column Separation For the determination of distribution coefficients and development of separation methods, the following radionuclides (no-carrier-added) were employed: 82 Sr, 133 Ba, 223 Ra, 88 Y, 139 Ce, 143 Pm, 149 Eu, 151 Gd, 168 Tm, 169 Yb, 173 Lu, and 225 As. The main nuclear-physical characteristicsof the radionuclides are listed in Table 2. Distribution coefficients as well as the separation yield of analyzed radionuclides were determined by γ -ray spectrometry. Gamma-ray spectrometry was performed using an Table 1 Ionic radius of AEE, REE, and Ac for a coordination number 6 and 8.[20] Ionic radius (R), pm Coordination number 6 8

Ra2+

Ba2+

Sr2+

Ac3+

Ce3+

Pm3+

Y3+

Yb3+

Lu3+

− 148

135 142

118 126

112 −

101 114

97 110

90 102

87 99

86 98

BEHAVIOR OF ACTINIUM, ALKALINE, AND RARE EARTH ELEMENTS IN SR-RESIN

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Table 2 Half-lives and main gamma emission characteristics of radionuclides used in this work.[21] Radionuclide 82 Sr 133 Ba 223 Ra 88 Y 139 Ce 143 Pm 149 Eu 151 Gd 168 Tm


169 Yb 173 Lu 225

As

T1/2

E, keV

Abundance, %

25.34 d 10.551 y. 11.435 d

776.5 356.0 269.46 271.23 898.042 165.858 741.98 327.526 153.6 815.99 307.74 272.1 440.5

15.08 62.05 13.9 10.8 94.4 79.9 38.5 4.03 6.2 50.95 10.05 21.2 25.9

106.63 d 137.64 d 265.0 d 93.1 d 123.9 d 93.1 d 32.02 d 1.37 y. 10.0 d

Ortec HPGe detector system and Samar software. The dead time of the detector was always kept below 7%. The radionuclides 88 Y, 139 Ce, 143 Pm, 149 Eu, 151 Gd, 168 Tm, 169 Yb, and 173 Lu were generated by proton bombardment of a tantalum target (4.5 g) with 650 MeV energy. The chemical preparation of these radionuclides in no-carrier added state has previously been described.[22] 223 Ra and 225 Ac were generated and separated from their parent radionuclides. 225 As was obtained via a generator system from 229 Th.[23] 223 Ra was separated from its parent 227 Ac with a cation exchange-HNO3 system.[4] 82 Sr was obtained from a Y target irradiated at proton energy of 300 MeV.[24] 133 Ba was produced by irradiation of a thorium target with 300 MeV protons. Isolation of Ba from the irradiated target was performed as described elsewhere.[25] All proton bombardments were performed at the Phasotron facilities at the Joint Institute of Nuclear Research (JINR), Dubna, Russian Federation. Stock solutions were obtained according to the acids used. To 200 µL of the 1 M acid an activity of radionuclides was added to obtain concentrations of 5 ± 2 KBq/10 µL. Sr-Resin Sr-resin (100-150 µm) is a crown-ether based resin containing 1.0 M 4,4’(5’)-dit-butylcyclohexano 18-crown-6 (crown ether) in 1-octanol and was provided by Triskem International (Bruz, France). For the measurement of the distribution coefficients, the Srresin was washed with water for removal of acid traces. The resin was then allowed to dry in air. For the dynamic separation, the columns filled with Sr-resin were washed with 0.01 M HClO4 (10 mL) and 9 M HClO4 (10 mL). Distribution Coefficients Distribution coefficients were determined by batch mode experiments according to the following procedures: 50 mg of dry pre-conditioned Sr-resin were placed in a 1.5 mL tube. Then, a 1 mL solution of the appropriate concentrations of acids (HNO3 , HCl, HBr, HClO4, or HPF6 )

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D. V. FILOSOFOV ET AL.

and 10 µL of the radionuclide stock solution were added. The mixture was vigorously stirred and allowed to equilibrate for 24 hours at room temperature. Next, the mixtures were centrifuged and 900 µL of the solution were taken. Activity of the whole sample (solution + resin) and 900 µL of solution were measured by γ -ray spectrometry. Further, activity of solution was normalized to total volume (1 mL). Activity of the resin was calculated by subtraction of activity of solution from total activity. The distribution coefficient Kd was calculated using equation (1), where Ceq (phase 1) and Ceq (phase 2) is equilibrium concentrations of element in resin and solution respectively, A1g (res.) and A1mL (sol.) are radionuclides activity presented in 1 g of resin and 1 mL of solution, A50mg(res.) is the radionuclide’s activity in 50 mg of the resin and A50µL(sol.) is the activity in 50 µL of solution, respectively.


eq.

Kd =

C phase 1 eq. C phase 2

=

A1g(res.) A50 mg(res.) = A1mL(sol.) A50 μL(sol.)

(1)

Separation of Ra, Ba, and Sr The solutions of the radionuclides 82 Sr, 133 Ba, and 223 Ra (in 9 M HClO4 ) were evaporated under IR lamp until only 100 µL remained, and then were transferred on a column filled with Sr-resin (2 mL, 100-150 µm) preconditioned to 9 M HClO4 . The column was then subsequently eluted with 9 M HClO4 (15 mL), 0.01 M HClO4 (27 mL), and finally 0.005 M HClO4 (8 mL). The volume of each measured fraction was 0.5 mL. Separation of REE and Actinium A mixture of the radionuclides 88 Y, 139 Ce, 143 Pm, 149 Eu, 151 Gd, 168 Tm, 173 Lu, and Ac from a stock solution was evaporated to dryness, and the remaining residue was then dissolved in 100 µL of 9 M HClO4 . This fraction was loaded on the column filled with Srresin (2 mL, 100-150 µm). The column was sequentially washed with 9 M HClO4 (5 mL), 8 M HClO4 (7 mL), 7 M HClO4 (4.5 mL), 6 M HClO4 (4.5 mL), and 4 M HClO4 (4.5 mL). The volume of each measured fraction was 0.5 mL. 225

RESULTS Distribution Coefficients Distribution coefficients for AEE, REE, and Ac in systems Sr-resin/HCl, HNO3 , HBr and Sr-resin/super acids are presented in Tables 3 and 4 and the tables in the supplemental material and Figs. 1–8. Table 3 shows Kd values for AEE, REE, and Ac in the Sr-resin/HNO3 system, AEE results are shown in Fig. 1. Kd values presented in Table 3 are very similar to values reported in the literature.[26] The sum of errors in values for Kd below 100 is mainly defined by determination of activity on the resin by subtraction. Others errors arising from counting statistics, weighting errors, measurement errors, and others were estimated to be 3%. Under the given conditions, the Sr-resin is very selective for Sr (maximum Kd values). Ba also has a large Kd at 1 and 4 M HNO3 ; the other evaluated elements exhibiit low affinity to the resin over the whole HNO3 concentration range. The fact that the Sr cation shows

BEHAVIOR OF ACTINIUM, ALKALINE, AND RARE EARTH ELEMENTS IN SR-RESIN

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Table 3 Distribution coefficients for AEE, REE, and Ac in the Sr-resin/HNO3 system. Errors are estimated to be 30% for Kd values less than 10, 10% for Kd values between 10 and 100, 3% for Kd values greater than 100. Kd


AEE

REE+Ac

[HNO3 ], M

Ra

Ba

Sr

Ac

Ce

Pm

Y

Yb

Lu

0.02 0.03 0.1 0.2 1.0 4.0 6.0 8.0 10.0

− − 6 − 17 7 − 5 4

− − 15 − 56 38 − 14 10

− − 14 − 100 180 − 145 160

7 4 14 3 4 5 1.8 1