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Effect of valence state on chromatographic fractionation of molybdenum isotope in aqueous hydrochloric acid solutions
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Energy (2017) 000–000 178–188 EnergyProcedia Procedia131 00 (2017)
5th International Symposium on Innovative Nuclear Energy Systems, INES-5, 31 October – 2 www.elsevier.com/locate/procedia November, 2016, Ookayama Campus, Tokyo Institute of Technology, JAPAN 5th International Symposium on Innovative Nuclear Energy Systems, INES-5, 31 October – 2 November, 2016, Ookayama Tokyo Institute of Technology, JAPANof Effect of valence state Campus, on chromatographic fractionation
molybdenum isotope aqueous hydrochloric acid solutions Thevalence 15th International Symposium on District Heating and Cooling of Effect of stateinon chromatographic fractionation a molybdenum isotope aqueous hydrochloric acid solutions Yu Tachibanaa, , Andri RahmainPutra , Toshitaka Kaneshikib, Masanobu Nogamic, Assessing the feasibility of using the heat demand-outdoor Tatsuya Suzukia, Masao Nomurab a, a b c Yu Tachibana function , Andri Rahma , Toshitaka Kaneshiki , Masanobu Nogami , temperature for aPutra long-term district heat demand forecast a b *
*
Tatsuya SuzukiGraduate , MasaoSchool Nomura Department of Nuclear System Safety Engineering, of Engineering, Nagaoka University of a,b,c a Kamitomioka-machi, a Technology, 1603-1, Nagaoka, 940-2188,c,Japan I.b Andrić *, A. Pina , P. Ferrão , J. Fournierb., Niigata B. Lacarrière O. Le Correc a Laboratory for Advanced Nuclear Energy, Tokyo Institute of Technology, 2-12-1, Ookayama, Department of Nuclear System Safety Engineering, Graduate School of Engineering, Nagaoka University of a IN+ Center for Innovation, Technology and Meguro-ku, Policy ResearchTokyo - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal 152-8550, Japan Technology, 1603-1, Kamitomioka-machi, Nagaoka, Niigata 940-2188, Japan b c Veolia Recherche Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France b Department of Electric and& Electronic Kindai University, 3-4-1, Kowakae, Laboratory for Advanced Nuclear Energy,Engineering, Tokyo Institute of4 Technology, 2-12-1, Ookayama, c Département Systèmes Énergétiques et Environnement IMT Atlantique, rue Alfred Kastler, 44300 Nantes, France Higashiōsaka-shi, Osaka 577-8502, Japan Meguro-ku, Tokyo 152-8550, Japan c Department of Electric and Electronic Engineering, Kindai University, 3-4-1, Kowakae, Higashiōsaka-shi, Osaka 577-8502, Japan a
Abstract Abstract
The Mo(V) and Mo(VI) isotope fractionation using typical anion-exchange resins was investigated in 0.10 M Abstract District heating 3networks are commonly addressed in the literature as one of the most effective solutions for decreasing the (M = mol / dm ) HCl solutions at 308 and 338 K. The examined resins were benzimidazole-type anion-exchange greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat resin embedded high-porous silica beads, which has twoanion-exchange types functional groups consisting of M 1and Mo(VI) isotope fractionation usingrenovation typical resins was investigated in 0.10 sales. The DueMo(V) to the in changed climate conditions and building policies,ofheat demand in the future could decrease, 3 methylbenzimidazole and 1,3-dimethylbenzimidazole (AR-01(Cl form)), weakly basic porous-type WA20 resin ) HCl solutions at 308 and 338 K. The examined resins were benzimidazole-type anion-exchange (M = mol /the dminvestment prolonging return period. (WA20(Cl form)), and PA316 which is onewhich porous-type strongly basic anion-exchange resin resin embedded high-porous silica beads, has twodemand types –ofoutdoor functional groups consisting of 1The main scope of in this paper is to resin, assess the feasibility ofofusing the heat temperature function for(PA316(Cl heat demand form)). As a result, the isotope separation coefficients of Mo(VI) species were obtained by using the isotope forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 methylbenzimidazole and 1,3-dimethylbenzimidazole (AR-01(Cl form)), weakly basic porous-type WA20 resin fractionation curve of both Mo(VI) species with AR-01(Cl andweather WA20(Cl form) resins while we couldn’t observe buildings that vary in construction period andone typology. Three scenarios medium, high) and (PA316(Cl three district (WA20(Cl form)), and PA316 resin, which is of form) porous-type strongly basic(low, anion-exchange resin the Mo(VI) in case of PA316 resin deep). and theToMo(V) isotope fractionation using these resins. It renovation were developed (shallow, intermediate, estimate the were error, obtained heat demand values were form)). As scenarios aisotope result,fractionation the isotope separation coefficients of Mo(VI) species obtained by using the isotope may be suggested that these tendencies forAR-01(Cl themodel, Mo isotope fractionation are caused weak adsorption of compared withcurve results a dynamic heatwith demand previously developed validated byby thethe authors. fractionation offrom Mo(VI) species form) and WA20(Cland form) resins while we couldn’t observe Mo(VI) species onto PA316 resinweather thechange Sn species usedcould for reduction ofusing Mo(VI) species TheMo(VI) results showed that when only isadsorption considered, the margin of isotope error be acceptable for some applications the isotope fractionation inand case ofstrong PA316 resin andof the Mo(V) fractionation these resins.for It these resins. (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation may be suggested that these tendencies for the Mo isotope fractionation are caused by the weak adsorption of scenarios, the error value increased to the 59.5% (depending on the and renovation scenarios of combination considered). Mo(VI) species onto PA316 resinup and strong adsorption of weather Sn species used for reduction Mo(VI) species for The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the © 2017 The Authors. Published by Elsevier Ltd. these resins. decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and ©renovation 2017 The Authors. by Elsevier Ltd. hand, function intercept increased for 7.8-12.7% per decade (depending on the scenariosPublished considered). On the other © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility the organizing the 5ththe International Symposiumfor on the Innovative Nuclear Energyand coupled scenarios). The valuesofsuggested could committee be used toofmodify function parameters scenarios considered, Systems. improve the accuracy of heat demand estimations. * Corresponding author. Tel.: +81-258-47-9570; fax: +81-258-47-9570.
© E-mail 2017 The Authors. Published by Elsevier Ltd. address: [email protected] Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +81-258-47-9570; fax: +81-258-47-9570. Cooling. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. E-mail address: [email protected] Peer-review under responsibility of the organizing committee of the 5th International Symposium on Innovative Nuclear Energy Systems. Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of the 5th International Symposium on Innovative Nuclear Energy Systems.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of the 5th International Symposium on Innovative Nuclear Energy Systems. 10.1016/j.egypro.2017.09.466
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Author name / Energy Procedia 00 (2017) 000–000
Peer-review under responsibility of the organizing committee 5thProcedia International Symposium Yu Tachibana et al.of/ the Energy 131 (2017) 178–188on Innovative Nuclear Energy 179 Systems.
Keywords:
Molybdenum isotope fractionation; valence state; anion-exchange chromatography; hydrochloric acid solution; adsorption
mechanism
1. Introduction 99m Tc, a metastable isomer of 99Tc, is of great interest from the viewpoint of the medical use of nuclear diagnostics due to the half life of T1/2 = 6.015 h and 143 keV [1]. In case of Japan, 99Mo, a raw material of 99mTc, has been imported from foreign countries such as Canada, Netherlands, and Belgium, etc. [2]. Nowadays, most 99Mo is produced by using nuclear research reactors with highly enriched 235U (HEU), which has intrinsically some serious worries for nuclear proliferation. These reactors have been getting decrepit and the realistic costs for specialized facilities for chemical treatments, storages, and the disposal of large amounts of highly radioactive wastes are not reasonable [3]. Recently, some researchers have suggested that 99Mo can be produced using the respective reactions of 98Mo(n, γ)99Mo, 100Mo(n, 2n)99Mo, and 100Mo(p, x)99Mo reactions [2,4]. Before their nuclear reactions, it also has been required to enrich 98Mo or 100Mo isotope for preparation of the enriched 99Mo isotope because of comparatively low natural abundance of 98Mo and 100Mo isotopes. The Mo isotope fractionation in chemical reactions is also particularly interesting for geochemists [5-7]. Our works which have examined the mechanisms of Mo isotope fractionation in solutions, may contribute to the understanding the nature of the isotope fraction of Mo in the natural world. Some researchers have studied the chemical enrichment of various nuclides by using chromatography [8-23]. In analogy of them, we have also performed some chromatographic isotope separation experiments of hexavalent Mo species using the synthesized benzimidazole-type anion-exchange resin embedded in high-porous silica beads in hydrochloric acid solutions [22]. It has been known that Mo species has various chemical forms in aqueous solutions and seven stable isotopes in nature [22]. In other words, the systematic understanding of adsorption and desorption behavior of Mo species is inevitable, compared with other elements. However, the chemical data on isotope fractionation of medium-heavy elements such as Mo are not well-known. Little information on the effect of different valence states on chromatographic fractionation of Mo isotopes in hydrochloric acid solutions is available. From these backgrounds, we have examined the effect of valence states on Mo isotope fractionation behavior in the hydrochloric acid solutions using typical anion-exchange resins (see Figure 1) such as benzimidazole-type anion-exchange resin embedded in high-porous silica beads, which has two types of functional groups consisted of 1-methylbenzimidazole and 1,3-dimethylbenzimidazole (AR-01(Cl form)), weakly basic porous-type WA20 resin (WA20(Cl form)), and PA316 resin, which is one of porous-type strongly basic anion-exchange resin (PA316(Cl form)).
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Figure 1. Structural formulas of anion-exchange resins used in the study. 2. Experimental 2.1. Materials Na2MoO4·2H2O (Purity: 99.0 %) and EDTA·4Na·4H2O (Purity: 98.0 %) were produced by Nacalai Tesque, Inc.. Sn(II)Cl2･2H2O (Purity: 97.0 %) was obtained from Wako Pure Chemical Ind., Ltd.. The foregoing Mo(VI) and Sn(II) salts were used without further purification. AR-01 resin was synthesized and supplied from Laboratory for Advanced Nuclear Energy, Tokyo Institute of Technology [19]. Both of WA20 and PA316 resins were obtained from Mitsubishi Chemical, Co., Ltd. and their structural details and chemical properties have been described elsewhere [24]. All chemicals for analyses were of special pure grade. 2.2. Sample preparations The acidic concentrations in solutions containing 1.0 mM (M = mol/dm3) Mo(V) or Mo(VI) species were adjusted to 0.10, 0.50, 1.0, 2.0, 4.0, 6.0, 9.0, and 11.2 M ([HCl]T, subscript T means total concentration) using 35 wt% HCl for Mo adsorption experiments, whereas each concentration of HCl in the solutions with 0.01 M Mo(V) species or with 0.10 and 0.50 M Mo(VI) species, was adjusted to 0.10 M for chromatographic experiments. By mixing with ultrapure water (18.2 MΩcm) produced with a Merck Millipore apparatus (Milli-Q Integral 3 Water Purification System), these sample solutions were prepared swiftly. For Mo adsorption experiments and chromatographic experiments, AR-01 (Cl form), WA20 (Cl form), and PA316 (Cl form) resins were used. The diameter of silica beads used for AR-01 resin was 40 - 60 μm [19]. The quaternization ratio of AR-01 resin was 58.8 % [19]. We have confirmed that the pentavalent state of Mo species can be obtained by adding a divalent Sn salt into the 0.10 M HCl solutions with hexavalent Mo species. Ultraviolet-visible absorption photospectrometry was used for the confirmation of valence state of Mo(V) species in 0.10 M HCl solutions at room temperature. 2.3. Adsorption experiments of Mo(V) and Mo(VI) species in HCl solutions The adsorption experiments were carried out by batch-wise techniques to evaluate the distribution coefficients (Kd) of Mo(V) and Mo(VI) species using AR-01(Cl form), WA20(Cl form), and PA316(Cl form) resins in aqueous solutions of various HCl concentration ranges ([HCl]T = 0.10, 0.50, 1.0, 2.0, 4.0, 6.0, 9.0, and 11.2 M) at room temperature. Each 0.50 g of these resins was respectively added into 10.0 mL aqueous HCl solutions containing Mo(V) and Mo(VI) species. The shaking time was 24 hours. The concentration of Mo species was measured using ICP/MS (7700x, Agilent) after all samples were passed through a glass fiber filter (MF-Millipore, pore size: 2.0 μm)
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to remove these resins. For comparison of concentrations of Mo(V) and Mo(VI) species before and after contacting these resins, the adsorption abilities of Mo(V) and Mo(VI) species on these resins were evaluated. All experiments for Mo(V) and Mo(VI) species have been carried out independently. 2.4. Chromatographic experiments of Mo(V) and Mo(VI) species in HCl solutions For the Mo(V) and Mo(VI) chromatographic isotope fractionation experiments, five and seven glass columns connected in series were used. Each column was equipped with water jacket. The length of one column was 1.0 m and its inner diameter was 8.0 mm. The above-mentioned AR-01(Cl form), WA20(Cl form), and PA316(Cl form) resins were packed into these glass columns. The total weight of these packed resins was 24.6, 120.7, and 132.3 g for the experiments for Mo(VI) species, respectively. In case of those for Mo(V) species, the weights of AR-01 and WA20 resins were 24.6 and 95.0 g, respectively. By using the circulator, the reaction temperature was kept constant at 308 K for AR-01 system and 338 K for WA20 and PA316 systems, respectively. The breakthrough experiments using 0.10 M HCl solutions containing 0.010 M Mo(V) and 0.10 and 0.50 M Mo(VI) species were performed under the constant flow rate of 0.05 - 1.00 mL/min at 308 - 338 K. The flow rate was controlled by the high-pressure pump (NP-KX-210, Nihon Seimitsu Kagaku, Co., Ltd.). The samples were taken every 10.0 or 15.0 g by using the fraction collector (CHF161RA, Advantech). All apparatuses were connected in series with the polytetrafluoroethylene tubes with 2.0 mm inner diameter. Each Mo(V) and Mo(VI) concentration and their isotope ratios were measured by using ICP/MS described above. By varying the concentration of metal ions and kinds of solvents and their concentration, we have observed the effect of the Mo isotope discrimination in ICP/MS measurements [25]. Therefore, the concentrations of Mo(V) and Mo(VI) species in the sample solutions were adjusted at ca. 10 ppb (ppb = ng/g) for the isotope ratio measurements. As a diluent for all ICP/MS measurements, 1.0 wt% HNO3 solution was used. The Mo(V) and Mo(VI) species adsorbed on these resins in the columns were completely removed by using EDTA·4Na·4H2O after the chromatographic experiments. 3. Results and Discussion The adsorption experiments of Mo(V) and Mo(VI) species using AR-01(Cl form), WA20(Cl form), and PA316(Cl form) resins were performed by batch-wise techniques in order to evaluate the Kd values of Mo(V) and Mo(VI) species in the aqueous HCl solutions of 0.10, 0.50, 1.0, 2.0, 4.0, 6.0, 9.0, and 11.2 M at room temperature. The Kd values were calculated using the following Eq. (1). Kd = ｛Cr / Cs × (Vs / Vr)｝ = {(C0 - Cs) / Cs} × (Vs / Vr)
(1)
where Cr, Cs, C0, Vs, and Vr are concentration of Mo(V) and Mo(VI) species on these resins at adsorption equilibrium, concentration of Mo(V) and Mo(VI) species in solution after adsorption equilibrium, initial concentration of Mo(V) and Mo(VI) species, volume of solution, and volume of resin, respectively. It is clear that the Kd values of Mo(V) and Mo(VI) species with these resins decrease sharply with an increase of [HCl]T in the region from 0.10 to 1.0 M as shown in Figure 2. In the range of [HCl]T = 1.0 - 4.0 M, the Kd values increase gradually with increasing [HCl]T, and the values of Kd are almost constant between 4.0 and 11.2 M HCl. Judging from our previous works on Mo(VI) species, it has been suggested that Mo7O21(OH)33-, H3MoO4+, and MoO2Cl3form in three HCl concentration ranges as main species, respectively [22]. Namely, these Mo(VI) species must be selectively adsorbed to these resins in the HCl solutions ranging from 0.10 to 11.2 M. On the other hand, it was found that the adsorption phenomena between Mo(V) species and these resins are analogous to those of Mo(VI) species although WA20 resin has no adsorption ability for Mo(V) species in the HCl concentration ranges of 0.50 2.0 M and the chemical forms of Mo(V) species in the HCl solutions are not well-known. The concentration of HCl should be adjusted at 0.10 M to perform the Mo(V) and Mo(VI) adsorption and their isotope separation experiments because the adsorption abilities of these resins for Mo species became stronger. Therefore, on the assumption that the 1 : 1 anion-exchange reactions is proceeded, Mo(V) + Resin(Cl form) ⇌ Resin･Mo(V) + Cl- and Mo(VI) + Resin(Cl form) ⇌ Resin･Mo(VI) + Cl- (Resin represents AR-01(Cl form), WA20(Cl form), and PA316(Cl form) resins) under the conditions; [Mo]T = 1.0 mM, [Sn]T = 1.5 or 5.0 mM, [Resin]T = 0.50 g, we have investigated the adsorption mechanisms of these resins to Mo(V) and Mo(VI) species in 0.10 M HCl solutions in further detail. The thermodynamic parameters (⊿H, ⊿S, and ⊿G values) for the adsorption of Mo(V) and Mo(VI) species on these
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resins, ranging in Temp. = 278 - 367 K, were calculated from the linear plots of ln Kd against (1/T) using the following Van’t Hoff equation (2) [26] (see Figure 3) and the obtained values were summarized in Table 1. ln Kd = - ⊿G / R·T = - ⊿H / R·T + ⊿S / R
(2)
ln |ri - r0| = ln |rfL - r0| - ks(L - xi) = ln |rfL - r0| - ks × XBi
(3)
Here, R and T represent gas constant and absolute temperature. The calculated ⊿G values were from - 25.9 to - 5.32 kJ / mol at 298 K. This results indicate that the spontaneous adsorption processes between these resins and Mo(V) or Mo(VI) species occur in the solution with 0.10 M HCl. The positive ⊿H values show the endothermic reactions of Mo(V) and Mo(VI) species with these resins. It can be considered that Mo(V) and Mo(VI) species are surrounded by plenty of water in 0.10 M HCl solutions because amino and methyl groups are generally regarded as hydrophilic and weak hydrophobic groups, respectively. When Mo(V) and Mo(VI) species are adsorbed onto these resins, the hydration shell of Mo(V) and Mo(VI) species must be broken before the adsorption reactions of Mo(V) and Mo(VI) species with these resins proceed in the 0.10 M HCl solution. Thus, these dehydration processes are expected to require energy. In addition, the positive values of ΔS also suggest an increase in randomness at the boundary between Mo species and these resins during the adsorption processes. In brief, this tendency implies that the randomness arises due to the destruction of hydration shell of Mo species superior to the adsorption of Mo species on the surface of these resins. Based on these results, the breakthrough experiments for Mo(V) and Mo(VI) isotope separation were carried out at 303 and 338 K. The typical isotope fractionation of Mo(VI) species is shown in Figure 4. In the figure, the notation of Mo isotope ratio deviation was defined as the isotopic ratios of Mo-98 / Mo-92 and Mo-100 / Mo-92 over effluent volume. The original isotope ratios of Mo-98 / Mo-92 and Mo-100 / Mo-92 were 1.83 and 0.786, respectively. It was found that the both Mo isotope ratios decrease sharply with increasing effluent volume and the isotope ratios eventually approach the original values. Therefore, this figure indicates that the heavier isotopes are disproportionately located in the solution phase. Judging from the result of Figure 2, it can be regarded that the three resins have sufficient adsorption ability in the Mo(VI) system. However, contrary to our expectations, in case of PA316 resin, we cannot observe the Mo(VI) isotope fractionation in our experimental conditions. Moreover, the degree of Mo(V) isotope fractionation among these resins was within their experimental errors. We have clarified that the degree of Mo isotope fractionation is very different in the experimental conditions and have suggested that these tendencies of the Mo isotope fractionation are caused by the weak adsorption of Mo(VI) for PA316(Cl form) resin and the strong adsorption of Sn species for these resins. This behavior may be attributable to the corresponding reaction temperature. In the ideal cases of the Mo isotope fractionation by the breakthrough displacement chromatography with a sufficiently long isotopic plateau of the original value, each of the isotopic ratio, the r values (r = 98Mo(VI)/92Mo(VI) and 100 Mo(VI)/92Mo(VI)) can be expressed by Eq. (3) and the details of this equation have been described elsewhere [15].
where r0, rfL, ks, L, x, and XB are the original isotopic ratio, the maximum isotopic ratio on the front boundary, the slope coefficient, the migration distance, the distance from the starting point of the migration, the distance from the front boundary, and the subscripts i and 0 denote the fraction number and original sample, respectively. The term of (L - xi), XBi represents the hypothetical distance between the boundary and the location of xi inside the band. The ks values are slope coefficient experimentally determined by plotting of ln (ri - r0) vs. XBi. Thus, the obtained slope coefficients of 98Mo(VI)/92Mo(VI) and 100Mo(VI)/92Mo(VI) ratios in the 0.10 M HCl solution were found to be ks = 5.5 × 10-2, 4.6 × 10-2 for AR-01 resin and 2.0 × 10-2, 7.6 × 10-2 for WA20 resin, respectively. The isotope separation coefficients (ε) per unit mass (ε / ⊿Mass), which have been frequently used for the analysis of isotope fractionation using ion exchange chromatography and the corresponding height equivalent to a theoretical plate (HETP) derived from the theory of displacement type chromatographic enrichment in the isotopically transient state, are calculated by using the breakthrough curve of 98Mo/92Mo and 100Mo/92Mo and their [Mo(VI)]T in sample solutions. The equation can be expressed by Eq. (4, 5) [11,13-15,17-23]. ε / ⊿Mass = (α - 1) / (MassH - MassL) = Σ(qi|Ri - R0|/{Q × R0(1 - R0)} / (MassH - MassL)
(4)
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HETP = (ε / |ks|) + (1 / ks2･L)
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(5)
Here, α, MassH, MassL, qi, Ri, and Q are the isotope fractionation factor, the mass of heavier isotope, the mass of lighter isotope, the amount of Mo in the fraction sample, the isotopic percentage of Mo, the total amount of adsorbed Mo species on these resins, respectively. The indication of fraction number is i = 0, 1, 2…. As a result, the calculated values of (ε / ⊿M) of 100Mo / 92Mo and 98Mo / 92Mo were summarized in Table 2. The (ε / ⊿M) values for transition metals such as Fe, Cu, Zn, Eu, Nd, and Gd have already been reported and their values including our present and previous works were plotted as shown in Figure 5 [11-15,20]. The plotted values were found to show a good linear relationship and the phenomenon indicates that the (ε / ⊿M) values of Mo(VI) species are proportional to the reciprocal square of the atomic weight, which is called mass shift effect [8].
Figure 2. Plots of Kd values of Mo species vs. [HCl]T at room temperature. [Mo]T = 1.0 mM, [Sn]T = 1.5 and 5.0 mM. Resin = 0.50 g.
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Figure 3. Plots of ln Kd values of Mo species vs. T-1 values at a temperature range of 278 - 367 K.
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Figure 4. Mo(VI) breakthrough curve and its isotope fractionation using WA20 resin in a 0.10 M HCl solution.
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Figure 5. Mass dependence of isotope separation coefficients per unit mass obtained from the ligand-exchange system in ion-exchange chromatography.
4. Conclusion The Mo(V) and Mo(VI) isotope fractionation using AR-01(Cl form), WA20(Cl form), and PA316(Cl form) resins, was examined in 0.10 M HCl solutions at 308 and 338 K. As a result, it was found that the heavier Mo(VI) isotopes are disproportionately located into a solution phase. We also have obtained the isotope separation coefficients of Mo(VI) species derived from the isotope fractionation curve of Mo(VI) species with these resins. It was confirmed that the (ε / ⊿M) values plotted from other well-known and our present data were found to show a good linear relationship. The phenomenon implied that the (ε / ⊿M) values of Mo(VI) species are strongly controlled by mass shift effect. However, we cannot observe the Mo(VI) isotope fractionation in case of PA316 resin and the Mo(V) isotope fractionation using these resins. It is suggested that these tendencies of the Mo isotope fractionation are caused by the weak adsorption of Mo(VI) species for PA316 resin and the adsorption strength of Sn species for these resins. Acknowledgements This work was partially supported by Nagaoka University of Technology Presidential Research Grant (No. 13). References [1] Heeg MJ, Jurisson SS. The role of inorganic chemistry in the development of radiometal agents for cancer therapy. Acc Chem Res 1999;32:1053-1060. [2] Nagai Y, Hatsukawa Y. Production of 99Mo for nuclear medicine by 100Mo(n, 2n)99Mo. J Phys Soc Jpn 2009;78:1-4. [3] Kimura A, Sato Y, Tanase M, Tsuchida K. Development of high density MoO3 pellets for production of 99Mo medical isotope. IOP Conf Series: Mater Sci Eng 2011;18:1-4.
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[4] Gagnon K, Bẻnard F, Kovacs M, Ruth TJ, Schaffer P, Wilson JS, McQuarrie SA. Cyclotron production of 99mTc: Experimental measurement of the 100Mo (p, x)99Mo, 99mTc and 99gTc excitation functions from 8 to 18 MeV. Nucl Med Biol 2011;38:907-916. [5] Barling J, Anbar AD. Molybdenum isotope fractionation during adsorption by manganese oxides. Earth Planet Sci Lett 2004;217:315-329. [6] Golgberg T, Archer C, Vance D, Poulton SW. Mo isotope fractionation during adsorption to Fe(oxyhydr)oxides. Geochim Cosmochim Acta 2009;73:6502-6516. [7] Kashiwabara T, Takahashi Y, Tanimizu M. A XAFS study on the mechanism of isotopic fractionation of molybdenum during its adsorption on ferromanganese oxides. Geochem J 2009;43:e31-e36. [8] Bigeleisen J, Mayer MG. Calculation of equilibrium constants for isotopic exchange reactions. J Chem Phys 1947;15:261-267. [9] Bigeleisen J. Nuclear size and shape effects in chemical reactions. Isotope chemistry of the heavy elements. J Am Chem Soc 1996;118:3676-3680. [10] Nomura M, Higuchi N, Fujii Y. Mass dependence of uranium isotope effects in the U(IV)-U(VI) exchange reaction. J Am Chem Soc 1996;118:9127-9130. [11] Ismail IM, Nomura M, Fujii Y. Isotope effects of europium in ligand exchange system and electron exchange system using ion-exchange displacement chromatography. J Chromatogr A 1998;808:185-191. [12] Matin MDA, Nomura M, Fujii Y, Chen J. Isotope effects of copper in ligand-exchange system observed by ionexchange displacement chromatography. Sep Sci Technol 1998;33:1075-1087. [13] Kim SH, Aida M, Nomura M, Rifaid MN, Fujii Y. Iron isotope effects studied by means of anion exchange redox chromatography. J Ion Exchange 2000;11:26-31. [14] Ismail IM, Fukami A, Nomura M, Fujii Y. Anomaly of 155Gd and 157Gd isotope effects in ligand exchange reactions observed by ion exchange chromatography. Anal Chem 2000;72:2841-2845. [15] Ban Y, Aida M, Nomura M, Fujii Y. Zinc isotope separation by ligand exchange chromatography using cation exchange resin. J Ion Exchange 2002;13:46-52. [16] Marẻchal C, Albarẻde F. Ion-exchange fractionation of copper and zinc isotopes. Geochim Cosmochim Acta 2002;66:1499-1509. [17] Hayasaka K, Kaneshiki T, Nomura M, Suzuki T, Fujii Y. Calcium ion selectivity and isotope effects studied by using benzo-18-crown-6 resins. Prog Nucl Energ 2008;50:510-513. [18] Ding X, Nomura M, Suzuki T, Fujii Y. Zinc isotope effects by chromatographic chelating exchange resin. Prog Nucl Energ 2010;52:164-167. [19] Suzuki T, Nomura M, Fujii Y, Ikeda-Ohno A, Takaoka T, Oguma K. Zinc isotope fractionation in anion exchange in hydrochloric acid solution. J Ion Exchange 2010; 21:328-333. [20] Ismail IM, Ibrahim M, Aly HF, Nomura M, Fujii Y. Chromatographic separation of neodymium isotopes by using chemical exchange process. J Chromatogr A 2011;1218:2923-2928. [21] Suzuki T, Tachibana Y, Nomura M, Fujii Y. Lithium isotope separation using cation exchange resin and crosslinkage effect on isotope fractionation. J Plasma Fusion Res Series 2015;11:45-48. [22] Tachibana Y, Yamazaki Y, Nomura M, Suzuki T. Molybdenum isotope fractionation in ion exchange reaction by using anion exchange chromatography. J Radioanal Nucl Chem 2015;303:1429-1434. [23] Fujii Y, Aida M, Okamoto M, Oi T. A theoretical study of isotope separation by displacement chromatography. Sep Sci Technol 1985;20:377-392. [24] Information of structural details and chemical properties of WA20 and PA316 resins. http://www.diaion.com/en/products/ion_exchange_resins/index.html. Accessed 30 October 2016. [25] Suzuki T, Kanzaki C, Nomura M, Fujii Y. Zinc isotope discrimination effect in inductively coupled plasma mass spectrometer. Rev Sci Instrum 2004;75:1931-1933. [26] Ilaiyaraja P, Deb AKS, Sivasubramanian K, Venkatraman PB. Adsorption of uranium from aqueous solution by PAMAM dendron functionalized styrene divinylbenzene. J Hazard Mater 2013;250-251:155-166.
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5th International Symposium on Innovative Nuclear Energy Systems, INES-5, 31 October – 2 www.elsevier.com/locate/procedia November, 2016, Ookayama Campus, Tokyo Institute of Technology, JAPAN 5th International Symposium on Innovative Nuclear Energy Systems, INES-5, 31 October – 2 November, 2016, Ookayama Tokyo Institute of Technology, JAPANof Effect of valence state Campus, on chromatographic fractionation
molybdenum isotope aqueous hydrochloric acid solutions Thevalence 15th International Symposium on District Heating and Cooling of Effect of stateinon chromatographic fractionation a molybdenum isotope aqueous hydrochloric acid solutions Yu Tachibanaa, , Andri RahmainPutra , Toshitaka Kaneshikib, Masanobu Nogamic, Assessing the feasibility of using the heat demand-outdoor Tatsuya Suzukia, Masao Nomurab a, a b c Yu Tachibana function , Andri Rahma , Toshitaka Kaneshiki , Masanobu Nogami , temperature for aPutra long-term district heat demand forecast a b *
*
Tatsuya SuzukiGraduate , MasaoSchool Nomura Department of Nuclear System Safety Engineering, of Engineering, Nagaoka University of a,b,c a Kamitomioka-machi, a Technology, 1603-1, Nagaoka, 940-2188,c,Japan I.b Andrić *, A. Pina , P. Ferrão , J. Fournierb., Niigata B. Lacarrière O. Le Correc a Laboratory for Advanced Nuclear Energy, Tokyo Institute of Technology, 2-12-1, Ookayama, Department of Nuclear System Safety Engineering, Graduate School of Engineering, Nagaoka University of a IN+ Center for Innovation, Technology and Meguro-ku, Policy ResearchTokyo - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal 152-8550, Japan Technology, 1603-1, Kamitomioka-machi, Nagaoka, Niigata 940-2188, Japan b c Veolia Recherche Innovation, 291 Avenue Dreyfous Daniel, 78520 Limay, France b Department of Electric and& Electronic Kindai University, 3-4-1, Kowakae, Laboratory for Advanced Nuclear Energy,Engineering, Tokyo Institute of4 Technology, 2-12-1, Ookayama, c Département Systèmes Énergétiques et Environnement IMT Atlantique, rue Alfred Kastler, 44300 Nantes, France Higashiōsaka-shi, Osaka 577-8502, Japan Meguro-ku, Tokyo 152-8550, Japan c Department of Electric and Electronic Engineering, Kindai University, 3-4-1, Kowakae, Higashiōsaka-shi, Osaka 577-8502, Japan a
Abstract Abstract
The Mo(V) and Mo(VI) isotope fractionation using typical anion-exchange resins was investigated in 0.10 M Abstract District heating 3networks are commonly addressed in the literature as one of the most effective solutions for decreasing the (M = mol / dm ) HCl solutions at 308 and 338 K. The examined resins were benzimidazole-type anion-exchange greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat resin embedded high-porous silica beads, which has twoanion-exchange types functional groups consisting of M 1and Mo(VI) isotope fractionation usingrenovation typical resins was investigated in 0.10 sales. The DueMo(V) to the in changed climate conditions and building policies,ofheat demand in the future could decrease, 3 methylbenzimidazole and 1,3-dimethylbenzimidazole (AR-01(Cl form)), weakly basic porous-type WA20 resin ) HCl solutions at 308 and 338 K. The examined resins were benzimidazole-type anion-exchange (M = mol /the dminvestment prolonging return period. (WA20(Cl form)), and PA316 which is onewhich porous-type strongly basic anion-exchange resin resin embedded high-porous silica beads, has twodemand types –ofoutdoor functional groups consisting of 1The main scope of in this paper is to resin, assess the feasibility ofofusing the heat temperature function for(PA316(Cl heat demand form)). As a result, the isotope separation coefficients of Mo(VI) species were obtained by using the isotope forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 methylbenzimidazole and 1,3-dimethylbenzimidazole (AR-01(Cl form)), weakly basic porous-type WA20 resin fractionation curve of both Mo(VI) species with AR-01(Cl andweather WA20(Cl form) resins while we couldn’t observe buildings that vary in construction period andone typology. Three scenarios medium, high) and (PA316(Cl three district (WA20(Cl form)), and PA316 resin, which is of form) porous-type strongly basic(low, anion-exchange resin the Mo(VI) in case of PA316 resin deep). and theToMo(V) isotope fractionation using these resins. It renovation were developed (shallow, intermediate, estimate the were error, obtained heat demand values were form)). As scenarios aisotope result,fractionation the isotope separation coefficients of Mo(VI) species obtained by using the isotope may be suggested that these tendencies forAR-01(Cl themodel, Mo isotope fractionation are caused weak adsorption of compared withcurve results a dynamic heatwith demand previously developed validated byby thethe authors. fractionation offrom Mo(VI) species form) and WA20(Cland form) resins while we couldn’t observe Mo(VI) species onto PA316 resinweather thechange Sn species usedcould for reduction ofusing Mo(VI) species TheMo(VI) results showed that when only isadsorption considered, the margin of isotope error be acceptable for some applications the isotope fractionation inand case ofstrong PA316 resin andof the Mo(V) fractionation these resins.for It these resins. (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation may be suggested that these tendencies for the Mo isotope fractionation are caused by the weak adsorption of scenarios, the error value increased to the 59.5% (depending on the and renovation scenarios of combination considered). Mo(VI) species onto PA316 resinup and strong adsorption of weather Sn species used for reduction Mo(VI) species for The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the © 2017 The Authors. Published by Elsevier Ltd. these resins. decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and ©renovation 2017 The Authors. by Elsevier Ltd. hand, function intercept increased for 7.8-12.7% per decade (depending on the scenariosPublished considered). On the other © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility the organizing the 5ththe International Symposiumfor on the Innovative Nuclear Energyand coupled scenarios). The valuesofsuggested could committee be used toofmodify function parameters scenarios considered, Systems. improve the accuracy of heat demand estimations. * Corresponding author. Tel.: +81-258-47-9570; fax: +81-258-47-9570.
© E-mail 2017 The Authors. Published by Elsevier Ltd. address: [email protected] Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +81-258-47-9570; fax: +81-258-47-9570. Cooling. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. E-mail address: [email protected] Peer-review under responsibility of the organizing committee of the 5th International Symposium on Innovative Nuclear Energy Systems. Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of the 5th International Symposium on Innovative Nuclear Energy Systems.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the organizing committee of the 5th International Symposium on Innovative Nuclear Energy Systems. 10.1016/j.egypro.2017.09.466
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Author name / Energy Procedia 00 (2017) 000–000
Peer-review under responsibility of the organizing committee 5thProcedia International Symposium Yu Tachibana et al.of/ the Energy 131 (2017) 178–188on Innovative Nuclear Energy 179 Systems.
Keywords:
Molybdenum isotope fractionation; valence state; anion-exchange chromatography; hydrochloric acid solution; adsorption
mechanism
1. Introduction 99m Tc, a metastable isomer of 99Tc, is of great interest from the viewpoint of the medical use of nuclear diagnostics due to the half life of T1/2 = 6.015 h and 143 keV [1]. In case of Japan, 99Mo, a raw material of 99mTc, has been imported from foreign countries such as Canada, Netherlands, and Belgium, etc. [2]. Nowadays, most 99Mo is produced by using nuclear research reactors with highly enriched 235U (HEU), which has intrinsically some serious worries for nuclear proliferation. These reactors have been getting decrepit and the realistic costs for specialized facilities for chemical treatments, storages, and the disposal of large amounts of highly radioactive wastes are not reasonable [3]. Recently, some researchers have suggested that 99Mo can be produced using the respective reactions of 98Mo(n, γ)99Mo, 100Mo(n, 2n)99Mo, and 100Mo(p, x)99Mo reactions [2,4]. Before their nuclear reactions, it also has been required to enrich 98Mo or 100Mo isotope for preparation of the enriched 99Mo isotope because of comparatively low natural abundance of 98Mo and 100Mo isotopes. The Mo isotope fractionation in chemical reactions is also particularly interesting for geochemists [5-7]. Our works which have examined the mechanisms of Mo isotope fractionation in solutions, may contribute to the understanding the nature of the isotope fraction of Mo in the natural world. Some researchers have studied the chemical enrichment of various nuclides by using chromatography [8-23]. In analogy of them, we have also performed some chromatographic isotope separation experiments of hexavalent Mo species using the synthesized benzimidazole-type anion-exchange resin embedded in high-porous silica beads in hydrochloric acid solutions [22]. It has been known that Mo species has various chemical forms in aqueous solutions and seven stable isotopes in nature [22]. In other words, the systematic understanding of adsorption and desorption behavior of Mo species is inevitable, compared with other elements. However, the chemical data on isotope fractionation of medium-heavy elements such as Mo are not well-known. Little information on the effect of different valence states on chromatographic fractionation of Mo isotopes in hydrochloric acid solutions is available. From these backgrounds, we have examined the effect of valence states on Mo isotope fractionation behavior in the hydrochloric acid solutions using typical anion-exchange resins (see Figure 1) such as benzimidazole-type anion-exchange resin embedded in high-porous silica beads, which has two types of functional groups consisted of 1-methylbenzimidazole and 1,3-dimethylbenzimidazole (AR-01(Cl form)), weakly basic porous-type WA20 resin (WA20(Cl form)), and PA316 resin, which is one of porous-type strongly basic anion-exchange resin (PA316(Cl form)).
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Figure 1. Structural formulas of anion-exchange resins used in the study. 2. Experimental 2.1. Materials Na2MoO4·2H2O (Purity: 99.0 %) and EDTA·4Na·4H2O (Purity: 98.0 %) were produced by Nacalai Tesque, Inc.. Sn(II)Cl2･2H2O (Purity: 97.0 %) was obtained from Wako Pure Chemical Ind., Ltd.. The foregoing Mo(VI) and Sn(II) salts were used without further purification. AR-01 resin was synthesized and supplied from Laboratory for Advanced Nuclear Energy, Tokyo Institute of Technology [19]. Both of WA20 and PA316 resins were obtained from Mitsubishi Chemical, Co., Ltd. and their structural details and chemical properties have been described elsewhere [24]. All chemicals for analyses were of special pure grade. 2.2. Sample preparations The acidic concentrations in solutions containing 1.0 mM (M = mol/dm3) Mo(V) or Mo(VI) species were adjusted to 0.10, 0.50, 1.0, 2.0, 4.0, 6.0, 9.0, and 11.2 M ([HCl]T, subscript T means total concentration) using 35 wt% HCl for Mo adsorption experiments, whereas each concentration of HCl in the solutions with 0.01 M Mo(V) species or with 0.10 and 0.50 M Mo(VI) species, was adjusted to 0.10 M for chromatographic experiments. By mixing with ultrapure water (18.2 MΩcm) produced with a Merck Millipore apparatus (Milli-Q Integral 3 Water Purification System), these sample solutions were prepared swiftly. For Mo adsorption experiments and chromatographic experiments, AR-01 (Cl form), WA20 (Cl form), and PA316 (Cl form) resins were used. The diameter of silica beads used for AR-01 resin was 40 - 60 μm [19]. The quaternization ratio of AR-01 resin was 58.8 % [19]. We have confirmed that the pentavalent state of Mo species can be obtained by adding a divalent Sn salt into the 0.10 M HCl solutions with hexavalent Mo species. Ultraviolet-visible absorption photospectrometry was used for the confirmation of valence state of Mo(V) species in 0.10 M HCl solutions at room temperature. 2.3. Adsorption experiments of Mo(V) and Mo(VI) species in HCl solutions The adsorption experiments were carried out by batch-wise techniques to evaluate the distribution coefficients (Kd) of Mo(V) and Mo(VI) species using AR-01(Cl form), WA20(Cl form), and PA316(Cl form) resins in aqueous solutions of various HCl concentration ranges ([HCl]T = 0.10, 0.50, 1.0, 2.0, 4.0, 6.0, 9.0, and 11.2 M) at room temperature. Each 0.50 g of these resins was respectively added into 10.0 mL aqueous HCl solutions containing Mo(V) and Mo(VI) species. The shaking time was 24 hours. The concentration of Mo species was measured using ICP/MS (7700x, Agilent) after all samples were passed through a glass fiber filter (MF-Millipore, pore size: 2.0 μm)
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to remove these resins. For comparison of concentrations of Mo(V) and Mo(VI) species before and after contacting these resins, the adsorption abilities of Mo(V) and Mo(VI) species on these resins were evaluated. All experiments for Mo(V) and Mo(VI) species have been carried out independently. 2.4. Chromatographic experiments of Mo(V) and Mo(VI) species in HCl solutions For the Mo(V) and Mo(VI) chromatographic isotope fractionation experiments, five and seven glass columns connected in series were used. Each column was equipped with water jacket. The length of one column was 1.0 m and its inner diameter was 8.0 mm. The above-mentioned AR-01(Cl form), WA20(Cl form), and PA316(Cl form) resins were packed into these glass columns. The total weight of these packed resins was 24.6, 120.7, and 132.3 g for the experiments for Mo(VI) species, respectively. In case of those for Mo(V) species, the weights of AR-01 and WA20 resins were 24.6 and 95.0 g, respectively. By using the circulator, the reaction temperature was kept constant at 308 K for AR-01 system and 338 K for WA20 and PA316 systems, respectively. The breakthrough experiments using 0.10 M HCl solutions containing 0.010 M Mo(V) and 0.10 and 0.50 M Mo(VI) species were performed under the constant flow rate of 0.05 - 1.00 mL/min at 308 - 338 K. The flow rate was controlled by the high-pressure pump (NP-KX-210, Nihon Seimitsu Kagaku, Co., Ltd.). The samples were taken every 10.0 or 15.0 g by using the fraction collector (CHF161RA, Advantech). All apparatuses were connected in series with the polytetrafluoroethylene tubes with 2.0 mm inner diameter. Each Mo(V) and Mo(VI) concentration and their isotope ratios were measured by using ICP/MS described above. By varying the concentration of metal ions and kinds of solvents and their concentration, we have observed the effect of the Mo isotope discrimination in ICP/MS measurements [25]. Therefore, the concentrations of Mo(V) and Mo(VI) species in the sample solutions were adjusted at ca. 10 ppb (ppb = ng/g) for the isotope ratio measurements. As a diluent for all ICP/MS measurements, 1.0 wt% HNO3 solution was used. The Mo(V) and Mo(VI) species adsorbed on these resins in the columns were completely removed by using EDTA·4Na·4H2O after the chromatographic experiments. 3. Results and Discussion The adsorption experiments of Mo(V) and Mo(VI) species using AR-01(Cl form), WA20(Cl form), and PA316(Cl form) resins were performed by batch-wise techniques in order to evaluate the Kd values of Mo(V) and Mo(VI) species in the aqueous HCl solutions of 0.10, 0.50, 1.0, 2.0, 4.0, 6.0, 9.0, and 11.2 M at room temperature. The Kd values were calculated using the following Eq. (1). Kd = ｛Cr / Cs × (Vs / Vr)｝ = {(C0 - Cs) / Cs} × (Vs / Vr)
(1)
where Cr, Cs, C0, Vs, and Vr are concentration of Mo(V) and Mo(VI) species on these resins at adsorption equilibrium, concentration of Mo(V) and Mo(VI) species in solution after adsorption equilibrium, initial concentration of Mo(V) and Mo(VI) species, volume of solution, and volume of resin, respectively. It is clear that the Kd values of Mo(V) and Mo(VI) species with these resins decrease sharply with an increase of [HCl]T in the region from 0.10 to 1.0 M as shown in Figure 2. In the range of [HCl]T = 1.0 - 4.0 M, the Kd values increase gradually with increasing [HCl]T, and the values of Kd are almost constant between 4.0 and 11.2 M HCl. Judging from our previous works on Mo(VI) species, it has been suggested that Mo7O21(OH)33-, H3MoO4+, and MoO2Cl3form in three HCl concentration ranges as main species, respectively [22]. Namely, these Mo(VI) species must be selectively adsorbed to these resins in the HCl solutions ranging from 0.10 to 11.2 M. On the other hand, it was found that the adsorption phenomena between Mo(V) species and these resins are analogous to those of Mo(VI) species although WA20 resin has no adsorption ability for Mo(V) species in the HCl concentration ranges of 0.50 2.0 M and the chemical forms of Mo(V) species in the HCl solutions are not well-known. The concentration of HCl should be adjusted at 0.10 M to perform the Mo(V) and Mo(VI) adsorption and their isotope separation experiments because the adsorption abilities of these resins for Mo species became stronger. Therefore, on the assumption that the 1 : 1 anion-exchange reactions is proceeded, Mo(V) + Resin(Cl form) ⇌ Resin･Mo(V) + Cl- and Mo(VI) + Resin(Cl form) ⇌ Resin･Mo(VI) + Cl- (Resin represents AR-01(Cl form), WA20(Cl form), and PA316(Cl form) resins) under the conditions; [Mo]T = 1.0 mM, [Sn]T = 1.5 or 5.0 mM, [Resin]T = 0.50 g, we have investigated the adsorption mechanisms of these resins to Mo(V) and Mo(VI) species in 0.10 M HCl solutions in further detail. The thermodynamic parameters (⊿H, ⊿S, and ⊿G values) for the adsorption of Mo(V) and Mo(VI) species on these
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resins, ranging in Temp. = 278 - 367 K, were calculated from the linear plots of ln Kd against (1/T) using the following Van’t Hoff equation (2) [26] (see Figure 3) and the obtained values were summarized in Table 1. ln Kd = - ⊿G / R·T = - ⊿H / R·T + ⊿S / R
(2)
ln |ri - r0| = ln |rfL - r0| - ks(L - xi) = ln |rfL - r0| - ks × XBi
(3)
Here, R and T represent gas constant and absolute temperature. The calculated ⊿G values were from - 25.9 to - 5.32 kJ / mol at 298 K. This results indicate that the spontaneous adsorption processes between these resins and Mo(V) or Mo(VI) species occur in the solution with 0.10 M HCl. The positive ⊿H values show the endothermic reactions of Mo(V) and Mo(VI) species with these resins. It can be considered that Mo(V) and Mo(VI) species are surrounded by plenty of water in 0.10 M HCl solutions because amino and methyl groups are generally regarded as hydrophilic and weak hydrophobic groups, respectively. When Mo(V) and Mo(VI) species are adsorbed onto these resins, the hydration shell of Mo(V) and Mo(VI) species must be broken before the adsorption reactions of Mo(V) and Mo(VI) species with these resins proceed in the 0.10 M HCl solution. Thus, these dehydration processes are expected to require energy. In addition, the positive values of ΔS also suggest an increase in randomness at the boundary between Mo species and these resins during the adsorption processes. In brief, this tendency implies that the randomness arises due to the destruction of hydration shell of Mo species superior to the adsorption of Mo species on the surface of these resins. Based on these results, the breakthrough experiments for Mo(V) and Mo(VI) isotope separation were carried out at 303 and 338 K. The typical isotope fractionation of Mo(VI) species is shown in Figure 4. In the figure, the notation of Mo isotope ratio deviation was defined as the isotopic ratios of Mo-98 / Mo-92 and Mo-100 / Mo-92 over effluent volume. The original isotope ratios of Mo-98 / Mo-92 and Mo-100 / Mo-92 were 1.83 and 0.786, respectively. It was found that the both Mo isotope ratios decrease sharply with increasing effluent volume and the isotope ratios eventually approach the original values. Therefore, this figure indicates that the heavier isotopes are disproportionately located in the solution phase. Judging from the result of Figure 2, it can be regarded that the three resins have sufficient adsorption ability in the Mo(VI) system. However, contrary to our expectations, in case of PA316 resin, we cannot observe the Mo(VI) isotope fractionation in our experimental conditions. Moreover, the degree of Mo(V) isotope fractionation among these resins was within their experimental errors. We have clarified that the degree of Mo isotope fractionation is very different in the experimental conditions and have suggested that these tendencies of the Mo isotope fractionation are caused by the weak adsorption of Mo(VI) for PA316(Cl form) resin and the strong adsorption of Sn species for these resins. This behavior may be attributable to the corresponding reaction temperature. In the ideal cases of the Mo isotope fractionation by the breakthrough displacement chromatography with a sufficiently long isotopic plateau of the original value, each of the isotopic ratio, the r values (r = 98Mo(VI)/92Mo(VI) and 100 Mo(VI)/92Mo(VI)) can be expressed by Eq. (3) and the details of this equation have been described elsewhere [15].
where r0, rfL, ks, L, x, and XB are the original isotopic ratio, the maximum isotopic ratio on the front boundary, the slope coefficient, the migration distance, the distance from the starting point of the migration, the distance from the front boundary, and the subscripts i and 0 denote the fraction number and original sample, respectively. The term of (L - xi), XBi represents the hypothetical distance between the boundary and the location of xi inside the band. The ks values are slope coefficient experimentally determined by plotting of ln (ri - r0) vs. XBi. Thus, the obtained slope coefficients of 98Mo(VI)/92Mo(VI) and 100Mo(VI)/92Mo(VI) ratios in the 0.10 M HCl solution were found to be ks = 5.5 × 10-2, 4.6 × 10-2 for AR-01 resin and 2.0 × 10-2, 7.6 × 10-2 for WA20 resin, respectively. The isotope separation coefficients (ε) per unit mass (ε / ⊿Mass), which have been frequently used for the analysis of isotope fractionation using ion exchange chromatography and the corresponding height equivalent to a theoretical plate (HETP) derived from the theory of displacement type chromatographic enrichment in the isotopically transient state, are calculated by using the breakthrough curve of 98Mo/92Mo and 100Mo/92Mo and their [Mo(VI)]T in sample solutions. The equation can be expressed by Eq. (4, 5) [11,13-15,17-23]. ε / ⊿Mass = (α - 1) / (MassH - MassL) = Σ(qi|Ri - R0|/{Q × R0(1 - R0)} / (MassH - MassL)
(4)
6
HETP = (ε / |ks|) + (1 / ks2･L)
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(5)
Here, α, MassH, MassL, qi, Ri, and Q are the isotope fractionation factor, the mass of heavier isotope, the mass of lighter isotope, the amount of Mo in the fraction sample, the isotopic percentage of Mo, the total amount of adsorbed Mo species on these resins, respectively. The indication of fraction number is i = 0, 1, 2…. As a result, the calculated values of (ε / ⊿M) of 100Mo / 92Mo and 98Mo / 92Mo were summarized in Table 2. The (ε / ⊿M) values for transition metals such as Fe, Cu, Zn, Eu, Nd, and Gd have already been reported and their values including our present and previous works were plotted as shown in Figure 5 [11-15,20]. The plotted values were found to show a good linear relationship and the phenomenon indicates that the (ε / ⊿M) values of Mo(VI) species are proportional to the reciprocal square of the atomic weight, which is called mass shift effect [8].
Figure 2. Plots of Kd values of Mo species vs. [HCl]T at room temperature. [Mo]T = 1.0 mM, [Sn]T = 1.5 and 5.0 mM. Resin = 0.50 g.
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Figure 3. Plots of ln Kd values of Mo species vs. T-1 values at a temperature range of 278 - 367 K.
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Figure 4. Mo(VI) breakthrough curve and its isotope fractionation using WA20 resin in a 0.10 M HCl solution.
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Figure 5. Mass dependence of isotope separation coefficients per unit mass obtained from the ligand-exchange system in ion-exchange chromatography.
4. Conclusion The Mo(V) and Mo(VI) isotope fractionation using AR-01(Cl form), WA20(Cl form), and PA316(Cl form) resins, was examined in 0.10 M HCl solutions at 308 and 338 K. As a result, it was found that the heavier Mo(VI) isotopes are disproportionately located into a solution phase. We also have obtained the isotope separation coefficients of Mo(VI) species derived from the isotope fractionation curve of Mo(VI) species with these resins. It was confirmed that the (ε / ⊿M) values plotted from other well-known and our present data were found to show a good linear relationship. The phenomenon implied that the (ε / ⊿M) values of Mo(VI) species are strongly controlled by mass shift effect. However, we cannot observe the Mo(VI) isotope fractionation in case of PA316 resin and the Mo(V) isotope fractionation using these resins. It is suggested that these tendencies of the Mo isotope fractionation are caused by the weak adsorption of Mo(VI) species for PA316 resin and the adsorption strength of Sn species for these resins. Acknowledgements This work was partially supported by Nagaoka University of Technology Presidential Research Grant (No. 13). References [1] Heeg MJ, Jurisson SS. The role of inorganic chemistry in the development of radiometal agents for cancer therapy. Acc Chem Res 1999;32:1053-1060. [2] Nagai Y, Hatsukawa Y. Production of 99Mo for nuclear medicine by 100Mo(n, 2n)99Mo. J Phys Soc Jpn 2009;78:1-4. [3] Kimura A, Sato Y, Tanase M, Tsuchida K. Development of high density MoO3 pellets for production of 99Mo medical isotope. IOP Conf Series: Mater Sci Eng 2011;18:1-4.
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