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An efficient elution method of tetravalent uranium from anion exchanger by using formic acid solution
Journal of Alloys and Compounds 451 (2008) 400–402
An efficient elution method of tetravalent uranium from anion exchanger by using formic acid solution Tsuyoshi Arai ∗ , Yuezhou Wei, Mikio Kumagai Institute of Research and Innovation (IRI), 1201 Takada, Kashiwa 277-0861, Japan Available online 19 April 2007
Abstract In recent years, we have been investigating the development of the ERIX (The Electrolytic Reduction and Ion Exchange) process for reprocessing spent FBR-MOX fuel. This process uses electrolytic reduction and ion exchange techniques to recover U, Pu from spent FBR-MOX fuel solution. It was found that despite of the high nitric acid concentration, U(VI) can be effectively reduced to U(IV) using a flow type electrolytic cell in the existence of hydrazine and the U(IV) can be completely separated from fission products by the anion exchanger, AR-01. In addition, it was proposed that a part of U is assigned to be recovered together with Pu and Np for reusing as a FBR-MOX fuel. For that purpose, we are investigating an efficient elution method of Pu(IV) and U(IV) from AR-01. In this work, to develop an efficient elution method of U(IV) from AR-01, we have examined the U(IV) elution behavior by formic acid and the complex-formation of U(IV) with HCOO− . © 2007 Elsevier B.V. All rights reserved. Keywords: Spent nuclear fuel; FBR-MOX; Reprocessing; Ion exchange; Separation; U(IV); Formic acid
1. Introduction In recent years, we have been investigating the development of the ERIX process for reprocessing spent FBR-MOX fuel. The ERIX process uses electrolytic reduction and ion exchange techniques to recover U, Pu, Np and the minor actinides from spent FBR-MOX fuel solution. The ERIX process is consists chiefly of “Pd and Ag removal system”, “electrolytic reduction system”, “ion exchange separation system”, “extraction chromatography separation system for minor actinides” [1,2]. From our research results, we have prospects for the ERIX process to have many advantages such as being organic solvent free, little nuclear waste generation, compacted equipment, simple operation procedure, economical improvement as a reprocessing technology for spent nuclear fuels [1,2]. And then, in previous work, it was found that U(VI) can be effectively reduced to U(IV) using the flow type electrolytic cell in the existence of hydrazine and U(IV) can be completely separated from fission products (FPs) by a new type of anion exchanger (AR-01) packed column in nitric acid medium [1–5]. In addition, it was proposed that a part of U is assigned to be recovered together with Pu and ∗
Corresponding author. Present address: 5-3-7, Midoridai, Kashiwa-shi, Chiba pref 277-0884, Japan. Tel.: +81 4 7144 8956; fax: +81 4 7144 7602. E-mail address: [email protected] (T. Arai). 0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.04.156
Np for reusing as a FBR-MOX fuel. For that purpose, we are investigating an efficient elution method of Pu(IV) and U(IV) from AR-01. There was a reported the adsorbed Pu(IV) was immediately eluted out by formic acid solution from AR-01 [6]. So, it was important to examine the elution behavior of U(IV) by formic acid solution. In the present work, to develop an efficient elution method of U(IV) from AR-01, we have examined the U(IV) elution behavior by formic acid and the complex-formation of U(IV) with HCOO− . 2. Experimental For the separation experiments, we used AR-01 anion exchanger which is the macro-reticular resin embedded in porous silica particles. Therefore, AR-01 is a hybrid anion exchanger of organic and inorganic materials. NMethylbenzimidazole and N,N -methylbenzimidazolium groups work as the functional group in the anion exchanger. The total exchange capacity is 3.4 mequiv./g-resin and quaternary capacity is 2.0 mequiv./g-resin. AR-01 is a spherical particle with a diameter of about 50 m. Separation experiments were conduced using a pressure-resistant glass column with 10 mm in inner diameter and length of 500 mm. Fig. 1 shows the schematic diagram of the column apparatus for separation experiments. AR-01 anion exchanger was packed into the column in slurry state at 0.1 MPa. The bed volume of AR-01 resin in the column was about 35 cm3 . The AR-01 packed column was kept at a constant temperature at 25 ◦ C with water jackets. Before the introduction of sample solution, the AR-01 was conditioned by passing 250 cm3 of 6 mol/dm3 nitric acid medium solution through the column. In the
T. Arai et al. / Journal of Alloys and Compounds 451 (2008) 400–402
Fig. 1. The schematic diagram of the column apparatus for separation experiments. separation experiment, a simulated process solution containing U, some typical FPs and 6 mol/dm3 nitric acid medium was fed to the column at a constant flow rate of 2.5 cm3 /min. Then 0.01–3 mol/dm3 as the eluent for U(IV) and washing solutions were passed through the column, successively. The effluents from the column were recovered using auto-fractional collector in 2.5 cm3 aliquots. The metal concentrations in each fraction were analyzed by ICP-OES.
3. Results and discussion To investigate the separation behavior of U(IV) and typical FPs, then the elution behavior of U(IV) using formic acid solution, separation experiments using AR-01 packed column were carried out for U(VI) and FPs containing solution after the electrolytic reduction. Fig. 2 shows the separation experiment results for the simulated spent FBR-MOX fuel solution after
Fig. 2. The separation experiment results for the simulated spent FBR-MOX fuel solution after electrolytic reduction.
401
electrolytic reduction. As can be seen in Fig. 2, all of the FPs including Ru showed almost no adsorption and breakthrough the column firstly. It is well known that Ru(III) presents a complicated adsorption-elution behavior in anion exchange column without electrolytic reduction. This result suggests that Ru(III) was completely reduced to a lower oxidation state, probably Ru(II), which exhibits no adsorption onto AR-01. As shown in Fig. 2, when 3 mol/dm3 formic acid solution was applied to the column, the adsorbed U(IV) was immediately eluted out resulting in a concentrated U(IV) eluate fraction. Almost all the total amount of U was collected in 15 cm3 fraction which is only 0.4 bed volumes of the AR-01 packed column. Moreover the U(IV) elution curve shows almost no tailing. Therefore, it was assumed that high concentration formic acid is an excellent eluent for U(IV). As identified above, it was suggested that the adsorbed U(IV) was eluted off by 3 mol/dm3 formic acid efficiently. And so, to investigate the elution behavior of U(IV) by formic acid, the U(IV) elution column experiment were carried out using 0.01–3 mol/dm3 formic acid as eluent. Fig. 3 shows the U(IV) elution column experiment results for the through concentration of formic acid as eluent changing from 0.01 to 3 mol/dm3 by the flow type UV spectroscopy at 547 nm. As can be seen in Fig. 3, it was found that the elution speed for U(IV) increased with the increase in concentration of formic acid. And then, the end of the U(IV) elution curve decreased with the increase in concentration of formic acid. Therefore, it was considered that high concentration formic acid as eluent was effective at low dose for the adsorbed U(IV) elution. Fig. 4 shows UV spectra changes of U(IV) in 6 mol/dm3 nitric acid medium with the change in concentration of formic acid. As can be seen in Fig. 4, it was found that the UV spectra for U(IV) changed with the increase in concentration of formic acid. From these experiment results, it was assumed that U(IV) was complexed with HCOO− and the U(IV)-HCOO− complex form a neutral or cation complex.
Fig. 3. The U(IV) elution column experiment results for the through concentration of formic acid as eluent changing from 0.01 to 3 mol/dm3 . (In this figure, Y axis on the left hand sides shows ABS at 547 nm by the flow type UV for U(IV) and right hand side shows pH.)
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T. Arai et al. / Journal of Alloys and Compounds 451 (2008) 400–402
4. Conclusions The adsorbed U(IV) on AR-01 could be quickly eluted with 0.01–3 mol/dm3 formic acid and the U(IV) elution curve shows almost no tailing. It was found that the elution speed for U(IV) increased with the increase in concentration of HCOOH. From this work, it was assumed that U(IV) was complexed with HCOO− and the U(IV)-HCOO− complex form a neutral or cation complex. Therefore, it was assumed that high concentration formic acid is an excellent eluent for U(IV). Acknowledgements A part of this paper is the results from “Development of the ERIX Process for Reprocessing Spent FBR-MOX Fuel” entrusted by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT). References
Fig. 4. UV spectra changes of U(IV) in 6 mol/dm3 nitric acid medium with the change in concentration of formic acid.
[1] Y.-Z. Wei, T. Arai, H. Hoshi, M. Kumagai, T. Asakura, Y. Morita, Proc. ICONE 13, Beijing, 2005, p. 50133. [2] T. Arai, Y.-Z. Wei, M. Kumagai, Proc. GLOBAL 2005, Tsukuba, 2005, p. 072. [3] T. Arai, Y.-Z. Wei, M. Kumagai, Proc. GLOBAL 2001, Paris, 2001, p. 004. [4] Y.-Z. Wei, B. Fang, T. Arai, M. Kumagai, J. Radioanal. Nucl. Chem. 262 (2004) 409–415. [5] Y.-Z. Wei, T. Arai, H. Hoshi, M. Kumagai, A. Bruggeman, M. Gysemans, T. Sawa, Proc. JAERI-Conf. NUCEF 2001, Tokai, 2001, pp. 225– 238. [6] Y.-Z. Wei, M. Kumagai, Y. Takashima, A. Bruggeman, M. Gysemans, J. Nucl. Sci. Technol. 36 (1999) 304–306.
An efficient elution method of tetravalent uranium from anion exchanger by using formic acid solution Tsuyoshi Arai ∗ , Yuezhou Wei, Mikio Kumagai Institute of Research and Innovation (IRI), 1201 Takada, Kashiwa 277-0861, Japan Available online 19 April 2007
Abstract In recent years, we have been investigating the development of the ERIX (The Electrolytic Reduction and Ion Exchange) process for reprocessing spent FBR-MOX fuel. This process uses electrolytic reduction and ion exchange techniques to recover U, Pu from spent FBR-MOX fuel solution. It was found that despite of the high nitric acid concentration, U(VI) can be effectively reduced to U(IV) using a flow type electrolytic cell in the existence of hydrazine and the U(IV) can be completely separated from fission products by the anion exchanger, AR-01. In addition, it was proposed that a part of U is assigned to be recovered together with Pu and Np for reusing as a FBR-MOX fuel. For that purpose, we are investigating an efficient elution method of Pu(IV) and U(IV) from AR-01. In this work, to develop an efficient elution method of U(IV) from AR-01, we have examined the U(IV) elution behavior by formic acid and the complex-formation of U(IV) with HCOO− . © 2007 Elsevier B.V. All rights reserved. Keywords: Spent nuclear fuel; FBR-MOX; Reprocessing; Ion exchange; Separation; U(IV); Formic acid
1. Introduction In recent years, we have been investigating the development of the ERIX process for reprocessing spent FBR-MOX fuel. The ERIX process uses electrolytic reduction and ion exchange techniques to recover U, Pu, Np and the minor actinides from spent FBR-MOX fuel solution. The ERIX process is consists chiefly of “Pd and Ag removal system”, “electrolytic reduction system”, “ion exchange separation system”, “extraction chromatography separation system for minor actinides” [1,2]. From our research results, we have prospects for the ERIX process to have many advantages such as being organic solvent free, little nuclear waste generation, compacted equipment, simple operation procedure, economical improvement as a reprocessing technology for spent nuclear fuels [1,2]. And then, in previous work, it was found that U(VI) can be effectively reduced to U(IV) using the flow type electrolytic cell in the existence of hydrazine and U(IV) can be completely separated from fission products (FPs) by a new type of anion exchanger (AR-01) packed column in nitric acid medium [1–5]. In addition, it was proposed that a part of U is assigned to be recovered together with Pu and ∗
Corresponding author. Present address: 5-3-7, Midoridai, Kashiwa-shi, Chiba pref 277-0884, Japan. Tel.: +81 4 7144 8956; fax: +81 4 7144 7602. E-mail address: [email protected] (T. Arai). 0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2007.04.156
Np for reusing as a FBR-MOX fuel. For that purpose, we are investigating an efficient elution method of Pu(IV) and U(IV) from AR-01. There was a reported the adsorbed Pu(IV) was immediately eluted out by formic acid solution from AR-01 [6]. So, it was important to examine the elution behavior of U(IV) by formic acid solution. In the present work, to develop an efficient elution method of U(IV) from AR-01, we have examined the U(IV) elution behavior by formic acid and the complex-formation of U(IV) with HCOO− . 2. Experimental For the separation experiments, we used AR-01 anion exchanger which is the macro-reticular resin embedded in porous silica particles. Therefore, AR-01 is a hybrid anion exchanger of organic and inorganic materials. NMethylbenzimidazole and N,N -methylbenzimidazolium groups work as the functional group in the anion exchanger. The total exchange capacity is 3.4 mequiv./g-resin and quaternary capacity is 2.0 mequiv./g-resin. AR-01 is a spherical particle with a diameter of about 50 m. Separation experiments were conduced using a pressure-resistant glass column with 10 mm in inner diameter and length of 500 mm. Fig. 1 shows the schematic diagram of the column apparatus for separation experiments. AR-01 anion exchanger was packed into the column in slurry state at 0.1 MPa. The bed volume of AR-01 resin in the column was about 35 cm3 . The AR-01 packed column was kept at a constant temperature at 25 ◦ C with water jackets. Before the introduction of sample solution, the AR-01 was conditioned by passing 250 cm3 of 6 mol/dm3 nitric acid medium solution through the column. In the
T. Arai et al. / Journal of Alloys and Compounds 451 (2008) 400–402
Fig. 1. The schematic diagram of the column apparatus for separation experiments. separation experiment, a simulated process solution containing U, some typical FPs and 6 mol/dm3 nitric acid medium was fed to the column at a constant flow rate of 2.5 cm3 /min. Then 0.01–3 mol/dm3 as the eluent for U(IV) and washing solutions were passed through the column, successively. The effluents from the column were recovered using auto-fractional collector in 2.5 cm3 aliquots. The metal concentrations in each fraction were analyzed by ICP-OES.
3. Results and discussion To investigate the separation behavior of U(IV) and typical FPs, then the elution behavior of U(IV) using formic acid solution, separation experiments using AR-01 packed column were carried out for U(VI) and FPs containing solution after the electrolytic reduction. Fig. 2 shows the separation experiment results for the simulated spent FBR-MOX fuel solution after
Fig. 2. The separation experiment results for the simulated spent FBR-MOX fuel solution after electrolytic reduction.
401
electrolytic reduction. As can be seen in Fig. 2, all of the FPs including Ru showed almost no adsorption and breakthrough the column firstly. It is well known that Ru(III) presents a complicated adsorption-elution behavior in anion exchange column without electrolytic reduction. This result suggests that Ru(III) was completely reduced to a lower oxidation state, probably Ru(II), which exhibits no adsorption onto AR-01. As shown in Fig. 2, when 3 mol/dm3 formic acid solution was applied to the column, the adsorbed U(IV) was immediately eluted out resulting in a concentrated U(IV) eluate fraction. Almost all the total amount of U was collected in 15 cm3 fraction which is only 0.4 bed volumes of the AR-01 packed column. Moreover the U(IV) elution curve shows almost no tailing. Therefore, it was assumed that high concentration formic acid is an excellent eluent for U(IV). As identified above, it was suggested that the adsorbed U(IV) was eluted off by 3 mol/dm3 formic acid efficiently. And so, to investigate the elution behavior of U(IV) by formic acid, the U(IV) elution column experiment were carried out using 0.01–3 mol/dm3 formic acid as eluent. Fig. 3 shows the U(IV) elution column experiment results for the through concentration of formic acid as eluent changing from 0.01 to 3 mol/dm3 by the flow type UV spectroscopy at 547 nm. As can be seen in Fig. 3, it was found that the elution speed for U(IV) increased with the increase in concentration of formic acid. And then, the end of the U(IV) elution curve decreased with the increase in concentration of formic acid. Therefore, it was considered that high concentration formic acid as eluent was effective at low dose for the adsorbed U(IV) elution. Fig. 4 shows UV spectra changes of U(IV) in 6 mol/dm3 nitric acid medium with the change in concentration of formic acid. As can be seen in Fig. 4, it was found that the UV spectra for U(IV) changed with the increase in concentration of formic acid. From these experiment results, it was assumed that U(IV) was complexed with HCOO− and the U(IV)-HCOO− complex form a neutral or cation complex.
Fig. 3. The U(IV) elution column experiment results for the through concentration of formic acid as eluent changing from 0.01 to 3 mol/dm3 . (In this figure, Y axis on the left hand sides shows ABS at 547 nm by the flow type UV for U(IV) and right hand side shows pH.)
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T. Arai et al. / Journal of Alloys and Compounds 451 (2008) 400–402
4. Conclusions The adsorbed U(IV) on AR-01 could be quickly eluted with 0.01–3 mol/dm3 formic acid and the U(IV) elution curve shows almost no tailing. It was found that the elution speed for U(IV) increased with the increase in concentration of HCOOH. From this work, it was assumed that U(IV) was complexed with HCOO− and the U(IV)-HCOO− complex form a neutral or cation complex. Therefore, it was assumed that high concentration formic acid is an excellent eluent for U(IV). Acknowledgements A part of this paper is the results from “Development of the ERIX Process for Reprocessing Spent FBR-MOX Fuel” entrusted by the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT). References
Fig. 4. UV spectra changes of U(IV) in 6 mol/dm3 nitric acid medium with the change in concentration of formic acid.
[1] Y.-Z. Wei, T. Arai, H. Hoshi, M. Kumagai, T. Asakura, Y. Morita, Proc. ICONE 13, Beijing, 2005, p. 50133. [2] T. Arai, Y.-Z. Wei, M. Kumagai, Proc. GLOBAL 2005, Tsukuba, 2005, p. 072. [3] T. Arai, Y.-Z. Wei, M. Kumagai, Proc. GLOBAL 2001, Paris, 2001, p. 004. [4] Y.-Z. Wei, B. Fang, T. Arai, M. Kumagai, J. Radioanal. Nucl. Chem. 262 (2004) 409–415. [5] Y.-Z. Wei, T. Arai, H. Hoshi, M. Kumagai, A. Bruggeman, M. Gysemans, T. Sawa, Proc. JAERI-Conf. NUCEF 2001, Tokai, 2001, pp. 225– 238. [6] Y.-Z. Wei, M. Kumagai, Y. Takashima, A. Bruggeman, M. Gysemans, J. Nucl. Sci. Technol. 36 (1999) 304–306.