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Selective Separation and Recovery of Cesium by Ammonium Tungstophosphate-Alginate Microcapsules

[+] Author Affiliations
Hitoshi Mimura, Yan Wu, Yufei Wang, Yuichi Niibori

Tohoku University, Sendai, Japan

Isao Yamagishi, Masaki Ozawa, Takashi Ohnishi, Shinichi Koyama

Japan Atomic Energy Agency, Ibaraki, Japan

Paper No. ICONE18-29091, pp. 419-427; 9 pages
doi:10.1115/ICONE18-29091
From:
  • 18th International Conference on Nuclear Engineering
  • 18th International Conference on Nuclear Engineering: Volume 1
  • Xi’an, China, May 17–21, 2010
  • Conference Sponsors: Nuclear Engineering Division
  • ISBN: 978-0-7918-4929-3
  • Copyright © 2010 by ASME

abstract

A fine crystalline ammonium tungstophosphate (AWP) exchanger with high selectivity toward Cs+ was encapsulated in biopolymer matrices (calcium alginate, CaALG). The characterization of the AWP-CaALG microcapsule was examined using SEM/WDS, IR and DTA/TG analyses, and the selective separation and recovery of 137 Cs were examined by the batch and column methods using simulated and real high-level liquid waste (HLLW). The free energy (ΔG0 ) of the ion exchange (NH4+ ↔ Cs+ ) for fine AWP crystals was determined at −13.2 kJ/mol, indicating the high selectivity of AWP towards Cs+ . Spherical and elastic AWP-CaALG microcapsules (∼700 μm in diameter) were obtained and fine AWP crystals were uniformly immobilized in alginate matrices. Relatively large Kd values of Cs+ above 105 cm3 /g were obtained in the presence of 10−3 ∼1 M Ca(NO3 )2 , resulting in a separation factor of Cs/Rb exceeding 102 . The irradiated samples (60 Co, 17.6 kGy) also exhibited large Kd values exceeding 105 cm3 /g in the presence of 2.5 M HNO3 . The Kd values in the presence of 0.1–9 M HNO3 for 67 elements were determined and the order of Kd value was Cs+ ≫ Rb+ > Ag+ . The breakthrough curve of Cs+ had an S-shaped profile, and the breakpoint increased with decreasing flow rate; the breakpoint and breakthrough capacity at a flow rate of 0.35 cm3 /min for the column (0.7 g AWP-CaALG) were estimated at 25.2 cm3 and 0.068 mmol/g, respectively. Good breakthrough and elution properties were retained even after thrice-repeated runs. The uptake (%) of Cs+ in simulated HLLW (28 metal components-1.92 M HNO3 , SW-11, JAEA) was estimated at 97%, and the distribution of Cs+ and Zr/Ru into the AWP and alginate phases, respectively, were observed by WDS analysis. Further, the selective uptake of 137 Cs exceeding 99% was confirmed by using real HLLW (FBR “JOYO”, JAEA). The AWP-CaALG microcapsules are thus effective for the selective separation and recovery of Cs+ from HLLWs.

Copyright © 2010 by ASME

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