Title: Mechanism of iodine release from iodoapatite in aqueous solution

Abstract

Safe disposal of nuclear waste is essential to ensure the sustainability of nuclear energy. This is especially true for the volatile radionuclide iodine-129 due to its long half-life (15.7 Ma) and high mobility in most disposal environments. The dissolution behaviour of lead vanadium iodoapatite (Pb₅(VO₄)₃I) synthesized to evaluate its possible use for immobilizing iodine-129 was investigated to understand the mechanism by which iodide is released. Experiments using a semi-dynamic method were carried out in cap-sealed Teflon vessels at a constant temperature 90 ± 0.5 °C with a fixed sample surface area-to-solution volume ratio of 16 m^-1. The leachates were analyzed using inductively coupled plasma mass spectrometry (ICP-MS) and the leached surfaces were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR). The results show that lead and vanadium dissolved congruently at a constant rate, while the iodine was initially released at a significantly higher rate than suggested by its stoichiometry with respect to lead and vanadium. The iodine-to-lead molar ratio in the solution gradually decreased over time, but iodine release remained superstoichiometric. The results suggest the release of iodide occurs by an ion-exchange process that is faster than the dissolution rate of the Pb–V–O framework. Analysismore » of the leached samples shows that the spectroscopic signature of OH groups in the leached samples is consistent with an ion exchange mechanism.« less

Authors:

Zhang, Z.  ^[1];

• Search DOE PAGES for author "Zhang, Z."
• Search DOE PAGES for ORCID "0000-0002-0807-8991"

Heath, A. ^[2]; Valsaraj, K. T. ^[2]; Ebert, W. L. ^[3]; Yao, T. ^[4]; Lian, J.  ^[4];

• Search DOE PAGES for author "Lian, J."
• Search DOE PAGES for ORCID "0000-0002-9060-8831"

Wang, J.  ^[1]

• Search DOE PAGES for author "Wang, J."
• Search DOE PAGES for ORCID "0000-0001-7671-0533"

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+ Show Author Affiliations

1. Department of Geology and Geophysics, Louisiana State University, Baton Rouge, USA
2. Department of Chemical Engineering, Louisiana State University, Baton Rouge, USA
3. Nuclear Engineering, Argonne National Lab, Lemont, USA
4. Department of Mechanical and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, USA

Publication Date:

Mon Jan 01 00:00:00 EST 2018

Research Org.:

Louisiana State Univ., Baton Rouge, LA (United States); Rensselaer Polytechnic Inst., Troy, NY (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1417677

Alternate Identifier(s):

OSTI ID: 1600980

Grant/Contract Number:  

SC0016584

Resource Type:

Published Article

Journal Name:

RSC Advances

Additional Journal Information:

Journal Name: RSC Advances Journal Volume: 8 Journal Issue: 8; Journal ID: ISSN 2046-2069

Publisher:

Royal Society of Chemistry

Country of Publication:

United Kingdom

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY