Competitive Incorporation of Perrhenate and Nitrate into Sodalite

Journal Article · Tue Oct 21 00:00:00 EDT 2014 · Environmental Science and Technology

DOI:https://doi.org/10.1021/es503156v· OSTI ID:1234080

Dickson, Johnbull O. ^[1]; Harsh, James B. ^[1]; Flury, Markus ^[1]; Lukens, Wayne W. ^[2]; Pierce, Eric M. ^[3]

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1. Department of Crop and Soil Sciences, Washington State University, P.O. Box 646420, Pullman, Washington 99164, United States
2. Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
3. Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, Tennessee 37831, United States

Nuclear waste storage tanks at the Hanford site in southeastern Washington have released highly alkaline solutions, containing radioactive and other contaminants, into subsurface sediments. When this waste reacts with subsurface sediments, feldspathoid minerals (sodalite, cancrinite) can form, sequestering pertechnetate (⁹⁹TcO₄^–) and other ions. This study investigates the potential for incorporation of perrhenate (ReO₄^–), a chemical surrogate for ⁹⁹TcO₄^–, into mixed perrhenate/nitrate (ReO₄^–/NO₃^–) sodalite. Mixed-anion sodalites were hydrothermally synthesized in the laboratory from zeolite A in sodium hydroxide, nitrate, and perrhenate solutions at 90 °C for 24 h. The resulting solids were characterized by bulk chemical analysis, X-ray diffraction, scanning electron microscopy, and X-ray absorption near edge structure spectroscopy (XANES) to determine the products’ chemical composition, structure, morphology, and Re oxidation state. The XANES data indicated that nearly all rhenium (Re) was incorporated as Re(VII)O₄^–. The nonlinear increase of the unit cell parameter with ReO₄^–/NO₃^– ratios suggests formation of two separate sodalite phases in lieu of a mixed-anion sodalite. The results reveal that the sodalite cage is highly selective toward NO₃^– over ReO₄^–. Calculated enthalpy and Gibbs free energy of formation at 298 K for NO₃^- and ReO₄^-sodalite suggest that NO₃^– incorporation into the cage is favored over the incorporation of the larger ReO₄^–, due to the smaller ionic radius of NO₃^–. In conclusion, based on these results, it is expected that NO₃^–, which is present at significantly higher concentrations in alkaline waste solutions than ⁹⁹TcO₄^–, will be strongly preferred for incorporation into the sodalite cage.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER); USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: AC05-00OR22725; AC02-05CH11231
• OSTI ID: 1234080
• Alternate ID(s): OSTI ID: 1373101
• Report Number(s): LBNL-181975
• Journal Information: Environmental Science and Technology, Journal Name: Environmental Science and Technology Vol. 48 Journal Issue: 21; ISSN 0013-936X
• Publisher: American Chemical Society
• Country of Publication: United States
• Language: English

Related Subjects

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
54 ENVIRONMENTAL SCIENCES