Residence time effects on technetium reduction in slag-based cementitious materials

JOURNAL OF HAZARDOUS MATERIALS

卷:342

Article

Arai, Yuji¹  Powell, Brian A.²  Kaplan, D. I.³ 

[1] Univ Illinois, Dept Nat Resources & Environm Sci, Urbana, IL 61801 USA

[2] LG Rich Environm Lab, Dept Environm Engn & Earth Sci, 342 Comp Court, Anderson, SC 29625 USA

[3] Savannah River Natl Lab Aiken, Aiken, SC 29808 USA

关键词: Technetium;    Cementitious materials;    Slag;    Grout;    XAS;    Immobilization;    Reduction;   

DOI  :  10.1016/j.jhazmat.2017.08.049

来源: Elsevier

【 摘 要 】

A long-term disposal of technetium-99 (Tc-99) has been considered in a type of cementitious formulation, slag-based grout, at the U.S. Department of Energy, Savannah River Site, Aiken SC, U.S.A. Blast furnace slag, which contains S and Fe electron donors, has been used in a mixture with fly ash, and Portland cement to immobilize Tc-99(VII)O-4-(aq) in low level radioactive waste via reductive precipitation reaction. However the long-term stability of Tc(IV) species is not clearly understood as oxygen gradually diffuses into the solid structure. In this study, aging effects of Tc speciation were investigated as a function of depth (<2.5 cm) in slag-based grout using X-ray absorption spectroscopy. All of Fe(II)in solids was oxidized to Fe(III) after 117d. However, elemental S, sulfide, and sulfoxide persists at the 0-8 mm depths even after 485d, suggesting the presence of a reduced zone below the surface few millimeters. Pertechnetate was successfully reduced to Tc(IV) after 29d. Distorted hydrolyzed Tc(IV) octahedral molecules were partially sulfidized and or polymerized at all depths (0-8 mm) and were stable in 485d aged sample. The results of this study suggest that variable S species contribute to stabilize the partially sulfidized Tc(IV) species in aged slag-based grout. (C) 2017 Elsevier B.V. All rights reserved.

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