Spatial distribution, chemical state, solubility of rhenium in a reducing cement waste form: Implications for predicting technetium mobility in saltstone

Yuji Arai, Amanda H. Meena, Brain Lenell, Brian A. Powell, Daniel I. Kaplan

Research output: Contribution to journalArticlepeer-review

Abstract

Reducing cementitious materials (RCMs) are presently being developed for the long-term, subsurface disposal of low-level radioactive waste within the United States Department of Energy complex. Slag is included in the formulation of the RCM to facilitate the reductive precipitation of redox-sensitive radionuclides, particularly 99Tc. Using Re(VII)O4 as a chemical surrogate for Tc(VII)O4, depth sequence Re distribution, solubility, and chemical state were evaluated to provide a spatial measure of the impact of atmospheric O2 migration into field aged (<300 d) RCM monoliths. Total digestion analysis showed that total Re concentration increased with decreasing depth, indicating more Re was concentrated at the surface. A synchrotron based X-ray microprobe energy map also supports this finding. There was no clear depth dependent trend in Re solubility. Overall 30–60% of the total Re was soluble at the depth up to ∼3 cm. Partial reduction of Re(VII) to Re(IV) was also observed at these depths. These results suggest that long-term immobilization of Tc in RCM waste forms may be more complicated than previous thought and may require the consideration of non-uniform distribution of redox sensitive Tc in RCMs.

Original languageEnglish (US)
Pages (from-to)180-187
Number of pages8
JournalApplied Geochemistry
Volume85
DOIs
StatePublished - Oct 2017

Keywords

  • Immobilization
  • Rhenium
  • Saltstone
  • Slag
  • Technetium

ASJC Scopus subject areas

  • Environmental Chemistry
  • Pollution
  • Geochemistry and Petrology

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