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

Yuji Arai, Brian A. Powell, D. I. Kaplan

Research output: Contribution to journalArticle

Abstract

A long-term disposal of technetium-99 (99Tc) 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 99Tc(VII)O4 (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.

Original languageEnglish (US)
Pages (from-to)510-518
Number of pages9
JournalJournal of Hazardous Materials
Volume342
DOIs
StatePublished - Jan 15 2018

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X-Ray Absorption Spectroscopy
Coal Ash
Radioactive Waste
Sodium Pertechnetate Tc 99m
Technetium
Sulfides
Rivers
Electrons
Oxygen
slag
Certificate of Need
Slags
grout
Butylene Glycols
technetium isotope
technetium
atomic absorption spectroscopy
fly ash
radioactive waste
X-ray spectroscopy

Keywords

  • Cementitious materials
  • Grout
  • Immobilization
  • Reduction
  • Slag
  • Technetium
  • XAS

ASJC Scopus subject areas

  • Environmental Engineering
  • Environmental Chemistry
  • Waste Management and Disposal
  • Pollution
  • Health, Toxicology and Mutagenesis

Cite this

Residence time effects on technetium reduction in slag-based cementitious materials. / Arai, Yuji; Powell, Brian A.; Kaplan, D. I.

In: Journal of Hazardous Materials, Vol. 342, 15.01.2018, p. 510-518.

Research output: Contribution to journalArticle

Arai, Yuji; Powell, Brian A.; Kaplan, D. I. / Residence time effects on technetium reduction in slag-based cementitious materials.

In: Journal of Hazardous Materials, Vol. 342, 15.01.2018, p. 510-518.

Research output: Contribution to journalArticle

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