title: Rhenium solubility in borosilicate nuclear waste glass: implications for the processing and immobilization of technetium-99.
abstract: The immobilization of technetium-99 ((99)Tc) in a suitable host matrix has proven to be a challenging task for researchers in the nuclear waste community around the world. In this context, the present work reports on the solubility and retention of rhenium, a nonradioactive surrogate for (99)Tc, in a sodium borosilicate glass. Glasses containing target Re concentrations from 0 to 10,000 ppm [by mass, added as KReO(4) (Re(7+))] were synthesized in vacuum-sealed quartz ampules to minimize the loss of Re from volatilization during melting at 1000 °C. The rhenium was found as Re(7+) in all of the glasses as observed by X-ray absorption near-edge structure. The solubility of Re in borosilicate glasses was determined to be ~3000 ppm (by mass) using inductively coupled plasma optical emission spectroscopy. At higher rhenium concentrations, additional rhenium was retained in the glasses as crystalline inclusions of alkali perrhenates detected with X-ray diffraction. Since (99)Tc concentrations in a glass waste form are predicted to be <10 ppm (by mass), these Re results implied that the solubility should not be a limiting factor in processing radioactive wastes, assuming Tc as Tc(7+) and similarities between Re(7+) and Tc(7+) behavior in this glass system.
authors.affiliation: Pacific Northwest National Laboratory, Richland, Washington 99352, USA. john.mccloy@pnnl.gov
authors.forename: John S
authors.initials: JS
authors.lastname: McCloy
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Riley
authors.forename: Ashutosh
authors.initials: A
authors.lastname: Goel
authors.forename: Martin
authors.initials: M
authors.lastname: Liezers
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Schweiger
authors.forename: Carmen P
authors.initials: CP
authors.lastname: Rodriguez
authors.forename: Pavel
authors.initials: P
authors.lastname: Hrma
authors.forename: Dong-Sang
authors.initials: DS
authors.lastname: Kim
authors.forename: Wayne W
authors.initials: WW
authors.lastname: Lukens
authors.forename: Albert A
authors.initials: AA
authors.lastname: Kruger
mesh_terms: D052918:Environmental Restoration and Remediation / Q000379:methods*; D005898:Glass / Q000737:chemistry*; D010084:Oxidation-Reduction; D011850:Radioactive Waste / Q000032:analysis* / Q000517:prevention & control; D012211:Rhenium / Q000737:chemistry*; D017640:Silicates / Q000737:chemistry*; D012995:Solubility; D013054:Spectrophotometry, Atomic; D013667:Technetium / Q000737:chemistry; D058989:Vitrification; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D011850:Radioactive Waste; D017640:Silicates; D012211:Rhenium; D013667:Technetium