Development of Tc(IV)-incorporated Fe minerals to enhance {sup 99}Tc retention in glass waste form - 15239
- Pacific Northwest National Laboratory (United States)
- US DOE ORP (United States)
Iron minerals have been considered to be good hosts for Tc immobilization because the Tc(IV) ion substitutes for Fe(III) in the crystal structure of the Fe oxide due to similarities in (1) cation size [Tc(IV) = 78.5 pm; Fe(III) = 69 or 78.5 pm], (2) metal-oxygen interatomic distance (Tc-O = 0.199 nm, Fe-O = 0.203 nm), (3) number of coordinating oxygen atoms (both 6-fold coordinated), and (4) the redox potential (Eh=ca. +20 mV at pH = 7) for a redox couple between Tc(VII)/Tc(IV) and Fe(III)/Fe(II). Magnetite, maghemite, and trevorite are iron oxide minerals and all belong to spinel mineral group. Laboratory testing shows that Tc can be removed from aqueous waste solutions by a process of Tc reduction from Tc(VII) to Tc(IV) followed by co-precipitation with iron oxide minerals during recrystallization of Fe(OH){sub 2}(s) used as an initial solid precursor. X-ray absorption near edge structure (XANES) spectroscopy confirmed that Tc was in the +4 oxidation state in final Tc-Fe minerals. The Tc-incorporated Fe minerals (Tc-goethite and Tc-magnetite/maghemite) were also tested for Tc retention in glass melts at different temperatures between 600 - 1,000 deg.C in a furnace. After being cooled in air, the solid glass specimens collected at different temperatures were analyzed for Tc oxidation state using XANES and Tc retention using liquid scintillation counting (LSC). Although Tc(IV) started to re-oxidize at 600 deg.C, Tc retention in the final glass specimen prepared with Tc-incorporated Fe mineral at high temperatures was at least two times higher than glass prepared with KTcO{sub 4} salt. Higher Tc retention in glass is considered to result from limited and delayed Tc volatilization process due to Fe mineral encapsulation for Tc. Therefore, the results showing the presence of Tc(IV) in the Fe mineral structure indicate strong possibility to enhance Tc retention in borosilicate glass as well as to reduce the remediation costs at the Hanford Site. (authors)
- Research Organization:
- WM Symposia, Inc., PO Box 27646, 85285-7646 Tempe, AZ (United States)
- OSTI ID:
- 22822767
- Report Number(s):
- INIS-US-19-WM-15239; TRN: US19V0757067682
- Resource Relation:
- Conference: WM2015: Annual Waste Management Symposium, Phoenix, AZ (United States), 15-19 Mar 2015; Other Information: Country of input: France; 9 refs.; Available online at: http://archive.wmsym.org/2015/index.html
- Country of Publication:
- United States
- Language:
- English
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Enhanced 99Tc retention in glass waste form using Tc(IV)-incorporated Fe minerals
Enhanced 99 Tc retention in glass waste form using Tc(IV)-incorporated Fe minerals
Related Subjects
12 MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
BOROSILICATE GLASS
COPRECIPITATION
CRYSTAL STRUCTURE
ENCAPSULATION
EVAPORATION
GOETHITE
IRON HYDROXIDES
IRON OXIDES
LIQUID WASTES
MAGNETITE
RECRYSTALLIZATION
REDOX POTENTIAL
REMEDIAL ACTION
SCINTILLATION COUNTING
SPINELS
TECHNETIUM 99
TECHNETIUM COMPOUNDS
TEMPERATURE RANGE 0400-1000 K
WASTE FORMS
X-RAY SPECTROSCOPY