Fe Oxide Waste Form for Tc Immobilization
EMSL Project ID
47481
Abstract
The objective of this work is to develop a waste form that will sequester Tc in a Goethite matrix that will be resistant to Tc-leaching. Goethite (?-FeOOH) is a low-temperature secondary weathering product of primary iron phases. Goethite is extremely stable at the Earth’s surface and under shallow waste burial conditions, and has little potential for weathering and dissolution. The structure of goethite consists of alternating double chains of Fe(III)O6 polyhedra and these chains are partially linked above and below by H-bonds. Goethite appears to co-precipitate with Tc(IV)O2 or incorporate Tc(IV) within its mineral lattice. The possibility of Tc(IV) substituting for Fe(III) is highly possible because of similarities in cation size [Tc(IV) = 78.5 pm ; Fe(III) = 69 or 78.5 pm], metal-oxygen bond length (Tc—O = 1.99 Å, Fe—O = 2.026 Å), and the number of coordinating oxygen atoms (both 6-fold octahedral coordinated). Substitution of Fe(III) by Tc(IV) would require a coupled substitution involving a monovalent cation (M+) to maintain charge balance, but a defect structure is also possible. Although it is not known where Tc(IV) resides in goethite-technetium solids, it is well-established that the Tc associated with goethite is recalcitrant to re-oxidation and leaching when exposed to oxidizing environments. Technetium from a secondary waste stream can be reduced and coprecipitated with goethite, while the added ferric iron slurries make goethite precipitate when the pH is abruptly made basic.
Project Details
Start Date
2012-10-01
End Date
2013-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Team Members
Related Publications
Cantrell KJ, W Um, BD Williams, ME Bowden, BN Gartman, WW Lukens, EC Buck, and EJ Mausolf. 2014. "Chemical Stabilization of Hanford Tank Residual Waste." Journal of Hazardous Materials 446(1-3):246-256. doi:10.1016/j.jnucmat.2013.10.060
Kabilan S, HB Jung, AP Kuprat, ANR Beck, T Varga, CA Fernandez, and W Um. 2016. "Numerical Simulation of Permeability Change in Wellbore Cement Fractures after Geomechanical Stress and Geochemical Reactions Using X-ray Computed Tomography Imaging." Environmental Science & Technology 50(12):6180–6188. doi:10. 1021/acs. est. 6b00159