title: Computational Investigation of Technetium(IV) Incorporation into Inverse Spinels: Magnetite (Fe3O4) and Trevorite (NiFe2O4).
abstract: Iron oxides and oxyhydroxides play an important role in minimizing the mobility of redox-sensitive elements in engineered and natural environments. For the radionuclide technetium-99 (Tc), these phases hold promise as primary hosts for increasing Tc loading into glass waste form matrices, or as secondary sinks during the long-term storage of nuclear materials. Recent experiments show that the inverse spinel, magnetite [Fe(II)Fe(III)2O4], can incorporate Tc(IV) into its octahedral sublattice. In that same class of materials, trevorite [Ni(II)Fe(III)2O4] is also being investigated for its ability to host Tc(IV). However, questions remain regarding the most energetically favorable charge-compensation mechanism for Tc(IV) incorporation in each structure, which will affect Tc behavior under changing waste processing or storage conditions. Here, quantum-mechanical methods were used to evaluate incorporation energies and optimized lattice bonding environments for three different, charge-balanced Tc(IV) incorporation mechanisms in magnetite and trevorite (∼5 wt % Tc). For both phases, the removal of two octahedral Fe(II) or Ni(II) ions upon the addition of Tc(IV) in an octahedral site is the most stable mechanism, relative to the creation of octahedral Fe(III) defects or increasing octahedral Fe(II) content. Following hydration-energy corrections, Tc(IV) incorporation into magnetite is energetically favorable while an energy barrier exists for trevorite.
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, United States.
authors.forename: Frances N
authors.initials: FN
authors.lastname: Smith
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, United States.|Pohang University of Science and Technology (POSTECH), Pohang, South Korea.
authors.forename: Wooyong
authors.initials: W
authors.lastname: Um
authors.affiliation: Fontana Corrosion Center, Materials Science and Engineering, The Ohio State University , Columbus Ohio 43210, United States.|Strategic Research and Innovation, DNV GL , Dublin Ohio 43017, United States.
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Taylor
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, United States.
authors.forename: Dong-Sang
authors.initials: DS
authors.lastname: Kim
authors.affiliation: Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Schweiger
authors.affiliation: United States Department of Energy, Office of River Protection, P.O. Box 450, Richland, Washington 99352, United States.
authors.forename: Albert A
authors.initials: AA
authors.lastname: Kruger
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry*; D052203:Ferrosoferric Oxide / Q000737:chemistry; D010084:Oxidation-Reduction; D013667:Technetium / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D013667:Technetium; D052203:Ferrosoferric Oxide