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首页> 外文期刊>Environmental Science & Technology: ES&T >Technetium Incorporation into Hematite (α-Fe2O3)
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Technetium Incorporation into Hematite (α-Fe2O3)

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摘要

Quantum-mechanical methods were used to evaluate mechanisms for possible structural incorporation of Tc species into the model iron oxide, hematite (α-Fe2O3). Using periodic supercell models, energies for charge-neutral incorporation of Tc~(4+) or TcO_4~- ions were calculated using either a Tc~(4+)/Fe~(2+) substitution scheme on the metal sublattice, or by insertion of TcO_4~- as an interstitial species within a hypothetical vacancy cluster. Although pertechnetate incorporation is found to be invariably unfavorable, incorporation of small amounts of Tc~(4+) (at least 2.6 wt ) is energetically feasible. Energy minimized bond distances around this impurity are provided to aid in future spectroscopic identification of these impurity species. The calculations also show that Fe~(2+) and Tc~(4+) prefer to cluster in the hematite lattice, attributed to less net Coulombic repulsion relative to that of Fe~(3+)-Fe~(3+). These modeling predictions are generally consistent with observed selective association of Tc with iron oxide under reducing conditions, and in residual waste solids from underground storage tanks at the U.S. Department of Energy Hanford Site (Washington, U.S.). Here, even though relatively high pH and oxidizing conditions are dominant, Tc incorporation into iron oxides and (oxy)hydroxides is prospectively enabled by prior reduction of TcO_4~- to Tc~(4+) via interaction with radiolytic species.

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