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Reduction and Simultaneous Removal of 99Tc and Cr by Fe(OH)2(s) Mineral Transformation.
Technetium (Tc) remains a priority remediation concern due to persistent challenges, including mobilization due to rapid reoxidation of immobilized Tc, and competing comingled contaminants, e.g., Cr(VI), that inhibit Tc(VII) reduction and incorporation into stable mineral phases. Here Fe(OH)2(s) is investigated as a comprehensive solution for overcoming these challenges, by serving as both the reductant, (Fe(II)), and the immobilization agent to form Tc-incorporated magnetite (Fe3O4). Trace metal analysis suggests removal of Tc(VII) and Cr(VI) from solution occurs simultaneously; however, complete removal and reduction of Cr(VI) is achieved earlier than the removal/reduction of comingled Tc(VII). Bulk oxidation state analysis of the final magnetite solid phase by XANES shows that the majority of Tc is Tc(IV), which is corroborated by XPS measurements. Furthermore, EXAFS results show successful, albeit partial, Tc(IV) incorporation into magnetite octahedral sites. Cr XPS analysis indicates reduction to Cr(III) and the formation of a Cr-incorporated spinel, Cr2O3, and Cr(OH)3 phases. Spinel (modeled as Fe3O4), goethite (α-FeOOH), and feroxyhyte (δ-FeOOH) are detected in all reacted final solid phase samples analyzed by XRD. Incorporation of Tc(IV) has little effect on the spinel lattice structure. Reaction of Fe(OH)2(s) in the presence of Cr(III) results in the formation of a spinel phase that is a solid solution between magnetite (Fe3O4) and chromite (FeCr2O4)
Reduction and Simultaneous Removal of <sup>99</sup>Tc and Cr by Fe(OH)<sub>2</sub>(s) Mineral Transformation
Technetium (Tc) remains a priority
remediation concern due to persistent
challenges, including mobilization due to rapid reoxidation of immobilized
Tc, and competing comingled contaminants, e.g., Cr(VI), that inhibit
Tc(VII) reduction and incorporation into stable mineral phases. Here
Fe(OH)<sub>2</sub>(s) is investigated as a comprehensive solution
for overcoming these challenges, by serving as both the reductant,
(Fe(II)), and the immobilization agent to form Tc-incorporated magnetite
(Fe<sub>3</sub>O<sub>4</sub>). Trace metal analysis suggests removal
of Tc(VII) and Cr(VI) from solution occurs simultaneously; however,
complete removal and reduction of Cr(VI) is achieved earlier than
the removal/reduction of comingled Tc(VII). Bulk oxidation state analysis
of the final magnetite solid phase by XANES shows that the majority
of Tc is Tc(IV), which is corroborated by XPS measurements. Furthermore,
EXAFS results show successful, albeit partial, Tc(IV) incorporation
into magnetite octahedral sites. Cr XPS analysis indicates reduction
to Cr(III) and the formation of a Cr-incorporated spinel, Cr<sub>2</sub>O<sub>3</sub>, and Cr(OH)<sub>3</sub> phases. Spinel (modeled as
Fe<sub>3</sub>O<sub>4</sub>), goethite (α-FeOOH), and feroxyhyte
(δ-FeOOH) are detected in all reacted final solid phase samples
analyzed by XRD. Incorporation of Tc(IV) has little effect on the
spinel lattice structure. Reaction of Fe(OH)<sub>2</sub>(s) in the
presence of Cr(III) results in the formation of a spinel phase that
is a solid solution between magnetite (Fe<sub>3</sub>O<sub>4</sub>) and chromite (FeCr<sub>2</sub>O<sub>4</sub>)