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Reduction of Tc(VII) by Fe(II) Sorbed on Al (hydr)oxides

Journal Article · · Environmental Science & Technology, 42(15):5499-5506
DOI:https://doi.org/10.1021/es8003156· OSTI ID:944503
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Technetium speciation, solubility and sorption behavior is strongly dependent on its valence state. Under oxic conditions, Tc exists as the soluble, weakly-sorbing pertechnetate [TcO4-] anion. The reduced form of technetium, Tc(IV), is stable in anoxic environments and is sparingly soluble as TcO2·xH2O(s). Here we investigate the heterogeneous reduction of Tc(VII) by Fe(II) sorbed on Al (hydr)oxides [diaspore (α-AlOOH) and corundum (α-Al2O3)]. Experiments were performed to study the kinetics of Tc(VII) reduction, examine changes in Fe surface speciation during Tc(VII) reduction (Mössbauer spectroscopy), and identify the nature of Tc(IV)-containing reaction products (X-ray absorption spectroscopy). We found that Tc(VII) was completely reduced by adsorbed Fe(II) within 11d (diaspore suspension) and 4d (corundum suspension). Mössbauer measurements revealed that the Fe(II) signal became less intense with Tc(VII) reduction, and was accompanied by increase in Fe(III) doublet and magnetically-ordered Fe(III) sextet signals, with latter parameters close to those for hematite. Formation of magnetically ordered Fe(III) did not depend on the oxidant nature, as both Tc(VII) or O2 lead to the formation of a virtually identical hematite-like phase. The Fe(II) doublet displayed no differences in Mössbauer parameters before and after Tc(VII) reduction, likely due to Fe(II) adsorption to similar sites and no Fe(II) sorption to or precipitation within solid phases formed. Tc-EXAFS spectroscopy revealed that the final heterogeneous redox product on corundum was similar to Tc(IV) oxyhydroxide, TcO2 ∙ xH2O. The formation of precursor polymeric TcnOy (4n-2y)+ chains prior to TcO2∙xH2O precipitation might explain the formation of the separate TcO2-like phase on corundum without coprecipitated Fe.

Research Organization:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Organization:
USDOE
DOE Contract Number:
AC05-76RL01830
OSTI ID:
944503
Report Number(s):
PNNL-SA-58538; 4594; KP1302000
Journal Information:
Environmental Science & Technology, 42(15):5499-5506, Journal Name: Environmental Science & Technology, 42(15):5499-5506 Journal Issue: 15 Vol. 42
Country of Publication:
United States
Language:
English

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Related Subjects

0001 surface
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ADSORPTION
ALUMINIUM HYDROXIDES
CATALYTIC EFFECTS
CORUNDUM
Environmental Molecular Sciences Laboratory
IRON
KINETICS
REDUCTION
SOLUBILITY
SORPTIVE PROPERTIES
TECHNETIUM
VALENCE
electron-transfer
iron
microbial reduction
pertechnetate
products solubility
ray-absorption spectroscopy
technetium
water interface