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

Journal Article · Fri Aug 01 00:00:00 EDT 2008 · Environmental Science & Technology, 42(15):5499-5506

DOI:https://doi.org/10.1021/es8003156· OSTI ID:944503

Peretyazhko, Tetyana; Zachara, John M; Heald, Steve M; Kukkadapu, Ravi K; Liu, Chongxuan; Plymale, Andrew E; Resch, Charles T

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 ∙ xH2_O. 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 Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 944503
• Report Number(s): PNNL-SA-58538; 4594; KP1302000; TRN: US0900546
• Journal Information: Environmental Science & Technology, 42(15):5499-5506, Vol. 42, Issue 15
• Country of Publication: United States
• Language: English

Related Subjects

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