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

Authors

T. Peretyazhko, Pacific Northwest National LaboratoryFollow
J.M. Zachara, Pacific Northwest National Laboratory
S.M. Heald, Argonne National Laboratory
Ravi K. Kukkadapu, Pacific Northwest National LaboratoryFollow
C. Liu, Pacific Northwest National Laboratory
A.E. Plymale, Pacific Northwest National Laboratory
C.T. Resch, Pacific Northwest National Laboratory

Date of this Version

2008

Citation

Environ. Sci. Technol. 2008, 42, 5499–5506

Abstract

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 ·nH₂O_(s). Here we investigate the heterogeneous reduction of Tc(VII) by Fe(II) adsorbed 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 11 (diaspore suspension) and 4 days(corundum suspension).Mössbauer measurements revealed that the Fe(II) signal became less intense with Tc(VII) reduction and was accompanied by an increase in the intensity of the Fe(III) doublet and magnetically ordered Fe(III) sextet signals. Tc-EXAFS spectroscopy revealed that the final heterogeneous redox product on corundum was similar to Tc(IV) oxyhydroxide, TcO₂ ·nH₂O.