Pertechnetate (TcO4−) reduction by reactive ferrous iron forms in naturally anoxic, redox transition zone sediments from the Hanford Site, USA

Retention of99mTc at Ultra-trace Levels in Flowing Column Experiments – Insights into Bioreduction and Biomineralization for Remediation at Nuclear Facilities

“…During bioreduction, the addition of an electron donor, for example acetate, promotes microbial respiration and a cascade of terminal electron accepting process develop as the bacteria couple the oxidation of the electron donor to the reduction of available electron acceptors in the subsurface in the order oxygen > nitrate > manganese > iron > sulfate > methane. The behavior of 99 Tc during bioreduction has been well studied in sediment microcosms Eagling et al 2012;Fredrickson et al 2004;Law et al 2010), microbial cultures (Liu et al 2002;Lloyd et al 2000) and pure biomineral systems (McBeth et al 2011;Morris et al 2008;Peretyazhko et al 2012;Thorpe et al 2014).…”

“…The rate of Tc(VII) reduction by Fe(II) is dependent on Fe(II) speciation with Fe (II) sorbed to Fe(III) oxides and Fe(II)-bearing minerals magnetite, green rust and iron sulfides yielding greater 99 Tc(VII) reduction rates than siderite and vivianite (Bishop et al 2012;Burke et al 2010;Fredrickson et al 2004;Liu et al 2008;Livens et al 2004;Peretyazhko et al 2012;Pepper et al 2003) and with aqueous Fe(II) being the least effective 99 Tc (VII) reductant (Lloyd et al 2000;Zachara et al 2007). …”

“…These studies have identified pH as a key control on the speciation of Fe(II), with higher pH promoting Fe(II)-bearing mineral precipitation and sorption of Fe(II) to mineral surfaces and thus favouring elevated Tc(VII)-reduction rates (Peretyazhko et al 2012). Although Fe(III)-reduction has been identified as a key biogeochemical process in controlling 99 Tc mobility, sediment studies have reported higher removal rates and partition coefficients (Kd) for 99 Tc in sufidic sediments when compared to Fe(III)-reducing sediments without sulfides present Lee et al 2014).…”

“…The medical radiotracer 99m Tc (half-life 6 h), allows high resolution imaging of sediments containing ultra-trace concentrations of 99m Tc (typically < 5 £ 10 ¡10 mol l ¡1 ) making it possible to conduct studies at technetium concentrations typical of far field contamination at nuclear sites down gradient of the contaminant plume source Corkhill et al 2013;Lear et al 2010;Vandehey et al 2012), and below the theoretical solubility limit of hydrous TcO 2 (»10 ¡8 mol l ¡1 ; Hess et al 2004). At these environmentally relevant concentrations of contaminant, bioavailable Fe will be in stoichiometric excess in typical bioreduced sediments and the rate of Tc(VII) reduction, and the mobility of 99 Tc will be controlled by the Fe(II) speciation Peretyazhko et al 2012;Wildung et al 2004).…”

Syntheses and crystal structures of Eu(III) and Sm(III) perrhenate complexes with 2,2′-(imino)bis(N,N′-diethylacetamide)

“…Recovery of Tc from high level radioactive liquid wastes (HLW) generated from reprocessing processes of spent nuclear fuels is one of the important issues, because of environmental impact due to the long halflife of 99 Tc (2.13 × 10 5 y) and relatively high mobility of TcO 4 − under the conditions of geological disposals [1][2][3][4][5]. Hence, a lot of studies have been devoted for the development of extractants with high selectivity to TcO 4 − [6][7][8][9][10][11][12][13].…”