Immobilization and Limited Reoxidation of Technetium-99 by Fe(II)-Goethite

Technetium Immobilization Forms Literature Survey

“…If such Tc incorporation into these solid phases takes place, then the mobility of Tc may depend on the stability of the host phase and not necessarily upon the reoxidation kinetics. a The coordination number refers to the number of associated ligands and LS and HS stand for "low-spin" and "high spin" configurations Um et al (2010Um et al ( , 2011aUm et al ( , 2012Um et al ( , and 2013Westsik et al 2011) have been conducting experimental studies on sequestering Tc in goethite and other iron oxide solid phases. Their first studies showed that goethite could sequester significant amounts (>90% of the initial Tc mass) of Tc present in simple and caustic brine simulants as long as additional aqueous Fe(II) was added and the pH of the slurry was adjusted to neutral to mildly caustic conditions.…”

Technetium Removal Using Tc-Goethite Coprecipitation

“…It is clear that comparison results from both Fe(OH) 2 (s) and ferrihydrite substrates show that high slurry pH and high temperature conditions favor more goethite formation from the transformation reaction. Unfortunately, we could not conduct 99 Tc removal using ferrihydrite as an initial substrate in this task, but based on previous results (Um et al 2010), ferrihydrite can also be used to remove 99 Tc with additional aqueous Fe(II). Transformation product from magnetite was very limited and there were only small amounts of maghemite and goethite formed from magnetite reacted as initial substrate under high pH and temperature conditions.…”

“…A previously well-developed method was used to prepare 99 Tc-goethite samples designated 2-2 (prepared without additional armoring process) and 2-5 (with additional Fe(III) armoring) according to the method in Um et al (2010Um et al ( , 2011. Between 2.75 and 3.5 g of synthesized goethite powder were resuspended in 250 mL of DI water in the anaerobic chamber to minimize the oxidation of the ferrous solution prior to its use.…”

“…Through a coprecipitation process with respect to goethite, this mineral has proven effective in capturing and sequestering 99 Tc from simulated off-gas scrubber solutions (Um et al 2010 Tc(IV) tends to have a full compatibility with the goethite and hematite lattice (Um et al 2011;Geckeis et al 2012) and quantum chemistry calculations predict energetically more favorable incorporation of 99 Tc(IV) in the hematite lattice than 99 Tc(VII) (Skomurski et al 2010). However, upon contact with O 2 , reduced 99 Tc(IV) species generally reoxidizes rapidly, and reoxidation leads to formation of the soluble 99 Tc(VII) oxyanion (Lukens et al 2005) in cementitious waste form.…”

“…Thus, both the stability of the waste form material and its ability to prevent reoxidation of 99 Tc(IV) to 99 Tc(VII) to limit the 99 Tc leachability are key to the success of any proposed immobilization strategy for waste form development. While many of the proposed disposal options rely on isolating 99 Tc(IV) from oxidizing components in gas or aqueous fluid, the reductive capacity of the material hosting 99 Tc(IV) and the mechanism preventing the reoxidation of 99 Tc(IV) Tc(IV), which then coprecipitates with the goethite-dominant iron (oxy)hydroxide mineral phase (Um et al 2010). The final product also exhibits very slow weathering and low 99 Tc leachability rates in subsurface environment conditions (Um et al 2011(Um et al , 2012.…”