Oxidative Stability of Tc(I) Tricarbonyl Species Relevant to the Hanford Tank Waste

Characterization of Non-pertechnetate Species Relevant to the Hanford Tank Waste

“…It is of particular importance to note the differences between the aqua species [Tc(CO) + •IDA. Under conditions of 5 M NaNO 3 and 0 -1 M NaOH, in the presence of ~10-100 fold excess of these ligands, we observed weak complexations by NTA and EDTA onto the [Tc(CO) 3 ] + center, and strong complexation by IDA using NMR measurements (Chatterjee et al 2015). The XAS data support these NMR observations, and suggest that polyaminocarboxylate chelators may affect [Tc(CO) 3 ] + chemistry in the tank waste.…”

“…Previous analysis of the SY-101 and SY-103 tank waste samples provided strong evidence that non-pertechnetate can be comprised of [fac-Tc(CO) 3 ] + complexes containing Tc in oxidation state +1 (Lukens et al 2004). During the last three years, our team has expanded this work and demonstrated that high-ionic-strength solutions typifying tank waste supernatants promote oxidative stability of the [fac-Tc(CO) 3 ] + species (Rapko et al 2013a;2013b;Levitskaia et al 2014;Chatterjee et al 2015). Results also suggest possible stabilization of Tc(VI) and potentially Tc(IV) oxidation states in the high-ionic-strength alkaline matrices particularly in the presence of organic chelators, so that Tc(IV, VI) can serve as important redox intermediates facilitating the reduction of Tc(VII) to Tc(I).…”

“…This task evaluates oxidative stability of model non-pertechnetate species to identify structural motifs of the Tc(I) [fac-Tc(CO) 3 ] + and Tc(IV, VI) complexes viable under the aggressive tank waste conditions. Testing was in part initiated in FY 2014 -2015 when a series of samples containing non-pertechnetate Tc generated ex situ or in situ in pseudo-Hanford tank supernatant simulant solutions was prepared, vi characterized, and monitored for oxidation to Tc(VII) (Levitskaia et al 2014;Chatterjee et al 2015). This work was continued and expanded in FY 2016 and showed that the generated samples contain significant fractions of Tc(I, IV, VI) even after 2.5 years when stored unprotected to exposure to air and light.…”

“…Studies to evaluate nature and time stability of the non-petechnetate species generated via chemical reduction studies of TcO 4 in Hanford tank supernatant simulant (see Table 1) have been ongoing for last 2.5 years. Experimental conditions and preliminary results are discussed in the FY 2014 and 2015 reports (Levitskaia et al 2015;Chatterjee et al 2015). In brief, the reduction was carried out under four different reaction conditions corresponding to Parr Reactions 1 -4 (Table 2).…”

“…In our previous studies, evaluation of the oxidative stabilities of [Tc(CO) 3 (H 2 O) 3-n (OH) n ] 1-n species in NaNO 3 /NaOH solutions were initiated in FY 2014 as described previously (Levitskaia et al 2014) and continued in FY 2015 (Chatterjee et al 2015). In these tests, (Et 4 N) 2 [Tc(CO) 3 Cl 3 ] was used to generate [Tc(CO) 3 (H 2 O) 3-n (OH) n ] 1-n species.…”