The stability constants for the Tc(IV) and V(IV) complexation with the polyamino polycarboxylate ligands IDA, NTA, HEDTA and DTPA were determined using liquid–liquid extraction techniques. These stability constants were then used to evaluate the validity of using V(IV) as a chemical analogue for Tc(IV). Results suggest that Tc(IV), as TcOOH+, will form β1−11 complexes with the selected ligands, while V(IV), as VO2+, will form β101 complexes. The values for these determined stability constants are (in log10 unit) 10.9 ± 0.1, 11.4 ± 0.1, 14.9 ± 0.1, and 20.1 ± 0.1 for Tc(IV) in 0.5 mol·L−1 NaCl at 25 °C, for IDA, NTA, HEDTA and DTPA, respectively, they are 9.3 ± 0.1, 11.6 ± 0.2, 15.8 ± 0.1, and 20.8 ± 0.1 for V(IV) in 0.5 mol·L−1 NaCl at 25 °C, for the same suite of ligands. The incorporation of a hydroxide into the metal ligand complexes formed by Tc(IV) is proposed as the largest factor differentiating the apparent stability constants of Tc(IV) and V(IV). This work shows that V(IV) is a poor analog for Tc(IV); however, despite the differences in complexation mechanism between V(IV) and Tc(IV), V(IV) still appears to have some use for predicting Tc(IV) complexation behavior.

In order to safeguard society and the environment, understanding radioactive waste glass alteration mechanisms in interactions with solutions and near-field materials, such as Fe, is essential to nuclear waste repository performance assessments. Alteration products are formed at the surface of glasses after reaction with solution. In this study, glass altered in the presence of Fe0 in aqueous solution formed two alteration layers: one embedded with Fe closer to the surface and one without Fe found deeper in the sample. Both layers were found to be thinner than the alteration layer found in glass altered in aqueous solution only. For the first time, Doppler Broadening Positron Annihilation Spectroscopy (DB-PAS) is used to non-destructively characterize the pore structures of glass altered in the presence of Fe0. Advantages and disadvantages of DB-PAS compared to other techniques used to analyze pore structures for altered glass samples are discussed. Ultimately, DB-PAS has shown to be an excellent choice for pore structure characterization for glasses with multiple alteration layers. Monte Carlo modeling predicted positron trajectories through the layers, and helped explain DB-PAS data, which showed that the deeper alteration layer without Fe had a similar composition and pore structure to layers on glass altered in water only.Download high-res image (584KB)Download full-size image

The motivation for this work was to develop and test a hematite (α-Fe2O3) film electrode for the detection of riboflavin using a less common preparation with rotating disk electrode linear sweep voltammetry. Two types of hematite electrodes were prepared, with a differential method and a one-step method (quicker preparation), and bare glassy carbon electrodes were used for comparison. The differential and one-step hematite electrodes were tested for cyclic voltammetry stability. Colloidal hematite (α-Fe2O3) was synthesized from iron nitrate nonahydrate from a two-line ferrihydrite transition and characterized with X-ray powder diffraction and Mössbauer spectroscopy. Both hematite film electrodes were prepared using a three-electrode electrochemical cell and rotating disk voltammetry. Rotating disk hematite electrode stability was demonstrated for up to 1000 cyclic voltammetry scans. A single use of the rotating disk hematite film electrode was shown to demonstrate quantitatively the detection of riboflavin reduction peaks with optimized differential square wave voltammetry. The limits of detection for the glassy carbon and rotating disk hematite film electrodes for riboflavin are 0.0028 ± 0.0009 mM and 0.0084 ± 0.0009 mM, respectively. The detection linear range for the glassy carbon and rotating disk hematite film electrodes is 0.0013–0.1 mM riboflavin. The sensitivities of the one-step and differential rotating disk hematite film electrodes are 0.216 ± 0.001 μA/μM and 0.27 ± 0.02 μA/μM riboflavin, respectively. The sensitivity of the bare glassy carbon electrode is 0.144 ± 0.003 μA/μM riboflavin.

Quantification of analytes present in organic solvents or high salt content aqueous solutions using ICP-OES with minimal to no sample processing is desirable to improve analysis turnaround time and decrease sample cost. This work describes procedures used for Sr, V, and Y quantifications in 1-pentanol, 1-octane, 1-decanol, n-octane, and kerosene, substitute seawater, and NaCl solutions, with concentrations as high as 5 molal, using ICP-OES with a standard nebulizer and spray chamber configuration. The detection limits of analyte in those extreme conditions decrease by less than a factor of ten compared to element quantification in dilute aqueous solution; however, the instrument maintained its normal precision and linearity in response. In dilute HNO3, Sr, V, and Y feature LODs of 4 × 10−2, 4, and 0.2 ng L−1, respectively. A medium of 5 m NaCl shows LODs of 1, 4, and 4 ng L−1 for Sr, V, and Y, respectively. Organic analyses revealed the presence of a number of molecular emissions that occurred during the ionization of carbon; these emissions drastically increased backgrounds in the region around 400 nm. Dodecane solutions were found to require the addition of a metal complexant (we used di-(2-ethylhexyl)phosphoric acid) to ensure elemental stability of solution. With the addition of the complexant to dodecane solutions, the LODs were 10, 5, and 4 ng L−1 for Sr, V, and Y, respectively.

Platinum group metals (PGMs), including rhodium, generated by the fission of 235U are present in significant quantities within spent nuclear fuel located on power generation sites in the United States, the amount of which is expected to exceed natural reserves by 2030. Yet, spent fuel raffinates are highly acidic media that may result in complex speciation of the PGM. This work provides an understanding of Rh(III) speciation up to 9 M HCl and HNO3, and utilizes a combination of ultraviolet–visible (UV-vis) and capillary zone electrophoresis data, along with computationally predicted thermochemistry and simulated UV-vis spectra to approximate the relative concentrations of potential species in solution as a function of acid concentration. One Rh(III) species, [Rh(NO3)3], is observed under all conditions in HNO3 and for Rh(III) concentrations smaller than 10–3 M. In contrast, a variety of chloridated Rh(III) species may exist simultaneously in a HCl medium. The species [RhCl2(H2O)4]+ and [RhCl3(H2O)3] are observed in HCl solutions of concentrations ranging from 0 to 1 M; the species [RhCl4(H2O)2]−, [RhCl5(H2O)]2–, and [Rh2Cl9]3– are observed between 2 and 9 M HCl.

Technetium99 poses a difficult problem at many nuclear waste disposal sites, as there have been multiple incidents of its release to the environment due to large quantities of fission products disposed in storage tanks. Tc is mostly present under two oxidation states, Tc(VII) and Tc(IV) and the separation of Tc(IV) from Tc(VII) is often crucial for laboratory-scale work performed for the study of Tc. This work offers a method for the rapid separation of Tc(IV) from Tc(VII), using a solvent extraction system containing iodonitrotetrazolium chloride and chloroform.

To understand the key processes affecting 99Tc mobility in the subsurface and help with the remediation of contaminated sites, the binding constants of several humic substances (humic and fulvic acids) with Tc(IV) were determined, using a solvent extraction technique. The novelty of this paper lies in the determination of the binding constants of the complexes formed with the individual species TcO(OH)+ and TcO(OH)20. Binding constants were found to be 6.8 and between 3.9 and 4.3, for logβ1,−1,1 and logβ1,−2,1, respectively; these values were little modified by a change of ionic strength, in most cases, between 0.1 and 1.0 M, nor were they by the nature and origin of the humic substances. Modeling calculations based on these show TcO(OH)−HA to be the predominant complex in a system containing 20 ppm HA and in the 4−6 pH range, whereas TcO(OH)20 and TcO(OH)2−HA are the major species, in the pH 6−8 range.

Molecular dynamics simulations were performed to examine trends in trivalent lanthanide [Ln(III)] sorption to ≡SiOH0 and ≡SiO– sites on the 001 surface of α-quartz across the 4f period. Complementary laser-induced fluorescence studies examined Eu(III) sorption to α-quartz at a series of ionic strengths from 1 × 10–4 M to 0.5 M such that properties of the surface-sorbed species could be extrapolated to zero ionic strength, the conditions under which the simulations are performed. Such extrapolation allows for a more direct comparison of the data and enables a molecular understanding of the surface-sorbed species and the role of the ion surface charge density upon the interfacial reactivity. Potential of mean force molecular dynamics as well as simulations of presorbed Ln(III) species agrees with the spectroscopic study of Eu(III) sorption, indicating that strongly bound inner-sphere complexes are formed upon sorption to an ≡SiO– site. The coordination shell of the ion contains 6–7 waters of hydration, and it is predicted that surface silanol OH groups transfer from the quartz to the inner coordination shell of Eu(III). Molecular simulations predict less-strongly bound inner-sphere species in early lanthanides and more strongly bound species in late lanthanides, following trends in the surface charge density of the 4f ions. Hydroxyl ligands that derive from the surface silanol groups are consistently observed to bind in the inner coordination shell of surface-sorbed inner-sphere Ln(III) ions, provided that the ion is able to migrate within 2.0–3.0 Å of the plane formed by the silanol O atoms (∼3.5 Å from an individual ≡SiO– group). Sorption to a fully protonated quartz surface is not predicted to be favorable by any Ln(III), except perhaps Lu. The present work demonstrates a combined theoretical and experimental approach in the prediction of the fate of trivalent radioactive contaminants at temporary and permanent nuclear waste storage sites.

Quantification of analytes present in organic solvents or high salt content aqueous solutions using ICP-OES with minimal to no sample processing is desirable to improve analysis turnaround time and decrease sample cost. This work describes procedures used for Sr, V, and Y quantifications in 1-pentanol, 1-octane, 1-decanol, n-octane, and kerosene, substitute seawater, and NaCl solutions, with concentrations as high as 5 molal, using ICP-OES with a standard nebulizer and spray chamber configuration. The detection limits of analyte in those extreme conditions decrease by less than a factor of ten compared to element quantification in dilute aqueous solution; however, the instrument maintained its normal precision and linearity in response. In dilute HNO3, Sr, V, and Y feature LODs of 4 × 10−2, 4, and 0.2 ng L−1, respectively. A medium of 5 m NaCl shows LODs of 1, 4, and 4 ng L−1 for Sr, V, and Y, respectively. Organic analyses revealed the presence of a number of molecular emissions that occurred during the ionization of carbon; these emissions drastically increased backgrounds in the region around 400 nm. Dodecane solutions were found to require the addition of a metal complexant (we used di-(2-ethylhexyl)phosphoric acid) to ensure elemental stability of solution. With the addition of the complexant to dodecane solutions, the LODs were 10, 5, and 4 ng L−1 for Sr, V, and Y, respectively.