Speciation Of Ruthenium Research Articles

Ruthenium speciation in radioactive wastes and state-of-the-art strategies for its recovery: A review

• Recovery of 106 Ru from spent nuclear fuel is required for its use in ocular cancer therapy. • Ruthenium speciation decides its separation strategy. So it is discussed in detail. • Ru recovery from acidic and alkaline radioactive feeds is given in detail. • Ru recovery by solvent extraction, precipitation and ion exchange is summarized. • Special mention is made to ion-exchange based separation methods. Ruthenium, mainly 106 Ru, is one of the notorious fission products present in the radioactive wastes. In view of its complex chemistry, it gets partitioned into various processing streams during the radioactive waste management steps. Also, due to the volatile nature of its tetraoxide, RuO 4 , it gets deposited in the process pipelines and stacks. Attempts have been made by various researchers, over the years, to separate radio-ruthenium from radioactive feeds including the acidic high level liquid waste (HLLW) as well as the alkaline low level liquid waste (LLLW) or intermediate level liquid wastes (ILLW). Solvent extraction, precipitation, ion-exchange, etc are some of the commonly employed techniques used for the separation of radio-ruthenium from radioactive feeds. The present review article gives a state-of-the-art of the separation of radio-ruthenium from radioactive waste feeds based on Ruthenium speciation in the system. Most of the published literature involves synthetic feeds rather than actual radioactive wastes. Nevertheless, the published data gives very important information on how to separate radio-ruthenium from different types of radioactive feeds. The aqueous chemistry of Ruthenium is quite complex due to the co-existence of different ionic species of different oxidation states. In view of this, this review article begins with a brief summary on the aqueous chemistry of Ruthenium in acidic as well as alkaline feeds and subsequently its separation from these solutions were discussed using various techniques under the light of its speciation.

Ruthenium recovery from alkaline radioactive feeds using an extraction chromatography resin containing Aliquat 336

The knowledge of ruthenium speciation under aqueous alkaline conditions was applied for the recovery of radio-ruthenium from the alkaline radioactive feeds using a Chromosorb W (dimethyldichlorosilane treated, acid washed celite diatomaceous silica; mesh size 60/80) based extraction chromatography resin (ECR) loaded with Aliquat 336, a quaternary ammonium compound. The experimental conditions were optimized for the uptake of Ru from alkaline feeds and its subsequent desorption using batch studies. Although the precipitation of the black RuO2·xH2O at the ECR surface helps in the quantitative (up to 500 ppm Ru) uptake of ruthenium, it’s desorption was not favorable. About 75% of the Ru was desorbed from the ECR by the batch method using sequential washing by alkaline hypochlorite solution and nitric acid solution. The sorption isotherm was studied for the above system under optimized conditions and the uptake data conformed to the Langmuir isotherm model while chemisorption was suggested to be the mechanism. Column studies, under optimized conditions, showed ~82% Ru recovery in the first cycle which sharply decreased to ~60% in the subsequent runs. The FTIR studies were undertaken to understand the mechanism for the ruthenium extraction from alkaline medium and it’s desorption from the resin.

Redox behavior of ruthenium in nuclear glass melt: ruthenium dioxide reduction reaction

Among platinoid fission products, ruthenium is a key element during the vitrification of high-level waste because it is poorly soluble in the glass matrix. It occurs mainly as RuO2 particles and sometimes as Ru0 particles in the glass melt and final cooled glass. Because the physical properties of ruthenium are very different from those of glass, the RuO2 particles change the glass melt properties such as the rheology, thermal conductivity and electrical conductivity. In addition, because the Ru0 properties are even more distinct from the glass properties, glass melts can be more sensitive to the presence of Ru0 particles. Thus, ruthenium speciation, specifically the RuO2 reduction into Ru0, was investigated in air and glass environments, and the experimental results were compared to thermodynamic calculations (Calphad method).Under air conditions, the thermodynamic modeling and experimental results are in good agreement. They show a reduction of RuO2 at 1403 °C and 1405 ± 7 °C, respectively. The experimental results indicate that the Ru0 particle formation may result from an autocatalysis mechanism, which involves the gaseous species of ruthenium.In the investigated glass, the first Ru0 particles appear at approximately 1280 °C. At 1280 °C < T < 1400 °C, only few particles are observed attributed to minor reduction phenomena: local redox reaction with iron or disproportionation reaction. At higher temperatures (T > 1400 °C), a much more significant reduction takes place. This one is attributed to the decomposition under temperature and oxygen pressure conditions, predicted by thermodynamic calculations. Based on the results obtained under air conditions, it is assumed that the reduction mechanism involves dissolved ruthenium species.

Highly efficient separation of ruthenium from alkaline radioactive feeds using an anion exchange resin

Abstract Ruthenium recovery from the alkaline media was attempted using solid phase extraction. UV-Vis and X-ray absorption studies were performed to understand the ruthenium speciation under different conditions relevant to its extraction from alkaline medium. Since Ru forms anionic complex in the alkaline solution, an anion exchange resin (Dowex 1x8) was selected for its recovery from alkaline media. The precipitation of black RuO2 at the resin surface hinders its back exaction. Experimental conditions were optimized for the quantitative uptake of Ru from alkaline feed and its subsequent back extraction by a series of batch studies. About 90 % of the Ruthenium was back extracted from the resin using alkaline hypochlorite solution and nitric acid solution at different stages in the Ru back extraction cycle. The column studies were done under the optimized condition and showed ~80 % Ru recovery with 5 mL of the eluent (8 M HNO3) and ~90 % recovery in 10 mL including the tailing. The mechanism for the ruthenium extraction from alkaline medium and its back extraction from the resin was proposed.

An efficient method for radio-ruthenium separation from acidic feeds: Extraction, transport and spectroscopic studies

Ruthenium is a troublesome product in spent fuel reprocessing/waste management plants. Its recovery from high level waste (HLW) is challenging due to variable speciation of Ruthenium under acidic condition of HLW. In this paper Ru recovery (103Ru tracer) was attempted from acidic feeds using NaIO4 as an oxidant and n-dodecane as the trapping agent for RuO4. The precipitation of RuO2 (black precipitate) in the organic phase after Ru extraction causes problem for back extraction of Ruthenium. We have used alkaline hypochlorite solution as the stripping agent which led to >90% Ruthenium back extraction into the aqueous phase in ca. 20 min. Membrane studies showed promising results for Ru recovery as the formation of RuO2 was avoided by simultaneous extraction and stripping in transport studies. Out of PTFE and PP flat sheet membranes used for the transport studies, the latter with n-dodecane filled pores showed fast transport of Ru from feed to strip side and >90% Ru recovery was achieved from acidic feed (3 M HNO3).

Speciation of Ruthenium(III) Chloro Complexes in Hydrochloric Acid Solutions and Their Extraction Characteristics with an Amide-Containing Amine Compound

The refining of platinum group metals is based mainly on solvent extraction methods, whereas Ru is selectively recovered by distillation as RuO4. Replacement of distillation by extraction is expected to simplify the purification process. To develop an effective extraction system for Ru, we analyzed the Ru species in HCl with ultraviolet-visible (UV-Vis) and Ru K-edge extended X-ray absorption fine structure (EXAFS) spectroscopies, and we examined the properties of Ru extracted with N-2-ethylhexyl-bis(N-di-2-ethylhexyl-ethylamide) amine (EHBAA) and trioctylamine (TOA). EXAFS and UV-Vis spectra of Ru in HCl solutions revealed that the predominant Ru species in 0.5–10 M HCl solutions changed from [RuCl4(H2O)2]− to [RuCl6]3− with the HCl concentration. The extraction percentages (E%) of Ru in the EHBAA system increased with increasing HCl concentration, reached 80% at [HCl] = 5 M, and decreased at higher HCl concentrations; the corresponding E% for TOA were low. EXAFS analysis of the extracted complex indicated that the Ru3+ had 5 Cl− and 1 H2O in its inner coordination sphere. The similarity of the dependence on HCl concentrations of the E% in the EHBAA system and the distribution profile of [RuCl5(H2O)]2− on [RuCln(H2O)6−n]3−n suggested that the EHBAA extracted the pentachlorido species.

Addressing Ruthenium Speciation in Tri-n-butyl-phosphate Solvent Extraction Process by Fourier Transform Infrared, Extended X-ray Absorption Fine Structure, and Single Crystal X-ray Diffraction

In industrial nuclear fuel reprocessing, small amounts of ruthenium are extracted by tri-n-butyl-phosphate (TBP) at the same time as uranium and plutonium. This behavior increases solvent radiolysis and requires secondary extraction cycles to minimize the residual ruthenium content in uranium and plutonium products. However, the solvent ruthenium extraction mechanism remains largely unexplored. This study addresses the speciation of ruthenium in solvent extraction conditions by complementary infrared and X-ray absorption spectroscopy. First, spectroscopic result interpretation is supported by a single crystal X-ray diffraction study on reference compounds to unambiguously demonstrate that the ruthenium extraction mechanism is driven by a weak outer-sphere Ru–TBP interaction. Second, the ruthenium coordination sphere is quantitatively characterized. Ruthenium speciation in the organic phase depends on the initial aqueous phase, and both monomeric ruthenium nitrosyl trinitrate complexes and a hydrolyzed dim...

Impact of Ag and NOx compounds on the transport of ruthenium in the primary circuit of nuclear power plant in a severe accident

Ruthenium is a semi-volatile element originating as a fission product in nuclear reactors that can be released in case of a severe nuclear accident. In this work, the impact of atmosphere composition on the transport of ruthenium through the primary circuit was examined. The effects of silver nanoparticles representing aerosols and NO2 gas as a product of air radiolysis were studied. Quantification of ruthenium transported both as gas and aerosol was performed. Chemical composition of ruthenium species was evaluated. The transport of gaseous ruthenium through the facility increased significantly when NO2 gas was fed into the atmosphere. When both silver aerosols and NO2 were fed into the atmosphere, the transport of ruthenium in gaseous and aerosol forms was promoted. It was concluded that the composition of atmosphere in the primary circuit will have a notable effect on the speciation of ruthenium transported into the containment building during a severe accident and thus on the potential radioactive release to the environment.

Interaction of ruthenium tetroxide with surfaces of nuclear reactor containment building

During a severe nuclear accident, different fission products will be released from the nuclear fuel and some of them may eventually reach the containment building. Ruthenium is considered to be an important fission product due to the possible formation of volatile oxides. Radiotoxicity and chemical toxicity of the volatile ruthenium compounds present a considerable hazard during a severe nuclear accident.In this work, experiments regarding behavior of ruthenium tetroxide in the reactor containment were performed. The interactions of ruthenium tetroxide (RuO4) with zinc, copper, aluminum and epoxy paint in dry and humid atmosphere were examined. SEM/EDX (scanning electron microscope/energy-dispersive X-ray spectroscopy), XPS (X-ray photoelectron spectroscopy) and EXAFS (extended X-ray absorption fine structure) techniques were used to identify the chemical composition of the deposits formed after the interaction of RuO4 with the different materials. Additionally, distribution of ruthenium between different metals was examined.Interaction of RuO4 with the studied samples led to formation of dark, ruthenium-rich deposits. Examination of these deposits showed different chemical speciation of ruthenium on the surface when compared to the deeper layers of deposits. Interaction of RuO4 with zinc, copper and aluminum resulted to different amounts of the deposited ruthenium on the metals.

Speciation of Ruthenium in Organic TBP/TPH Organic Phases: A Study about Acidity of Nitric Solutions

Ruthenium extraction with uranium and plutonium during the reprocessing of nuclear used fuel is an important element to follow because its presence leads to a decrease of the decontamination factors and causes enhanced radiolysis of the solvent. A study was carried out on the speciation of ruthenium in both aqueous and organic phases by complementary spectroscopic techniques such as FTIR and X-ray absorption spectroscopy. By providing a better understanding of the ruthenium extraction mechanism, this study will help to support the modeling of related processes.

Ruthenium Volatilisation in Nuclear Waste Systems - Studying the Baseline Thermodynamics of Ru(III)

Spent Fuel Management at Sellafield includes the reprocessing of spent nuclear fuel from stations across the UK and also the reprocessing of spent fuel from overseas customers. At Sellafield, methods have been developed for the processing of high level wastes, including highly active liquors (HAL), which is a result of reprocessing irradiated nuclear fuel. This Highly Active (HA) raffinate / waste stream is concentrated in evaporators and storage tanks in the Highly Active Liquor Evaporation & Storage (HALES) facility before feeding to the Waste Vitrification Plant (WVP). Here, the resultant HAL feed is calcined and combined with glass before pouring into containers to produce an immobilised HA wasteform. Ruthenium is a fission product possessed of two relatively long lived stable isotopes: Ru-103 (t1/2 = 39.8 days) and Ru-106 (t1/2= 1 year). Both isotopes form part of the inventory of HA waste raffinate during reprocessing of spent fuel. Volatilisation of fission products in nuclear waste generally occurs at high temperature – apart from ruthenium where volatilisation occurs at the lower temperature stages of the vitrification process. Given its volatile nature and high specific radioactivity, ruthenium presents a strong challenge to the nuclear industry in effectively managing its abatement. Part of the challenge is to fully understand the highly complex solution chemistry under conditions relevant to HA waste streams and associated abatement systems. Experimental work within the National Nuclear Laboratory (NNL), UK has demonstrated that the presence of oxidising metal ions in HA waste (e.g. Ce(IV)) can enhance the volatility of ruthenium through a chemical conversion of Ru(III) species to what is assumed to be RuO4. A better understanding of these species, their electrochemical processes and reaction kinetics is required to underpin the empirical evidence gathered to date, in particular to develop gravimetric, electrochemical and spectroscopic analytical methods that will improve the understanding of ruthenium speciation in high nitric acid environments, establish the kinetics of inter-conversion between ruthenium species and establish the mechanism by which metal ions such as Ce(IV) may oxidise ruthenium. We have studied the baseline electrochemical behaviour of ruthenium and present here for the first time the intrinsic thermodynamics of uncomplexed Ru(III) using electrochemical methods to determine as bought RuCl3 to be a mixture of Ru(III) and Ru(IV). We have achieved this via cyclic voltammetry of RuCl3 in HClO4 which yielded two peaks, namely at 0.55 and 0.95 V. A similar peak has been seen by Maya [1] at 0.9 V, reported to be tetramer oxidation. Analysis of the solution using UV-vis shows as bought RuCl3 to be a mixture of Ru(III) and Ru(IV). Subsequently a successful method to electroreduce the mixture to a pure solution of Ru(III) was developed. Cyclic voltammetry of the electroreduced Ru(III) shows an absence of the previously seen peak at 0.55 V, suggesting this peak was associated to the oxidation of Ru(IV), whilst the previously observed peak at 0.95 V had been shifted to ~ 0.8 V suggesting that this peak was not in fact an observation of tetramer oxidation, as proposed by Maya. The latter peak was further interrogated using a scan rate dependence study, which shows the peak potential increasing as scan rate increases showing we have an irreversible, kinetically slow process occurring. A linear relationship between the square root of the scan rate against peak current indicates the oxidation is occurring in solution. The n number of this transition was experimentally determined to be 0.33 and we have confirmed a diffusion coefficient of 4x10-10 m2 s-1 for RuCl3. This shows we have a trimer in solution which is oxidised from: 3 Ru(III) to Ru(III)-Ru(IV)-Ru(III). Future work will focus on the ruthenium nitrosyl species found in spent fuel to understand what effect NO complexation has on the system with the aim of comparing the uncomplexed ruthenium system with the complexed ruthenium system. [1] Maya, L., J. Inorg. Nucl. Chem., 41, 1978, 67

Speciation of Ruthenium as a Reduction Promoter of Silica-Supported Co Catalysts: A Time-Resolved in Situ XAS Investigation

Complete reduction of the metal phase in cobalt-containing catalysts is often difficult to reach and can be promoted by a small amount of noble metals. Because these costly promoters are introduced in a very low quantity, their speciation and their chemical interaction with cobalt have seldom been studied in detail. We present here a time-resolved in situ X-ray absorption spectroscopy investigation of the speciation of ruthenium, used as a reduction promoter of cobalt, throughout the preparation of Co/SiO2 catalysts. In the cobalt(II) nitrate impregnation solution, ruthenium is detected as hydrated Ru(OH)4 short-chain oligomers that are deposited on silica upon drying. Co3O4 forms during calcination in air and catalyzes the elimination in the gas phase of 60% of Ru. The addition of a polyol, sorbitol, in the impregnation solution stabilizes the whole of Ru on the catalyst. Upon calcination, Ru(IV) ions are inserted inside Co3O4 nanoparticles. Reduction of the oxidic phase takes place in two distinct steps, at approximately the same temperatures regardless of the ruthenium content: first to Ru(III)-containing CoO nanoparticles (Ru ions modifying the intrinsic electronic properties of the oxidic nanoparticles); then to bimetallic Co nanoparticles containing Ru(0) atoms, via an autocatalytic process. Ru loadings as low as 0.2 wt % are sufficient to afford complete reduction of cobalt. Close association between Ru and Co from the beginning of the synthesis is thus necessary for a maximum promoting effect.

Metallomics for drug development: a further insight into intracellular activation chemistry of a ruthenium(iii)-based anticancer drug gained using a multidimensional analytical approach

The mechanism by which the most relevant ruthenium anticancer drugs are activated in tumors to commence their tumor-inhibiting action remains one of the challenging research tasks of present-day metallomics. This contribution aims to capture and identify eventually more reactive species of one of two bis-indazole tetrachloridoruthenate(III) compounds that are progressing in clinical trials. In view of the fact that the transport of ruthenium into cancer cells is governed by transferrin receptors, the susceptibility of the Ru drug adduct with holo-transferrin to exposure by glutathione and ascorbic acid (at their cancer cytosol concentrations) was studied by inductively coupled plasma mass spectrometry (ICP-MS), following isolation of the reaction products by ultrafiltration. Next, capillary electrophoresis coupled to ICP-MS was applied to monitor changes in the Ru speciation both under simulated cancer cytosol conditions and in real cytosol and to assign the charge state of novel metal species. The latter were identified by using tandem electrospray ionization MS in the respective ion mode. The formation of ruthenium(II) species was for the first time revealed, in which the central metal is coordinated by the reduced (GSH) or the oxidized (GSSG) form of glutathione, i.e. [Ru(II)HindCl4(GSH)](2-) and [Ru(II)HindCl4(GSSG)](2-), respectively (Hind = indazole). Ascorbic acid released the ruthenium functionality from the protein-bound form in a different way, the products of adduct cleavage containing aqua ligands. Distribution of low-molecular mass species of Ru in human cytosol was found to have very much in common with the ruthenium speciation assayed under simulated cytosol conditions.

EPR as a probe of the intracellular speciation of ruthenium(iii) anticancer compounds

EPR (electron paramagnetic resonance) has been used to study interactions of the Ru(III) anticancer compounds imidazolium [trans-RuCl4(1H-imidazole)(DMSO-S)] (NAMI-A) and indazolium [trans-RuCl4(1H-indazole)2] (KP1019) with isolated subcellular components and whole cells of the yeast Saccharomyces cerevisiae. These studies are the first to probe the intracellular speciation of ruthenium using the EPR technique. Initially, NAMI-A and KP1019 were incubated at 30 °C, for time periods up to 24 hours with isolated cell wall, mitochondrial, cytoplasmic, and nuclear fractions of S. cerevisiae. EPR measurements demonstrate that NAMI-A initially forms non-coordinate interactions with each cell component. After longer incubation times these are replaced by coordinated species, particularly with cytoplasmic proteins. KP1019 shows a greater tendency to coordinate directly with cell components, demonstrating significant interactions with mitochondria and cytoplasmic proteins. Subsequently, each complex was incubated with whole cells of S. cerevisiae at 30 °C and whole-cell EPR measurements detected Ru(III) species in measurable concentrations even after 24 hours of incubation. Analysis of the resulting EPR spectra suggests NAMI-A interacts predominantly with cell walls, while KP1019 was found to be coordinating with both the mitochondrial and cytoplasmic protein fractions. Comparison of the signal intensity of these data with those from incubation with whole cells at 4 °C indicates different modes of transmembrane transport for each complex. These studies demonstrate that EPR can provide valuable insight into the oxidation state and speciation of ruthenium compounds in cellular environments.

Reversible NOx storage over Ru/Na–Y zeolite

Ruthenium loaded Na–Y zeolite was found to be an efficient adsorbent for achieving NOx adsorption–desorption cycles comprising adsorption under oxidizing and desorption under reducing conditions. The speciation of ruthenium was investigated using TEM, EXAFS, 99Ru Mossbauer spectroscopy and XRD in combination with Rietveld refinement. The sodium cation siting was monitored using 23Na MAS NMR. Characterization of the Ru/Na–Y adsorbent in NOx saturated and regenerated state revealed a unique cooperation of supported ruthenium nano metal particles and isolated Ru atoms in framework cavities affecting the sodium cations. Supported ruthenium nanoparticles assume a catalytic role in NO oxidation. Ruthenium atoms in framework cavities undergo switching of oxidation state during adsorption–desorption cycles. It triggers reversible sodium cation migrations from coordination with the framework in the regenerated state to coordination in sodium–water networks in supercages providing adsorption sites for NOx during adsorption. The peculiar ruthenium organization is naturally obtained upon lean–rich cycling. Ru/Na–Y adsorbent is insensitive to SOx and to the presence of CO during reductive regeneration.

Ruthenium Speciation and Promoting Activity in Unsupported Core-Shell Pt-Ru Nanoparticle Electrocatalysts

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On the transport and speciation of ruthenium in high temperature oxidising conditions

Summary In this paper, the transport and speciation of ruthenium under conditions simulating an air ingress accident was studied. Ruthenium dioxide was exposed to an oxidising environment at high temperatures (&gt;1200 °C) in a tubular flow furnace. At these conditions, volatile ruthenium species were formed. A major part of the released ruthenium was deposited in the tube as RuO2. Depending on the experimental conditions, 12–35 wt. % of the released ruthenium was trapped in the outlet filter as RuO2 particles. At completely dry conditions using stainless steel tubes, only 0.1–0.2 wt. % of the released ruthenium reached the trapping bottle as gaseous RuO4. However, when alumina was applied as tube material or the atmosphere contained some water vapour and silver seed particles, the fraction of gaseous ruthenium reaching the trapping bottle increased to 5 wt. % which is close to thermodynamic equilibrium. This indicates that RuO2 does not catalyse the decomposition of RuO4.