Recovery of high-value ruthenium from used nuclear fuel

Abstract

The present disclosure provides for methods of recovering high-value ruthenium from used nuclear fuel. A ruthenium suspension can be oxidized to deposit a ruthenium oxide onto a substrate using an oxidizing agent. Then, the ruthenium oxide can be recovered from the substrate. Ruthenium oxide can be recovered from the substrate by dissolving the substrate with one or more solvents or calcining the substrate. The substrate can then be filtered to recover the ruthenium oxide.

Description

Docket U24-092 (222120-2120)RECOVERY OF HIGH-VALUE RUTHENIUM FROM USED NUCLEAR FUELCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application entitled “RECOVERY OF HIGH-VALUE RUTHENIUM FROM USED NUCLEAR FUEL” and having serial number 63 / 673,241 filed on July 19, 2024, which is incorporated herein by reference in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with government support under grant number AR0001689 awarded by Department of Energy. The government has certain rights in this invention.

[0003] The United States Government has rights in this invention pursuant to contract no. DE-AC05-00OR22725 between the United States Department of Energy and UT-Battelle, LLC.BACKGROUND

[0004] During fission of nuclear fuel, several products can be produced. Ruthenium can be one of the most challenging fission products in used nuclear fuel due to its complex redox chemistry and high abundance in nitric acid dissolution solutions. In addition to its seven stable isotopes (96Ru,98Ru, "Ru,100Ru,101Ru,102Ru, and104Ru), 34 radioactive isotopes have been identified. These ruthenium isotopes can be useful in various industries, including medicine. Most notably,106Ru is a soft beta emitter and is utilized in eye cancer treatment, highlighting ruthenium’s relevance beyond nuclear waste management. However, ruthenium can be expensive to obtain.

[0005] Nuclear fuel is often stockpiled after use, which can contain significant quantities of ruthenium. However, ruthenium can be unstable and difficult to recover from the fuel. In nitric acid, ruthenium primarily exists as a mixture of Ru(lll) nitrosyl nitrate and nitro complexes-at least nine species have been identified in aged solutions. These species, with the general formula [RuNO(NO3)x(NO2)y(OH)z(H2O)5-x-y-z]3 xyz, often coexist with other polymeric Ru(IV) hydroxo-nitrate species such as [Ru(OH)x(H2O)6-x](NO3)4-x and binuclear Ru-O-Ru bridges. Additionally, ruthenium nitrosyls are photolytically unstable, dissociating to Ru(lll),Docket U24-092 (222120-2120)which readily oxidize to Ru(IV) in aerated nitric acid. This dynamic and multivalent speciation-particularly the variable extractability of ruthenium trinitrato complexes-complicates separation processes.SUMMARY

[0006] One aspect of the present disclosure encompasses embodiments of a method of recovering ruthenium, comprising the steps of oxidizing a ruthenium suspension to deposit a ruthenium oxide onto a substrate using an oxidizing agent and recovering the ruthenium oxide from the substrate.

[0007] In some embodiments of this aspect of the disclosure, recovering ruthenium oxide from the substrate can further comprise the steps of dissolving the substrate with one or more solvents or calcining the substrate to form a solution and filtering the solution to recover the ruthenium oxide.

[0008] In some embodiments of this aspect of the disclosure, the substrate can comprise a polymer material.

[0009] In some embodiments of this aspect of the disclosure, the substrate can comprise a wax material.

[0010] In some embodiments of this aspect of the disclosure, the substrate can comprise a rubber material.

[0011] In some embodiments of this aspect of the disclosure, the substrate can be a bead, a stopper, a film, or a membrane.

[0012] In some embodiments of this aspect of the disclosure, the oxidizing agent has a standard reduction potential of at least 1.4 V.

[0013] In some embodiments of this aspect of the disclosure, the oxidizing agent is sodium bismuthate (NaBiCh), sodium periodate (Nal04), potassium permanganate (KMnO4), ceric ammonium nitrate, ozone, or chlorine dioxide (CIO2).

[0014] In some embodiments of this aspect of the disclosure, the one or more solvents comprise toluene, chloroform, tetrahydrofuran (THF), acetone, xylene, ether, petroleum ether, turpentine, benzene, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, water, or hexane.

[0015] In some embodiments of this aspect of the disclosure, the substrate has a melting point of at least 50°C.Docket U24-092 (222120-2120)

[0016] In some embodiments of this aspect of the disclosure, the substrate has a porosity of at least 50%.

[0017] In some embodiments of this aspect of the disclosure, at least 50% of the ruthenium oxide is recovered.

[0018] Another aspect of the present disclosure encompasses embodiments of a method for removing ruthenium from used nuclear fuel, comprising the steps of mixing a nuclear fuel with an oxidizing agent to volatilize a ruthenium compound into a RuO4gas, exposing the RUO4gas to a substrate, wherein the RuO4gas deposits onto the substrate and is reduced to RuO2, and recovering the RuO2from the substrate.

[0019] In some embodiments of this aspect of the disclosure, recovering the RuO2from the substrate further comprises the steps of dissolving the substrate with one or more solvents or calcining the substrate, and filtering the substrate to recover the RuO2.

[0020] In some embodiments of this aspect of the disclosure, about 90% of the RuO2is deposited onto the substrate.

[0021] In some embodiments of this aspect of the disclosure, the substrate is wax.

[0022] In some embodiments of this aspect of the disclosure, recovering the RuO2further comprises melting the substrate, volatilizing the substrate, burning the substrate, or a combination thereof.

[0023] In some embodiments of this aspect of the disclosure, at least 50% of the ruthenium oxide is recovered.

[0024] In some embodiments of this aspect of the disclosure, the substrate comprises a polymer material.

[0025] In some embodiments of this aspect of the disclosure, the substrate comprises a rubber material.

[0026] In some embodiments of this aspect of the disclosure, the substrate is a bead, a stopper, a film, or a membrane.

[0027] In some embodiments of this aspect of the disclosure, the oxidizing agent is sodium bismuthate (NaBiCh), sodium periodate (NalO4), potassium permanganate (KMnO4), ceric ammonium nitrate, ozone, or chlorine dioxide (CIO2).

[0028] In some embodiments of this aspect of the disclosure, the one or more solvents comprise toluene, chloroform, tetrahydrofuran (THF), acetone, xylene, ether, petroleum ether, turpentine, benzene, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, water, or hexane.Docket U24-092 (222120-2120)

[0029] In some embodiments of this aspect of the disclosure, the substrate has a melting point of at least 50°C.

[0030] In some embodiments of this aspect of the disclosure, the substrate has a porosity of at least 50%.

[0031] In some embodiments of this aspect of the disclosure, the oxidizing agent has a standard reduction potential of at least 1.4 V.

[0032] Yet another aspect of the present disclosure encompasses a method of recovering ruthenium, comprising the steps of mixing a first solution comprising a ruthenium compound with an oxidizing agent to volatilize the ruthenium compound into RuC>4, reacting the RUC>4 with a substrate according to the following reaction mechanism:\ / | XTA ; \ / J. RuQ., - *. i - - + RuQ*> / \ ■' !7S / ■ \* , wherein the substrate comprises one or more olefinic carbon bonds, and recovering a ruthenium oxide from the substrate.

[0033] In some embodiments of this aspect of the disclosure, recovering ruthenium oxide from the substrate further comprises the steps of dissolving the substrate with one or more solvents or heating the substrate to form a second solution, and filtering the second solution to recover the ruthenium oxide.

[0034] In some embodiments of this aspect of the disclosure, the substrate comprises a polymer material.

[0035] In some embodiments of this aspect of the disclosure, the substrate comprises a wax material.

[0036] In some embodiments of this aspect of the disclosure, the substrate comprises a rubber material.

[0037] In some embodiments of this aspect of the disclosure, the substrate is a bead, a stopper, a film, or a membrane.

[0038] In some embodiments of this aspect of the disclosure, the oxidizing agent is sodium bismuthate (NaBiCh), sodium periodate (Nal04), potassium permanganate (KMnO4), ceric ammonium nitrate, ozone, or chlorine dioxide (CIO2).

[0039] In some embodiments of this aspect of the disclosure, the one or more solvents comprise toluene, chloroform, tetrahydrofuran (THF), acetone, xylene, ether, petroleum ether,Docket U24-092 (222120-2120)turpentine, benzene, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, water, or hexane.

[0040] In some embodiments of this aspect of the disclosure, the substrate has a melting point of at least 50°C.

[0041] In some embodiments of this aspect of the disclosure, the substrate has a porosity of at least 50%.

[0042] In some embodiments of this aspect of the disclosure, about 50% of the RuO2is deposited onto the substrate.

[0043] In some embodiments of this aspect of the disclosure, recovering the RuO2further comprises melting the substrate, volatilizing the substrate, burning the substrate, or a combination thereof.

[0044] In some embodiments of this aspect of the disclosure, the oxidizing agent has a standard reduction potential of at least 1.4 V.

[0045] A further aspect of the present disclosure encompasses a method of recovering ruthenium, comprising the steps of mixing a first solution comprising a ruthenium compound with an oxidizing agent to volatilize the ruthenium compound into RuO4, reacting the RuO4with moisture to deposit RuO2onto a substrate, and recovering RuO2from the substrate.

[0046] In some embodiments of this aspect of the disclosure, recovering the RuO2from the substrate further comprises the steps of dissolving the substrate with one or more solvents or heating the substrate to form a second solution, and filtering the second solution to recover the RuO2.

[0047] In some embodiments of this aspect of the disclosure, the substrate comprises a polymer material.

[0048] In some embodiments of this aspect of the disclosure, the substrate comprises a wax material.

[0049] In some embodiments of this aspect of the disclosure, the substrate comprises a rubber material.

[0050] In some embodiments of this aspect of the disclosure, the substrate is a bead, a stopper, a film, or a membrane.

[0051] In some embodiments of this aspect of the disclosure, the oxidizing agent is sodium bismuthate (NaBiCh), sodium periodate (NalO4), potassium permanganate (KMnO4), ceric ammonium nitrate, ozone, or chlorine dioxide (CIO2).Docket U24-092 (222120-2120)

[0052] In some embodiments of this aspect of the disclosure, the one or more solvents comprise toluene, chloroform, tetrahydrofuran (THF), acetone, xylene, ether, petroleum ether, turpentine, benzene, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, water, or hexane.

[0053] In some embodiments of this aspect of the disclosure, the substrate has a melting point of at least 50°C.

[0054] In some embodiments of this aspect of the disclosure, the substrate has a porosity of at least 50%.

[0055] In some embodiments of this aspect of the disclosure, about 50% of the RuO2is deposited onto the substrate.

[0056] In some embodiments of this aspect of the disclosure, recovering the RuO2further comprises melting the substrate, volatilizing the substrate, burning the substrate, or a combination thereof.

[0057] In some embodiments of this aspect of the disclosure, the oxidizing agent has a standard reduction potential of at least 1.4 V.

[0058] In some embodiments of this aspect of the disclosure, reacting the RuO4with moisture to deposit RuO2onto the substrate further comprises reacting the RuO4with moisture according to a reaction mechanism, wherein the reaction mechanism comprises an oxidationreduction reaction.BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Further aspects of the present disclosure will be more readily appreciated upon review of the detailed description of its various embodiments, described below, when taken in conjunction with the accompanying drawings.

[0060] Aspects of the present disclosure can be better understood with reference to the following drawings. It is noted that the elements in the drawings are not necessarily to scale, with emphasis instead being placed upon clearly illustrating the principles of the embodiments. In the drawings, like reference numerals designate like or corresponding, but not necessarily the same, elements throughout the several views.

[0061] Figure 1 illustrates volatilization of 5.2 mM Ru from 3.0 M nitric acid with 100 mg NaBiCh over time.

[0062] Figure 2 shows a proposed mechanism of C=C bond cleavage between RUO4and olefinic carbon bonds in parafilm.Docket U24-092 (222120-2120)

[0063] Figure 3 shows a FTIR spectra of pristine parafilm (blue) and parafilm with adsorbed RuO2(red).

[0064] Figure 4 shows an XPS spectra of the (a) C 1s + Ru 3d and (b) O 1s regions of the pristine (purple) and Ru deposited (light blue) parafilm substrate.

[0065] Figure 5 shows an XPS spectra of the (a) C 1s + Ru 3d, (b) O 1s, (c) Al 2p + Ru 4s, and (d) Al 2s regions of the pristine (red) and Ru deposited (green) Al foil substrate.

[0066] Figure 6 shows a typical reaction setup consisting of a sealed roundbottom flask with Ru (5.2 mM) and nitric acid (3.0 M) with sodium bismuthate. The polystyrene beads are in an open test tube.

[0067] Figures 7A-7D shows the deposition of RuO4onto polystyrene beads as RUO2over time. The times were (7A) 0 min, (7B) 30 min, (7C) 2 h, and (7D) 6 h.

[0068] Figure 8 shows recovered polystyrene beads with deposited RuO2after heating the reaction vessel at 60 °C for 6 h.

[0069] Figure 9 shows a reaction flask after 6 h of heating at 60 °C. The dark brown solution attributed to the Ru species is now clear and colorless. The Ru has been deposited onto the parafilm as black RuO2.

[0070] Figure 10 shows a piece of parafilm with RuO2was dissolved in hexanes.

[0071] Figure 11 shows recovered ceria substrate with deposited RuO2after heating the reaction vessel at 60 °C for 6 h.

[0072] Figure 12 shows recovered aluminum foil after heating the reaction vessel at 60 °C for 6 h.

[0073] Figure 13 shows recovered LDPE substrate with deposited RuO2after heating the reaction vessel at 60 °C for 6 h.

[0074] Figure 14 shows recovered Teflon substrate with deposited RuO2before (left) and after (right) heating the reaction vessel at 60 °C for 6 h.

[0075] Figure 15 shows a FTIR spectra of pristine LDPE (blue) and LDPE with adsorbed RuO2(red).

[0076] Figure 16 shows survey spectra and surface composition (inset table) for the pristine (purple) and Ru-deposited (light blue) parafilm substrate.

[0077] Figure 17 shows survey spectra and surface composition (inset table) for the pristine (red) and Ru-deposited (green) Al foil substrate.Docket U24-092 (222120-2120)DETAILED DESCRIPTION

[0078] The present disclosure is directed to methods for recovering high-value ruthenium from used nuclear fuel.

[0079] Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims.

[0080] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit (unless the context clearly dictates otherwise), between the upper and lower limit of that range, and any other stated or intervening value in that stated range, is encompassed within the disclosure. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed within the disclosure, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the disclosure.

[0081] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disclosure, the preferred methods and materials are now described.

[0082] As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.

[0083] Embodiments of the present disclosure will employ, unless otherwise indicated, techniques of medicine, organic chemistry, biochemistry, molecular biology, pharmacology, and the like, which are within the skill of the art. Such techniques are explained fully in the literature.

[0084] The following description and examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to perform the methods and use the compositions and compounds disclosed and claimed herein. Efforts haveDocket U24-092 (222120-2120)been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C, and pressure is in bar or psi. Standard temperature and pressure are defined as 25 °C and 1 bar.

[0085] Before the embodiments of the present disclosure are described in detail, it is to be understood that, unless otherwise indicated, the present disclosure is not limited to particular materials, reagents, reaction materials, manufacturing processes, or the like, as such can vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. It is also possible in the present disclosure that steps can be executed in different sequence where this is logically possible. Different stereochemistry is also possible, such as products of cis or trans orientation around a carbon-carbon double bond or syn or anti addition could be both possible even if only one is drawn in an embodiment.

[0086] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a support” includes a plurality of supports. In this specification and in the claims that follow, reference will be made to a number of terms that shall be defined to have the following meanings unless a contrary intention is apparent.Definitions

[0087] In describing and claiming the disclosed subject matter, the following terminology will be used in accordance with the definitions set forth below.

[0088] Unless otherwise defined, all terms of art, notations and other scientific terminology used herein are intended to have the meanings commonly understood by those of skill in the art to which this disclosure pertains. In some cases, terms with commonly understood meanings are defined herein for clarity and / or for ready reference, and the inclusion of such definitions herein should not necessarily be construed to represent a substantial difference over what is generally understood in the art. The techniques and procedures described or referenced herein are generally well understood and commonly employed using conventional methodology by those skilled in the art.

[0089] As used herein, a “ruthenium suspension” can refer to a composition having dispersed particles or colloidal forms of ruthenium or a ruthenium-containing compound within a continuous liquid medium, such as water, an organic solvent, or a mixture thereof. The suspension can include stabilizing agents, surfactants, or other additives to maintain particleDocket U24-092 (222120-2120)dispersion, prevent agglomeration, and enhance chemical or physical stability. The ruthenium component can be present in elemental, ionic, oxide, complex, or nanoparticulate form. In some aspects of the present disclosure, a ruthenium suspension can be a nuclear fuel.

[0090] As used herein, “ruthenium oxide” can refer to an inorganic compound of ruthenium and oxygen. In various aspects, ruthenium oxide can refer to ruthenium(IV) oxide, ruthenium(lll) oxide, ruthenium(VIII) oxide, ruthenium(VI) oxide, ruthenium(V) oxide, ora mixed-valence oxide (e.g., RuO2xH2O, Ru3O8, etc.). In various aspects, ruthenium oxide can be formed from various ruthenium-containing compounds by oxidation with an oxidizing agent, as described herein.

[0091] As used herein, a “substrate” can refer to a surface, material, or structure that serves as a support or base layer upon which a ruthenium-containing compound can be deposited. The substrate can be rigid or flexible, and can include materials such as metal, wax, polymer, or rubber, depending on the intended application. The substrate can be inert or functionally active and can include pre-existing layers, patterns, or treatments to facilitate adhesion of a ruthenium-containing compound. In various aspects, the substrate can be in the form of a bead, a stopper, a film, a membrane, or any other physical form that facilitates deposition of a ruthenium-containing compound onto the substrate. In various aspects, the substrate can have a porosity of at least 0.001% and up to 99.99%. In preferred aspects, the substrate can have a porosity of at least 50%.

[0092] As used herein, a “rubber” can refer to a class of elastomeric polymeric materials, either of natural origin (e.g., c / s-1,4-polyisoprene derived from natural latex) or synthetically produced through polymerization or copolymerization processes. Synthetic rubbers can include, but are not limited to, styrene-butadiene rubber (SBR), nitrile rubber (NBR), ethylene-propylene-diene monomer (EPDM) rubber, butyl rubber (HR), chloroprene rubber (CR), and silicone-based elastomers. Rubber, as used herein, is considered a reactive or functional chemical medium that can participate in, influence, or be modified by chemical processes, including but not limited to vulcanization, crosslinking, grating, surface modification, or chemical compatibilization with other compounds or materials. Rubber can be used as a substrate and can incorporate various additives such as fillers, stabilizers, plasticizers, curatives, accelerators, and compatibilizers to achieve desired physicochemical properties. Unless otherwise specified, references to rubber can include both unvulcanized and vulcanized forms.

[0093] As used herein, a “polymer” can refer to a substance composed of macromolecules formed by the chemical bonding of a large number of repeating structural units, or monomers. The monomers can be covalently bonded in a chain-like or network structure, andDocket U24-092 (222120-2120)can result in materials that can range from linear to branched or crosslinked architectures. Polymers can be natural (e.g., cellulose, natural rubber, proteins) or synthetic and can be formed through addition polymerization or condensation polymerization processes. The term polymer can encompass homopolymers derived from a single type of monomer, copolymers derived from two or more different monomers, and terpolymers, as well as block, random, alternating, and graft copolymers. Unless otherwise specified, polymer can include both thermoplastic and thermosetting polymers, and can also refer to polymers that have been functionalized, blended, or chemically modified. Suitable polymers used herein can have a melting temperature from about 50°C to about 1000°C, or from about 100°C to about 500°C. In some examples, a polymer can include divinyl benzene copolymer, Teflon, polyethylene, etc.

[0094] As used herein, a “wax” can refer to a solid or highly viscous material comprised of long hydrocarbon chains of varying saturation, made from of monomers containing single, double, or triple carbon-carbon bonds. A wax can be a lipid, a mineral wax, or combination thereof, wherein the lipid, mineral wax, or combination thereof has a melting point of approximately 25°C to approximately 500°C. In a preferred aspect, the wax can have a melting point greater than approximately 50°C. The wax can be a lipid, such as a monoglyceride, diglyceride, triglyceride, fatty acid, fatty alcohol, esterified fatty acid, epoxidized lipid, maleated lipid, hydrogenated lipid, alkyd resin derived from a lipid, sucrose polyester, or combinations thereof. The wax can also be a mineral wax such as a linear alkane, a branched alkane, or combinations thereof. The waxes can be partially or fully hydrogenated materials, or combinations and mixtures thereof, that were formally liquids at room temperature in their unmodified forms. When the temperature is above the melting temperature of the wax, it is a liquid oil. When in the molten state, the wax can be referred to as an “oil”. The terms “wax” and “oil” only have meaning when measured at 25°C. The wax will be a solid at 25°C. Otherwise they are used interchangeably above 25°C.

[0095] Because the wax may contain a distribution of melting temperatures to generate a peak melting temperature, the wax melting temperature is defined as having a peak melting temperature 25°C or above as defined as when >50 weight percent of the wax component melts at or above 25°C. This measurement can be made using a differential scanning calorimeter (DSC), where the heat of fusion is equated to the weight percent fraction of the wax. The wax number average molecular weight, as determined by gel permeation chromatography (GPC), should be less than 2kDa, preferably less than 1.5 kDa.

[0096] Non-limiting examples of waxes contemplated in the compositions disclosed herein include beef tallow, castor wax, coconut wax, coconut seed wax, corn germ wax,Docket U24-092 (222120-2120)cottonseed wax, fish wax, linseed wax, olive wax, oiticica wax, palm kernel wax, palm wax, palm seed wax, peanut wax, rapeseed wax, safflower wax, soybean wax, sperm wax, sunflower seed wax, tall wax, tung wax, whale wax, and combinations thereof. Non-limiting examples of specific triglycerides include triglycerides such as, for example, tristearin, tripalmitin, 1,2-dipalmitoolein, 1 ,3-dipalmitoolein, 1-palmito-3-stearo-2-olein, 1-palmito-2-stearo-3-olein, 2-palmito-1-stearo-3-olein, 1 ,2-dipalmitolinolein, 1,2-distearo-olein, 1,3-distearo-olein, trimyristin, tri I aurin and combinations thereof. Non-limiting examples of specific fatty acids contemplated include capric acid, caproic acid, caprylic acid, lauric acid, myristic acid, palmitic acid, stearic acid, and mixtures thereof. Other specific waxes contemplated include hydrogenated soy bean oil, partially hydrogenated soy bean oil, partially hydrogenated palm kernel oil, and combinations thereof. Inedible waxes from Jatropha and rapeseed oil can also be used. The wax can be selected from the group consisting of a hydrogenated plant oil, a partially hydrogenated plant oil, an epoxidized plant oil, a maleated plant oil. Specific examples of such plant oils include soy bean oil, corn oil, canola oil, and palm kernel oil. Specific examples of mineral wax include paraffin (including petrolatum), Montan wax, as well as polyolefin waxes produced from cracking processes, preferentially polyethylene derived waxes. Mineral waxes and plant derived waxes can be combined together. Plant based waxes can be differentiated by their carbon-14 content.

[0097] As used herein, “oxidizing agent” can refer to an oxidant or oxidizer and can be a chemical species that facilitates an oxidation reaction by accepting electrons from another substance. In doing so, the oxidizing agent becomes reduced. Oxidants can include, but are not limited to, compounds such as NaBiOs, NalO4, KMnO4, ceric ammonium nitrate, ozone, chlorine dioxide (CIO2), etc. In various aspects, the Ru(IV) / Ru(VIII) redox couple is approximately 1.4 V. Therefore, in preferred aspects, oxidants can be any oxidizing agents that have a standard reduction potential above approximately 1.4 V. In various aspects, the oxidizing agent can be present in any amount that is greater than the amount of a ruthenium-containing compound.

[0098] As used herein, “solvent” can refer to any substance capable of dissolving, suspending, or extracting other substances (solutes) without chemically altering either the solvent or the solute. A solvent can function as a medium in which chemical reactions or formulations can occur, or in which substances may be dispersed to form a homogenous solution. Solvents can include, but are not limited to, organic solvents (e.g., alcohols, ketones, esters, hydrocarbons, chlorinated solvents, etc.), inorganic solvents (e.g., water, liquid ammonia), or mixtures thereof. Unless otherwise specified, the term solvent encompasses both single-component systems and solvent blends, and includes solvents used in processing,Docket U24-092 (222120-2120)purification, cleaning, formulation, reaction media, or as carriers or diluents in the aspects described herein.

[0099] As used herein, “porosity” can refer to the measure of the void spaces (pores) within a solid material, typically expressed as a percentage or fraction of the total volume of the material. Porosity can be used to characterize the extent to which a material contains open space, and can influence or determine properties such as permeability, density, mechanical strength, fluid absorption, and diffusivity.

[0100] As used herein, “nuclear fuel” can refer to any material containing fissile or fertile isotopes that is capable of sustaining a nuclear fission chain reaction when used in a nuclear reactor. Nuclear fuel can serve as the primary source of energy generation within the reactor core through the process of nuclear fission, wherein atomic nuclei split into smaller nuclei, releasing energy in the form of heat. The term nuclear fuel can encompass various physical and chemical forms including, but not limited to, ceramic fuel pellets, metallic fuels, oxide fuels, carbide fuels, nitride fuels, and molten salt fuels, whether in solid, liquid, or composite form.

[0101] As used herein, “solution” can refer to a homogenous mixture comprising one or more substances (solutes) molecularly or ionically dispersed within a solvent. A solution can be characterized by a single-phase system in which the solute is uniformly distributed at the molecular or ionic level, resulting in no distinguishable separation between the solute and the solvent. The solvent can be a liquid, solid, or gas, although the term “solution” typically refers to liquid-phase systems unless otherwise specified. The solute can be in solid, liquid, or gaseous form prior to dissolution. Solvents can include, but are not limited to, aqueous systems (e.g., water) or organic solvents (e.g., alcohols, ketones, ethers, hydrocarbons, chlorinated solvents, etc.) and can be single-component or multi-component solvent systems.

[0102] Further definitions are provided in context below. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art of chemistry, materials science, or the like. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described herein.Discussion

[0103] The present disclosure provides for methods of recovering high-value ruthenium from used nuclear fuel. Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, andDocket U24-092 (222120-2120)as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims.

[0104] The present disclosure provides a method of recovering ruthenium, including oxidizing a ruthenium suspension to deposit a ruthenium oxide onto a substrate using an oxidizing agent and recovering the ruthenium oxide from the substrate. In an aspect, recovering ruthenium oxide from the substrate can further involve dissolving the substrate with one or more solvents or calcining the substrate. In an aspect, the substrate can be filtered to recover the ruthenium oxide.

[0105] In an aspect, the substrate can include a polymer material. In another aspect, the substrate can include a wax material. In another aspect, the substrate can include a rubber material. In various aspects, the substrate can be in the form of a bead, a stopper, a film, or a membrane. In an aspect, the substrate can have a melting point of about 50°C to about 1000°C. In a preferred aspect, the substrate can have a melting point of at least 50°C. In an aspect, the substrate can have a porosity of about 0.001% to about 99.99%. In a preferred aspect, the substrate can have a porosity of at least 50%. In various aspects, the porosity of the substrate can affect the amount of ruthenium oxide deposited onto the substrate. In some aspects, the amount of ruthenium oxide that can be recovered from a substrate is based at least in part on a porosity of the substrate.

[0106] In some aspects, the substrate can be a wax material and recovering ruthenium oxide from the substrate can involve dissolving the wax material with one or more solvents and filtering out ruthenium oxide from the solution. In other aspects, the substrate can be a rubber material or a polymer material and recovering ruthenium oxide from the substrate can involve calcining the substrate or heating the substrate to a melting point of the substrate to breakdown the substrate and subsequently filter out the ruthenium oxide from the solution. In some aspects, a substrate having a lower molecular weight can be dissolved. In some aspects, a substrate having a higher molecular weight can be calcined or heated.

[0107] In an aspect, the oxidizing agent can have a standard reduction potential of at least 1.4 V. In an aspect, the oxidizing agent can be sodium bismuthate (NaBiO3), sodium periodate (Nal04), potassium permanganate (KMnO4), ceric ammonium nitrate, ozone, or chlorine dioxide (CIO2).

[0108] In an aspect, the one or more solvents can include one or more organic solvents. In various aspects, the one or more solvents can include toluene, chloroform,Docket U24-092 (222120-2120)tetrahydrofuran (THF), acetone, xylene, ether, petroleum ether, turpentine, benzene, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, water, or hexane.

[0109] In an aspect, about 0.0001% to about 99.999% of the ruthenium oxide can be recovered. In a preferred aspect, at least 50% of the ruthenium oxide can be recovered.

[0110] The present disclosure also provides for a method for removing ruthenium from used nuclear fuel, including mixing a nuclear fuel with an oxidizing agent to volatilize a ruthenium compound into a RuO4gas, exposing the RuO4gas to a substrate, wherein the RuO4gas deposits onto the substrate and is reduced to RuO2, and recovering the RuO2from the substrate.

[0111] In an aspect, recovering the RuO2from the substrate can include dissolving the substrate with one or more solvents or calcining the substrate. In an aspect, the substrate can then be filtered to recover the RuO2. In various aspects, recovering the RuO2can include melting the substrate, volatilizing the substrate, burning the substrate, or a combination thereof.

[0112] In an aspect, about 0.0001% to about 99.99% of the RuO2can be deposited onto the substrate. In a preferred aspect, at least 50% of the RuO2can be deposited onto the substrate.

[0113] The present disclosure provides a method of recovering ruthenium, including mixing a solution having a ruthenium compound with an oxidizing agent to volatilize the ruthenium compound into RuO4. The RuO4can be reacted with a substrate according to the following reaction mechanism:\ W / 4 - - I OJO I | - - \ to « / ■xi I / '■j O U §L J, wherein the substrate includes one or more olefinic carbon bonds. A ruthenium oxide can be recovered from the substrate. In an aspect, recovering ruthenium oxide from the substrate further includes dissolving the substrate with one or more solvents or heating the substrate to form a solution and filtering the solution to recover the ruthenium oxide.EXAMPLES

[0114] Now having described the embodiments of the disclosure, in general, the examples describe some additional embodiments. While embodiments of the present disclosure are described in connection with the example and the corresponding text and figures, there isDocket U24-092 (222120-2120)no intent to limit embodiments of the disclosure to these descriptions. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of embodiments of the present disclosure.Example 1

[0115] Ruthenium can be one of the most challenging fission products in used nuclear fuel due to its complex redox chemistry and high abundance in nitric acid dissolution solutions. [1, 2] In addition to its seven stable isotopes (96Ru,98Ru, "Ru,100Ru,101Ru,102Ru, and104Ru), 34 radioactive isotopes have been identified. Most notably,106Ru is a soft beta emitter and is utilized in eye cancer treatment, highlighting ruthenium’s relevance beyond nuclear waste management.[2] In nitric acid, ruthenium primarily exists as a mixture of Ru(lll) nitrosyl nitrate and nitro complexes-at least nine species have been identified in aged solutions. These species, with the general formula [RuNO(NO3)x(NO2)y(OH)z(H2O)5-x-y-z]3';<'y'z, often coexist with other polymeric Ru(IV) hydroxo-nitrate species such as [Ru(OH)x(H2O)6-x](NO3)4-x and binuclear Ru-O-Ru bridges. [3] Additionally, ruthenium nitrosyls are photolytically unstable, dissociating to Ru(lll), which readily oxidize to Ru(IV) in aerated nitric acid. [4] This dynamic and multivalent speciation-particularly the variable extractability of ruthenium trinitrato complexes-complicates separation processes such as PUREX, as discussed in numerous reviews. [3, 5-8]

[0116] One strategy for managing ruthenium during reprocessing of dissolved fuel is to suppress its extraction. Oxidation of Ru(IV) with nitrous acid or minimizing contact time have been explored, and Ru(IV) generated by H2O2 oxidation is largely non-extractable by TBP, though this conversion is often incomplete. [4] Ruthenium can also reach higher oxidation states; for example, during bismuthate-driven americium extraction, Ru competes with Am for the oxidant, complicating separation. [9] Given the standard potentials for Am(lll) / (VI) and Ru(IV) / (VI 11) couples are 1.7 V

[0010] and ~1.4 V,

[0010] respectively, an oxidant strong enough to oxidize Am can also oxidize Ru to volatile Ru(VIII) tetroxide (RuO4).

[0117] Octavalent Ru (RuO4) is a neutral, tetrahedral, and highly volatile species at room temperature.

[0011] While volatility of radioactive materials is typically undesirable, as this can pose corrosion and safety risks, [1, 12-15] it also offers a unique pathway for selective ruthenium separation from nitric acid media. Strategies using chemical oxidants like ceric ammonium nitrate, [3, 12] potassium permanganate,

[0016] and electrovolatilization

[0017] have been explored for this purpose. In one approach, the RuO4formed by oxidation with ceric nitrate was extracted into n-paraffin oil, where it was reduced to insoluble RUO2, filtered, and the solvent recycled.

[0012] However, this method faced challenges, particularly with incomplete extractionDocket U24-092 (222120-2120)from solutions rich in Ru nitrosyl complexes, and reduced efficiency at elevated nitric acid concentrations. Another approach used sodium bismuthate to remove ruthenium from simulated PUREX raffinate solutions, where it was determined that RuO4reduced to black RuC>2 in nonpolar solvents, which can pose a risk of back extraction. The rate of reduction varied with solvent type, occurring faster with aromatics and alcohols compared to alkanes. Loosely crosslinked polymer beads absorbed and reduced RuC>4 over several hours, whereas crosslinked polymer beads pre-saturated with reducing solvents were able to absorb and reduce RUO4in approximately one minute.

[0018]

[0118] The present disclosure has pursued a complementary approach through the co-crystallization of transuranics (CoXTL) concept. This method targets a single-step cocrystallization of hexavalent actinides (An(VI)) with uranyl nitrate hexahydrate (UNH) as a first step immediately after dissolution of UNF in hot HNC>3.

[0019] Using sodium bismuthate, transuranic (TRU) species like Np(VI), Pu(VI), and Am(VI)-as linear dioxo actinyl cations (AnC>22+)-are removed in near proportion to U(VI). Yields of 80-90% with high purity (separation factors >81 from Cs+, Sr2+, Nd3+, and Zr4+) crystals have been achieved.

[0020] Recent studies show that other fission products, including Mo, Re, and Ru, are not incorporated into the UNH crystals either.

[0021] Most importantly, the same oxidation potential that enables Am(lll) to Am(VI) oxidation also volatilizes Ru, providing an added advantage to the CoXTL process by enabling concurrent Ru removal and recovery.

[0119] The goal of the present disclosure is to develop an effective, practical method for ruthenium removal from crystallizer solution, supporting future radioisotope recovery efforts. Sodium bismuthate was employed to oxidize Ru to RuO4and deposit it onto various substrates under conditions relevant to the used nuclear fuel cycle. The deposition kinetics and process performance in the presence of fission product concentrations typical of clarified UNF solutions were systematically evaluated. Results demonstrate that ruthenium can be efficiently and practically removed from the nuclear fuel reprocessing flowsheet using a simple, practical approach.Materials and MethodsMaterials

[0120] Uranyl nitrate hexahydrate (98 - 102%, ACS Grade, UO2(NO3)2-6H2O) was purchased from Bio-Analytical Industries, Inc.; cesium nitrate (99.8%, CsNCh), neodymium nitrate hexahydrate (99.99% Nd basis, Nd(NC>3)3-6H2O), strontium nitrate (99.0%, Sr(NOs)2), and zirconyl chloride octahydrate (98%, ZrOCl3-8H2O) were purchased from Alfa Aesar; nitric acid (Trace metal grade, HNO3), ruthenium(lll) chloride (97%, RuCh), and sodium molybdateDocket U24-092 (222120-2120)(>99.5% trace metal basis, Na2MoO4) were purchased from Fisher Scientific; ruthenium(lll) nitrosyl nitrate solution (1.5% Ru in dilute nitric acid, ca. 1.5 M, Ru(NO)(NO3)x(OH)y,x+y=3) was purchased from Sigma-Aldrich; hydrazine monohydrate (>98.0%, N2H4-H2O) was purchased from TCI Chemicals; ammonium perrhenate (99%, NI-UReC ) and sodium bismuthate (ACS Grade, NaBiO3) were purchased from VWR. Deionized (DI) H2O was obtained from a Milli-Q water system operated at 18.2 MQ cm at 24 °C.

[0121] ICP-OES data were collected on a ThermoFisher Scientific iCAP 7400. Concentrations of U and fission products were measured by inductively coupled plasma-optical emission spectroscopy (ICP-OES) using a Thermofisher Scientific iCAP 7400 equipped with a prepFAST M5x automatic dilution sample loader (Elemental Scientific). Commercial elemental standards for Cs, Sr, Zr, Nd, Mo, Re, Ru, and U (Inorganic Ventures) were used to generate a 7-point standard curve. X-ray photoelectron spectroscopy (XPS) was performed on a Thermo Scientific (Waltham, MA, USA) K-Alpha XPS instrument. Survey spectra were applied for qualitative analysis and the detailed chemical composition was analyzed by high-resolution core level spectra.Ru Deposition onto Substrates

[0122] In a typical experiment nitric acid (15.8 M, 4.75 mL) and water (17.68 mL) were added to a 250 mL roundbottom flask with 2.5 g NaBiO3and a glass stir bar. Ruthenium nitrosyl nitrate was added to solution (1.5 M, 69.3 pL). The final concentration of nitric acid was 3 M to simulate conditions commonly used in UNF crystallizations.

[0022] To the suspension a test tube 9.5 cm in length with an internal diameter of 2 cm was added that contains the target substrate. The roundbottom was sealed with a glass stopper, and the suspension was stirred at 300 rpm at 60 °C for 6 h. During this time, a black film would appear on the substrate as RUO2(S). An aliquot was diluted in nitric acid containing hydrazine to reduce RuC>4 prior and then passed through a syringe filter (Tisch Scientific, Nylon Syringe Filter, 25 mm diameter, 0.1 pm pore size) to remove any suspended sodium bismuthate prior to ICP-OES analysis.Ru Recovery from Substrates

[0123] The substrate loaded with RuO2(s) was recovered and hexanes were used to dissolve the substrate. The suspension containing black solids was filtered, and the recovered solids were weighed, dissolved in 15 mL of 10 M nitric acid, and analyzed with ICP-OES.Kinetic Experiments

[0124] For the kinetic experiments, 10 mL solutions were prepared with water (8.07 mL), nitric acid (15.8 M, 1.90 mL), and ruthenium(lll) nitrosyl nitrate solution (34.7 pL). The final concentration of nitric acid was 3 M and the final Ru concentration was 5.2 mM. To theDocket U24-092 (222120-2120)suspension a test tube 9.5 cm in length with an internal diameter of 2 cm was added that contained parafilm (1.39 ± 0.2 g). The roundbottom was sealed with a glass stopper, and the suspension was stirred at 300 rpm at 60 °C. Aliquots of the suspension were pulled at various time intervals and added to a solution of 2% HNO3 and quenched with hydrazine. Solutions were then passed through a syringe filter to remove any suspended sodium bismuthate prior to ICP-OES analysis.Results and DiscussionDeposition and Recovery of Ru onto Various Substrates

[0125] Initial studies were conducted to identify the most effective substrate for depositing uC>2 and achieving maximum ruthenium removal from solution. Previous reports indicated that stainless steel and painted surfaces had little influence on RuC>2 precipitation, although ruthenium adsorption into polymer beads from nitric acid media has been observed.

[0018] A range of substrates (Table 1) composed of hydrocarbons or metals were selected, designed to remain out of direct contact within the solution to enable volatile RuC>4 deposition. Ceria (CeC>2) was included due to its well-known redox behavior between Ce4+and Ce3+.[23, 24] Among the materials tested, only the hydrocarbon-based substrates showed significant Ru capture. After heating the suspension at 60 °C for 6 h under conditions relevant to UNF crystallization, the polymer substrates darkened over time, indicating RuO4diffusion and deposition (Figures 7A-D). The black material observed is attributed to RuC>2 formation.

[0018] Notably, solutions containing parafilm as the substrate were completely colorless after 6 h, suggesting near-complete Ru removal.

[0126] Quantification by ICP-OES / MS confirmed these observations. Substrates such as aluminum foil and ceria removed only 5.2% and 10.6% of the initial Ru, respectively. This is likely attributed to a protective layer of aluminum or cerium oxide that is created by oxidation of the metal in air.

[0013] The low conductivity of this protective later makes the metal impossible to oxidize because of the low electron transfer rate from the metal.

[0025] In contrast, polymer-based substrates achieved significantly higher removal efficiencies: 85.2% with polystyrene beads, 90.2% with rubber septa, and 95.6% with parafilm. Some variability is expected due to differences in substrate surface area; however, parafilm was ultimately selected for further study due to its superior Ru removal and the reduced complexity it offers for subsequent Ru recovery (vide infra), avoiding the need for organic solvent extraction.Table 1. Ruthenium removal from solution and deposition onto various substrates.Substrate % Ru Removal [Ru]i (mM) [Ru]F(mM)Docket U24-092 (222120-2120)Poly Beads 85.2 ± 1.2 5.21 ± 0.09 0.77 ±0.08 Al Foil 5.2 ± 0.8 5.26 ± 0.07 4.99 ± 0.11 Ce2O310.6 ± 0.16 5.31 ± 0.11 4.75 ± 0.09 Parafilm 95.6 ± 1.2 5.18 ± 0.13 0.23 ± 0.07 Rubber 90.2 ± 1.6 5.27 ± 0.06 0.52 ± 0.09 LDPE 94.5 ± 1.7 5.81 ± 0.09 0.32 ± 0.04 Teflon 63.8 ± 1.1 5.73 ± 0.06 2.07 ± 0.07Recovery Studies

[0127] The recovery of ruthenium from the substrate is as important as its deposition and should be nearly quantitative to minimize downstream process issues, prevent damage to reprocessing infrastructure, and avoid negative impacts on vitrification and storage. [3] The method described here achieves near-quantitative recovery of the ruthenium deposited onto the parafilm substrate. A solution of Ru was treated with sodium bismuthate as previously described (vide supra), resulting in 98.4 ± 1.7% of the Ru being deposited onto 0.5 g of parafilm, leaving less than 0.1 mM of Ru in solution. (Table 2). The RuC>2-coated parafilm was then dissolved in hexanes or dichloromethane, producing a clear suspension containing floating black Ru solids. These solids were subsequently redissolved in nitric acid, and their concentration was measured using ICP-OES (

[0128] Table 3). This process was able to recover 99.6 ± 1.0% of the Ru from the parafilm, corresponding to an overall of 98.0% from the initial solution.Table 2. The concentrations of ruthenium in equal volume solutions before ([Ru]i) and after ([RU]F) treatment with sodium bismuthate.[Ru]i (mM) [RU]F(mM) Ru Deposited onto Parafilm (%) 5.3 ± 0.1 0.09 ± 0.01 98.4 ± 1.7Table 3. Amount of ruthenium recovered after dissolution ([Ru]^) of parafilm.[Ru]piss (mM) Ru Recovered from Parafilm (%)5.2 ± 0.1 99.6 ± 1.0RUO4Sorption Over Time

[0129] The same oxidation and deposition procedures were performed on the solution containing NaBiO3and Ru in 3 M nitric acid with parafilm, LDPE, or Teflon substrates.Docket U24-092 (222120-2120)Samples were pulled over the course of 6 h and the %Ru remaining in solution is highlighted in Error! Reference source not found..

[0130] Ruthenium is deposited onto parafilm as a black solid, where it undergoes a bond cleavage reaction with the olefinic (C=C) groups in the polymer matrix (Error! Reference source not found.). The appearance of weak ketone absorption bands at 1706 cm-1

[0026] confirms the oxidative cleavage of the double bonds by RuCk [27-29] Additionally, broad water-associated peaks at 1632 and ~3500 crrH-commonly observed in Ru-deposited substrates such as carbon nanotubes

[0030] and stainless steel

[0031] -are attributed to surface hydration, a result of the hygroscopic nature of RuO2and the formation of a condensed water layer under humid conditions.

[0013] While Ru deposition on metal substrates typically occurs via physisorption, forming monolayers of RuO2followed by surface hydration, the interaction with organic substrates is more complex. Here, RuC not only adsorbs onto the surface but also chemically reacts with the polyolefin double bonds, leading to deeper incorporation. This dual mechanism is advantageous by an in-tandem type process of concentrating RuC>4 at the surface to enhance the reactivity as it employs an in-tandem process that concentrates RuC>4 at the surface, thereby enhancing its reactivity while simultaneously facilitating the effective immobilization of Ru. This behavior is observed with LDPE, a polymer composed entirely of saturated C-C and C-H bonds, as the FTIR spectrum (Error! Reference source not found.) shows the presence of carbonyl stretching. This is likely a result of a radical mechanism through C-H bond activation leading to ketone or carboxylic acid formation, which is facilitated by the water vapor in the chamber (Figure 15). [14, 32, 33]RUO4Deposition and Recovery from UNF Simulant

[0131] Crystallization experiments were then conducted under conditions simulating the CoXTL process, incorporating key fission products, Cs, Sr, Nd, Zr, Mo, and Re, into the NaBiO3suspension at concentrations representative of clarified UNF.

[0034] The suspension was heated at 60 °C for 6 h. The results are summarized in Table 4. During the heating process, the supernatant visibly transitions from dark brown to the characteristic green from the U ion, while the parafilm darkened, consistent with RuO2deposition. After 6 h, the Ru concentration in solution decreased from 5.35 ± 0.10 mM to below the limit of detection for ICP-OES(0.001 mM), corresponding to 99.98 ± 0.02% removal onto the parafilm. Importantly, the concentrations of other fission products remained largely unchanged, indicating selective removal of Ru under these conditions. [22, 35, 36]Table 4. U and fission composition of UNF simulant solution in 3 M HNO3.Constituent Concentration (mM) before Concentration after (mM)Docket U24-092 (222120-2120)U 3031.7 ± 25.2 3040.0 + 27.9 Cs 9.04 ± 0.38 9.13 ± 0.45Sr 9.56 ±0.27 9.17 + 0.38Nd 29.60 ± 0.07 29.91 ± 0.05 Zr 8.85 ±0.15 9.08 ± 0.10Mo 4.79 ±0.07 4.49 ± 0.09Re 2.06 ±0.02 2.18 ± 0.03Ru 5.35 ±0.10 <0.001 ± 0.001aabelow limit of detection (3CT) of Ru.XPS of Al Foil and Parafilm Substrates

[0132] The surface composition and chemical states of the as-prepared substrates were characterized using X-ray photoelectron spectroscopy (XPS). Error! Reference source not found, compares the survey spectra of pristine and Ru-coated parafilm, with only C, Ru, and O as the dominant elements observed. Two distinct core-level signals for Ru are observed: the Ru 3p doublet between 450 and 495 eV, and the main Ru 3d Ru signal, which overlaps with C 1s peak.

[0037] To quantify the Ru content, both the Ru 3p signal and a peak-fitting analysis of the overlapping C 1s and Ru 3d region were compared, and the reported Ru values are based on the Ru 3p data. Error! Reference source not found. A highlights the overlapping C 1s and Ru 3d peaks; while the pristine parafilm shows a single peak corresponding to C-C bonds, the Ru-coated sample contains an additional peak at 281.0 eV, characteristic of Ru(IV) as the RUO2. The O 1s region (Error! Reference source not found. B), which is weak in the pristine sample, displays a new feature assigned to O-Ru bonds after the Ru deposition.

[0133] XPS analysis was also performed on an inorganic-based substrate Al foil to determine whether the chemical composition or binding of deposited Ru changed on a noninteracting surface. The survey spectra of the two Al foil samples (Error! Reference source not found.) show only Al, O, and C in the pristine sample, while the Ru-coated sample displays an additional Ru peak. Error! Reference source not found.A shows the C1s and Ru 3d regions, where the C 1s spectrum of the pristine Al foil is typical for air-exposed surfaces, featuring a main C-C peak at 284.6 eV, a shoulder at 286.5 eV (attributed to C-O), and a peak at 290 eV (assigned to O=C-O). The same set of three carbon-related peaks were used to fit the C 1s and Ru 3d spectra of the Ru-coated sample. After deposition, two Ru 3d doublets appear, with the Ru 3ds / 2 peak at 281.4 eV corresponding to RuC>2. In the O 1 s region (Error! Reference source not found. B), the pristine sample is primarily O-AI, with likely overlapping O / C species. When Ru is present, a shoulder appears at lower binding energy, attributed to O-Ru bonding.Error! Reference source not found. C and 5D show the Al 2p and Al 2s regions, respectively; The Al 2p peak overlaps with the Ru 4s feature. Both the Al 2p and Al 2s signals for the pristineDocket U24-092 (222120-2120)foil show contributions from metallic Al and Al oxide species. In both substrates, Ru is unambiguously present as RuC>2, with no indication of direct chemical interaction with the substrate, which has previously been observed;

[0014] rather, Ru interacts exclusively though oxygen atoms through Ru-0 linkages. It is likely that impurities such as water vapor can act as a reductant of RuC>4.

[0038] It was previously reported that this process corresponds neither to chemisorption or physisorption and that the process is nearly proportional to surface area and is indicative of an adsorption-type interaction of RuC onto the substrates.Conclusions

[0134] The present disclosure demonstrates the effective removal of ruthenium-a known problematic fission product in used nuclear fuel processing-using sodium bismuthate as a strong oxidizing agent. Ruthenium is fully oxidized to volatile RuC within approximately six hours in the presence of excess sodium bismuthate. Once formed, the RuO4 is efficiently captured by hydrocarbon-based substrates such as a parafilm, polyethylene beads, and rubber, where it is reduced to insoluble black RuO2. Among the tested substrates, parafilm exhibited the highest adsorption efficiency, capturing >95% of the ruthenium from solution. The Ru can then be recovered from parafilm and 98% of the initial Ru is recovered from the whole process. XPS analysis confirmed that the Ru is present as RUO2 on both parafilm and aluminum foil substrates, with no evidence of direct chemical interaction between Ru and the substrates. Instead, Ru binds exclusively through Ru-0 bonds, suggesting an adsorption-type interaction of RuO4 onto the surfaces. Under more chemically complex conditions that simulate used nuclear fuel environments, ruthenium was removed quantitatively while other fission products remained in solution. This straightforward, substrate-based approach can allow for both mitigating the accumulation of volatile ruthenium species-known to damage reactor components-and potentially recovering ruthenium for radiotherapeutic applications.References[1] C. Mun, L. Cantrel, C. Madic, Review of literature on ruthenium behavior in nuclear power plant severe accidents, Nuclear technology, 156 (2006) 332-346.[2] D. Boglaienko, G.B. Hall, N.L. D'Annunzio, T.G. Levitskaia, Ruthenium speciation and distribution in the environment: A review, Science of The Total Environment, 951 (2024) 175629.[3] P. Swain, C. Mallika, R. Srinivasan, U.K. Mudali, R. Natarajan, Separation and recovery of ruthenium: a review, Journal of Radioanalytical and Nuclear Chemistry, 298 (2013) 781-796.[4] L. Maya, Ruthenium (IV) in nitric acid media, Journal of Inorganic and Nuclear Chemistry, 41 (1979) 67-71.Docket U24-092 (222120-2120)[5] A. Siczek, M. Steindler, The chemistry of ruthenium and zirconium in the PUREX solvent extraction process, Atomic Energy Review, 16 (1978) 575-618.[6] P.K. Verma, P.K. Mohapatra, Ruthenium speciation in radioactive wastes and state-of-the-art strategies for its recovery: a review, Sep. Purif. Technol., 275 (2021) 119148.[7] D. Sood, S. Patil, Chemistry of nuclear fuel reprocessing: current status, Journal of Radioanalytical and Nuclear Chemistry, 203 (1996) 547-573.[8] P. Moeyaert, M. Miguirditchian, M. Masson, B. Dinh, X. Heres, S. De Sio, C. Sorel, Experimental and modelling study of ruthenium extraction with tri-n-butylphosphate in the purex process, Chemical Engineering Science, 158 (2017) 580-586.[9] Atomic Energy Review, Vol. 16 (1978), No. 4, INTERNATIONALATOMIC ENERGY AGENCY, Vienna.

[0010] A. J. Bard, R. Parsons, J. Jordan, Standard potentials in aqueous solution, Routledge, 2017.

[0011] G. Tojo, M. Fernandez, Ruthenium Tetroxide and Other Ruthenium Compounds, in: Oxidation of Primary Alcohols to Carboxylic Acids: A Guide to Current Common Practice, Springer New York, New York, NY, 2007, pp. 61-78.

[0012] K. Motojima, Removal of Ruthenium from PUREX Process Extraction of Ruthenium Tetroxide with Paraffin Oil and Filtration of Ruthenium Dioxide, Journal of Nuclear Science and Technology, 26 (1989) 358-364.

[0013] I. Kajan, H. Lasseson, I. Persson, C. Ekberg, Interaction of ruthenium tetroxide with surfaces of nuclear reactor containment building, Journal of Nuclear Science and Technology, 53 (2016) 1397-1408.

[0014] C. Mun, L. Cantrel, C. Madic, Study of RuO4 decomposition in dry and moist air, Radiochimica Acta, 95 (2007) 643-656.

[0015] C. Mun, L. Cantrel, C. Madic, Oxidation of ruthenium oxide deposits by ozone, Radiochimica Acta, 96 (2008) 375-384.

[0016] M. Haas, P. Weuta, A. Wolf, O.-K. Schlueter, in: US (Ed.), 2008.

[0017] L. Koch, R. Wellum, Proceedings of the workshop on partitioning and transmutation of minor actinides, Karlsruhe, 16-18 October 1989, EUR(Luxembourg), (1991).

[0018] J.M. Richards, B.J. Mincher, Selective Partitioning of Ruthenium from Nitric Acid Media, Solvent Extraction and Ion Exchange, 35 (2017) 49-60.

[0019] J.D. Burns, B.A. Moyer, Group Hexavalent Actinide Separations: A New Approach to Used Nuclear Fuel Recycling, Inorganic Chemistry, 55 (2016) 8913-8919.Docket U24-092 (222120-2120)

[0020] J.D. Burns, B.A. Moyer, Uranyl nitrate hexahydrate solubility in nitric acid and its crystallization selectivity in the presence of nitrate salts, Journal of Cleaner Production, 172 (2018) 867-871.

[0021] J.M. Pyles, J.D. Einkauf, D. Ray, L.R. Sadergaski, L.H. Delmau, A. Martin, T.J. Keever, B.A. Moyer, V.S. Bryantsev, J.D. Burns, Recovering High-Purity Uranyl Nitrate from Simulated Used Nuclear Fuel Dissolver Solutions by Crystallization: Rejecting Technetium, Sep. Purif. Technol., In Submission (2025).

[0022] J.D. Burns, B.A. Moyer, Group Hexavalent Actinide Separations: A New Approach to Used Nuclear Fuel Recycling, Inorg. Chem., 55 (2016) 8913.

[0023] J. Hayles, H. Bao, The reduction and oxidation of ceria: A natural abundance triple oxygen isotope perspective, Geochimica et Cosmochimica Acta, 159 (2015) 220-230.

[0024] V. Perrichon, A. Laachir, G. Bergeret, R. Frety, L. Tournayan, O. Touret, Reduction of cerias with different textures by hydrogen and their reoxidation by oxygen, Journal of the Chemical Society, Faraday Transactions, 90 (1994) 773-781.

[0025] I. Olefjord, A. Nylund, Surface analysis of oxidized aluminium. 2. Oxidation of aluminium in dry and humid atmosphere studied by ESCA, SEM, SAM and EDX, Surface and Interface Analysis, 21 (1994) 290-297.

[0026] E. Pretsch, P. Buhlmann, M. Badertscher, IR Spectroscopy, in: Structure Determination of Organic Compounds: Tables of Spectral Data, Springer Berlin Heidelberg, Berlin, Heidelberg, 2009, pp. 1-67.

[0027] L.M. Berkowitz, PN. Rylander, Use of Ruthenium Tetroxide as a Multi-purpose Oxidant, Journal of the American Chemical Society, 80 (1958) 6682-6684.

[0028] F. Dean, J. Knight, 930. Spirans. Part IV. The oxidation of 3-alkylidenegrisens to grisen-3-ones by ruthenium tetroxide, Journal of the Chemical Society (Resumed), (1962) 4745-4752.

[0029] G. Snatzke, H.-W. Fehlhaber, Eine einfache Methode zur Lokalisierung isolierter Doppelbindungen in Steroiden und Triterpenen, Justus Liebigs Annalen der Chemie, 663 (1963) 123-135.

[0030] M. Skunik-Nuckowska, P. Bqcal, P. Kulesza, Charge storage and capacitance-type properties of multi-walled carbon nanotubes modified with ruthenium analogue of Prussian Blue, Journal of Solid State Electrochemistry, 19 (2015).

[0031] R.S. Ingole, B.Y. Fugare, B.J. Lokhande, Ultrahigh specific capacitance of spray deposited nanoporous interconnected ruthenium oxide electrode fabric for supercharged capacitor, Journal of Materials Science: Materials in Electronics, 28 (2017) 16374-16383.Docket U24-092 (222120-2120)

[0032] T. Seki, K.-Y. Chiang, C.-C. Yu, X. Yu, M. Okuno, J. Hunger, Y Nagata, M. Bonn, The Bending Mode of Water: A Powerful Probe for Hydrogen Bond Structure of Aqueous Systems, The Journal of Physical Chemistry Letters, 11 (2020) 8459-8469.

[0033] A. Tenaglia, E. Terranova, B. Waegell, Ruthenium-catalyzed carbon-hydrogen bond activation. Oxyfunctionalization of nonactivated carbon-hydrogen bonds in the cedrane series with ruthenium tetraoxide generated in situ, The Journal of Organic Chemistry, 57 (1992) 5523-5528.

[0034] S.l. Sinkov, G.B. Hall, F.D. Heller, G.J. Lumetta, Neptunium redox speciation and determination of its total concentration in dissolved fuel simulant solutions by spectrophotometry, Journal of Radioanalytical and Nuclear Chemistry, 331 (2022) 5579-5595.

[0035] J.D. Burns, B.A. Moyer, Uranyl Nitrate Hexahydrate Solubility in Nitric Acid and Its Crystallization Selectivity in the Presence of Nitrate Salts, J. Clean. Prod., 172 (2018) 867.

[0036] J.D. Einkauf, J.D. Burns, Recovery of Oxidized Actinides, Np(VI), Pu(VI), andAm(VI), from Cocrystallized Uranyl Nitrate Hexahydrate: A Single Technology Approach to Used Nuclear Fuel Recycling, Industrial & Engineering Chemistry Research, 59 (2020) 4756-4761.

[0037] C. Mun, J. J. Ehrhardt, J. Lambert, C. Madic, XPS investigations of ruthenium deposited onto representative inner surfaces of nuclear reactor containment buildings, Applied Surface Science, 253 (2007) 7613-7621.

[0038] T. Sakurai, Y. Hinatsu, A. Takahashi, G. Fujisawa, Adsorption of ruthenium tetroxide on metal surfaces, The Journal of Physical Chemistry, 89 (1985) 1892-1896.

[0135] It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. To illustrate, a concentration range of “about 0.1% to about 5%” should be interpreted to include not only the explicitly recited concentration of about 0.1 wt% to about 5 wt%, but also include individual concentrations (e.g., 1%, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1%, 2.2%, 3.3%, and 4.4%) within the indicated range. In an embodiment, the term “about” can include traditional rounding according to significant figures of the numerical value. In addition, the phrase “about ‘x’ to ‘y’” includes “about ‘x’ to about ‘y’”.Docket U24-092 (222120-2120)

[0136] It should be emphasized that the above-described embodiments of the present disclosure are merely possible examples of implementations, and are set forth only for a clear understanding of the principles of the disclosure. Many variations and modifications may be made to the above-described embodiments of the disclosure without departing substantially from the spirit and principles of the disclosure. All such modifications and variations are intended to be included herein within the scope of this disclosure.

Claims

WHAT IS CLAIMED IS:

1. A method of recovering ruthenium, comprising:oxidizing a ruthenium suspension to deposit a ruthenium oxide onto a substrate using an oxidizing agent; andrecovering the ruthenium oxide from the substrate, wherein recovering ruthenium oxide from the substrate further comprises:dissolving the substrate with one or more solvents or calcining the substrate to form a solution; andfiltering the solution to recover the ruthenium oxide.

2. The method of claim 1 , wherein the substrate comprises a polymer material.

3. The method of claim 1 , wherein the substrate comprises a wax material.

4. The method of claim 1 , wherein the substrate comprises a rubber material.

5. The method of claims 1-4, wherein the substrate is a bead, a stopper, a film, or a membrane.

6. The method of claims 1-5, wherein the oxidizing agent has a standard reduction potential of at least 1.4 V.

7. The method of claims 1-6, wherein the oxidizing agent is sodium bismuthate (NaBiCh), sodium periodate (Nal04), potassium permanganate (KMnO4), ceric ammonium nitrate, ozone, or chlorine dioxide (CIO2).

8. The method of claims 1-7, wherein the one or more solvents comprise toluene, chloroform, tetrahydrofuran (THF), acetone, xylene, ether, petroleum ether, turpentine, benzene, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, water, or hexane.

9. The method of claims 1-8, wherein the substrate has a melting point of at least 50°C.

10. The method of claims 1-9, wherein the substrate has a porosity of at least 50%.

11. The method of claims 1-10, wherein at least 50% of the ruthenium oxide is recovered.

12. A method for removing ruthenium from used nuclear fuel, comprising:mixing a nuclear fuel with an oxidizing agent to volatilize a ruthenium compound into a RUC>4 gas;exposing the RuC gas to a substrate, wherein the RuO4 gas deposits onto the substrate and is reduced to RUO2; andrecovering the RuC>2 from the substrate.

13. The method of claim 11 , wherein recovering the RuC>2 from the substrate further comprises:dissolving the substrate with one or more solvents or calcining the substrate; and filtering the substrate to recover the RuC>2.

14. The method of claims 12 or 13, wherein about 90% of the RuC>2 is deposited onto the substrate.

15. The method of claims 12-14, wherein the substrate is wax.

16. The method of claims 12-15, wherein recovering the RuC>2 further comprises melting the substrate, volatilizing the substrate, burning the substrate, or a combination thereof.

17. The method of claims 12-16, wherein at least 50% of the ruthenium oxide is recovered.

18. The method of claims 12-14 or 16-17, wherein the substrate comprises a polymer material.

19. The method of claims 12-14 or 16-17, wherein the substrate comprises a rubber material.

20. The method of claims 12-19, wherein the substrate is a bead, a stopper, a film, or a membrane.

21. The method of claims 12-20, wherein the oxidizing agent is sodium bismuthate (NaBiC ), sodium periodate (Nal04), potassium permanganate (KMnO4), ceric ammonium nitrate, ozone, or chlorine dioxide (CIO2).

22. The method of claims 12-21 , wherein the one or more solvents comprise toluene, chloroform, tetrahydrofuran (THE), acetone, xylene, ether, petroleum ether, turpentine, benzene, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, water, or hexane.

23. The method of claims 12-22, wherein the substrate has a melting point of at least 50°C.

24. The method of claims 12-23, wherein the substrate has a porosity of at least 50%.

25. The method of claims 12-24, wherein the oxidizing agent has a standard reduction potential of at least 1.4 V.

26. A method of recovering ruthenium, comprising:mixing a first solution comprising a ruthenium compound with an oxidizing agent to volatilize the ruthenium compound into RuO4;reacting the RuO4with a substrate according to the following reaction mechanism:'5= / RUO4- » i d.Lfo I - » to ♦ Qsx / RuO-> / \ : S / \L, wherein the substrate comprises one or more olefinic carbon bonds; andrecovering a ruthenium oxide from the substrate, wherein recovering ruthenium oxide from the substrate further comprises:dissolving the substrate with one or more solvents or heating the substrate to form a second solution; andfiltering the second solution to recover the ruthenium oxide.

27. The method of claim 26, wherein the substrate comprises a polymer material.

28. The method of claim 26, wherein the substrate comprises a wax material.

29. The method of claim 26, wherein the substrate comprises a rubber material.

30. The method of claims 26-29, wherein the substrate is a bead, a stopper, a film, or a membrane.

31. The method of claims 26-30, wherein the oxidizing agent is sodium bismuthate (NaBiCh), sodium periodate (Nal04), potassium permanganate (KMnO4), ceric ammonium nitrate, ozone, or chlorine dioxide (CIO2).

32. The method of claims 26-31 , wherein the one or more solvents comprise toluene, chloroform, tetrahydrofuran (THF), acetone, xylene, ether, petroleum ether, turpentine, benzene, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, water, or hexane.

33. The method of claims 26-32, wherein the substrate has a melting point of at least 50°C.

34. The method of claims 26-33, wherein the substrate has a porosity of at least 50%.

35. The method of claims 26-34, wherein about 50% of the RuC>2 is deposited onto the substrate.

36. The method of claims 26-35, wherein recovering the RuC>2 further comprises melting the substrate, volatilizing the substrate, burning the substrate, or a combination thereof.

37. The method of claims 26-36, wherein the oxidizing agent has a standard reduction potential of at least 1.4 V.

38. A method of recovering ruthenium, comprising:mixing a first solution comprising a ruthenium compound with an oxidizing agent to volatilize the ruthenium compound into RuC ;reacting the RuCU with moisture to deposit RuC>2 onto a substrate; andrecovering RuC>2 from the substrate, wherein recovering the RuC>2 from the substrate further comprises:dissolving the substrate with one or more solvents or heating the substrate to form a second solution; andfiltering the second solution to recover the RuO2.

39. The method of claim 38, wherein the substrate comprises a polymer material.

40. The method of claim 38, wherein the substrate comprises a wax material.

41. The method of claim 38, wherein the substrate comprises a rubber material.

42. The method of claims 38-41, wherein the substrate is a bead, a stopper, a film, or a membrane.

43. The method of claims 38-42, wherein the oxidizing agent is sodium bismuthate (NaBiCh), sodium periodate (NaIC ), potassium permanganate (KMnCU), ceric ammonium nitrate, ozone, or chlorine dioxide (CIO2).

44. The method of claims 38-43, wherein the one or more solvents comprise toluene, chloroform, tetrahydrofuran (THF), acetone, xylene, ether, petroleum ether, turpentine, benzene, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), ethanol, water, or hexane.

45. The method of claims 38-44, wherein the substrate has a melting point of at least 50°C.

46. The method of claims 38-45, wherein the substrate has a porosity of at least 50%.

47. The method of claims 38-46, wherein about 50% of the RuC>2 is deposited onto the substrate.

48. The method of claims 38-47, wherein recovering the RuC>2 further comprises melting the substrate, volatilizing the substrate, burning the substrate, or a combination thereof.

49. The method of claims 38-48, wherein the oxidizing agent has a standard reduction potential of at least 1.4 V.

50. The method of claims 38-49, wherein reacting the RuC>4 with moisture to deposit RuC>2 onto the substrate further comprises reacting the RuC with moisture according to a reaction mechanism, wherein the reaction mechanism comprises an oxidation-reduction reaction.

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