Oxidation and hydrolysis of thorium doped uranium nitride fuel for use in LWR

Uranium nitride is being investigated as a replacement for UO2 as it shows enhanced thermal properties and seems to be a promising accident tolerant fuel (ATF) candidate. The main drawback of UN fuel is its innate low oxidation resistance in air/water environments. This becomes a challenge for the implementation of UN fuel in water-cooled reactors. The effect of thorium doping in the stability of uranium nitride microspheres and pellets sintered by spark plasma sintering (SPS) was investigated in oxidizing environments using thermogravimetric analysis and autoclave testing. It was found that during oxidation in air the density had a noticeable effect, increasing the reaction onset temperatures in pellets with higher densities. In addition, thorium doping improved the oxidation resistance of pellets in air by increasing the maximal reaction rate temperature by approximately 50 K. However, this effect was almost nonexistent in highly porous doped microspheres. The interaction with water at 373 K showed that pellets manufactured using SPS can survive unchanged for at least six hours in boiling water, which is an improvement to cold-pressed pellets. At 473 and 573 K, the pellets were oxidized and disintegration into an oxide powder was observed. Thorium-doped uranium nitride pellets did not present any improvement with respect to the oxidation resistance of UN in water at these temperatures

Recovery of Rare-Earth Elements from Neodymium Magnet Waste Using Glycolic, Maleic, and Ascorbic Acids Followed by Solvent Extraction

Rare-earth elements (REEs) play a key role in modern societies as their usage keeps increasing in new technologies and green energy sources. However, they are also considered the most critical raw materials in the EU and the USA in terms of supply. There is an increased global interest in the recycling of REEs from end-of-life products and industrial waste. Some REEs, such as Nd, Pr, and Dy, can be recovered from neodymium magnets. These magnets are of special interest since they are present in various technological wastes, such as hard disk drives, electric generators for wind turbines, electric motors, etc. Separation of REEs from other magnet components, such as Fe, which is the main part of the alloy, and further reprocessing of REEs, is the main goal of this work. In this work, neodymium magnet powder was successfully leached using the fully combustible organic lixiviants maleic, glycolic, and ascorbic acids, in order to potentially decrease the usage of strong mineral acids in the hydrometallurgical recovery of REEs. Subsequently, the REEs were selectively extracted from these leachates. For this separation step, several phosphate extractants (TBP, D2EHPA, Cyanex 272, and 923) were investigated, alongside TODGA, which follows the CHON principle and is fully combustible, with no ash or acidic gases being produced. The influences of various diluents (1-octanol, cyclohexanone, hexane, pentane, and dodecane) on the extraction were also studied since the diluents can play an important role in the extraction process and increase selectivity between the extraction of REEs and other impurities. Leaching was shown to be more efficient with maleic and glycolic acids than with ascorbic acid, even at room temperature. Values above 95% were reached for REEs with 1 M concentration and 1/80 solid/liquid ratio. For ascorbic acid, heating the leaching system to 70 A degrees C allowed similar values to be reached. D2EHPA has shown good extraction properties for the recovery of REEs from both glycolic and maleic leachate, mostly with nonpolar diluents such as pentane and hexane, without extracting transition metals (distribution ratios under 0.1). TODGA also showed good extraction of REEs and selectivity between elements, but only in the maleic leachate. As expected, the increasing concentration of the D2EHPA led to the increased distribution ratios. Thus, glycolic, maleic, and ascorbic organic acids, which have not been used before for leaching of neodymium magnet waste, showed good potential for the recovery of REEs from neodymium magnets and for the further development of large-scale recovery processes for REEs

Separation of Heavy Rare-Earth Elements from Light Rare-Earth Elements Via Solvent Extraction from a Neodymium Magnet Leachate and the Effects of Diluents

In recent decades, rare-earth elements (REEs) have seen a considerable increase in usage in modern technologies and the so-called green energy sources. The REEs are currently regarded to be among the most critical elements by the European Union (EU) and the United States (USA). Large investments are made in the research of recycling of the REEs from end-of-life products and E-scrap. One potential source for recycling of larger amounts of neodymium and dysprosium are end-of-life neodymium magnets. In this work, the selective extraction of REEs from a sulfuric media leachate (containing Nd, Dy, Pr, Gd, Co, and B) obtained by selective roasting of NdFeB waste and leaching was investigated. The extracting agent D2EHPA (di-(2-ethylhexyl) phosphoric acid) diluted in Solvent 70, hexane, octane, cyclohexanone, chloroform, 1-octanol, and toluene was used for the investigation of the effects of using different diluents on the extraction of REEs and the separation between the light and the heavy REEs. The concentrations of D2EHPA in the used diluents were 0.3, 0.6, 0.9, and 1.2 M. The highest separation factors between the heavy and the light REEs were achieved using 0.3 M D2EHPA in hexane, while no B or Co extraction was measurable. The REEs were completely extracted as a group using 0.9 M or 1.2 M D2EHPA in either octane or hexane, also with no B or Co extraction. The aliphatic nonpolar diluents showed better properties than the aromatic and polar ones. The complete stripping of REEs from the loaded organic phases was proven to be efficient using hydrochloric acid at concentrations of 2 M or higher

Characterization and Leaching of Neodymium Magnet Waste and Solvent Extraction of the Rare-Earth Elements Using TODGA

The rare-earth elements (REEs) are considered as some of the most critical elements in the EU and the USA today. E-scrap, such as end-of-life neodymium magnets, could be a viable secondary source for the recovery of these elements. Neodymium magnets (NdFeB) consist of considerable amounts of Nd, Dy, Pr, and some other REEs, depending on the specific application. Apart from REEs, neodymium magnets are made up of around 60% iron, which can pose a challenge in their recycling. For example, iron can be dissolved along with other elements during leaching or co-extracted during solvent extraction. In this work, extraction of REEs with TODGA (tetraoctyl-diglycolamide) from a real leachate, obtained by neodymium magnet powder dissolution in nitric acid, was studied. The goal was to selectively extract the REEs from other elements in the solution. TODGA was used as the extracting agent due to its selective extraction properties for REEs and other f-block elements. The influence of the diluent on the overall extraction and the selectivity of the extraction was studied in order to determine application feasibility of future processes. To this end, experiments using Solvent 70 (hydrocarbons C11-C14, ae 0.5 wt% aromatics), hexane, toluene, cyclohexanone and 1-octanol as the diluents were performed. TODGA has shown good selectivity between REEs and other elements in solution under almost all conditions, reaching the highest distribution ratios of REEs in the aliphatic diluents, while the distribution ratios of other non-REEs reach a mere value of 0.1. An exception was cyclohexanone, which has the ability to extract small amounts of ions itself. The highest separation factors between Dy and the light REEs (Nd and Pr) were observed with a 0.01 M solution of TODGA in Solvent 70. REEs, as group, were extracted with 0.1 M solutions of TODGA in all diluents except for cyclohexanone, which led to extraction of Al and B at amounts greater than 10%. Stripping with over 98% efficiency was achieved using MQ water in one step

Preparation of Chromium doped uranium nitride via Sol-Gel and Carbothermic reduction

Uranium nitride (UN) has been proposed as an accident tolerant fuel due to its enhanced thermal properties compared to the standard UO2. However, due to its low oxidation resistance, its implementation in water cooled reactors has not been allowed. A method to improve the corrosion resistance involves doping with oxide scale forming elements such as aluminum or chromium. In this work, UN microspheres were produced by an internal gelation method followed by carbothermic reduction and nitridation. Chromium was added as dopant in the solution to produce a homogenous mixture with uranium. The ternary phase (U2CrN3) was observed for the first time in Cr-doped UN microspheres produced via sol-gel and carbothermic reduction. Materials with and without the ternary phase were produced, and a mechanism of reaction was proposed. Chromium precipitations were also observed on the surface of the microspheres produced, indicating low solubility of Cr compounds in the UN matrix. ICP-MS and XRF measurements showed that Cr content is reduced after heating treatments, probably due to evaporation. Additionally, these results showed that Cr in the ternary phase is completely soluble in aqua regia, unlike the Cr in the material without the ternary phase

Application of SPS in the fabrication of UN and (U,Th)N pellets from microspheres

In this study, the process involved in the fabrication of a potential accident tolerant fuel is described. Homogeneous uranium nitride microspheres doped with different thorium content were successfully manufactured using an internal gelation process followed by carbothermic reduction, and nitridation. Elemental analysis of the materials showed low carbon and oxygen content, the two major impurities found in the products of carbothermic reduction. Uranium nitride microspheres were pressed and sintered using spark plasma sintering (SPS) to produce pellets with variable density. Final density can be tailored by choosing the sintering temperature, pressure and time. Density values of 77–98% of theoretical density (%TD) were found. As expected, higher temperatures and pressures resulted in a denser material. Furthermore, a direct correlation between the onset sintering temperature and thorium content in the materials was observed. The change of onset temperature has been related to an increment in the activation energy for self-diffusion due to the substitution of uranium atoms by thorium in the crystal structure

Leaching and recovery of rare-earth elements from neodymium magnet waste using organic acids

Over the last decade, rare-earth elements (REEs) have become critical in the European Union (EU) in terms of supply risk, and they remain critical to this day. End-of-life electronic scrap (e-scrap) recycling can provide a partial solution to the supply of REEs in the EU. One such product is end-of-life neodymium (NdFeB) magnets, which can be a feasible source of Nd, Dy, and Pr. REEs are normally leached out of NdFeB magnet waste using strong mineral acids, which can have an adverse impact on the environment in case of accidental release. Organic acids can be a solution to this problem due to easier handling, degradability, and less poisonous gas evolution during leaching. However, the literature on leaching NdFeB magnets waste with organic acids is very scarce and poorly investigated. This paper investigates the recovery of Nd, Pr, and Dy from NdFeB magnets waste powder using leaching and solvent extraction. The goal was to determine potential selectivity between the recovery of REEs and other impurities in the material. Citric acid and acetic acid were used as leaching agents, while di-(2-ethylhexyl) phosphoric acid (D2EHPA) was used for preliminary solvent extraction tests. The highest leaching efficiencies were achieved with 1 mol/L citric acid (where almost 100% of the REEs were leached after 24 h) and 1 mol/L acetic acid (where >95% of the REEs were leached). Fe and Co—two major impurities—were co-leached into the solution, and no leaching selectivity was achieved between the impurities and the REEs. The solvent extraction experiments with D2EHPA in Solvent 70 on 1 mol/L leachates of both acetic acid and citric acid showed much higher affinity for Nd than Fe, with better extraction properties observed in acetic acid leachate. The results showed that acetic acid and citric acid are feasible for the recovery of REEs out of NdFeB waste under certain conditions

Mercury Removal from Concentrated Sulfuric Acid by Electrochemical Alloy Formation on Platinum

Mercury is a highly toxic heavy metal, and improved removal processes are required in a range of industrial applications to limit the environmental impacts. At present, no viable removal methods exist commercially for mercury removal of aqueous solutions at high acidic conditions, such as concentrated sulfuric acid. Herein, we show that electrochemical mercury removal based on electrochemical alloy formation on platinum, forming PtHg4, can be used to remove mercury from concentrated sulfuric acid. Thin platinum film electrodes and porous electrodes with supported platinum are used to remove more than 90% of mercury from concentrated acid from a zinc smelter with an initial mercury concentration of 0.3-0.9 mg/kg, achieving high-quality acid (<0.08 mg/kg) within 80 h. The removal process is carried out in 50 mL laboratory-scale experiments and scaled up to a 20 L pilot reactor with retained removal efficiency, highlighting excellent scalability of the method. In addition, the removal efficiency and stability of different electrode substrate materials are studied to ensure high-quality acid and a long lifetime of the electrodes in harsh chemical conditions, offering a potential method for future large-scale mercury decontamination of sulfuric acid

A MOOC in Nuclear- and Radio-Chemistry: from the design to the feedback

Recently, the loss of expertise in the nuclear- and radio-chemistry (NRC) is becoming an issue of concern, because of few engaging curricula and career prospects. To counteract this trend, the Massive Open Online Course “Essential Radiochemistry for Society” has been developed with the intent of letting young students in scientific matters discover all the benefits of NRC to society and improving their awareness of these disciplines. The MOOC development process as well as the feedbacks collected in the first MOOC editions are analyzed by highlighting strong points and weakness of the followed strategy

The influence of Diluents and Side Groups of the Ligands on Liquid-Liquid Extraction of Actinides and Lanthanides

Fossil fuels are no longer a choice for energy production, both because of their diminishing availability and the bi-products of their combustion processes. A possibility to replace the fossil fuels would be utilization of nuclear power. No green-house gases are produced, but as any industry, it generates wastes.A proper plan for reusing valuable nuclides, both by preparing another kind of fuel or by transmutation, which, besides transforming the long-lived nuclides into short-lived ones, generates energy, seem to be P&T (partitioning and transmutation).The partitioning is the process of separation nuclides from the rest of the waste and involves a separation process which utilize an organic solvent containing one or several molecules and a diluent for extraction purposes.Among the last extractant families developed in Europe, 6,6’-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-benzo[1,2,4]triazin-3-yl)-[2,2’]bipyridine (BTBP) is the most promising molecule for an eventual industrial application. The present work focuses on several aspects insufficiently studied before and concerns strictly the BTBP family. The importance of the diluents regarding both the extraction capabilities of the formed system and the role of the diluents in protecting the molecule against radiolysiswithout adding a scavenging molecule will be discussed. The importance of the side groups added to the molecule first to facilitate dissolution, easing the phase transfer and thus enhancing the extraction capabilities and the role the side groups, in protecting the molecule against the radiolysis will also be discussed.Keywords: liquid-liquid extraction, Am, Eu, radionuclides, irradiation, side group, diluents