8,381 research outputs found

    Hyperstructures in Chemical Hyperstructures of Redox Reactions with Three and Four Oxidation States

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    Hyperstructures find numerous applications across various disciplines. One notable application is in chemistry, particularly in the context of chemical reactions. In 2014, Davvaz introduced the concept of bi-hyperstructures, but their application specifically in chemical reactions, has yet to be thoroughly explored in previous studies. Thus, the primary aim of this paper is to examine and analyze the different types of bi-hyperstructures present within chemical hyperstructures. The scope of this study focuses on two types of chemical hyperstructures: redox reactions and reactions in electrochemical cells. Within these chemical hyperstructures, we investigate the possibility of bi-hyperstructures among bi-semihypergroups, bi-hypergroups, bi-H_v-semigroups, and bi-H_v-groups. Next, some properties of bi-hyperstructures related to hyperstructures are also investigate

    Understanding the Chemistry of Acetohydroxamic Acid (AHA) in the Presence of Fe(III) in the Context of an Advanced PUREX Process

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    Since the 1950s, the majority of operating commercial nuclear fuel reprocessing plants, including those in the UK, France, Russia and Japan, have used the well-proven hydrometallurgical PUREX (plutonium uranium extraction) process, or a variant PUREXbased process to chemically separate uranium (U) and plutonium (Pu) from used nuclear fuel. However, enhancements to PUREX are needed for future fuel cycles to improve its proliferation resistance, its capability to handle higher burnup fuels and to minimize its waste arisings. A key objective within the development of an Advanced PUREX process is the effective control of the actinides U, neptunium (Np) and Pu within a single cycle flowsheet. Simple hydroxamic acids such as acetohydroxamic acid (AHA) have the ability to strip Pu(IV) and Np(IV) from tri-butyl phosphate into nitric acid and have thus been identified as suitable reagents for this purpose. Utilising this in an Advanced PUREX process will ultimately allow for the generation of a co-processed Pu/Np product and a high purity U product, addressing some of the shortcomings of traditional PUREX. There are however a few key knowledge gaps that must be addressed before AHA can be implemented in such a process. Firstly, it is known that simple hydroxamic acids hydrolyse to hydroxylamine (NH2OH) and the parent carboxylic acid in acidic media, the former product being known to react autocatalytically / explosively with nitric acid which is ubiquitous in reprocessing flowsheets. Whether the reaction mechanism or product distribution changes when the AHA is complexed to a metal ion is unclear. Additionally, observations that Pu(IV) is reduced to Pu(III) during complex hydrolysis have opened up the possibility of their use as replacements for U(IV)/N2H4 or NH2OH in advanced PUREX processes, but whether the reducing agent is the hydroxamate itself, or NH2OH, is still in question. To answer these questions, Fe(III) has been used as a non-active analogue to Pu(IV) and Np(IV), as it exhibits analogous complexation with AHA and whilst thermodynamically possible, redox chemistry mechanistically analogous to that of Pu(IV) is thought to be kinetically hindered at high hydrogen ion concentrations to the point where it can be ignored on the timescales of AHA hydrolysis. However, initial studies by Raman spectroscopy showed identical AHA hydrolysis products in the absence and presence of initial Fe(III), but with differing final yields. Further quantification techniques were then explored including a titrimetric method for hydroxylamine, UV-Vis spectroscopy for nitrous acid and Fe(II), and ion chromatography (IC) for multiple species, all of which suggested redox chemistry akin to Pu(IV). A library of data to describe these systems has been gathered utilising a single column ion chromatography system to measure a number of key ions over time in nitric acid solutions of varying temperatures and initial Fe(III) and AHA concentrations. These key species include the acetate ion (CH3COO- ) and protonated hydroxylamine (NH3OH+) from the hydrolysis of AHA, and the reduced form of the metal ion, Fe(II), which has been not previously been seen during hydrolysis of the Fe(III)-AHA complex. Our analysis therefore shows that the current definition of Fe(III) as a non-oxidizing metal ion with regards to AHA needs revising. Using CH3COOingrowth as a direct measure of AHA loss and assuming redox chemistry of Fe(III) mechanistically analogous to Pu(IV), these studies have additionally been combined with kinetic modelling in the software platform gPROMS (General PROcess Modelling System), and have thus provided key insights into the nature of the reducing agent in these systems

    Cyclic Imide Dioximes as Practical Extractants of Vanadium from Complex Mixtures

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    This thesis focuses on the development of an acid-stable chelating agent for the facile and selective extraction of pentavalent vanadium ions, V(V), from mixed metal solutions. Two cyclic imide dioxime-based ligands, phthalimidedioxime (H2CIDII) and naphthalimidedioxime (H2CIDIII), were initially evaluated for stability, scalability, and coordination to V(V). Interestingly, H2CIDIII exhibited strong coordination with V(V) and was further investigated for V(V) extraction. The six-chapter thesis discusses the essential factors for transitioning material and technology from laboratory scale to practical application. Chapter One reviews conventional V(V) extraction technologies, emphasizing the environmental impacts and limitations of current and emerging methods. The chapter introduces cyclic imide dioximes and oil sands tailings as potential materials and source for V(V) extraction. Chapter Two delves into H2CIDIII's development, evaluating scalability, stability, and toxicity using advanced spectroscopic techniques and toxicity assays. Chapter Three highlights H2CIDIII's effectiveness in V(V) recovery, achieving complete complexation in 45 minutes and instant precipitation through pH adjustment. With an extraction capacity of 205.4 mg/g, H2CIDIII ranks among the top 2% in effectiveness. Selective precipitation of the V(V)-CIDIII complexes was achieved in acidic conditions and attributed to the formation of unique and acid stable vanadium complexes. H2CIDIII was easily regenerated for multiple extraction cycles, and the extraction process was optimized and tested with simulated and real oil sands tailings. Chapter Four explores the extraction mechanism through X-ray diffraction, NMR, FTIR, and DFT calculations, revealing the pivotal roles of the negative charge and acid resistance of V(V)-CIDIII complexes in the separation and recovery of V(V). The formation of a non-oxido vanadium complex illustrates the strong interaction between V(V) and H2CIDIII, explaining its high affinity during the extraction process. Chapter Five investigates the binding constants and coordination modes of the ligands and metal ions, further highlighting H2CIDIII's higher affinity for V(V). The final chapter explores potential applications of recovered V(V) and its complexes in redox batteries and epoxidation reactions. A provisional patent has been filed, and a manuscript is undergoing final revisions for publication in Nature Communications, underscoring the project's potential impact

    Actinide Triamidoamine (Tren<sup>R</sup>) Chemistry:Uranium and Thorium Derivatives Supported by a Diphenyl鈥恡ert鈥怋utyl鈥怱ilyl鈥怲ren Ligand

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    We report the synthesis and characterisation of thorium(IV), uranium(III), and uranium(IV) complexes supported by a sterically demanding triamidoamine ligand with N-diphenyl-tert-butyl-silyl substituents. Treatment of ThCl4(THF)3.5 or UCl4 with [Li3(TrenDPBS)] (TrenDPBS = {N(CH2CH2NSiPh2But)3}3-) afforded [An(TrenDPBS)Cl] (An = Th, 1Th; U, 1U). Complexes 1An react with benzyl potassium to afford the cyclometallates (TrenDPBScyclomet) [An{N(CH2CH2NSiPh2But)2(CH2CH2NSiPhButC6H4)}] (An = Th, 2Th; U, 2U). Treatment of 1An with sodium azide affords [An(TrenDPBS)N3] (An = Th, 3Th; U, 3U). Reaction of 3Th with potassium graphite affords 2Th. In contrast, 3Th reacts with cesium graphite to afford the doubly-cyclometallated (TrenDPBSd-cyclomet) ate complex [Th{N(CH2CH2NSiPh2But) CH2CH2NSiPhButC6H4)}2Cs(THF)3] (4). In contrast to 3Th, reaction of 3U with potassium graphite produces the uranium(III) complex [U(TrenDPBS)] (5), and 5 can also be prepared by reaction of potassium graphite with 1U. The loss of azide instead of conversion to nitrides contrasts to prior work when the silyl group is iso-propyl silyl, underscoring how ligand substituents profoundly drive the reaction chemistry. Several complexes exhibit T-shaped meta-C-H路路路phenyl and staggered parallel p-p-stacking interactions, demonstrating subtle weak interactions that drive ancillary ligand geometries. Compounds 1An-3An, 4, and 5 have been variously characterised by single crystal X-ray diffraction, multi-nuclear NMR spectroscopy, infrared spectroscopy, UV/Vis/NIR spectroscopy, and elemental analyses

    Predominance of the alkaline earth (II) triscarbonatoactinyl (VI) complexes in different geochemical contexts: Review of existing data and estimation of potentially unidentified species

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    International audienceFrom the available thermodynamic data in the literature, a review of the impact of the formation of complexes between triscarbonatoactinyl(VI) and alkaline earth(II) (Ae) is estimated under varying conditions. First, using the ascertained thermodynamic data available from the commissioned reviews from the Nuclear Energy Agency (Organization for the Economic Cooperation and Development) Thermochemical DataBank Project on actinides (An) U, Np, and Pu, and from recently determined Aen_nUO2_2(CO3_3)3_3(42n)^{(4-2n)-} thermodynamic functions, the formation of Aen_nUO2_2(CO3_3)3_3(42n)^{(4-2n)-} complexes for Pu(VI) and Np(VI) are estimated using linear free energy relationships (LFERs). The data are in good agreement with the sole determination of AePuO2_2(CO3_3)3_32^{2-} from Jo et al. (Dalton Trans. 49, 11605), which gives a relative confidence in the LFERs, and allows the application to actual situations. From existing uranium data, first, the impact of the origin of the data on the calculated predominance is addressed under 0.1 M NaCl and atmospheric CO2_2(g); second, the influence of ionic strength and salinity on predominance is estimated; and finally, the influence of temperature up to 50 掳C on the solubility of uraninite in a deep geological radioactive waste storage or disposal site is calculated. For neptunium and plutonium, the impact of the potential log10_{10}\beta掳(Aen_nUO2_2(CO3_3)3_3(42n)^{(4-2n)-}) on Pourbaix diagrams of Pu and Np in Mg-Ca-CO3_3 media are estimated from Jo et al. (Dalton Trans. 49, 11605) and LFERs. Finally, the application to the speciation of Pu and Np in seawater is proposed

    Activating Methane and Other Small Molecules: Computational study of Zeolites and Actinides

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    Exploring the catalytic properties and reactivity of actinide complexes towards activation of small molecules is important as human activities have led to the increased distribution of these species in nature. Toward this end, it is important to have a computational protocol for studying these species, in this thesis we provide details on the performance of multiconfigurational pair-density functional theory (MC-PDFT) in actinide chemistry. MC-PDFT and Kohn-Sham Density Functional Theory (KS-DFT) perform well for these species with indications that the former can be used for species with even greater static electron correlation effect. In addition, we study the activity of organometallic trans-uranium complexes towards the electrocatalytic reduction of water. We conclude that, with a guided choice of ligand, neptunium complexes can provide similar reactivity when compared to organometallic uranium complexes.Conversion of methane to methanol has been a major focus of research interest over the years. This is largely due to the abundance of natural gas, of which methane is the major constituent. Copper-exchanged zeolites have been shown to be able to kinetically trap activated methane as strongly-bound methoxy groups, preventing over-oxidation to CO2, CO and HCOOH. In this stepwise process, there are three cycles; an initial activation step to form the copper oxo active site, methane C-H activation and lastly simultaneous desorption of methanol and re -activation of the active site.. We provide detailed description of the pathway for the formation of over oxidation products. It is observed that to ensure high selectivity to methanol and prevent further hydrogen atom abstraction by extra-framework species, the methyl group must be stabilized from the copper-oxo active sites. There is a temperature gradient between the steps in the methane-to-methanol conversion cycle which is an impediment to industrial adoption of this approach for methane-to-methanol conversion. To mitigate this, we have investigated the impact of heterometallic extra-framework motifs on the temperature gradients of each step. Using periodic DFT, we provide detailed descriptions of the mechanistic pathways for each of the three steps. We were subsequently able to design motif(s) with great methane C-H activities as well as the abilities to be formed and regenerated at nearly the same temperatures. We found [Cu-O-Ag] and [Cu-O-Pd] to be potential candidates for isothermal or near-isothermal operations of the methane-to-methanol conversion cycle. Finally, we provide insights to the changes in optical spectra of activated copper-exchanged zeolites, gaining an understanding of the evolution of these systems on a molecular level will provide opportunities to achieve improved reactivity

    First measurements of p11B fusion in a magnetically confined plasma

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    Proton-boron (p11B) fusion is an attractive potential energy source but technically challenging to implement. Developing techniques to realize its potential requires first developing the experimental capability to produce p11B fusion in the magnetically-confined, thermonuclear plasma environment. Here we report clear experimental measurements supported by simulation of p11B fusion with high-energy neutral beams and boron powder injection in a high-temperature fusion plasma (the Large Helical Device) that have resulted in diagnostically significant levels of alpha particle emission. The injection of boron powder into the plasma edge results in boron accumulation in the core. Three 2 MW, 160 kV hydrogen neutral beam injectors create a large population of well-confined, high -energy protons to react with the boron plasma. The fusion products, MeV alpha particles, are measured with a custom designed particle detector which gives a fusion rate in very good relative agreement with calculations of the global rate. This is the first such realization of p11B fusion in a magnetically confined plasma

    Solidification/stabilization technology for radioactive wastes using cement: an appraisal

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    Across the world, any activity associated with the nuclear fuel cycle such as nuclear facility operation and decommissioning that produces radioactive materials generates ultramodern civilian radioactive waste, which is quite hazardous to human health and the ecosystem. Therefore, the development of effectual and commanding management is the need of the hour to make certain the sustainability of the nuclear industries. During the management process of waste, its immobilization is one of the key activities conducted with a view to producing a durable waste form which can perform with sustainability for longer time frames. The cementation of radioactive waste is a widespread move towards its encapsulation, solidification, and finally disposal. Conventionally, Portland cement (PC) is expansively employed as an encapsulant material for storage, transportation and, more significantly, as a radiation safeguard to vigorous several radioactive waste streams. Cement solidification/stabilization (S/S) is the most widely employed treatment technique for radioactive wastes due to its superb structural strength and shielding effects. On the other hand, the eye-catching pros of cement such as the higher mechanical strength of the resulting solidified waste form, trouble-free operation and cost-effectiveness have attracted researchers to employ it most commonly for the immobilization of radionuclides. In the interest to boost the solidified waste performances, such as their mechanical properties, durability, and reduction in the leaching of radionuclides, vast attempts have been made in the past to enhance the cementation technology. Additionally, special types of cement were developed based on Portland cement to solidify these perilous radioactive wastes. The present paper reviews not only the solidification/stabilization technology of radioactive wastes using cement but also addresses the challenges that stand in the path of the design of durable cementitious waste forms for these problematical functioning wastes. In addition, the manuscript presents a review of modern cement technologies for the S/S of radioactive waste, taking into consideration the engineering attributes and chemistry of pure cement, cement incorporated with SCM, calcium sulpho鈥揳luminate-based cement, magnesium-based cement, along with their applications in the S/S of hazardous radioactive wastes