L'acide nitrique est largement utilisé dans le procédé de retraitement du combustible nucléaire usé, le procédé PUREX (Plutonium and Uranium Refining by EXtration). Ce procédé est fondé sur l'extraction liquide-liquide de l'uranium et du plutonium aux degrés d'oxydation (+VI) et (+IV) respectivement. Le plutonium est ensuite désextrait, et ainsi séparé de l'uranium par ajout d'uranium (+IV) stabilisé en milieu acide nitrique par des ions hydrazinium (N2H5+). Or, la radiolyse de l'acide nitrique, inhérente à la présence d'émetteurs α dans ces solutions, génère des espèces radicalaires et moléculaires susceptible de modifier, d'une part, le comportement redox des actinides et, d'autre part, de réagir avec les ions hydrazinium. Le but de ce travail est de mieux maîtriser les paramètres chimiques et physico-chimiques susceptibles de modifier les degrés d'oxydation de l'uranium et du plutonium dans les solutions d'acide nitrique. Parmi ces paramètres, le rôle de l'acide nitreux et du peroxyde d'hydrogène, générés par radiolyse de l'acide nitrique, est primordial. L'objectif est de repréciser les cinétiques de formation du peroxyde d'hydrogène et de l'acide nitreux par radiolyse alpha des milieux acide nitrique / nitrate de sodium en fonction des paramètres : acidité, concentration des ions nitrate et transfert d'énergie linéique du rayonnement ionisant.Il a été montré que la formation de peroxyde d'hydrogène diminue avec l'augmentation de la concentration des ions nitrate et augmente fortement avec l'acidité de la solution, jusqu'à atteindre une valeur stationnaire pour une acidité proche de 0,2 mol L-1. Pour sa part, la formation de l'acide nitreux est favorisée par l'augmentation de la concentration des ions nitrate. Il a été observé que G(HNO2) évolue selon deux tendance distincte, la première dans les solutions diluées d'ions nitrate et la seconde dans les solutions concentrées d‘ions nitrate. Ces deux variations traduisent des phénomènes radiolytiques directs et indirects modifiant les mécanismes de formation de HNO2. L'étude de l'acidité des solutions irradié a montré que la formation de H2O2 et de HNO2 est favorisé avec l'augmentation de la concentration des ions hydronium, jusqu'à atteindre une valeur stationnaire pour une acidité proche de 0,2 - 0,5 mol L-1.Par ailleurs, les effets induits par la nature du rayonnement ionisants (,,,…), sur les rendements de formation de H2O2 et HNO2, ont été étudiés. Il a été montré que le transfert d'énergie linéique (TEL), compris entre 0,2 keV µm-1 (caractéristique d'un rayonnement gamma) et 130 keV µm-1 (caractéristique d'un rayonnement alpha émis par la décroissance radioactive d'un actinide), a une influence significative sur les rendements de formation de H2O2 et de HNO2. Il a été observé que l'impact des ions nitrate sur le rendement de formation de H2O2 devient plus marqué, lorsque le TEL augmente. A contrario, l'impact des ions nitrate favorisant le rendement de formation de HNO2, diminue lorsque le TEL augmente. Sur la base des résultats acquis durant cette étude et des données présentes dans la littérature, deux équations paramétriques ont été développées. L'intérêt de cette paramétrisation des effets est de prédire les rendements radiolytiques de formation de H2O2 et de HNO2 selon les conditions chimique du milieu ([NO3-] ≤ 4 mol L-1 et 10-5 mol L-1 ≤ [H+] ≤ 4 mol L-1) et selon la nature du faisceau (TEL compris entre 0,2 – 130 keV µm-1).La finalité de cette étude serait de prédire les quantités de H2O2 et de HNO2 formés par radiolyse de HNO3/NaNO3 dans les étapes du procédé de retraitement des combustibles nucléaires. / Nitric acid is widely used in spent nuclear fuel reprocessing, especially in PUREX process (Plutonium and Uranium Refining by Extraction). This process is based on liquid-liquid extraction of Uranium (+VI) and Plutonium (+IV). Plutonium is separated from Uranium by addition of Uranium (+IV) in nitric acid, stabilized by hydrazinium ion (N2H5+). However, the radiolysis of nitric acid, result of the presence of alpha emitting radionuclides, generates in solutions free radicals and molecular species. These species are capable of modifying the redox state of actinides and reacting with hydrazinium ions.The aim of this work is to reveal the chemical and physical-chemical parameters that may modify the oxidation states of Uranium and Plutonium in nitric acid solutions. Among these parameters, the role of nitrous acid and hydrogen peroxide, generated by radiolysis of the nitric acid, is very important. The objective is to redefine the kinetics of formation of hydrogen peroxide and nitrous acid during alpha radiolysis of nitric acid / sodium nitrate, as a function of three parameters: acidity, nitrate concentration and the linear energy transfer of ionizing radiation.It was shown that the formation of hydrogen peroxide decreases with increasing nitrate ions concentration and increases greatly with the acidity of the solution (until it reaches a stationary value for an acidity of 0.2 mol L-1). The formation of nitrous acid is promoted by the increase the nitrate ions concentration. It was observed that G(HNO2) varies according to two trends. The first one in dilute nitrate solutions and the second in concentrated nitrate solutions. These two trends reflect the direct and indirect radiolytic phenomena, modifying the mechanisms of formation of HNO2. The study of acidity has showed that the formation of H2O2 and HNO2 is promoted by increasing the concentration of hydronium ions, until it reaches a steady state value for an acidity close to 0.2-0.5 mol L-1.Furthermore, the effects induced by ionizing radiation (,,,…) on formation yields of H2O2 and HNO2 were studied. It has been shown that the linear energy transfer (LET), between 0.2 keV µm-1 (characteristic of a gamma radiation) and 130 keV µm-1 (characteristic of the alpha radiation emitted by radioactive decay of actinides), has a significant influence on formation yield of H2O2 and HNO2. It was observed that the impact of nitrate ions on the formation yield of H2O2 becomes more pronounced when the LET increases. Conversely, the impact of nitrate ions which promote the formation of HNO2, decreases when the LET increases.Based on these results, two parametric equations were developed. The advantage of this parameterization is to predict the radiolytic yields formation of H2O2 and HNO2 according to chemical conditions ([NO3-] ≤ 4 mol L-1 and 10-5 mol L-1 ≤ [H+] ≤ 4 mol L-1) and the nature of the beam (LET between 0.2 to 130 keV µm-1).The purpose of this study is to predict the quantity of H2O2 and HNO2 formed by radiolysis of HNO3/NaNO3, during the different steps of the nuclear fuel reprocessing.

Accurate measurements of ammonia, nitric acid and formic acid are important for achieving a complete understanding of their atmospheric role. Models and measurements of formic acid in the atmosphere continue to show disagreements. Also, the contributions of NMHCs and reactive nitrogen (HNO3 and NH3) to organic and inorganic aerosol formation are important to quantify as gaps in the knowledge of atmospheric aerosols are a source of uncertainty in climate science. In this thesis, concentrations of ammonia were measured in the atmosphere and the production of formic acid from the ozonolysis of isoprene was measured in the EXTRA (EXTreme RAnge) chamber. Both gases were studied using chemical ionisation mass spectrometry (CIMS). The kinetics of the reactions of sesquiterpenes and terminal alkenes with ozone were studied in theEXTRA chamber using the relative rates technique and GC-FID. The ozonolysis rate coefficients of a homologous series of terminal alkenes were measured at elevated temperatures and found to be invariant with the carbon number. This led to the conclusion that previous measurements of these rate coefficients were subject to experimental artefacts. The elevated temperature protocol was employed to study the ozonolysis of sesquiterpenes, leading to revisions in ko3 for β-caryophyllene and α-humulene of 3 orders of magnitude. It was thus concluded that ozonolysis only accounts for 9-15% of sesquiterpeneoxidation in the atmosphere. A field intercomparison of CIMS for measuring ammonia was conducted wherein CIMS was found to perform well alongside instruments of comparable time response and limits of detection. This thesis also characterised inlet materials used in atmospheric measurements in the first systematic study on the uptake onto inlet walls in a flow tube system coupled to CIMS. It was found that PFA is the preferable material for atmospheric measurements, both for its kinetic qualities and its ready availability and ease of use. Finally, CIMS was used to measure the yield of formic acid from isoprene ozonolysis as a function of relative humidity. Formic acid yield was found to increase between 0-40% RH to a maximum of 0.18. Using the measured formic acid yields in a global chemistry model leads to an estimate that formic acid production from isoprene ozonolysis is ~9.5 Tg yr-1.

In recent years, nanostructured materials incorporated with inorganic particles and polymers have attracted attention for simultaneous multifunctional biomedical applications. This thesis summarized three works, which are preparation of mesoporous silica coated superparamagnetic iron oxide (Fe3O4@mSiO2) nanoparticles (NPs) as magnetic resonance imaging T2 contrast agents, polymer grafted Fe3O4@mSiO2 NPs response to temperature change, synthesis and biocompatibility evaluation of high aspect ratio (AR) gold nanorods. Monodisperse Fe3O4@mSiO2 NPs have been prepared through a sol-gel process. The coating thickness and particle sizes can be precisely controlled by varying the synthesis parameters. Impact of surface coatings on magnetometric and relaxometric properties of Fe3O4 NPs is studied. The efficiency of these contrast agents, evaluated by MR relaxivities ratio (r2/r1), is much higher than that of the commercial ones. This coating-thickness dependent relaxation behavior is explained due to the effects of mSiO2 coatings on water exclusion. Multifunctional core-shell composite NPs have been developed by growing thermo-sensitive poly(N-isopropylacrylamide-co-acrylamide) (P(NIPAAm-co-AAm)) on Fe3O4@mSiO2 NPs through free radical polymerization. Their phase transition behavior is studied, and their lower critical solution temperature (LCST) can be subtly tuned from ca. 34 to ca. 42 °C, suitable for further in vivo applications. A seedless surfactant-mediated protocol has been applied for synthesis of high AR gold nanorods with the additive of HNO3. A growth mechanism based on the effect of nitrate ions on surfactant micelle elongation and Ostwald ripening process is proposed. The biocompatibility of high AR nanorods was evaluated on primary human monocyte derived dendritic cells (MDDCs). Their minor effects on viability and immune regulatory markers support further development for medical applications. / QC 20110701

<p dir="ltr">Since before the Apollo era, the rocket propulsion sector has been a key player in developing standards of cleanliness and compatibility when designing, building, and operating systems with toxic propellants. The advent of hypergols and the widespread use of propellants like N₂O₄, Mixed Oxides of Nitrogen (MON), and hydrazine have forced new standards to be developed to meet the ever-growing need for safety when working with dangerous substances. These systems have only continued to grow more complex and many propellant combinations remain toxic and corrosive to most substances as the industry seeks the optimal methods for deriving the most efficient, highest performing, and generally more capable. ASTM International and other standards organizations carry on documenting standards for cleaning and passivation to ensure safe use today to meet the needs of the ever-expanding propulsion industry.</p><p dir="ltr">This thesis aims to determine the feasibility of using Raman spectroscopy as a method of characterizing interactions between metals and propellants. First, a background of knowledge regarding the spectroscopic method, propellants, and industry practices was researched and current areas of possible application were identified. The passivation and propellant storage phases of system lifecycles were determined to be the scope and target for experimentation. A multilevel passivation study consisting of exposing three metal types to different concentrations of nitric acid for various durations was conducted to begin developing a greater understanding of the applicability of and the techniques required to make Raman spectroscopy work as a complement to the ASTM passivation verification tests. Lessons learned from this and a short-duration compatibility study with MON and similar metal samples were documented and will be used for a larger scale and longer duration compatibility study in conjunction with NASA White Sands Test Facility (WSTF). The buildup of safe and adequate facilities for such a study was undertaken, completed, and documented in this work.</p><p dir="ltr">The results of testing in this thesis suggest the promising and desirable non-destructive and minimally invasive features of Raman spectroscopy have the potential to be used extensively in the propulsion sector. Suggestions for developing key techniques and methods for this application are developed and outlined as they were learned throughout the study's conduction.</p>

No description available.

Objective: Twenty-two million Americans or roughly 8% of the population are hearing impaired. This affects more than just the ability for one to hear. In the last three decades, younger Americans have shown a sharp increase in hearing impairment. Hearing loss affects social and emotional well being and thus has the ability to decrease one's quality of life. This study was designed to examine the association between smoking, workplace chemical exposure, and hearing loss.Methods: This cross-sectional population-based study was conducted in an occupational health clinic setting in Virginia. The study population consisted of employees from local businesses who visited the clinic during the period of 1/1/03 to 1/1/05 for pure tone audiometry. Chart reviews supplemented by telephone interviews were conducted to extract data for analysis. All study subjects were eligible to participate except for those who were unable to communicate due to a language barrier. Prevalence and crude prevalence ratios were calculated. Adjusted prevalence ratios and prevalence odds ratios were calculated using Cox and logistic regression models. Data entry and statistical analysis were accomplished with the SPSS Data Builder and the SPSS 13.0 statistical software. SAS statistical software was also used for a portion of the statistical analysis.Results: In a Cox regression model controlling for many potential confounding factors (age, race, smoking, chemical exposure, military service, as well as others) cigarette smoking was not associated with hearing loss PR(95% CI), 1.0 (0.7, 1.3). Similarly, exposure to chemicals was not associated with hearing loss 1.1 (0.7, 1.6).Conclusion: This study did not find an association between cigarette smoking and hearing loss and exposure to industrial chemicals and hearing loss in persons who worked in a noisy occupational environment.

O processo Humifert é uma alternativa para produção de compostos fertilizantes fosfatados, com solubilização mais lenta do que os fertilizantes tradicionais, resultando em um tempo de nutrição da planta maior. No processo, utilizam-se rochas fosfáticas com algum tipo de limitação para o aproveitamento normal, seja pelos teores menores, seja por dificuldades de tratamento industrial dos minérios, além de materiais orgânicos. O objetivo deste trabalho foi melhorar o equipamento existente no Instituto de Geociências, para tornar possível condições de produção de NOx, no Processo Humifert, capaz de produzir um teor de fósforo disponibilizado em condições controladas de processo. Empregando-se planejamento estatístico de experimentos foi possível selecionar as variáveis de entrada mais importantes ao processo (agitação da mistura de rocha fosfática, matéria orgânica e umidade, A codificada; temperatura de oxidação da amônia, B codificada; umidade da mistura, C codificada; porosidade da placa difusora, D codificada; vazão do ar auxiliar, E codificada). A análise estatística, também, permitiu construir modelos de regressão nos quais as influências das variáveis de processo foram sentidas na solubilidade do fósforo nos extratores: ácido cítrico, solução 2% (Pácido cítrico); água, (Págua); citrato neutro de amônio mais água, (PCNA+água). Estas últimas variáveis aqui denominadas de variáveis de saída ou de resposta. A manipulação dos referidos modelos permite obter o fertilizante de acordo com as necessidades da cultura e do solo. O estudo, também, permitiu concluir que a maior quantidade de fósforo disponível nos compostos organofosfatados foi o solúvel em ácido cítrico, portanto, a maior quantidade de compostos gerados encontra-se na melhor condição de disponibilidade pela planta. / Humiphert process is an alternative used for producing phosphated compound fertilizers with a slower solubilization when compared to other traditional fertilizers, resulting in a longer period of plant nutrition. During the process, phosphatic rocks are used along with some sort of limitation according to the normal development, both by their lower content percentage and by treatment of difficulties of industrial ores, besides organic materials. This work aim to improve an equipment existing at the Instituto de Geociências in order to find out the best process condition to produce NOX in Humifert process. This way, the process is able to produce an available phosphorus content under process conditions controlled. The process variables were select by using of experimental design. These variables were: agitation of phosphatic rock mixture (rock, organic material and humidity), A coded; ammonia oxidation temperature, B coded; humidity of mixture, C coded; porosity of the diffusing board, D coded; auxiliary air, E coded. Statistical analysis also allowed to build regression models in which the influences of process variables were felt in the solubility of phosphorus in the extractors: 2% solution of citric acid (Pacid Citric), water (Pwater); ammonium neutral citrate plus water (PCNA + water). These last variables here called output variable or response. The manipulation of these models allows to obtain the fertilizer according to the needs of the crop and soil. The study still conclude that the greater amount of available phosphorus in compound was soluble in citric acid, therefore, a greater amount of compounds generated is in the best condition of availability for the plant. The study still conclude that the greater amount of available phosphorus in the organophosphated compounds were soluble in citric acid. Therefore, the greater amount of compounds generated is in the best condition of availability for the plant.

Bio-refining of renewable resources such as waste biomass into value added products has increased rapidly over the last decades. The aim is to find new environmentally friendly yet economically feasible ways of replacing current utilization of non renewable resources. It can be expected that a commercially viable next generation bio-ethanol will be produced from lignocellulosic feedstock in the near future.This master thesis set out to look at a specific Canadian company in depth (Pure Lignin Environmental Technology Ltd), known as PLET henceforth. PLET has a new approach in pre-treatment of biomass, with a recently patented environmentally friendly technology, which could be extremely lucrative if applied in the right context. It is desirable to look at the possibility of using the master thesis as a take-off platform to launch a consulting bio-tech company directly after completion.There are several different ways to process biomass into higher value added products. In this master thesis focus is laid upon biomass waste, but the same principles could be applied on biomass processing in general. That is the separation and purification of products. In order to put the technology of PLET into a context, other company approaches are used as a comparison, such as SEKAB E-Technology, Lignoboost and Borregaard Lignotech.It is however hard to find suitable examples equivalent to the PLET approach since the technology of PLET considers all the three constituents of wood as raw material for production of three stand alone commercial products; pure lignin, pure cellulose and hemi-cellulose. These three products are separated and purified in the pre-treatment process at high yield and practically no formation of by-products. Process parameters are only moderately adjusted depending on what raw material is used.The catalytic reactor process (=CRP), is performed by PLET as a pre-treatment in a continuous and batch system, in which lignocellulosic material (= wood chips, saw dust or other waste biomass) undergo acid catalyzed hydrolysis by dilute nitric acid. The impregnated wood chips are partially depolymerised from the lignin matrix when heated in the low pressure catalytic reactor. After that, follows distillation, condensation and almost complete recovery of dilute nitric acid. After CRP, the cellulose pulp is separated from the black liquor by an alkaline solution (=NaOH). The obtained black liquor is pumped to a separation tank to precipitate lignin and sweet liquor through filtration. The final step is to dry the lignin, while the sweet liquor is utilized by Torula yeast (=Candida utilis) in order to produce unicellular protein.It would be interesting to see if the pre-treatment that PLET provides, could be exploited in a context of production of next generation of cellulosic ethanol from the cellulosic part of waste biomass. In this master thesis, an evaluation of producing next generation ethanol from dilute-nitric acid pre-treated cellulose rich softwood was performed and dilute sulphuric acid pre-treated hemi-cellulose rich hardwood birch pulp was used as a comparison.The technical part of this master thesis was conducted on a laboratory scale, using samples from two companies, referred to as PLET and SEKAB E-technology (Sweden). The strategy of PLET is currently to find a commercial platform to produce value added products from waste biomass generated by saw mills and pulping industries, while SEKAB E-Technology mainly works with Swedish softwood as a raw material.ivExperiments of this master thesis includes a series of fermentation trials using either SSF (= Simultaneous Saccharification and Fermentation) or SHF (= Separate Hydrolysis and Fermentation). Yields of the enzymatic hydrolysis and subsequent fermentations were estimated with HPLC measurements complemented with dry weight measurements.Obtained experimental data support the potential to make lignocellulosic ethanol out of either softwood or hardwood. Ethanol yield from dry material from SEKAB E-Technology hardwood birch slurry was 0.43 (g ethanol / g dry raw material), whereas samples supplied by PLET achieved the following results. The ethanol yield from dry material from softwood pine washed cellulose was 0.33 g (ethanol / g cellulose). The ethanol yield from dry material obtained for softwood pine unwashed cellulose in the three SHF was 0.47; 0.34 and 0.19 (g ethanol / g cellulose) respectively, while the yield in the two SSF was 0.45 and 0.46 (g ethanol / g glucose).The economical part of this master thesis includes the use of Business Model Canvas and the NABC- model (= Need, Approach, Benefit and Competition) to define the basic topics and tasks that need to be addressed in the start up phase of a small consulting bio-tech company.At least 6 million US dollars is needed as a minimum starting capital to be able to construct a small commercially viable pilot plant, according to PLET. This investment would cover the basic requirements and is scalable. The construction could preferably be done in Sweden in the vicinity of an existing saw mill or paper pulp industry or elsewhere, where a steady supply of cheap raw material could be assured. The size of the operation envisioned, depends greatly on location and adjacent businesses. Large pulp mills in the range of 400-500 MWh would be preferred, the largest pulp mills in Canada process 5000 ton per day which is equivalent to a capacity of 1 GW wood per day (GW = giga watt), but the concept of the technology of PLET must first prove its value on a smaller scale.According to PLET, a future full scale production plant could be designed for processing 56 tons of wood chips per day of wood chips would generate annual revenues of ≈ 7500000 US dollars. The annual profit would be ≈ 2500000 US dollars, and capital cost (equipments) ≈ 5000000 US dollars, while the payback time on investment would be 2-3 years. According to PLET, the products are estimated to have the following values; 25 tons/day of pure cellulose with a market value of 400-500 US dollars/ton, 10 tons/day of pure lignin with a market value of 1000-1200 US dollars/ton and finally 21 tons/day of sweet liquor with a market value of 50-100 US dollars/ton. / Program: Masterutbildning i Energi- och materialåtervinning - industriell bioteknik

O processo Humifert é uma alternativa para produção de compostos fertilizantes fosfatados, com solubilização mais lenta do que os fertilizantes tradicionais, resultando em um tempo de nutrição da planta maior. No processo, utilizam-se rochas fosfáticas com algum tipo de limitação para o aproveitamento normal, seja pelos teores menores, seja por dificuldades de tratamento industrial dos minérios, além de materiais orgânicos. O objetivo deste trabalho foi melhorar o equipamento existente no Instituto de Geociências, para tornar possível condições de produção de NOx, no Processo Humifert, capaz de produzir um teor de fósforo disponibilizado em condições controladas de processo. Empregando-se planejamento estatístico de experimentos foi possível selecionar as variáveis de entrada mais importantes ao processo (agitação da mistura de rocha fosfática, matéria orgânica e umidade, A codificada; temperatura de oxidação da amônia, B codificada; umidade da mistura, C codificada; porosidade da placa difusora, D codificada; vazão do ar auxiliar, E codificada). A análise estatística, também, permitiu construir modelos de regressão nos quais as influências das variáveis de processo foram sentidas na solubilidade do fósforo nos extratores: ácido cítrico, solução 2% (Pácido cítrico); água, (Págua); citrato neutro de amônio mais água, (PCNA+água). Estas últimas variáveis aqui denominadas de variáveis de saída ou de resposta. A manipulação dos referidos modelos permite obter o fertilizante de acordo com as necessidades da cultura e do solo. O estudo, também, permitiu concluir que a maior quantidade de fósforo disponível nos compostos organofosfatados foi o solúvel em ácido cítrico, portanto, a maior quantidade de compostos gerados encontra-se na melhor condição de disponibilidade pela planta. / Humiphert process is an alternative used for producing phosphated compound fertilizers with a slower solubilization when compared to other traditional fertilizers, resulting in a longer period of plant nutrition. During the process, phosphatic rocks are used along with some sort of limitation according to the normal development, both by their lower content percentage and by treatment of difficulties of industrial ores, besides organic materials. This work aim to improve an equipment existing at the Instituto de Geociências in order to find out the best process condition to produce NOX in Humifert process. This way, the process is able to produce an available phosphorus content under process conditions controlled. The process variables were select by using of experimental design. These variables were: agitation of phosphatic rock mixture (rock, organic material and humidity), A coded; ammonia oxidation temperature, B coded; humidity of mixture, C coded; porosity of the diffusing board, D coded; auxiliary air, E coded. Statistical analysis also allowed to build regression models in which the influences of process variables were felt in the solubility of phosphorus in the extractors: 2% solution of citric acid (Pacid Citric), water (Pwater); ammonium neutral citrate plus water (PCNA + water). These last variables here called output variable or response. The manipulation of these models allows to obtain the fertilizer according to the needs of the crop and soil. The study still conclude that the greater amount of available phosphorus in compound was soluble in citric acid, therefore, a greater amount of compounds generated is in the best condition of availability for the plant. The study still conclude that the greater amount of available phosphorus in the organophosphated compounds were soluble in citric acid. Therefore, the greater amount of compounds generated is in the best condition of availability for the plant.

Neptunium, with its rich redox chemistry, has a special position in the chemistry of actinides. With a decades-long history of development of aqueous separation methods for used nuclear fuel (UNF), management of neptunium remains an unresolved issue because of its not clearly defined redox speciation. Neptunium is present in two, pentavalent (V) and hexavalent (VI) oxidation states, both in their dioxocation O=Np=O neptunyl form, which differ greatly in their solvent extraction behavior. While the neptunium(VI) dioxocation is being very well extracted, the dioxocation of pentavalent neptunium is practically non-extractable by an organic solvent. As a result, neptunium is not well separated and remains distributed in both organic and aqueous extraction phases. The aim of this study was to develop or enhance the understanding of several key topics governing the redox behavior of neptunium in nitric acid medium, which are of vital importance for the engineering design of industrial-scale liquid-liquid separation systems. In this work, reactions of neptunium(V) and (VI) with vanadium(V) and acetohydroxamic acid - two redox agents envisioned for adjusting the neptunium oxidation state in aqueous separations ��� were studied in order to determine their kinetic characteristics, rate laws and rate constants, as a function of temperature and nitric acid concentration. Further were analyzed the interactions of neptunium(V) and (VI) with nitrous acid, which is formed as a product of radiolytic degradation of nitric acid caused by high levels of radioactivity present in such systems. Once HNO��� is distributed between both the aqueous solutions and organic solvent, nitrous acid is also formed in both phases and has a key influence on redox speciation of neptunium; therefore, the effects of gamma-radiation on the redox speciation of neptunium were investigated. The work also includes the results of examination of scavenging of nitrous acid by hydrogen peroxide, which is generated along with nitrous acid during radiolysis of aqueous solutions of nitric acid, and also by chemical reactions with added scavenging agents (methylurea, acetohydroxamic acid). / Graduation date: 2013