Increasing HNO3 Concentration Research Articles

Plutonium and Americium Alpha Radiolysis of Nitric Acid Solutions.

The yield of HNO2, as a function of absorbed dose and HNO3 concentration, from the α-radiolysis of aerated HNO3 solutions containing plutonium or americium has been investigated. There are significant differences in the yields measured from solutions of the two different radionuclides. For 0.1 mol dm-3 HNO3 solutions, the radiolytic yield of HNO2 produced by americium α-decay is below the detection limit, whereas for plutonium α-decay the yield is considerably greater than that found previously for γ-radiolysis. The differences between the solutions of the two radionuclides are a consequence of redox reactions involving plutonium and the products of aqueous HNO3 radiolysis, in particular H2O2 and HNO2 and its precursors. This radiation chemical behavior is HNO3 concentration dependent with the differences between plutonium and americium α-radiolysis decreasing with increasing HNO3 concentration. This change may be interpreted as a combination of α-radiolysis direct effects and acidity influencing the plutonium oxidation state distribution, which in turn affects the radiation chemistry of the system.

Electrochemical dissolution of Тс–Ru alloys in nitric acid solutions

Electrochemical dissolution of Тс–19 wt % Ru, Тс–45 wt % Ru, and Тс–70 wt % Ru in 1 to 6 M HNO3 solutions in the amperostatic mode was studied. In the solutions formed from anodic dissolution of Тс–Ru alloys, Ru is present in the form of Ru(IV), and Тс, in the form of Тс(VII). A kinetic study of the electrochemical dissolution of the Тс–70 wt % Ru alloy in the examined interval of HNO3 concentrations showed that the alloy dissolved congruently and the Тс(VII) and Ru(IV) accumulation in the solution linearly depended on time. Anodic dissolution of Tc–Ru alloys with lower Ru content was also characterized by a linear increase in the Тс(VII) concentration in the solution with time. On the other hand, formation of poorly soluble hydrated Ru(IV) oxide on the electrode surface was observed simultaneously with accumulation of soluble Ru(IV) species in solution. The rate of electrochemical dissolution of the Тс–70 wt % Ru alloy linearly increased with increasing HNO3 concentration. The rates of electrochemical dissolution of Tc, determined for alloys with lower Ru content, were independent of the HNO3 concentration in the electrolyte. Oxidation of water with the evolution of oxygen on the surface of Tc–Ru alloys was observed simultaneously with the anodic dissolution of Tc and Ru. This process leads to a decrease in the current efficiency of the Tc and Ru dissolution. Examination of the corrosion damage of the working electrode surfaces by scanning electron microscopy shows that the electrochemical dissolution of Tc–Ru alloys leads to uniform corrosion of their surface.

New vinylpyridine anion exchangers for recovering thorium and nonferrous metals from nitric and hydrochloric acid solutions

The ability of new vinylpyridine anion exchangers of AXIONIT VPA series, produced by Axion—Rare and Noble Metals Joint-Stock Company (Russia), to take up Th from nitric acid solutions was studied. The static capacity of the sorbents for Th increases with increasing HNO3 concentration in the initial solution and reaches a maximum at 7–8 M HNO3. The sorbed Th can be completely desorbed with dilute HNO3 solutions. The stability of the sorption characteristics of the ion exchangers in multiple sorption–desorption cycles was evaluated. Vinylpyridine anion exchangers of AXIONIT VPA series well compete in the sorption and kinetic characteristics with VP-1Ap anion exchanger and can be successfully used for recovering Th and Pu from nitric acid solutions. Sorbents of the AXIONIT VPA series also take up copper and cobalt chloride complexes from hydrochloric acid solutions, which allows their use, e.g., for treatment of alkali metal chloride solutions to remove nonferrous metal impurities.

Chemical durability and radiation resistance of sorbents based on N,N,N′,N′-tetra-n-octyldiglycolamide

The chemical durability and radiation resistance of sorbents based on N,N,N′,N′-tetra-n-octyldiglycolamide (TODGA), produced in Russia by impregnating a polymeric support (BAU-1M sorbent) and by introducing TODGA in the step of styrene copolymerization with divinylbenzene (AXIONIT MND 40Т sorbent), were studied. The degree of the extractant washout in nitric acid solutions increases with increasing HNO3 concentration. The amount of TODGA washed out from BAU-1M sorbent is 4–5 times higher than the amount washed out from AXIONIT MND 40Т sorbent. The radiation resistance of AXIONIT MND 40Т TODGA-containing sorbent is relatively low. Upon irradiation to a dose of 2.5 MGy, the capacity of this sorbent decreases by half.

Solution extraction of several lanthanides from nitric acid with isohexyl-BTP in [Cnmim][NTf2] ionic liquid

The extraction behavior of several lanthanides (La3+, Eu3+, Lu3+) from nitric acid (HNO3) solution was studied using a novel extraction system based on 2,6-bis(5,6-dihexyl-1,2,4-triazin-3-yl) pyridine (isohexyl-BTP) as extractant in 1-alkyl-3-methylimidazolium bis(trifluoromethylsufonyl)imide ([Cnmim][NTf2]) ionic liquid. Isohexyl-BTP in ionic liquids exhibited remarkably better extraction performance for lanthanides than that in octanol-dodecane (3:7 v/v) system. Lower HNO3 concentration and short alkyl chain length of [Cnmim]+ were more favourable for removal of lanthanides. Besides, it was confirmed that isohexyl-BTP in ILs formed a 1:3 complex [Ln(BTP)3(NO3)n](3–n)+ (n=0, 1) by slope analysis. In addition, [C2mim][NTf2] preferred to extract lanthanides via a cation exchange mechanism at lower acidity, which was proved via UV-Vis measurement. It was speculated that extraction mechanism shifted from cation exchange to neutral species extraction with increase in HNO3 concentration and alkyl chain length of [Cnmim]+ due to the H+ completion, NO3− inhibition and hydrophobicity of IL.

Extraction of uranyl ion into ionic liquid by N,N,N′,N′-tetrabutylsuccinamide and spectroscopic study of uranyl complex

Interactions of uranyl with an amide ligand N,N,N′,N′-tetrabutylsuccinamide (TBSA) in ionic liquid [Bmim][NTf2] was investigated. [UO2(TBSA)3]2+ is formed from uranyl and excess TBSA, with two TBSA ligands in bidentate mode and the third in monodentate mode. The efficiency of uranyl extraction by TBSA in [Bmim][NTf2] is dependent on the aqueous nitric acid concentrations. At low HNO3 concentration as 0.01 mol·L−1, the distribution ratio (D) is over 20 times larger than that in common organic solvents, and the extracted complex is [UO2(TBSA)3]2+. The D value decreases drastically with increase of HNO3 concentration.

English

Oxidation of thiamine hydrochloride (Vit. B1) by PDP mediated by micro amounts (10 -6 mol dm -3 to 10 - 4 ) of Ru (III) in aqueous nitric acid medium has been studied at 25˚C. The reaction is second order in both PDP and Ru (III) concentrations. The order with respect to B1 concentration varies first order to zero order as the vitamin B1 concentration increases, An increase in HNO3 concentration decrease the reation rate. The active species of Oxidant and catalyst are (PDP) and (Ru(H2O)6) 3 A possible mechanism is proposed and reaction constants involved have been determined. Ruthenium (III) is an efficient catalyst in many redox reactions involving different complexities due to the formation of intermediate complexes, free radicals and multiple oxidation states of ruthenium PDP is a well Known oxidant in acidic media PDP was act as predominant active species in the concentration range 0.30 - 2.0 moldm-3 of Nitric acid, but it role has not received much attention so far the oxidation of thiamine hydrochloride with alkaline potassium ferricyanide, hypo iodide, chlorite and N-chloro benzene sulphonamide were studied. The literature survey reveals that there were no report on the oxidation of thiamine hydrochloride by PDP the mechanism may be quite complicated due to the formation of different PDP and Ru (III) Complexes in the form of active complexes in nitric acid medium. Hence, we have investigated the Ru(III) mediated oxidation of vit B1 by PDP in order to understand the behaviour of active species of oxidant and catalyst to propose a suitable mechanism. Reagent grade chemicals were used double distilled water was used through for the preparation of solutions. The stock solution of the oxidant has obtained by dissolving PDP in 1.0 mol dm -3 H2SO4. The solution was standardized by a Known method. A stock solution of thiamine hydrochloride was prepared by dissolving thiamine hydrochloride in distilled water. The Ruthenium (III) stock solution was prepared by dissolving Rucl3 in 0.20 mol dm -3 Hcl and its concentration was assayed by EDTA titration. The stock solution was diluted as required before use. KNO3 and HNO3 were used to provide the required ionic strength and acidity All Kinetic measurement were carried out under Pseudo first order conditions, where thiamine hydrochloride was in excess over PDP at a constant ionic strength of 1.10 mol dm -3 . The reaction was initiated by mixing thermally equilibrated (25

Engineering highly active TiO2 photocatalysts via the surface-phase junction strategy employing a titanate nanotube precursor

TiO2 photocatalysts were synthesized by the hydrothermal treatment of titanate nanotube precursor at different HNO3 concentrations. Their structures were characterized, and their photocatalytic activity in H2 production from water was evaluated. The phase structure of TiO2 photocatalysts is dependent on the HNO3 concentration employed during the hydrothermal treatment and varies from pure anatase to pure rutile with increasing HNO3 concentration, with the heterophase in-between. The heterophase TiO2 photocatalysts exhibit large specific surface areas and intimately contacting anatase–brookite and anatase–rutile surface junctions. The presence of anatase–brookite and anatase–rutile-phase junctions on heterophase TiO2 photocatalysts was found to efficiently suppress recombination of photoinduced charge carriers in TiO2. The heterophase TiO2 photocatalysts are photocatalytically active in H2 production from water. TiO2 photocatalysts consisting of 72.9wt% anatase, 24.6wt% brookite, and 2.5wt% rutile exhibits a photocatalytic H2 yield of 179μmolh−1g−1 under Xe lamp irradiation, about four times that of P25 (45.3μmolh−1g−1) under the same reaction conditions. These results demonstrate that the surface-phase junction strategy is very useful for engineering highly active TiO2 photocatalysts, and there still exists plenty of space to explore.

Extraction and thermodynamic behavior of U(VI) and Th(IV) from nitric acid solution with tri-isoamyl phosphate

The extraction behavior of U(VI) and Th(IV) with tri-isoamyl phosphate–kerosene (TiAP–KO) from nitric acid medium was investigated in detail using the batch extraction method as a function of aqueous-phase acidity, TiAP concentration and temperature, then the thermodynamic parameters associated with the extraction were derived by the second-law method. It could be noted that the distribution ratios of U(VI) or Th(IV) increased with increasing HNO3 concentration until 6 or 5 M from 0.1 M. However, a good separation factor (D U(VI)/D Th(IV)) of 88.25 was achieved at 6 M HNO3, and the stripping of U(VI) from TiAP–KO with deionized water or diluted nitric acid was easier than that of Th(IV). The probable extracted species were deduced by log D-log c plot at different temperatures as UO2(NO3)2·(TiAP)(1–2) and Th(NO3)4·(TiAP)(2–3), respectively. Additionally, △H, △G and △S for the extraction of U(VI) and Th(IV) revealed that the extraction of U(VI) by TiAP was an exothermic process and was counteracted by entropy change, while the extraction of Th(IV) was an endothermic process and was driven by entropy change.

Nitric Acid Concentration Dependence of Dicesium Plutonium(IV) Nitrate Formation during Solution Growth of Uranyl Nitrate Hexahydrate

A crystallization process has been under development for the recovery of U as uranyl nitrate hexahydrate (UNH) crystals. Two experiments, solubility of Cs2Pu(NO3)6 and U crystallization, were performed to evaluate the influence of HNO3 concentration in solution on the precipitation behavior of Cs2Pu(NO3)6. The solubility of Cs2Pu(NO3)6 in a uranyl nitrate solution has been found to decrease with increasing HNO3 concentration in the solution. These experimental results imply that Cs2Pu(NO3)6 is readily formed in high HNO3 concentration solutions. Based on the solubility of Cs2Pu(NO3)6 in uranyl nitrate solutions, U crystallization experiments were performed with a range of HNO3 concentrations in the feed solution. At an HNO3 concentration of 4.5 mol/dm3 in the feed solution, the HNO3 concentration of the mother liquor was 6.5 mol/dm3. The decontamination factor (DF) of Cs for the UNH crystals was 8.61 after crystal washing. In this case, Cs2Pu(NO3)6 precipitated upon cooling of the feed solution and was not separated from the UNH crystals after crystal washing. On the other hand, the DF of Cs was 174 after the UNH crystals were washed when the HNO3 concentration in the feed solution was 3.2 mol/dm3. With a lower HNO3 concentration in the feed solution, nearly all Cs remained in the mother liquor during the U crystallization process. Therefore, to suppress Cs2Pu(NO3)6 precipitation, a lower HNO3 concentration must be maintained in the feed solution.

Carrier facilitated transport of uranium across supported liquid membrane using dinonyl phenyl phosphoric acid and its mixture with neutral donors

Carrier facilitated transport of U(VI) from nitric acid medium across supported liquid membrane (SLM) has been studied under varying experimental conditions, namely feed, carrier, receiver phase compositions, pore size and membrane thickness etc. Microporous polytetrafluoroethylene (PTFE) membranes were used as a solid support and dinonyl phenyl phosphoric acid (DNPPA) either alone or in combination with neutral donors dissolved in n-paraffin was used as carrier. Receiver phases like H2SO4, Oxalic acid, Citric acid and Na2CO3 were evaluated. 2M H2SO4 appeared to be most effective as receiver for U(VI) transport across SLM under the conditions of these studies. The permeability coefficient (P) evaluated for 0.1M DNPPA in combination with 0.05M neutral donors showed the U(VI) transport order: Cyanex 923~TOPO>TBP>TEHP. The permeability (P) of U(VI) decreased with increase in HNO3 concentration and with metal ion concentration in feed solution. The variation of Cyanex 923 concentration at fixed DNPPA concentration (0.1M) revealed that U(VI) permeation across SLM was maximum at 1:2.5 mole ratio. The synergistic mixture of 0.1M DNPPA+0.05M Cyanex 923 was used for uranium recovery from uranyl nitrate raffinate (UNR) solution.

Studies on extraction behaviour of molybdenum (VI) from acidic radioactive waste using 2(ethylhexyl) phosphonic acids, mono 2(ethylhexyl) ester (PC-88A)/n-dodecane

This paper describes the studies on the extraction of molybdenum (VI) from aqueous nitric acid medium by (2-ethylhexyl) phosphonic acid, mono (2-ethylhexyl) ester (PC-88A). The extraction affecting parameters such as concentration of HNO3 in aqueous feed, effect of concentration of extractants, effect of diluents, and molybdenum concentration in the aqueous phase are investigated to optimize the extraction conditions for the quantitative separation of molybdenum from nitric acid medium. With increase of HNO3 concentration in aqueous phase, percentage extraction was found to be decreased in all the cases. Percentage extraction of molybdenum increases with increase in PC-88A concentration till the 0.15 M of PC88A, and after that it becomes constant. Kerosene and n-dodecane was found to be most suitable diluents. Among the various strippants used 0.2 M (w/v) solution of Na2CO3 and 0.2 M (w/v) solution (NH4)2CO3 are found to be the equally suitable for stripping of molybdenum from the loaded organic phase. The stripping of molybdenum from loaded organic layer by various reagents followed the order: (NH4)2CO3 >Na2CO3 >0.1 M sodium salt of EDTA >2 M NaOH >8 M HNO3. The optimized process conditions are employed to extract molybdenum (VI) from actual Davies–Gray waste as well as from diluted high level waste generated in the purex stream. More than 94% Mo(VI) was extracted from radioanalytical as well as from high level waste of purex process and quantitative recovery was achieved in both the cases when 0.2 M sodium carbonate was used as stripping agent.

Thermal Analysis of Multi-walled Carbon Nanotubes by Kissinger’s Corrected Kinetic Equation

ABSTRACTCarbon nanotubes (CNTs) have been a popular material in recent years, but their thermal characteristics have not been understood completely. We investigated the unique thermal stability of multi-walled carbon nanotubes (MWCNTs) and used nitric acid (HNO3) to purify MWCNTs to promote its activation energy (Ea). The study used differential scanning calorimetry (DSC), thermogravimetric analyzer (TGA), and Fourier transform infrared (FTIR) spectrometer to analyze as-grown MWCNTs and modified MWCNTs. For DSC, the heating rate was chosen to be 0.25 to 2.0 °C/min. From DSC results, Ea and exothermic onset temperature (T0) of the modified MWCNTs increased with increasing HNO3 concentration. The TGA results showed that both as-grown and modified MWCNTs’ decomposition temperatures were higher than 500°C in air. The infrared spectra of as-grown MWCNTs and modified MWCNTs have shown that the gas phase composition is CO2 after TGA linked with FTIR. By Kissinger’s corrected kinetic equation, Ea increased with increasing HNO3 concentration. Through this study, we realized that as-grown MWCNTs and modified MWCNTs are thermally hazardous materials with high potential heat of decomposition, especially under fire exposure. Thus, it is important to know the thermal hazard characteristics of material with a measure to prevent its thermal damage during perturbed situations.

Selectivity of bis[n-butyl(hydroxyl)phosphoryl]dibenzo crown ether endoreceptors in metal extraction from nitric acid solutions

Diphosphorylated dibenzo crown ethers with 4,4′(5′)-bis[n-butyl(hydroxy)]phosphoryl substituents at the benzene rings of dibenzo-18-crown-6 (I), dibenzo-21-crown-7 (II), and dibenzo-24-crown-8 (III) were prepared and studied with the aim of developing new highly effective and selective extractants for recovery and separation of metals. Extraction of a solution containing Al, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Ge, In, K, La, Li, Mg, Mn, Mo, Na, Ni, Pb, Re, Sc, Sr, Tl, V, Y, and Zn (10 ppm each) and an Am(III) solution in 0.01–5 M HNO3 with 0.05 M solutions of the endoreceptors in chloroform was studied. For endoreceptor III, the maximal distribution ratios of metals Dmmax are ranked in the following order: Sc (>103) > Am (162) > Mo (129) > V (75.9) > In (29.3) > Bi (16.5) > Fe (4.7) > Rb (1.0) > Pb (0.34) > Ga (0.18) > Ge (0.11) > Al, B, Ba, Ca, Cd, Co, Cr, Cu, K, La, Li, Mg, Mn, Na, Ni, Re, Sr, Tl, V, Zn (<0.1). The distribution ratio Dm in all the examined equilibrium systems decreases with increasing HNO3 concentration in the range 0.01–3 M. The fact that this decrease is significantly less pronounced than that for the known organophosphorus acids suggests complex extraction mechanism, presumably via formation of scorpion-like host-guest complexes. Thus, diphosphorylated dibenzo crown ethers with phosphoric acid substituents are very strong and highly selective endoreceptors in extraction of Sc, Mo, In, and Am from nitric acid solutions and can be used in practice for preconcentration of these elements and their separation from concomitant impurities.

A comparative study on the corrosion behavior of NdFeB magnets in different electrolyte solutions

AbstractSintered NdFeB magnets possess excellent magnetic properties. However, the corrosion resistance property of NdFeB is very poor due to its multiphase microstructure consisting of matrix phase Nd2Fe14B, Nd‐rich phase, and B‐rich phase. The corrosion behavior of NdFeB magnets in sodium hydroxide (NaOH), sodium chloride (NaCl), nitric acid (HNO3), and oxalic acid (H2C2O4) solutions was investigated by immersion and electrochemical tests. HNO3is the strongest corrosive electrolyte compared with the other three solutions. The increase in HNO3concentration can accelerate the corrosion of NdFeB magnets. NaCl belongs to medium corrosion electrolyte. A NaCl concentration of 0.5 M shows the severest corrosive feature in comparison with other concentrations of NaCl solution. NdFeB hardly suffers corrosion in NaOH and H2C2O4solutions owing to the formation of passivation films on the surface of magnets. Based on the corrosion behavior of NdFeB in different electrolytes, the possible corrosion mechanisms are discussed.

Solubility of plutonium nitrate in uranyl nitrate hexahydrate melt

At a weight fraction below 20%, Pu(IV) nitrate is isomorphically dissolved and homogeneously distributed in the uranyl nitrate hexahydrate phase, the solubility being independent of the HNO3 concentration in the mixed U-Pu melt up to the acid concentration of 7 M. In dissolving solid Pu(IV) nitrate in 1–6 M HNO3, Pu(IV) disproportionates to form Pu(III) and Pu(VI). With increasing HNO3 concentration to above 10 M, Pu(IV) passes into solution as Pu(NO3)62−, and no disproportionation is observed.

Highly Selective Extraction of TcO4−, ReO4−, and MoO42− by the New Ligand, 2,2′-(Methylimino)bis(N,N-Dioctylacetamide) (MIDOA)

Abstract Highly selective extraction of oxonium anions can be achieved by the new ligand, 2,2′-(methylimino)bis(N,N-dioctylacetamide) (MIDOA). MIDOA has a high solubility in n-dodecane, any types of diluents can be employed for the solvent extraction. The extraction using MIDOA was performed under the condition, HNO3 and n-dodecane, considering the chemical process of high-level radioactive liquid waste. It was obvious that the oxonium anions, like TcO4−, ReO4−, Cr2O72−, MoO42−, and WO42−, are extracted, and the distribution ratios (D) decrease with increase of HNO3 concentration.

Hydrothermal synthesis of titanium dioxide using acidic peptizing agents and their photocatalytic activity

We have prepared TiO2 nanoparticles by the hydrolysis of titanium tetraisopropoxide (TTIP) using HNO3 as a peptizing agent in the hydrothermal method. The physical properties of nanosized TiO2 have been investigated by TEM, XRD and FT-IR. The photocatalytic degradation of orange II has been studied by using a batch reactor in the presence of UV light. When the molar ratio of HNO3/TTIP was 1.0, the rutile phase appeared on the titania and the photocatalytic activity decreased with an increase of HNO3 concentration. The crystallite size of the anatase phase increased from 6.6 to 24.2 nm as the calcination temperature increased from 300 °C to 600 °C. The highest activity on the photocatalytic decomposition of orange II was obtained with titania particles dried at 105 °C without a calcination and the photocatalytic activity decreased with increasing the calcination temperature. In addition, the titania particles prepared at 180 °C showed the highest activity on the photocatalytic decomposition of orange II.

A modeling study of the effect of nitric acid on cloud properties

The effect of nitric acid (HNO3) on cloud microphysical and radiative properties is studied using an adiabatic cloud parcel model for a range of aerosol size distributions, different water vapor mass accommodation coefficients, and HNO3 concentrations. Results show that HNO3 not only increases cloud drop number concentration Nd, but also leads to significantly broader droplet size spectra at both the small‐ and large‐size ends. The broader spectra are generally the result of competition for H2O and HNO3 among the polydisperse droplets. The increase in the number of activated cloud droplets in the presence of HNO3, and the deactivation of some of the small cloud droplets due to the outgasing of HNO3, lead to spectral broadening at the small‐size end. At the large‐size end the broadening is caused by an increase in the driving force for growth. For small drops the driving force tends to be decreased by the presence of HNO3. Although Nd increases with increasing HNO3 concentration, the increases in cloud optical depth and albedo due to HNO3 cannot necessarily be predicted by the commonly used relationships for cloud optical properties. The dependence of the cloud optical depth on Nd to the one‐third power is shown to be an overestimate because droplet spectra are significantly broadened by HNO3. We show that broadening effects due to HNO3 and other chemical or microphysical factors need to be considered when estimating cloud optical properties and their effect on climate.

Thermochemical Oxidation of Components of Extraction Solutions and Boundary Conditions of Thermal Explosion: 6. Thermal Stability of Two-Phase Systems TBP-HNO3and TBP-Dodecane-HNO3in Sealed Vessels

Thermochemical degradation of two-phase systems TBP-HNO3 and 30% TBP in dodecane-HNO3 (HNO3 concentration 1.5-10 M) on heating in a sealed vessel to 130-170°C is studied. Heating to 130-150°C promotes exothermic oxidation of the organic phase, resulting in its self-heating. The oxidation rate (self-heating and specific volume of gaseous products) increases with increasing HNO3 concentration in the aqueous phase. Irradiation of the organic phase decreases the thermal resistance of the systems, which is reflected in a decrease in the onset temperature of exothermic reactions. In the organic phase 30% TBP in dodecane, irradiated to doses of 1.5-2.4 MGy, in contact with 14 M HNO3, exothermic reactions start at 85-95°C.