Range Of Nitric Acid Concentrations Research Articles

Development of a Simultaneous Quantification Method for Multiple Modes of Nitrogen in Leaf Models Using Near-Infrared Spectroscopic Measurement.

By focusing our attention on nitrogen components in plants, which are important for cultivation management in data-driven agriculture, we developed a simple, rapid, non-chemical and simultaneous quantification method for proteinic and nitrate nitrogen in a leaf model based on near-infrared (NIR) spectroscopic information obtained using a compact Fourier Transform NIR (FT-NIR) spectrometer. The NIR spectra of wet leaf models impregnated with a protein-nitric acid mixed solution and a dry leaf model obtained by drying filter paper were acquired. For spectral acquisition, a compact MEMS (Micro Electro Mechanical Systems) FT-NIR spectrometer equipped with a diffuse reflectance probe accessory was used. Partial least square regression analysis was performed using the spectral information of the extracted absorption bands based on the determination coefficients between the spectral absorption intensities and the contents of the two-dimensional spectral analysis between NIR and mid-infrared spectral information. Proteinic nitrogen content in the dry leaf model was well predicted using the MEMS FT-NIR spectroscopic method. Additionally, nitrate nitrogen in the dry leaf model was also determined by the provided method, but the necessity of adding the data for a wider range of nitric acid concentrations was experimentally indicated for the prediction of nitrate nitrogen content in the wet leaf model. Consequently, these results experimentally suggest the possibility of the application of the compact MEMS FT-NIR for obtaining the bioinformation of crops at agricultural on-sites.

Hydrophilic Sulfonated 2,9-Diamide-1,10-phenanthroline Endowed with a Highly Effective Ligand for Separation of Americium(III) from Europium(III): Extraction, Spectroscopy, and Density Functional Theory Calculations.

The design and development of a water-soluble heterocyclic ligand are believed to be an alternative way for improving the separation efficiency of actinides from lanthanides. Herein, we designed and synthesized a novel hydrophilic multidentate ligand: disulfonated N,N'-diphenyl-2,9-diamide-1,10-phenanthroline (DS-Ph-DAPhen) with soft and hard donor atoms, as a masking agent in aqueous solutions for Am(III) separation. The combination of N,N,N',N'-tetraoctyldiglycolamide in kerosene and DS-Ph-DAPhen in aqueous phases could separate Am(III) from Eu(III) across a range of nitric acid concentrations with very high selectivity. The coordination behaviors of Eu(III) with DS-Ph-DAPhen in aqueous solutions were studied by UV-vis titration, electrospray ionization mass spectrometry, and Fourier transform infrared spectra. The results indicated that Eu(III) ions could form both 1:1 and 1:2 complexes with the DS-Ph-DAPhen ligand in aqueous solution. Density functional theory calculation suggests that there are more covalent characters for Am-N bonds than that for Eu-N bonds in the complexes, which supports the better selectivity of the DS-Ph-DAPhen ligand toward Am(III) over Eu(III). This work demonstrates a feasible alternative approach to separating trivalent actinides from lanthanides with high selectivity.

Phosphazenes as Collective Extractants of Rare-Earth Elements

The extraction ability of some linear phosphazenes with respect to rare-earth elements (REEs) in a nitrate medium is studied. Some possible mechanisms of interaction between phosphazenes of different types and REEs at various acidities are discussed. It has been established that imido- and amidophosphazenes are very strong extractants of REEs within a broad range of nitric acid concentrations in the aqueous phase. It has been shown that phosphazenes can be efficient collective extractants of REEs.

Recycling Scrap from Un-Irradiated Nuclear Fuel by HNO3 Leaching

The work describes the wet chemical route process to recover and recycle a defective un-irradiated uranium dioxide sintered pellets. The optimal conditions of the un-irradiated UO2 sintered pellets dissolution in Nitric acid solutions has been examined. The effects of acid concentration, contact time and temperature on dissolution action have been studied. The samples were exposed to leaching over a range of nitric acid concentrations 2–8 mol/L and temperatures from 20 to 70 °C. The stoichiometry of the dissolution reaction depends on the acidity of the solution. The shrinking core model (product diffusion control model and chemical reaction control model) was used to correlate the experimental results. Kinetics study shows that the chemical reaction model controls the dissolution of UO2 sintered pellets in nitric acid solution. The average value of apparent activation energy estimated from the temperature effect of the chemical reaction was found to be about 101.40 kJ/mol. The optimal conditions to dissolve the UO2 sintered pellets in nitric acid solution have been proposed.

Aqueous solubility of tri-iso-amyl phosphate (TiAP) - Effect of acidity, temperature and metal ions

In recent times, tri-iso-amyl phosphate (TiAP) has been emerged as an alternate solvent to the existing tri-butyl phosphate (TBP) mainly for the aqueous reprocessing of high Plutonium content fast reactor fuels adopting the conventional PUREX process. Little solubility of the solvent in aqueous phase during extraction can lead to complex issues in further operations especially during the evaporation of raffinate. In this context, the aqueous solubility of tri-iso-amyl phosphate (TiAP) in a wide range of nitric acid concentrations from 0 to 14 M has been determined at three different experimental temperatures 298, 313 and 328 K. Various process parameters such as aqueous phase acidity and presence of heavy metal ions which affect the solubility of solvent are also discussed.

Kinetics of the Autoreduction of Hexavalent Americium in Aqueous Nitric Acid

The rate of reduction of hexavalent 243Am due to self-radiolysis was measured across a range of total americium and nitric acid concentrations. These so-called autoreduction rates exhibited zero-order kinetics with respect to the concentration of hexavalent americium, and pseudo-first-order kinetics with respect to the total concentration of americium. However, the rate constants did vary with nitric acid concentration, resulting in values of 0.0048 ± 0.0003, 0.0075 ± 0.0005, and 0.0054 ± 0.0003 h-1 for 1.0, 3.0, and 6.5 M HNO3, respectively. This indicates that reduction is due to reaction of hexavalent americium with the radiolysis products of total americium decay. The concentration changes of Am(III), Am(V), and Am(VI) were determined by UV-vis spectroscopy. The Am(III) molar extinction coefficients are known; however, the unknown values for the Am(V) and Am(VI) absorbances across the studied range of nitric acid concentrations were determined by sensitivity analysis in which a mass balance with the known total americium concentration was obtained. The new extinction coefficients and reduction rate constants have been tabulated here. Multiscale radiation chemical modeling using a reaction set with both known and optimized rate coefficients was employed to achieve excellent agreement with the experimental results, and indicates that radiolytically produced nitrous acid from nitric acid radiolysis and hydrogen peroxide from water radiolysis are the important reducing agents. Since these species also react with each other, modeling indicated that the highest concentrations of these species available for Am(VI) reduction occurred at 3.0 M HNO3. This is in agreement with the empirical finding that the highest rate constant for autoreduction occurred at the intermediate acid concentration.

Desorption of copper ions from the polyamine-functionalized adsorbents: Behaviors and mechanisms

This paper is aiming at analyzing the desorption performance of the four polyamine-functionalized adsorbents after copper ion adsorption, with nitric acid as the desorption agent. The four adsorbents (namely, P-EDA, P-DETA, P-TETA and P-TEPA) studied were immobilized with ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA) and tetraethylenepentamine (TEPA), respectively. Nitric acid concentration, ionic strength, and solid-to-liquid (S/L) ratio were taken into consideration as the influencing factors on the desorption performance. The findings showed that higher desorption efficiency had no necessary connection with the higher concentration of nitric acid, and the highest desorption efficiency was realized for P-EDA and P-DETA at 0.10 mmol/L, and for P-TETA and P-TEPA at 0.25 mmol/L, in the nitric acid concentration range of 0.01–2.00 mmol/L studied. In addition, Ionic strength showed obvious influence on the desorption efficiency, and higher ionic strength resulted in significant lower desorption efficiency. Different S/L ratios studied showed almost no differences on the desorption efficiency. The copper ion desorption kinetics, best described by the Elovich model, was discovered to be very fast that more than 85% of the desorption efficiency was attained within 2 min. A slight decrease in Cu ion adsorption capacity was found through ten cycles of adsorption-desorption-regeneration for all the four adsorbents.

Sequential Determination of Free Acidity and Plutonium Concentration in the Dissolver Solution of Fast-Breeder Reactor Spent Fuels in a Single Aliquot.

A simple potentiometric method for determining the free acidity without complexation in the presence of hydrolysable metal ions and sequentially determining the plutonium concentration by a direct spectrophotometric method using a single aliquot was developed. Interference from the major fission products, which are susceptible to hydrolysis at lower acidities, had been investigated in the free acidity measurement. This method is applicable for determining the free acidity over a wide range of nitric acid concentrations as well as the plutonium concentration in the irradiated fuel solution prior to solvent extraction. Since no complexing agent is introduced during the measurement of the free acidity, the purification step is eliminated during the plutonium estimation, and the resultant analytical waste is free from corrosive chemicals and any complexing agent. Hence, uranium and plutonium can be easily recovered from analytical waste by the conventional solvent extraction method. The error involved in determining the free acidity and plutonium is within ±1% and thus this method is superior to the complexation method for routine analysis of plant samples and is also amenable for remote analysis.

N,N-dialkyl-2-hydroxyacetamides for modifier-free separation of trivalent actinides from nitric acid medium

Abstract The alkyl derivatives of N,N,-dialkyl-2-hydroxyacetamide (DAHyA), namely, N,N,-dihexyl-2-hydroxyacetamide (DHHyA), N,N,-dioctyl-2-hydroxyacetamide (DOHyA), N,N,-didecyl-2-hydroxyacetamide (DDHyA), were synthesized and characterized by FT-IR, and NMR spectroscopy. The extraction behaviour of Am(III) in a solution of DAHyA in n-dodecane was studied as a function of various parameters to evaluate the feasibility of using DAHyA for partitioning of trivalent actinides from high-level liquid waste (HLLW). The distribution ratio of Am(III) (D Am(III)) in 0.1 M DAHyA/n-DD increased from 10−4 to > 200 with increase in nitric acid concentration from 1 M to 6 M. A D Am(III) value 10–70 was obtained in a nitric acid concentration range from 3–4 M. The extraction of Am(III) in 0.1 M DAHyA/n-dodecane decreased in the order DHHyA > DOHyA > DDHyA. The third-phase formation behaviour of nitric acid and neodymium (III) in 0.2 M DAHyA/n-dodecane was studied. Near stoichiometric amount of neodymium (III) can be loaded in octyl and decyl derivatives without any third-phase formation from 3–4 M nitric acid medium. Unlike other extractants, the loaded trivalent metal ion in DAHyA can be recovered even with 1 M nitric acid. Therefore, the study revealed that N,N,-dialkyl-2-hydroxyacetamides are promising candidates for partitioning the trivalent actinides from HLLW.

Relationship between chemical structure and extraction efficiency toward palladium with ketonic derivatives of p-tert-octylcalix[4]arene in nitric acid media

A p-tert-octylcalix[4]arene derivative with four phenyl ketonic side arms has been synthesized as a solvent extraction reagent for precious metal ions in order to compare the extraction behavior with that of the corresponding methyl ketonic derivative of p-tert-octylcalix[4]arene in nitric acid media. The extraction efficiency of the phenyl ketonic derivative for palladium was superior to that of the methyl ketonic one over the whole nitric acid concentration range. Silver and platinum were also moderately extracted by the phenyl ketonic derivative in low nitric acid concentration. The results demonstrated that the extraction behavior of the ligands towards precious metals is related to several structural factors, such as the flexibility of the side arms, the electric charge on the carbonyl oxygen atoms and the lipophilic properties. This work also determined the extraction mechanism of palladium with the phenyl ketonic derivative of p-tert-octylcalix[4]arene based on slope analysis and the peak shift for the FT-IR spectra of the ligand before and after the metal loading. Stripping from the organic phase after forward extraction was performed to separate palladium and silver.

Supercritical fluid extraction and separation of uranium from other actinides

The feasibility of separating U from nitric acid solutions of mixed actinides using tri-n-butylphosphate (TBP)-modified supercritical fluid carbon dioxide (sc-CO2) was investigated. The actinides U, Np, Pu, and Am were extracted into sc-CO2 modified with TBP from a range of nitric acid concentrations, in the absence of, or in the presence of, a number of traditional reducing and/or complexing agents to demonstrate the separation of these metals from U under sc-CO2 conditions. The separation of U from Pu using sc-CO2 was successful at nitric acid concentrations of less than 3M in the presence of acetohydroxamic acid (AHA) or oxalic acid (OA) to mitigate Pu extraction, and the separation of U from Np was successful at nitric acid concentrations of less than 1M in the presence of AHA, OA, or sodium nitrite to mitigate Np extraction. Americium was not well extracted under any condition studied.

Dissolution of uranium mixed oxides: The role of oxygen vacancies vs the redox reactions

While uranium-based mixed oxides are interesting materials for several concepts of nuclear reactors, the effects of trivalent elements in the fluorite structure and the redox reactions at the solid/solution interface during the dissolution of such compounds remain widely unknown. In order to underline the influence of those parameters, various dissolution experiments were carried out on different compositions (i.e. U0.75Ce0.25O2, U0.75Th0.25O2, Th0.75Nd0.25O1.875 and U0.75Ln0.25O1.875 with Ln = Nd, Gd). These tests were performed on sintered pellets in nitric acid solutions (from 10−2 M to 4 M) at different temperatures (22°C–90°C) under dynamic conditions. Therefore, a multiparametric study of the dissolution kinetics was then achieved in order to determine the partial order of dissolution reaction regarding to H3O+ activity and the activation energy. The obtained results gave evidence of the strong dependency of the dissolution rate with the nitric acid concentration. In fact, for concentrations higher than 2 M, the dissolution process is almost controlled by the oxidation of U(IV) to U(VI). On the contrary the effect of oxygen vacancies became predominant for acid concentrations lower than 0.5 M. Under these conditions, the systems containing trivalent elements exhibited the lowest chemical durability. The partial order of the reaction regarding to the H3O+ activity reached n = 2.1 for U0.75Th0.25O2 and was found to be constant over the entire acidity range. A variation of the partial order of the dissolution reaction regarding to H3O+ was observed along the nitric acid concentration range for U0.75Ln0.25O1.875 solid solutions, that underlines the predominance of different controlling reactions in the dissolution mechanism: surface-controlling reaction involving H3O+ at low pH (i.e. n < 1) for CHNO3 ≤ 0.5 M, and uranium oxidation (i.e. n > 1) for CHNO3 ≥ 1 M.

Diamylamylphosphonate Solvent Extraction of Am(VI) from Nuclear Fuel Raffinate Simulant Solution

The separation of hexavalent americium from the lanthanides in simulated PUREX raffinate solution using 1 M diamylamylphosphonate in dodecane extraction was investigated. Hexavalent americium was prepared using room-temperature sodium bismuthate oxidation. Under these conditions the majority of the lanthanides were not oxidized and remained inextractable. A separation factor of ∼50 was provided for americium from europium over the nitric acid concentration range 6–7 M. Cerium was the exception with oxidation to CeIV resulting in its co-extraction with AmVI. However, since americium is readily reduced to AmIII it was easily stripped with a dilute acidic solution of hydrogen peroxide. Although hydrogen peroxide also reduces cerium, it does so slowly, and a selective americium strip was achieved, with a separation factor of as high as 35. Alternatively, since americium spontaneously reduced in the loaded organic phase, samples allowed to stand for 2 hours could be selectively stripped of americium by contact with 1 M HNO3 containing no additional reagents. Further, the separation was demonstrated using solutions containing macro-amounts of cerium and americium. The implications for use in fuel cycle separations are discussed.

A TRUEX-Based Separation of Americium from the Lanthanides

The inextractability of the actinide AnO2 + ions by the TRUEX solvent suggests the possibility of a separation of americium from the lanthanides using oxidation to Am(V). The only current method for the direct oxidation of americium to Am(V) in strongly acidic media is with sodium bismuthate. We prepared Am(V) over a wide range of nitric acid concentrations and investigated its solvent-extraction behavior for comparison to europium. While a separation is achievable in principal, the presence of macro amounts of cerium competes for the sparingly soluble oxidant and the oxidant itself competes for CMPO complexation. These factors conspire to reduce the Eu/Am separation factor from ∼40 using tracer solutions to ∼5 for extractions from the first-cycle raffinate simulant solution. To separate pentavalent americium directly from the lanthanides using the TRUEX process, an alternative oxidizing agent may be necessary.

Process Optimization for Synthesis of CL-20

Optimization of process parameters for synthesis of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) of desired particle size have been described. CL-20, the most powerful high explosive, is being synthesized at the High Energy Materials Research Laboratory (HEMRL, Pune, India) by nitration of 2,6,8,12-tetraacetyl-2,4,6,8,10,12-hexaazaisowurtzitane (TAIW). Nitration of TAIW is a mild exothermic reaction. Although information on synthesis of CL-20 is reported, no information is available on process optimization. In order to optimize the process parameters for synthesis of CL-20 to obtain higher yield and purity, a study was carried out with variation of different parametric conditions like temperature, time, concentration of nitric acid, mole ratio of reactants, quantity of solvent/anti-solvent, etc. The effect of each parameter was studied by keeping other parameters constant. In the present study it was found that for ∼85% yield, optimized temperature envelope was 72–85°C, nitric acid concentration range from 98 to 92%, reaction time was 1 h, and temperature during the addition of TAIW into the mixed acid was 25–40°C. In order to improve the particle size of CL-20, during the recrystallization process, the effect of parameters like addition rate of anti-solvent and rate of agitation were studied and optimum conditions identified. CL-20 synthesized under optimized conditions was characterized and confirmed by different analytical methods like 1H-NMR, Fourier transform infrared spectroscopy (FTIR), elemental analysis, differential scanning calorimetry (DSC), etc. Purity of CL-20 was estimated by high-performance liquid chromatography (HPLC). Particle size of ∼150 µm was achieved by crystallization under optimized process conditions.

Tributylphosphate Extraction Behavior of Bismuthate-Oxidized Americium

Higher oxidation states of americium have long been known; however, options for their preparation in acidic solution are limited. The conventional choice, silver-catalyzed peroxydisulfate, is not useful at nitric acid concentrations above about 0.3 M. We investigated the use of sodium bismuthate as an oxidant for Am (3+) in acidic solution. Room-temperature oxidation produced AmO 2 (2+) quantitatively, whereas oxidation at 80 degrees C produced AmO 2 (+) quantitatively. The efficacy of the method for the production of oxidized americium was verified by fluoride precipitation and by spectroscopic absorbance measurements. We performed absorbance measurements using a conventional 1 cm cell for high americium concentrations and a 100 cm liquid waveguide capillary cell for low americium concentrations. Extinction coefficients for the absorbance of Am (3+) at 503 nm, AmO 2 (+) at 514 nm, and AmO 2 (2+) at 666 nm in 0.1 M nitric acid are reported. We also performed solvent extraction experiments with the hexavalent americium using the common actinide extraction ligand tributyl phosphate (TBP) for comparison to the other hexavalent actinides. Contact with 30% tributyl phosphate in dodecane reduced americium; it was nevertheless extracted using short contact times. The TBP extraction of AmO 2 (2+) over a range of nitric acid concentrations is shown for the first time and was found to be analogous to that of uranyl, neptunyl, and plutonyl ions.

Extraction of uranium(VI) from nitric acid medium by 1.1M tri-n-butylphosphate in ionic liquid diluent

A systematic study on the extraction of U(VI) from nitric acid medium by tri-n-butylphosphate (TBP) dissolved in a non-traditional diluent namely 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6) ionic liquid (IL) is reported. The results are compared with those obtained using TBP/n-dodecane (DD). The distribution ratio for the extraction of U(VI) from nitric acid by 1.1M TBP/bmimPF6 increases with increasing nitric acid concentration. The U(VI) distribution ratios are comparable in the nitric acid concentration range of 0.01M to 4M, to the ratios measured using 1.1M TBP/DD. In contrast to the extraction behavior of TBP/DD, the D values continued to increase with the increase in the concentration of nitric acid above 4.0M. The stoichiometry of uranyl solvate extracted by 1.1M TBP/IL is similar to that of TBP/DD system, wherein two molecules of TBP are associated with one molecule of uranyl nitrate in the organic phase. Ionic liquid alone also extracts uranium from nitric acid, albeit to a small extent. The exothermic enthalpy accompanying the extraction of U(VI) in TBP/bmimPF6 decreases with increasing nitric acid and with TBP concentrations.

Preparation and characterization of FeAg granular alloys

Fe10Ag90 granular alloys have been fabricated, using a sol-gel method, for a range of nitric acid concentrations in the start solution. The samples have been characterized by X-ray diffraction and magnetization measurements. The average Fe particle sizes derived from X-ray diffraction are in the range 24-29 nm, indicating a large variation. The coercivity obtained from the hysteresis curve is two orders of magnitude larger that of pure iron in all the samples. Moreover, the hysteresis curves do not saturate, even in fields of up to 1 T. These observations indicate that the samples contain both superparamagnetic and blocked particles. A comparison between the coercive field and the average particle diameter, determined by the Sherrer's formula, is displayed in all acid concentrations.

PARTITIONING OF MERCURY FROM ACTINIDES IN THE TRUEX PROCESS

A mercury complexant, L-cysteine hydrochloride, was tested for use in separating Hg(II) from actinides during transuranic extraction (TRUEX) processing of wastes at the Idaho National Engineering and Environmental Laboratory (INEEL). Mercury, americium, plutonium, and uranyl distributions for the TRUEX solvent were characterized over a nitric acid concentration range of 0.01 to 2 M with and without cysteine. The applicability of cysteine was evaluated for selective Hg(II) complexation in an INEEL sodium-bearing waste simulant. A test was also conducted to evaluate the applicability of cysteine to separate Hg(II) from Sr in the strontium extraction (SREX) process with Sr Resin used as a stand-in for the SREX process solvent. In all cases, the use of L-cysteine HCl retained Hg in the aqueous phase while causing no or little perturbation in the actinide and Sr distribution behavior.

An improved extraction chromatographic resin for the separation of uranium from acidic nitrate media

The preparation and characterization of a new extraction chromatographic resin exhibiting extraordinarily strong retention of hexavalent uranyl ion over a wide range of nitric acid concentrations and very high selectivity for U(VI) over Fe(III) and numerous other cations is described. This new material (designated U/TEVA-2) comprises a novel liquid stationary phase consisting of an equimolar mixture of diamyl amylphosphonate (DA[AP]) and Cyanex 923 ® (a commercially available trialkyl-phosphine oxide, TRPO) sorbed on silanized silica or Amberchrom CG-71. Cyanex 923 is shown to be preferable to a related TRPO, Cyanex 925 ®, due to its lower viscosity and higher selectivity for U(VI) over Fe(III). The retention of uranyl nitrate by the U/TEVA-2 resin, as measured by the k′ values (number of free column values to peak maximum) is >5000 from approximately 0.1 to 8 M HNO 3. The ability of the new resin to strongly and selectively retain U(VI) from such a wide range of acid concentrations, along with its favorable physical properties, make it a good candidate for application in the separation and preconcentration of U(VI) from complex environmental, biological, and nuclear waste samples for subsequent determination.