High Nitric Acid Concentrations Research Articles

Improved Process for High Concentration of Nitric Acid Using Magnesium Nitrate

The high concentration of weak nitric acid using magnesium nitrate is a proven technology since years. Due to higher requirements in regard to product quality, effluent gas and effluent water as well as due to the necessity to reduce the energy consumption of the process and the amount of raw materials the process has to be adapted. By introducing additional process steps using recycled water condensate, which is produced in the process the losses of nitric acid with the effluent gas and the process condensate are minimized on the one hand. On the other hand simultaneously the NO x content of the effluent gas and the nitrate content of the effluent water are minimized. Due to the improvements an eco-efficient process for high concentration of nitric acid is now available using best available techniques (BAT) and a design according to European guidelines for Integrated Pollution Prevention and Control (IPPC).

Carboxyl-Terminated Isotactic Polypropylene. Preparation, Characterization, Kinetics, and Reactivities

The present contribution describes an unsophisticated yet highly efficient process to make dicarboxyl telechelic isotactic polypropylene containing pendant nitro groups via the oxidative degradation of commercially available crystalline polypropylene with nitric acid. The obtained crystalline polymer has a narrow molecular weight distribution (Mw/Mn = 2−4) and maintains the same degree of isotacticity as the virgin polypropylene. The molecular weights of the product can be well controlled by varying the reaction temperature, reaction time, or the concentration of nitric acid. It was found that the higher reaction temperature and higher concentration of nitric acid, the faster the degradation is. Kinetic studies shown that the reaction is 4.2 orders in nitric acid, indicative of the complex nature of the reaction mechanism. Both liquid/solid and gas/solid interface interactions were found simultaneously existing in the present system. The carboxyl-capped polypropylene with low NO2/COOH ratio can be produce...

Tri-iso-amyl phosphate (TAP): An alternative extractant to tri-butyl phosphate (TBP) for reactor fuel reprocessing

Tri-iso-amyl phosphate (TAP), an indigenously prepared extractant was utilized for reactor fuel reprocessing and compared with tri-butyl phosphate (TBP) and tri-n-hexyl phosphate (THP). The potential of these extractants was found to be in the order TAP>THP>TBP by calculating the acid uptake value (KH). The effect of various parameters such as solvent degradation due to acid hydrolysis, radiation effect, decontamination factor and phase separation were investigated and it was found that TAP was always a better extractant in comparison to THP and TBP. In addition to this, the extraction of fission product contaminants such as 144 Ce, 137 Cs, 106 Ru, 95 Zr was almost negligible, even at very high nitric acid concentrations in the aqueous phase, indicating the potential application of TAP in actinide partitioning. Sodium carbonate solution or acidified distilled water was a good strippant for U(VI), similarly, uranium(IV) nitrate stripped Pu(IV) from the organic phase.

Dissolution of Mo/Al Bilayers in Phosphoric Acid

In the phosphoric acid based etchant, the dissolution rates of Mo films were measured by microgravimetry and the corrosion potentials of Mo and Al were estimated by Tafel plot method with various concentrations of nitric acid. Dissolution rate of Mo increased with the nitric acid concentration and reached a limiting value at high concentration of nitric acid in ambient condition. Corrosion potentials of Mo and Al shifted to positive direction and the difference between potentials of both metals was about 1,100 mV and 1,200 mV with 1% and above 4% of HNO 3 , respectively. For a Mo/Al bilayers, the dissolution rate inversion is the main reason for good taper angle in shower etching process. Taper angles are observed by scanning electron microscope (SEM) after wet etching process for Mo/Al layered films with different concentrations of HNO 3 . In the etch side profile, it was found that Al corroded faster than Mo below 4% of HNO 3 in dip etching process, however, Mo corroded faster above 4%. Trend for variation of taper angle of etched side of Mo/Al layered film can be explained by considering the effect corrosion rates of both metals with various concentrations of HNO 3 .

Solvent Extraction of Alkaline Earth Metal Ions by Diglycolic Amides from Nitric Acid Solutions

N,N,N′,N′‐Tetraoctyl‐3‐oxapentane diamide (TODGA) and its homologues were shown to be usefully applied to the extraction of divalent alkaline earth metal: M(II) ions from aqueous solutions of high nitric acid concentration, specifically around 3 M. The stoichiometry of the extracted Sr(II)‐DGA species was found to depend mainly on the concentration of nitric acid and molecular structure of DGA. The degree of extraction of M(II) by TODGA decreases in the order of Ca(II) > Sr(II) > Ba(II).

Tricyclohexylphosphate—A Unique Member in the Neutral Organophosphate Family

Tricyclohexylphosphate (TcyHP) was synthesised and characterized. The extraction of U(VI) and Th(IV) by TcyHP in n‐dodecane was studied and compared with tributylphosphate (TBP). The feasibility of the separation of Th and U with TcyHP has been explored and reported. The solubility of TcyHP in water at room temperature has been measured. The stoichiometry of the TcyHP solvates with Th(NO3)4 and UO2(NO3)2 was evaluated. The enthalpy of extraction of U(VI) by TcyHP was measured. The results of column runs with TcyHP impregnated Amberlite XAD‐7 resin for studying the loading and elution behavior of uranium from nitric acid medium are also reported in this paper. Hexavalent actinides form third phase with neutral organophosphate extractants only at very high nitric acid concentrations and high metal loading. However the presence of the three closed ring alkyl moieties in TcyHP is seen to lead to certain unique features with regard to the third phase formation behavior. It has been observed, for instance, that U(VI) forms third phase with this extractant even with highly polar diluents like 1‐chlorooctane. Further, the tendency for third phase formation with U(VI) is even higher than in the case of Th(IV), in contrast to the trend observed so far with other extractants.

Selective Catalytic Reduction of NO by Methane on Copper Catalysts: the Effects of Modifying the Catalysts with Acids on ?-alumina

This work compares the performance of copper catalysts modified with that of acids. Hence, γ-alumina is used to support the catalyst in the selective catalytic reduction of nitric oxide by hydrocarbons (HC-SCR) using methane at temperatures from 623-1023 K in the presence of oxygen. The copper catalysts were prepared by the incipient wet impregnation of a modified support of γ-alumina with copper nitrate, and by modifying the using nitric, acetic and phosphoric acids, respectively. The effectiveness of the transformation with nitric oxide over the catalysts, determined by comparing the conversion of nitric oxide with non-modified Cu/γ-Al2O3, to that by modified Cu/γ-Al2O3, implied that the reduction of transformation nitric oxide was most efficient when the catalyst modified with nitric acid. Modifying a copper catalyst with nitric acid markedly was found to increase the efficiency of reduction, whereas treatment with acetic and phosphoric acids did not promote the reduction of NO. However, a higher concentration of nitric acid corresponds to a higher efficiency of transformation nitric oxide; thus, converting nitric oxide using the catalyst modified with nitric acid is favored. Pre-treating the support γ-alumina with a higher concentration of acid solution promotes higher activity and greater acidity of the transforming nitric oxide reaction over a copper catalyst, because such pretreatment with acid enlarges the pores in the support, increasing the internal mass transfer and the reactivity over the catalyst. Notably, the presence of Cu (I) and Cu (II) at active sites may also affect the efficiency of the transformative reaction with nitric oxide. When the inlet gas is methane, the corresponding efficiency of the transformation nitric oxide shows that methane is an effective reducing agent.

ALLEGHENY LUDLUM AL 610

Abstract Allegheny Ludlum alloy AL 610 is an austenitic stainless steel alloy with a special composition including high silicon to specifically resist high concentrations of nitric acid. This datasheet provides information on composition, physical properties, hardness, and tensile properties. It also includes information on corrosion resistance as well as joining. Filing Code: SS-819. Producer or source: Allegheny Ludlum Corporation.

THE NOVEL EXTRACTANTS, DIGLYCOLAMIDES, FOR THE EXTRACTION OF LANTHANIDES AND ACTINIDES IN HNO3–n-DODECANE SYSTEM

The novel extractants, six diglycolamides synthesized in our laboratory, were investigated for actinide extraction from nitric acid into n-dodecane. The dependence of the distribution coefficients of Eu(III) and Am(III) on the length of alkyl chain in the extractants was examined. Among the diglycolamides studied, N,N,N′,N′-tetraoctyl-3-oxapentanediamide (TOOPDA) and N,N,N′,N′-tetradecyl-3-oxapentanediamide (TDOPDA) showed a sufficient solubility in n-dodecane, due to their appropriate lipophilicity modified by increasing the length of the alkyl chain attached to amidic N atoms. The distribution coefficients, D M, of actinides obtained by TOOPDA increased with an increase in HNO3 concentration. The number of diglycolamide molecules coordinated to the actinide ions was estimated to be three for Th(IV), U(VI), Pu(IV), and four for Am(III) and Cm(III) by slope analysis. The order of D M for the actinides at high nitric acid concentrations is An(III), An(IV) > An(VI) > An(V) and that for lanthanides, heavier > lighter. It is concluded that TOOPDA diluted in n-dodecane can extract both actinides and lanthanides completely from aqueous HNO3 solution.

Solvent extraction of lanthanides with triisoamylphosphate and di-(2-ethylhexyl)phosphoric acid from trichloroacetic acid and nitric acid solutions

The study on solvent extraction of some rare earth elements with triisoamyl phosphate (TiAP) and a mixture of TiAP and di-(2-ethylhexyl)phosphoric acid (D2EHPA) from trichloroacetic acid and nitric acid solutions has been carried out. It was found that Y has been more effectively extracted with TiAP from the trichloroacetic acid solution than from the mono and dichloroacetic acid solutions. The influence of various factors such as acid, RE and salting-out agent concentrations on the distribution ratio has been studied. The synergistic extraction effects were observed for low trichloroacetic acid and high nitric acid concentrations. The influence of the TiAP–D2EHPA ratio and the total concentration of two extractants, as well as acid concentration on the synergistic extraction ratio has been investigated. RE extraction isotherms by TiAP and D2EHPA alone and by a mixture of these extractants in the above extraction systems were established.

N,N-Dihexyl Hexanamide: A Promising Extractant for Nuclear Fuel Reprocessing

N,N-Dialkyl amides have drawn the attention of radiochemists engaged in the development of alternate extractants to tri-n-butyl phosphate (TBP) for the reprocessing of irradiated fuels, particularly with high radiation fields and high plutonium content. Dihexyl hexanamide (DHHA) has been found to be a promising extractant in this direction. Log K ex values for the extraction of UO2(NO3)2·2DHHA and Pu(NO3)4·2DHHA in n-dodecane were found to be 1.43 and 3.62, respectively. At high nitric acid concentration (5 M), the amide undergoes protonation and extracts U(VI) and Pu(IV) as ion pairs of the type (UO2(NO3)3 −)(HDHHA+) and (Pu(NO3)6 2−)(HDHHA+)2. At trace level concentrations, the distribution coefficient (D) of Pu(IV) and U(VI) with a 1 M solution of DHHA in n-dodecane at 3.5 M HNO3 are 41.2 and 13.5, respectively. Similarly, at 50% uranium saturation of the organic phase the D values of Pu(IV) and U(VI) are 9.2 and 4.2, respectively. These results suggest the distinct advantages of DHHA over TBP in improved extraction of Pu and ease of stripping of uranium. The separation factors for 0.5 M DHHA at 30 Mrad are obtained as ∼37 (U/Zr) and ∼75 (Pu/Zr), suggesting that this extractant is particularly promising for the selectivity of Pu and U over Zr from irradiated solutions as compared to TBP. Results obtained during this work demonstrate the potential of amides in meeting the challenges posed by the large Pu content and high radiation fields encountered during the reprocessing of Pu-based fuels discharged from thermal as well as fast power reactors.

Removal of Cu(II), Zn(II), Cd(III) and Hg(II) from waste water by poly(acrylaminophosphonic)-type chelating fiber

The distribution coefficients (D) for Cu(II), Cd(II), Zn(II) and Hg(II) ions and adsorption isotherms of Cd(II) and Hg(II) ions on the poly(acrylaminophosphonic)-type chelating fiber were investigated using the batch reactor system. It was found that D values for the tested metal ions were above the magnitude of 10 3 at pH 5.0, and the order of metal ion affinities was: Hg(II) > Cu(II) > Zn(II) > Cd(II). At low pH value (2.0), D value for Hg(II) ion was higher than that of the other ions, above 10 3. The adsorption of Hg(II) and Cd(II) ions on the new chelating fiber followed a Langtnuir-type adsorption isotherm. The elution of the metal ions from the chelating fiber column using dilute nitric and hydrochloric acid as eluent were examined. The results show that the elution for Cu(II), Cd(II) and Zn(II) ion was complete using appropriate concentration of hydrochloric acid, while the high concentration of dilute nitric acid was necessary for the quantitative desorption of fig(II) ion. The breakthrough curves for the metal ions were determined, and the efficient removal of the listed metal ions from model or waste water by the newly developed fibrous sorbent was achieved.

Leaching of Lead Sulfide with Nitric Acid

ABSTRACT Galena, lead sulfide, is leached with nitric acid in order to prepare higher value-added products such as lead nitrate, lead carbonate, lead basic carbonate, etc. Leaching behavior has varied with the concentration of nitric acid. At the lower concentration of nitric acid, galena is dissolved into lead nitrate and hydrogen sulfide. However, at the higher concentration of nitric acid, galena is not dissolved but it is changed into lead sulfate as precipitate. The leaching efficiency is strongly dependent upon temperature and nitric acid concentration. The optimal conditions are found to be 40°C and 4–8 N nitric acid where about 95% of lead can be dissolved from lead sulfide.

Characterization of the vapor-phase molecular and atomic absorption from sea water matrices in electrothermal atomic absorption spectrometry

Vaporization of sea water was investigated by molecular and atomic absorption spectrometry. Using the combination of an ultraviolet spectrometer with multi-channel detector and an electrothermal atomizer, vapor-phase absorption was monitored in the wavelength region between 200 and 400 nm. The effects of the vaporization temperature, thermal pretreatment, internal gas flow and use of nitric acid as matrix modifier on the composition of the vapor phase were investigated using tube, platform and filter furnaces. Moreover, solutions of the main components of sea water (chlorides and sulfates of sodium, magnesium and calcium) were vaporized to clarify the contribution of each salt to the overall absorption. The addition of nitric acid to sea water led to partial suppression of the intense NaCl bands and to the appearance of oxygen containing species. Total suppression of chlorides could not be attained even with high concentration of nitric acid (more than 8% m/m). Molecular bands attributed to NaCl, NaO x , MgCl, CaCl, SO x and NO species were observed at different stages of the vaporization process. In the filter furnace, the bands of the oxygen containing molecules were less intense due to the reaction with carbon. An intense spectral continuum, attributed to light scattering, was decreased with the filter furnace relative to that observed for the tube and platform furnaces with the gas stop mode of operation.

THE SOLVENT EXTRACTION OF AMERICIUM(III) IN HCl SOLUTIONS BY 2,6-BIS[(DIPHENYLPHOSPHINO)METHYL]PYRIDINE N,P,P'- TRIOXIDE

ABSTRACT The liquid/liquid extraction of Am(III) from nitric acid solutions with chloroform solutions of 2,6 bis[(diphenylphosphino)methyl] pyridine N,P,P′ trioxide (ENOPOPO) is examined. Americium(IU) is efficiently extracted from aqueous solutions at high nitric acid concentrations (DAM0>3000 at 6M HNO3) and can be totally back extracted from the organic phase at 0.01M HNO3. The ligand dependency data suggest that two ligand molecules are coordinated to the americium. Additional aspects of the extraction mechanism are described.

Effect of dissolved chromium species on the corrosionof stainless steel in nitric acid

The effect of Cr(vi) species in HNO3 (concentrations 15–3m) on the corrosion rate of stainless steel has been investigated. The gaseous phase over the HNO3 was carefully controlled using Ar, NO, NO2 or N2 purging. With Ar purging the corrosion rate increased when the Cr(vi) concentrations were above 0.05m. There was evidence that the reduction of Cr(vi) leads to insoluble Cr reduction products on the surface of the steel. Sparging of nitric acid by NO and/or NO2 caused the reduction of any Cr(vi) species present in the solution, to Cr(iii) in a few minutes. However, with no Cr(vi) present, the effect of continuous purging with NO and/or NO2 was to increase the steel corrosion rate when compared with Ar purged solutions, due to catalysis of nitrate reduction by the NOx. The conversion of Cr(iii) to Cr(vi) by nitric acid was shown to require high concentrations of nitric acid, high temperatures and low partial pressures of NO2 over the liquid phase.

Recovery of plutonium and americium from laboratory acidic waste solutions using tri- n-octylamine and octylphenyl- N- N- diisobutylcarbamoylmethylphosphine oxide

Plutonium from acidic waste solutions has been recovered quantitatively using tri- n-octylamine (TnOA) in xylene and americium using a mixture of octylphenyl- N- N- diisobutylcarbamoylmethylphosphine oxide (CMPO) and TBP in dodecane by extraction and extraction chromatographic methods. The Pu( IV) TnOA species extracted into the organic phase from higher nitric acid concentrations has been confirmed as (R 3NH) 2Pu(NO 3) 6 (where R 3N = TnOA by employing slope analysis as well as spectrophotometric studies.

The Mechanism of the Photoelectrochemical Etching of p‐InP in Nitric Acid Solutions

The mechanism of the photoelectrochemical (PEC) etching of p‐InP in nitric acid was investigated. The success of the procedure is shown to be due to the chemical oxidation of the photoproduced metallic indium by nitric acid. The study gives insight into how the photoreduction of p‐InP and protons occur simultaneously. Plots of the etch rate vs. nitric acid concentration for two p‐InP electrodes with different carrier concentrations and etch pit densities (EPD) indicated that defects play a role in the photoreduction process. The effect of EPD on the photoreductions has been interpreted in terms of surface states which originate from EPD; the EPD are correlated with the magnitude of the surface states. The total number of coulombs passed in the PEG etching region was found to be relatively constant for each p‐InP electrode. Comparison of the charge transferred with the PEC etch rates indicated that the majority of protons are photoreduced via surface states. A positive shift of the onset potential for photocurrent with increasing nitric acid concentrations implied a decrease in the density of surface states. This observation was correlated with the participation of the conduction band in the photoreduction of p‐InP. At higher nitric acid concentrations, experiments indicate that the photoreduction of protons is possible at both the surface states and conduction band. Energy diagrams lend support to these suppositions.

Observations of high concentrations of total reactive nitrogen (NOy) and nitric acid (HNO3) in the lower Arctic stratosphere during the Stratosphere‐Troposphere Experiment by Aircraft Measurements (STREAM) II campaign in February 1995

Simultaneous in situ measurements of NOy, HNO3, O3, N2O, and CO have been performed in the lower stratosphere during the Stratosphere‐Troposphere Experiment by Aircraft Measurements (STREAM) II intensive winter campaign in February 1995 from Kiruna airport (northern Sweden) with a Cessna Citation II twinjet aircraft up to a maximum altitude of 12.8 km. The flights were coordinated with the Arctic Second European Stratospheric Arctic and Midlatitude Experiment (SESAME) winter campaign. Strongly elevated levels of total reactive nitrogen (NOy) and its most abundant contributing species, nitric acid (HNO3), with mixing ratios up to 9 parts per billion by volume (ppbv), were observed during all flights at altitudes near 12 km. On average, the measured NOy concentrations exceed the expected levels by a factor of 2–3. Normal background NOy has been calculated from observed N2O mixing ratios using the NOy‐N2O correlation reported for the undisturbed northern hemisphere. This indicates that subsidence of air in the vortex alone cannot explain these findings. We propose that the elevated NOy concentrations were caused by nitrification of the lower stratosphere associated with sedimentation and evaporation of polar stratospheric cloud particles that carry down HNO3 from higher altitudes, that is, from altitudes up to about 25 km.

Modified TRUEX Process for the Treatment of High-Level Liquid Waste

The TRUEX process has been examined to recover Am and Cm from the high-level liquid waste of Purex reprocessing plant. Continuous counter current extraction and back-extraction experiments were carried out by a mixersettler using simulated waste solution for three process flowsheets, i.e. a process flowsheet developed by Argonne National Laboratory and other two process flowsheets which were modified in the scrub stage. The result indicates that the process flowsheet of Argonne National Laboratory cannot be applied for the high-level liquid waste containing high concentrations of lanthanide and actinide elements because of the formation of insoluble salts of these elements with oxalic acid, which is added to restrict the extraction of fission products such as Mo and Zr. A modified process flowsheet, which had only one scrub stage with high concentration of nitric acid, was found to be the best of three process flowsheets examined, where Nd as a simulated element of Am and Cm was sufficiently recovered and any precipitation of oxalate salt was not observed.