High Nitric Acid Concentrations Research Articles

THE SOLVENT EXTRACTION OF AMERICIUM(III) IN HNO3 SOLUTIONS BY 2,6-BIS[(DIPHENYIJHOSPHINO) 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.

Extraction of uranium (VI), plutonium (IV) and some fission products by tri-iso-amyl phosphate

The extractive properties of tri-isoamyl-phosphate (TAP), an indigenously prepared extractant, and the loading capacity of extraction solvent containing TAP for U(VI) and Pu(IV) ions in nitric solution have been investigated. The dependence of the distribution ratio on the concentration of nitric acid showed that TAP has an ability to extract these actinides, while the fission product contaminants are poorly extracted. The distribution data revealed a quantitative extraction of both U(VI) and Pu(IV) from moderate nitric acidities in the range 2–7 mol · dm−3. Slope analysis proved predominant formation of the disolvated organic phase complex of the type UO2(NO3). 2TAP and Pu(NO3)4·2TAP with U(VI) and PU(IV), respectively. On the contrary, the extraction of fission product contaminants such as144Ce,137Cs,9Nb.,147Pr,106Ru,95Zr was almost negligible even at very high nitric acid concentrations in the aqueous phase indicating its potential application in actinide partitioning. The recovery of TAP from the loaded actinides could be easily accomplished by using a dilute sodium carbonate solution or acidified distiled water (≈0.01 mol · dm−3 HNO3) as the strippant for U(VI) and using uranous nitrate or ferrous sulphamate as that for Pu(IV). Radiation stability of TAP was adequate for most of the process applications.

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...

Solvent extraction of metal ions from nitric acid solution using N,N ′-substituted malonamides. Experimental and crystallographic evidence for two mechanisms of extraction, metal complexation and ion-pair formation

The solvent extraction of actinides including Am III and Cm III together with some trivalent lanthanides from nitric acid solutions by two newly synthesized malonamides, N,N′-dimethyl-N,N′ -diphenyltetradecylmalonamide (dmptdma) and N,N′-dicyclohexyl-N,N′ -dimethyltetradecylmalonamide (dcmtdma) has been investigated and compared with data for the reference malonamide, N,N′-dibutyl-N,N′ -dimethyloctadecylmalonamide (dbmocma). The dependence of the extraction on the nitric acid and malonamide concentrations together with the probable molecular structure of the extraction species from nitric acid solution suggests that there are two principal mechanisms of extraction. For low nitric acid concentrations (up to 1 mol dm -3 ) a co-ordinative mechanism dominates for the extraction of metal cations, whereas at higher nitric acid concentrations (1–14 mol dm -3 ) an ion-pair mechanism involving the mono- or di-protonated malonamide and the metal anions [M(NO 3 ) 4 ] - or [M(NO 3 ) 5 ] 2- appears to be more important. Crystal structures show that in the protonated, unalkylated species Hdcmma + (dcmma = N,N′-dicyclohexyl-N ,N′-dimethylmalonamide) and in the chelated complexes [Nd(NO 3 ) 3 (dcmma) 2 ], [Nd(NO 3 ) 3 (H 2 O) 2 (dmpma)] and [Yb(NO 3 ) 3 (H 2 O)(dmpma)] (dmpma = N,N′-dimethyl-N ,N′-diphenylmalonamide) the carbonyl oxygens lie cis to each other suggesting that it is the cis form which is involved in extraction. However, crystal structures of the free unalkylated malonamides N,N′-dicyclohexyl-N,N′ -diethylmalonamide and N,N′-dicyclohexyl-N,N′ -diisopropylmalonamide show that the carbonyl amide groups adopt a trans configuration in which the carbonyl oxygens are at maximum separation. By contrast, in the crystal structure of the diphenyl derivative dmpma the carbonyl amide groups adopt a gauche configuration with an OC · · · C O torsion angle of 57.2°. Conformational analysis confirms that the differences in these structures reflect the differences between the lowest-energy gas-phase conformations and are not caused by packing effects.

EXTRACTION SEPARATION OF MOLYBDENUM(VI) AND TUNGSTEN(VI) BY α-HYDROXY OXIM

ABSTRACT Solvent extraction of molybdenum(VI) and tungsten(VI) with α-hydroxy oxime, 5,8-diethyl-7-hydroxydodecan-6-one oxime (LIX 63) from acidic and neutral solutions was studied. The rate of extraction of molybdenum(VI) was much higher than that of tungsten(Vl). Molybdenum(VI) was almost quantitatively extracted from nitric acid solutions up to 5 M, and the extraction decreased at higher acid concentrations. The extraction of tungsten was rather low at short contact time. The separation of molybdenum(VI) from a large amount of tungsten(VI) was accomplished around pH 1 by contacting for 10 minutes, yielding the separation factor of αMo( = DMo/DW) = 166. Molybdenum(VI) was separated from several metal ions such as Fe(III), Co(II), Ni(II), Zn(II) and Cu(II). At high nitric acid concentrations, tungsten(VI) was preferentially extracted for a long shaking time. The elemental analyses of the extracted species and their IR and NMR spectra suggest the coordination of two molecules of LIX 63 onto MoO2 2+ and WO...

MERCURY EXTRACTION BY THE TRUEX PROCESS SOLVENT. I. KINETICS, EXTRACTABLE SPECIES, & DEPENDENCE ON NITRIC ACID CONCENTRATION1

ABSTRACT Mercury extraction from acidic aqueous solutions by the TRUEX process solvent (0.2 M CMPO - 1.4 M TBP in n-dodecane) has not extensively been examined. Research at the Idaho Chemical Processing Plant (ICPP) is currently being conducted to evaluate the TRUEX process for actinide removal from several acidic waste streams, including liquid sodium-bearing waste (SBW), which contains significant quantities of mercury. Preliminary experiments were performed involving the extraction of Hg203, added as HgCl2, from 0.01 to 10 M HNO3 solutions. Mercury distribution coefficients (DHg) range between 3 and 60 from 0.01 M to 2 M HNO3. At higher nitric acid concentrations, i.e. 5 M HNO3 or greater, DHg significantly decreases to values less than 1. These results indicate mercury is extracted from acidic solutions ˜5 M HNO3. Experimental results indicate the extractable species is HgCl2 from nitrate media, i.e., chloride must be present in the nitrate feed to e...

イオン交換速度に及ぼすアンチモン酸リチウムへのカリウム添加の影響

Lithium antimonate (Sample L) and lithium antimonate containing 5 mol % of potassium antimonate (Sample K) were synthesized by a pyrometallurgical method. Lithium ion in lithium antimonate was exchanged with proton in a nitric acid solution by using the column method and the batch method. The effects of temperature and nitric acid concentration on the ion exchange rate were investigated, and following results were obtained.(1) The ion exchange of sample K proceeded more rapid than that of sample L.(2) The ion exchange rate was fit to the following equation.1-2/3a-(1-a)2/3=ktwhere a, k, and t are fraction reacted, apparent rate constant, and time, respectively.(3) Arrhenius plots of the apparent rate constant showed that the apparent activation energy for the sample K and sample L were about 100kJ/mol and 130 kJ/mol, respectively.(4) The nitric acid did not affect the apparent rate constant at high concentration region.(5) The rate-controlling step for the ion exchange was diffusion of lithium ion in the sample at high nitric acid concentration region.(6) The enhancement of the ion exchange rate can be attributed to the formation of potassium solid solution and the decrease in particle size by the coexistence of potassium antimonate.

Effect of Some Substituted Anilines on the Corrosion of Iron in Nitric Acid Solutions

Introduction The corrosion of iron has been extensively studied in various media. In nitric acid solutions, the corrosion of iron is much faster than in other mineral acids at comparable concentrations. This is attributed to an autocatalytic process involving some nitrogen oxides, nitrous acid and/or some iron complexes. At high nitric acid concentrations, passivation of iron takes place. The factors affecting the dissolution and the passivation processes are not fully understood. The effect of various inhibitors on the corrosion of iron in acid media has been studied. Thus Ammar et al. have studied the passivation of iron and the effect of some anions, e.g. Br− and I− on the passive film. The effect of amides as inhibitors for iron in nitric acid has been reported by Fouda and Gouda. These authors have found that the corrosion process is controlled by the reaction of amides with HNO3 and not by the surface reaction. The effect of aniline and some aminobenzoic acids on the rate of corrosion of iron has been reported. The present work is aimed at examining the efficiencies of some aniline substitutes as corrosion inhibitors for the corrosion of iron in concentrated nitric acid solution.

Separation and preconcentration of actinides from acidic media by extraction chromatography

A systematic examination of the effect of nitric and hydrochloric acid concentrations and of macro levels of selected elements on the sorption of actinide ions by a novel extraction chromatographic resin comprised of a solution of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide in tri-n-butyl phosphate supported on an inert polymeric substrate is described. Actinide sorption is demostrated to be most efficient at high ( > 1 M) nitric acid concentrations, although tetra- and hexavalent actinides are strongly retained even from dilute (e.g., 0.05 M) nitric acid solutions. Macro concentrations of several common anions (e.g., PO−34 and SO2−4 or complexing agents (e.g., oxalic acid) are shown not to adversely affect the sorption of trivalent actinides, while reducing the sorption of tetravalents. Such effects, together with oxidation state adjustments, are shown to provide a basis for the sequential elution of individual actinides and for actinide isolation from environmental and biological matrices.

Application of ultrasonic nebulization for the determination of rare earth elements in phosphates and related sedimentary rocks using inductively coupled plasma atomic emission spectrometry with comments on dissolution procedures

Low concentrations of all the rare earth elements (REE) can be determined in geological materials using ultrasonic nebulization and inductively coupled plasma atomic emission spectrometry (USN-ICP-AES). Using a matrix matched calibration procedure to compensate for an acid effect on REE spectral line intensities, caused by high concentrations of nitric acid, in-house and international geological reference materials were analysed. Provided that a total decomposition method was used, the data obtained compared well with those from the literature. Yttrium, La, Ce, Eu and Yb were also determined directly because of their superior limits of detection, relatively high abundance in geological samples, and freedom from spectral line interference as a result of the high resolution of the spectrometers. Various Sample decomposition procedures were evaluated for the determination of REE in sedimentary rocks. The solutions obtained by decomposition with various acids (HCl, HNO3, HClO4 and HF) and sodium peroxide sintering and leaching were preconcentrated using a DOWEX 50 W × 8 ion-exchange column. Significant differences in Y, La and Ce concentrations occurred when the sediment samples were submitted to different methods of sample decomposition. Indeed, REE distributions between acid soluble and total samples differed significantly, having different Y:Ce, Y:La and La:Ce ratios.

Technetium-99 Removal from Process Solutions and Contaminated Groundwater

Abstract The predominant form of technetium under oxic conditions is the pertechnetate anion (TcO4 −), which is highly soluble in water and readily mobile in the environment. Technetium-99 is of particular concern because of its persistence and mobility. Various equipment decontamination and uranium recovery operations at the Portsmouth Gaseous Diffusion Plant generate a “raffinate” waste stream characterized by toxic heavy metals, high concentration of nitric acid, and low levels of radionuclides (235u and 99Tc). Dilution and adjustment of solution pH to a value of 8.2 to 8.5 precipitates a heavy-metals-sludge and a filtrate. The removal of 99Tc from these waste streams and from contaminated groundwater can be accomplished using anionic ion-exchange resins. Batch equilibrium and packed column breakthrough and regeneration studies were performed using inorganic sorbenta and organic ion-exchange resins (Dowex SRB-OH and Reillex resins). These studies were performed on actual and surrogate raw raffinates, f...

Determination of nitric acid concentration by using europium ion fluorescence

A method is presented for the determination of 2–1O M nitric acid based on the fact that the presence of high nitric acid concentration causes an enhancement of the intensity of some bands in the fluorescence spectra of rare earth ions in solution. The 616-nm band of Eu 3+ shows the most dramatic intensity enhancement with increasing nitric acid concentration. The present method, based on the measurement of the ratio of Eu 3+ fluorescent band intensities is shown to be independent of Eu 3+ concentration and realtively free of interference. This robust method allows the presence of an interferent to be determined from the experimental data.

A comparison of the effects on Canadian boreal forest lichens of nitric and sulphuric acids as sources of rain acidity.

The effects of different levels of nitrate and sulphate in acidic precipitation on the growth of the lichens Cladina rangiferina (L.) Wigg. and C. stellaris (Opiz.) Brodo were compared. Permanent Held plots in a Canadian boreal forest ecosystem received two years of spraying with artificial rains of pH 4.2 (ambient), 3.5 or 2.8, each containing one of four molar ratios of sulphate to nitrate, i.e. sulphuric acid alone, nitric acid alone: 2:1 or 1:2. A substantial fertilization effect was observed when C. rangiferina was watered with rain of pH 2.8, derived from nitric acid alone. Compared with before-treatment values, gains in mean dry weight (+ 62%) and mean podetial height (+14%) were obtained for this species, in addition to elevated levels of N in air-dried tissues. Post-treatment values for the mean dry weight of C. rangiferina were significantly reduced for those podetia sprayed with rain of low pH, derived from sulphuric acid alone. Although podetia of C. stellaris were stimulated by rains of pH 4.2, based on a higher concentration of nitric acid, there was no N fertilization following the most acidic sprays. Data from this study support the view that the N content of acidic rain can cause a short-term growth stimulation for those species able to absorb nitrate from solution. However, beneficial effects on growth of prolonged fertilization via acid rain inputs are unlikely.

Photochemical oxidant pollution and vegetation: Effects of mixtures of gases, fog and particles

Photochemical ‘smog’ contains mixtures of gases (e.g. ozone, nitrogen dioxide), and dry particles (e.g. nitrates). Intermittent fog in the same geographical area can be acidic with high concentrations of nitric acid. Results from recent field studies in the Los Angeles Basin have emphasized the relative toxicity of these components of photochemical air pollution. Studies have focused on gaseous+fog or gaseous+dry particulate effects on conifers, gaseous+fog effects on crops, and the effects of trace pollutants produced during generation of ozone on crops. Data from these studies indicate that direct alterations in growth and physiological responses were observed only with gaseous pollutants (primarily ozone), or repeated applications of highly acidic fogs (pH < 2·7). Direct particle dry deposition effects are unclear. Few interactions have been found between gaseous pollutants and acidic fog. Charcoal-filtered open-top chambers are highly effective in removing pollutants in the following order: fog (100%) > peroxyacetyl nitrate > ozone > nitrogen dioxide > sulfur dioxide > nitrate ion > ammonium ion > sulfate ion. However, nitric oxide concentrations are higher in charcoal-filtered chambers than in ambient air. The studies point out the importance of considering other components of photochemical pollution in addition to ozone, especially when investigating subtle, long-term effects on vegetation.

Graphite-furnace AAS - Application of reduced palladium as a chemical modifier

Chemical modification techniques are widely used in graphite furnace atomic absorption spectrometry (GFAAS). Palladium is a very effective chemical modifier and can be used to stabilize many elements to several hundred degrees higher than the temperatures possible with current methods [1-9]. Of the elements tested, the greatest temperature shifts are achieved for the semi-metallic elements such as As, Se, Te, Bi, Sb, Pb, TI, Ga, Ge and P. Ash temperatures can be raised 400-800 'C higher than current methods allow. Temperature shifts are somewhat less for the transition elements and ash temperatures can be raised 200-500'C. Palladium has no similar effect on elements in Groups I and 11 of the Periodic Table. The change in stability is believed to be due to the formation of an intermetallic species. This improvement in stability permits more efficient removal of matrix constituents during the ash step and vaporization into a hotter environment during the atomize step. Background and interference problems are thus reduced or eliminated. Steps taken to guarantee that palladium is present as the reduced metal as early as possible greatly improve performance of the modifier. The palladium modifier solution can be pre-injected and the graphite tube heated to 1000 'C. Such a method has been used to stabilize mercury [10]. It is assumed that at this temperature palladium metal is present on the graphite surface. The sample can then be introduced. The addition of a reducing agent such as 5% hydrogen in 95% argon, ascorbic acid, or hydroxylamine hydrochloride also appears to guarantee that the palladium is present as the metal early in the temperature program. The use of hydrogen as a reducing agent appears to be the method of choice for a number of reasons. It is cleaner, leaves no residue, and is less subject to contamination. It is also easy to use. A pre-mixed gas of 5% hydrogen in 95% argon can simply be introduced into the furnace. More importantly, the problem encountered with high concentrations of nitric acid is eliminated with the use of hydrogen. Reduced palladium metal allows the retention of the analyte element on the graphite surface until a higher gas phase temperature is achieved. This appears to give many of the analytical advantages normally associated with platform atomization while using the simpler wall atomization technique. Investigations to elucidate the mechanism of palladium chemical modification have been conducted. Also, comparison of palladium modifier methods with current modifier methods in spike recovery studies from difficult matrices was accomplished. Scanning electron micrographs of graphite surfaces with palladium deposits obtained by different reduction methods were obtained to investigate whether the physical form of palladium influenced the modifier behavior. It was found that reduced palladium metal was indeed present on the graphite surface after reduction and that the most effective reduction method was the use of 5% hydrogen in 95% argon with a palladium solution containing 1% glycerol. The scanning electron micrograph of the surface produced under these conditions is shown in figure 1. The palladium particles are considerably smaller and more highly dispersed than those produced by other methods. The average particle diameter is 0.05-0.15 pAm. The smaller particles result in a great increase in palladium surface area. Spike recovery studies from difficult matrices showed that smaller, highly dispersed particles produced improved interference performance. The interference performance of a palladium/ hydrogen/glycerol method for tin was compared with the performance of a commonly used method. The commonly used method requires the use of the platform and chemical modifiers of ammonium dihydrogen phosphate and magnesium nitrate. Wall atomization was used for the palladium method. The results of this study are listed in table 1. While both methods performed well in concentrated HCl, in most instances the palladium gave slightly better interference performance. It was significantly better in overcoming interferences from NaCI and seawater matrices. Other elements have been tested in the same matrices and, in virtually every instance, palladium gave as good as or better interference performance (wall) as did the currently used methods (platform).

Modification of cation-exchange properties of activated carbon by treatment with nitric acid

The uptake of inorganic cations by high-surface-area activated carbon can be increased by an order of magnitude by controlled exposure to high concentrations of nitric acid at elevated temperatures. Distribution coefficients of cations are also increased. Acid strength of the functional groups from the nitric acid treatment is greater than those of the starting material. Surface area measurements and small- angel neutron scattering indicate that the increase in effective ion-exchange capacity is not accompanied by gross changes in the structure of the material. 13C NMR on solid samples suggests that the concentration of carboxyl and phenolic functional groups in the carbon is increased by the treatment.

Denitrification of nitrate and nitric acid with methanol as carbon source

A methanol/nitrate-medium and anaerobic conditions yielded an enrichment culture which consisted ofHyphomicrobium andParacoccus. This mixed culture proved to be very effective in denitrification of solutions containing high concentrations of nitrate and free nitric acid when grown in a chemostat (D=0.04 h-1). With 0.1 mol/l nitric acid solution as feed medium the pH in the culture vessel adjusted itself to 5.8. For the reduction of 1 g NO3−N 2.6 g methanol were consumed and 0.56 g cells were produced.

On the Sorption Behaviour of Some Cations on Cobalt Hexacyanoferrate(III) Exchanger. Binary Separations of Rb+ and Cs+ on Columns

Abstract Sorption behaviour of Ag, Cs, Rb, Co(II), Zn(II), and Fe(III) ions at low concentration (0.2 mmol) is studied in different concentrations of nitric acid and ammonium nitrate on cobalt hexacyanoferrate(III) exchanger. logKdvs. log concentration plots show that the sorption of these ions is not followed through ion exchange mechanism, only. In case of Rb+ and Cs+, a very low Kd is observed at high concentration of nitric acid (&amp;gt;5 mol dm−3) thereby showing the possibility of their elution on columns. For various other ions, such as Ba, Sr, Mn, Hg(II), Mg, Cd, Ca, Pb, Ni, La, and Th, the Kd values are almost zero. Thus the binary separation of Rb+ and Cs+ from a number of ions on the columns of this exchanger has been carried out.

Spectrophotometric determination of selenium with dithizone

Microgram amounts of selenium(IV) are determined by measuring the decrease in absorbance of dithizone in carbon tetrachloride solution at 620 nm. Relative standard deviations for samples containing 0.20 and 1.00 μg of selenium(IV) are 0.6% and 0.4%, respectively. Of several metals tested only copper (at the 1.0-μg level) and iron (at the 100-μg level) interfere but high concentrations of nitric or perchloric acid cause low results. A reinvestigation of the reaction of selenium(IV) with dithizone suggests a formula Se(HDz) 4 for the dithizonate.

Kinetics, mechanism, and stoicheiometry of the oxidation of hydroxylamine by nitric acid

Hydroxylamine is oxidised by nitric acid to form dinitrogen monoxide and nitrous acid, the proportions varying with reaction conditions. The yield [HNO2]∞/[NH3OH+]0 is a maximum at ca. 4–5 mol dm–3 HNO3, and is also a function of the hydroxylamine concentration. In 5 mol dm–3 HNO3 the limiting yield is ca. 0.85 at very low initial hydroxylamine concentrations, but decreases towards zero at higher values of [NH3OH+]0. Reaction is only observed at sufficiently high nitric acid concentrations; at 25°C the cut-off point is ca. 2.5 mol dm–3 HNO3. The reaction is characterised by an induction period, followed by a rapid autocatalytic process. Addition of nitrite eliminates the induction period, while addition of nitrite scavengers completely prevents any reaction. Nitrous acid is an essential catalyst for the reaction, and the initial rate of reaction obeys the equation d[HNO2]/dt=V0=K[HNO2][NH3OH+]. Isotopic experiments, using 15N-enriched hydroxylamine show that virtually all of the N2O arises from reaction between HNO2 and hydroxylamine. The mechanism suggested involves oxidation of unprotonated hydroxylamine by N2O4 to form the nitroxyl diradical HNO; this is then further oxidised to HNO2, which reacts with hydroxylamine to form N2O.