Function Of Nitric Acid Concentration Research Articles

EFFECT OF EXTRACTANT STRUCTURE ON THIRD PHASE FORMATION IN THE EXTRACTION OF URANIUM AND NITRIC ACID BY N,N-DIALKYL AMIDES

The influence of the molecular structure of amides on the third phase formation in the extraction of uranium and nitric acid was investigated. Nine amides namely, dibutyl hexanamide (DBHA), diisobutyl hexanamide (DiBHA), dibutyl octanamide (DBOA), dihexyl hexanamide (DHHA), dibutyl dodecanamide (DBDA), diiso-octyl butanamide (DiOBA), di n-octyl isobutanamide (DOiBA), di n-octyl butanamide (DOBA), and di n-octyl hexanamide (DOHA) were synthesized and used. The limiting organic concentration (LOC) of uranium (VI) for third phase formation was studied as a function of nitric acid concentration using 0.5 M solutions of these amides in dodecane. The LOC for extraction from neutral medium (with near zero free acidity) was also measured at four different temperatures. The LOC values were found to increase in general with an increase in the total number of carbon atoms in the amide from 14 to 22. The LOC values of DBHA (C. No. 14), DiBHA (C. No. 14), DBOA (C. No. 16) were lower compared to that of DHHA (C. No. 18), DBDA (C. No. 20), DOHA (C. No. 22), which have relatively longer carbon chain length. Further it was observed that introduction of branching at the nitrogen side increases the LOC value as compared to the straight chain analogue, as in the case of DiOBA and DiBHA. In the latter case, however, this effect is not very pronounced perhaps due to the smaller carbon chain length. Introduction of branching at the position alpha to the carbonyl group was found to sharply decrease the LOC value due to steric hindrance as can be seen in the case of DOBA and DOiBA. Further, by varying the carbon chain length on both acyl and nitrogen sides, keeping the total carbon number invariant, it was found that the LOC increases considerably on increasing the chain length on the acyl side. On the contrary, the LOC for nitric acid extraction was not influenced significantly by the structure of the amide. Nevertheless, the distribution ratio at the point of dissolution of the third phase was found to decrease with introduction of branching on either end of the amide and more so, if branching was introduced on the acyl end of the amide.

THIRD PHASE FORMATION IN THE EXTRACTION OF URANYL NITRATE BY N,N-DIALKYL ALIPHATIC AMIDES

ABSTRACT Studies on third phase formation during the extraction of uranyl nitrate from nitric acid media by N,N-dihexyl derivatives of n-hexanamide (DHHA) and n-octanamide (DHOA) in n-dodecane have been carried out. Limiting organic concentration (LOC) of uranium(VI), above which the third phase formation takes place, has been evaluated as a function of nitric acid concentration, extractant concentration, temperature and the ionic strength of the aqueous phase. Limiting organic concentration (LOC) of HNO3, above which the third phase formation occurs has been evaluated as a function of nitric acid concentration as well as extractant concentration. The influence of phase modifiers on LOC is also examined. Results indicate that the LOC value obtained for DHOA is significantly higher as compared to that for DHHA. Uranium analysis of third phase formed has been carried out. Viscosity data on U(VI) - DHOA -n dodecane system has also been obtained.

N,N,N',N'-tetrahexylsuccinylamide as a new extractant for the extraction of nitric acid, uranium(VI) and thorium(IV) ions

N,N,N′,N′-tetrahexylsuccinylamide (THSA) was used for the extraction of U(VI) and Th(IV) ions from nitric acid media into n-dodecane. Extraction distribution ratios of U(VI) and Th(IV) as a function of nitric acid concentration, extractant concentration and temperature have been studied. It was found that THSA as a new extractant is superior in some aspects to TBP for extraction of U(VI) and Th(IV). The extraction of nitric acid was also investigated. At low acidity, the main adduct of THSA and HNO3 is THSA·HNO3. THSA·(HNO3)2 and THSA·(HNO3)3 also formed at high acidity. The composition of the species, equilibrium constants and enthalpies of the extraction reactions have also been calculated. The suggested formation of the 1:2:1 ratio of uranyl(VI) ion and the 1:4:2 ratio of thorium(IV) ion, nitrate ion and THSA as the extracted species was further confirmed by the IR spectra of U(VI) and Th(IV) extracts.

Quantitative separation of carrier-free cerium from fission products

The extraction of Ce (IV) by di-(2-ethylhexyl)-phosphoric acid (HDEHP) has been studied as a function of nitric acid concentration. Using the distribution coefficient data, the optimum conditions for recovery of Ce (IV) from nitric acid medium were arrived at. Under the conditions employed for Ce(IV), a small percentage of Ru was also found to be extracted. Cerium could be selectively stripped from the organic phase with 8M HNO3/30% H2O2 solution. This procedure led to the recovery of144Ce free of106Ru. Based on the solvent extraction data, an extraction-chromatographic procedure employing HDEHP (40% w/w) loaded on Amberlite XAD-7 as the stationary phase was developed for the isolation of pure, carrier-free144Ce from the spent fuel solution.

Nitrogen isotope exchange between nitric oxide and nitric acid

The rate of nitrogen isotope exchange between NO and HNO3 has been measured as a function of nitric acid concentration of 1.5–4M·1−1. The exchange rate law is shown to beR=k[HNO3]2[N2O3] and the measured activation energy isE=67.78kJ ·M−1 (16.2 kcal·M−1). It is concluded that N2O3 participates in15N/14N exchange between NO and HNO3 at nitric acid concentrations higher than 1.5M·1−1.

SORPTION BEHAVIOR OF PERRHENATE ION ON REILLEX™-HP ANION EXCHANGE RESIN FROM NITRIC ACID AND SODIUM NITRATE/HYDROXIDE SOLUTIONS

ABSTRACT The distribution coefficients (K' d) are reported for perrhenate on the nitrate form of Reillex™-HP, a weak base anion exchange resin, as a function of nitric acid concentration from 0.100 to 10.0 M. Perrhenate K' d values were determined in 1.00 M NaNO3 from pH 2 to 13. The K'd values were determined in solutions containing 1.35 M NaNO3 and variable NaOH, 0.155 to 4.66 M, and in solutions containing 0.655 M NaOH and variable NaNO3,0.46 to 5.35 M. Maximum perrhenate loadings were <2.7% of theoretical capacity. The K' d is defined by the following equation: The total mmol of rhenium initially added is Retotal and [Re]sol is the analytical molarity of rhenium in Vsot mL of solution after a batch contact. At 1.0 M HNO3 the value of K'd is 73 mL/g. The behavior of the perrhenate system in acid can be described by assuming that perrhenic acid, HReO4, is formed with a derived acid dissociation constant of about 6.5 M. In 1.00M NaNO3from pH 2 to 13 the sorption behavior is initially what is expected for a weak base resin with an acid dissociation constant of 1.24 × 10−55 M. Thus, the K' d value decreases with pH values above the pKa value. However, instead of the value of K' d decreasing to zero at higher pH values, it becomes constant at 15 mL/g. In a solution containing 1.00 M NaOH and 1.00 M NaNO3, the value of K'd is 25 mL/g. The unusual behavior of the Reillex™-HP anion exchange resin suggests that the resin's unprotonated pyridine functionality is solvating a {Na+,ReO4 −} ion pair. The interaction of the perrhenate ion with Reillex™-HP is more involved than a simple ion exchange phenomenon and the presence of NaOH affects the resin-perrhenate interactions.

SORPTION BEHAVIOR OF PERRHENATE AND OXOCHROMIUM(VI) ON REILLEX™-HPQ ANION EXCHANGE RESIN FROM NITRIC ACID SOLUTION

ABSTRACT The distribution coefficients (K'd) are reported for perrhenate and oxochromium(VI) ions on the nitrate form of Reillex™-HPQ anion exchange resin as a function of nitric acid concentration. Maximum loadings of <5.1 equivalent % were used. K'd is defined by the following equation where Mtotal is the total mmol of metal ion added and (Msol) is the analytical molarity of metal ion in Vsol mL of Solution. The values of K'd) for perrhenate at 10.0, 5.00, and 1.00 M HNO3 are 5.00, 16.9, and 186 ml/g dry resin, respectively. The average value of K'd) for oxochromium(VI) between 10.0 and 4.0 M HNO3 is 1.21 ± 0.23 ml /g dry resin. At 1.0 MHNO3, the value is 1.80 rnl /g dry resin. The behavior of the perrhenate system can be best described by assuming that the acid, HReO4, is formed with a derived acid dissociation constant of 2.32 M. The behavior of the oxochromium(VI) system is more complex. It is described phenomenologically by a simple inverse [HNO3] dependence.

Numerical Modeling for Coextraction of Tc(VII) with U(VI) by n-Octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine Oxide from Nitric Acid Solution.

The coextraction model of Tc(VII) and U(VI) from nitric acid solution was developed on a tributyl phosphate (TBP)/n-dodecane system involving n-octyl(pheny1)-N, N-diisobutylcarbamoyl-methylphosphine oxide (CMPO). Technetium was considered to be extracted by the formation of Tc-CMPO and U-Tc-CMPO complexes in the presence of uranium. The distribution coefficient of technetium in the presence of uranium was defined by taking these complexes into account, and expressed as a function of nitric acid concentration, free CMPO concentration, and distribution coefficient of uranium. The equation of the distribution coefficient derived was applied to the previous data obtained in the mixed system of CMPO-TBP-dodecane at the low nitric acid concentration. It was found that the distribution behavior of technetium in the presence of uranium could be successfully simulated by the present coextraction model.

EXTRACTION OF ACTINIDES BY BIFUNCTIONAL PHOSPHINIC ACID RESIN

ABSTRACT The extraction of U(VI), Am( III), Pu( IV), Np( IV) and ThIV) by bifunctional phosphinic acid resin of various cross linkages is reported as function of nitric acid concentration. From the comparison of the distribution coefficient values it is suggested that the recovery of these actinide elements from waste solutions as we II as their mutual separations is possible by using phosphinic acid resin.

ION-EXCHANGE EQUILIBRIUM OF THE Cu2+/H+, Zn2+/H+AND Pb2+/H+IONS ON HYDRATED FERRIC OXIDE

ABSTRACT The ion exchange of trace amounts of Cu2+, Zn2+ and Pb2+ with the hydrogen-form of hydrated ferric oxide as a function of nitric acid concentration has been studied at 25, 30,35 and 60°C. Ion exchange of these cations increases with increasing temperature in the investigated temperature range. From these results, equilibrium constants for the Cu2+/H+, Zn2+/H+ and Pb2+/H+ ion exchange on hydrated ferric oxide and thermodynamic quantities for these reactions were calculated, and some predictions made for the exchange process taking place in this material. The selectivity series is Zn2+ > Cu2+ > Pb2+.

Solvent extraction of heptavalent technetium

An extraction study was performed on technetium in its highest oxidation state as a function of nitric acid concentration at 25, 50 and 70 °C. A long chain amine (tri-n-octylamine TOA) and an organophosphorus solvent (TBP) have been investigated. Addition of NH4NO3 has a salting-out effect on the extraction of TBP in the aqueous phase and therefore decreases the distribution coefficient for heptavalent technetium. The mechanism of extraction is discussed in the light of the results obtained.

Extraction behavior of yttriuí with diisodecylphosphoric acid from nitric acid solution

Extraction of yttrium and some of the lanthanoids by diisodecylphosphoric acid (DIDPA) has been studied as a function of nitric acid concentration in the aqueous phase and concentration of the DIDPA in n-dodecane. The distribution ratio of yttrium was found to increase with the second power of concentration of the extractant and decrease with the third power of concentration of nitric acid. As the concentration of yttrium in the organic phase increased, an amorphous solid was found to precipitate and the composition of the solid was determined to be Y(DIDP)3. To dissolve Y(DIDP)3 into n-dodecane, a 14-fold molar excess of DIDPA was required over Y(DIDP)3. The distribution ratio of yttrium was found to be too high to back-extract this element by nitric acid of medium concentration.

Graft polymerization of 4‐vinylpyridine onto cellulosic fibres by the ceric ion method, II. The ph effect

AbstractThe effect of pH on the graft polymerization of 4‐vinylpyridine (4‐VP) onto cellulose and on partially carboxymethylated cotton (PCMC) initiated by ceric ammonium nitrate (CAN) in dilute nitric acid was examined. The grafting parameters grafting efficiency (GE), graft yield (G), graft frequency (GF), and ceric ion consumption (Ce(IV)c) were studied as a function of nitric acid concentration. Also the effect of pH on the graft polymerization was examined and the total nitrate ion concentration was maintained high and constant at 0.86 mol/1 by addition of sodium nitrate. Maximum grafting and total conversion occurred at pH 1, but these values were smaller than the ones obtained in the previous case. For comparison some experiments were carried out using ceric sulfate as initiator.

THE SEPARATION OF NEPTUNIUM AND PLUTONIUM FROM NITRIC ACID USING n-OCTYL(PHENYL)-N, N DIISOBUTYLCARBAMOYLMETHYLPHOSPHINE OXIDE EXTRACTION AND SELECTIVE STRIPPING†

ABSTRACT The extraction of neptunium and plutonium in several oxidation states was studied as a function of nitric acid concentration for 0.1M n-octyl(phenyl)-N, N-diisobutylcarbamoyl -methylphosphine oxide in 1.4M tributylphosphate with dodecane diluent. Np(V) is only weakly extractable over the range of acid concentrations studied while Np(IV) and Np(VI) are highly extractable. Pu(IV) and Pu(VI) are also highly extractable while Pu(III) was extracted but with lower efficiency. An Fe(II) reductant was used to reduce neptunium to Np(IV) and plutonium to Pu(III) for the initial extraction. Pu(III) was then stripped with dilute HNO3 in the presence of a holding reductant leaving the Np(IV) in the organic phase. Neptunium may then be recovered to an aqueous phase with one of a number of complexing agents.

Spectroscopic study of the Eu 3+ ion in nitric acid aqueous solutions

The fluorescence spectra of europium(III)-nitric acid aqueous solutions were investigated at constant europium concentration (3.29 × 10 2− M) as a function of nitric acid concentration ranging from 5 × 10 −2 to 9 M. High resolution spectra of the 5D 0 → 7F 0 transition shows the simultaneous existence of at least three aquonitrato complexes in this range of acid concentration. Comparison with the europium nitrate hexahydrate crystal spectrum suggests that one of these is the neutral [Eu(NO 3) 3(H 2O) 4] 0 with three bidentate nitrates and four water molecules. Quantitative analysis of the bands of these complexes and equilibrium considerations indicate that another complex, always present, is probably a bis-nitrato aquocomplex. The third complex in this concentration range appears to have an environment richer in NO 3 − ions. A fourth aquocomplex was detected in sufficiently dilute nitric acid solutions.

Ion-exchange behaviour of copper ferricyanide

A new inorganic ion exchanger, copper ferricyanide prepared by adding copper nitrate to a potassium ferricyanide solution at 80°C has been found to be stable in acids and salt solutions. It has been characterized by chemical analysis, thermogravimetry. X-ray and infrared spectroscopy. Distribution coefficients determined for various metal ions show that the exchanger has a high affinity for heavy univalent cations. The variation of Kd for a number of metal ions as a function of nitric acid concentration and ammonium nitrate has been investigated to elucidate the probable exchange mechanism and to work out conditions for elution. Binary separations of Cs from a number of other metal ions were achieved on the column of exchanger. The exchanger is useful for the separation of137Cs.

Foam Fractionation of Mercury(ll) Nitro Complexes

Abstract Using a recycle foam separation apparatus, the foam fractionation distribution factor, γ/C, of the anionic metal nitro complexes of mercury(II) with the cationic surfactant, hexadecyltrimethylammonium bromide, was determined. The distribution factor was measured as a function of nitric acid concentration. The maximum occurred at 0.1 N nitric acid, which is in agreement with the anionic ion-exchange column distribution coefficient. Total reflux foam fractionation experiments yielded a 150-fold increase in the enrichment factor with a 20% recovery of the mercury(II) ion.

Ca 2+/H + Exchange on zirconium phosphate at temperatures up to 250°

The ion exchange of trace amounts of 45Ca 2+ on amorphous zirconium phosphate as a function of temperature and concentration of nitric acid was studied. The effect of temperature, at consant pressure (80 atm.), was investigated as a function of nitric acid concentrations in aqueous solution. The experiments were made at 25, 50, 110, 150, 200 and 250°. Ion exchange of 45Ca 2+ decreases with increasing temperature in the investigated temperature range. From these results, equilibrium constants for the Ca 2+/H + ion exchange on amorphous zirconium phosphate and thermodynamic quantities for these reactions were calculated.

Radiolysis of nitric acid solution : L.E.T. effects

The radiolysis of nitric acid solutions was investigated using gamma, beta and alpha radiation. Solutions were gamma-irradiated under various conditions and analyzed for all stable products. Solutions that were alpha- or beta-irradiated were analyzed for nitrite ion only. Nitrite ion, the major radiolysis product, was determined as a function of nitric acid concentration. A nitrite scavenger, p-nitroaniline, was added to prevent the nitrite ion from reacting prior to analysis. The nitrite yields from alpha irradiation were appreciably lower than the yields from gamma and beta irradiations at lower acid concentrations but continually increased with increasing acid concentration. The nitrite yields from gamma or beta irradiation increased with increasing acid concentration up to about 1 M but then decreased. Similarity of the gamma and beta yields substantiated this unusual trend. Previous investigations of neutral nitrate solutions have always shown an increase in yields at the higher nitrate concentrations. A mechanism, based on L.E.T. effects on three radiolytic reactions, has been postulated to explain the differences in yields between alpha and gamma (or beta) irradiation.