Nitric acid distribution coefficients

These variations permit the separation of other components, if desired. Additional data on uranium, plutonium, and nitric acid distribution coefficients as a function of TBP concentration, solvent saturation, and salting strength are available (24,25). Algorithms have also been developed for the prediction of fission product distributions in the PUREX process (23). 

The distribution of highly extractable solutes such as and Pu between the aqueous and organic phases is strongly dependent upon the nitrate anion concentration in the aqueous phase. This salting effect permits extraction or reextraction (stripping) of the solute by controlling the nitric acid concentration in the aqueous phase. The distribution coefficient, D, of the solute is expressed as... 

One of the first bed materials was based on the extractant diamyl amylphosphonate (DAAP marketed under the name U-TEVA-Spec ) and was designed for purification of the tetravalent actinides (U (IV), Th (IV), Pu (IV)) and hexavalent uranium (U(VI)). This material is characterized by high (>10-100) distribution coefficients for U and Th in significant (>3 M) concentrations of both nitric and hydrochloric acids, and so is useful for both U and Th purification (Horwitz et al. 1992 Goldstein et al. 1997 Eikenberg et al. 2001a). 

The extraction of Tc (VII) and Tc (IV) from nitric acid has been investigated as function of tetraphenylarsonium chloride concentration in chloroform The ratio KJCf, (distribution coefficient divided by the concentration of tetraphenyl-arsoniiun chloride in the organic phase) is found to be approximately constant. 

The chromatographic separation of technetium from molybdenum is based on the different extent to which molybdate and pertechnetate are adsorbed from alkaline and acid solutions. The distribution coefficient of molybdate between the anion exchanger Dowex 1-X8 and 3 M NaOH is 12, while it is 10 for pertechnetate under the same conditions. Molybdate is also adsorbed to a much lesser extent from hydrochloric acid solutions than pertechnetate. Thus, molybdemun can be eluted by hydroxide or HCl solutions while nitric acid, perchlorate or thiocyanate are used for the elution of technetium . 

Kumar, Sh., Koganti, S.B. 2001. Modelling of tritium distribution coefficients in 30 vol% TBP/ -dodecane/U02(N03)2/nitric acid system. Indian J. Chem. Technol. 8 (1) 51-53. 

The distribution coefficient of HN03 between the toluene and acid layers is 0.066 at 5°C and the concentration of sulphuric acid 70% H2S03. At lower acid concentrations it is practically zero. This means that on heterogeneous nitration nitric acid passes into the organic layer only in small quantities. Therefore there is practically no nitration in this layer. 

Another important feature in the nitration of dinitrotoluene is the coefficient of distribution of nitric acid between the mineral and organic layers. The data for sulphuric acid of 93% H2S04 at 90°C are given in Table 72. 

Nitration of toluene to mononitrotoluene and of the latter to dinitrotoluene in heterogeneous conditions should be considered mainly a surface reaction. This is deduced from the feet that the rate of the reaction depends on the intensity of stirring. The reaction of nitration of dinitrotoluene to trinitrotoluene in heterogeneous system is not limited to the surface dividing the two phases. This is proved by the fact that the rate of nitration depends very little on the rate of stirring. The reactants - dinitrotoluene Mid nitric acid - are distributed between two phases according to their coefficients of distribution and to the ratio between... 

Investigation of the performance of ISMA-1 sorbents, when used to recover lithium from seawater, has yielded the following information (1) Li ion distribution coefficients of 4x lO" cm g prevail (Eq. (4) (2) the sorbents are easily regenerated with nitric acid (3) they exhibit a high capacity for Li ions of about 20 mg/g and (4) lithium concentrates con-... 

G. Jia, G. Torri, M. Petruzzi, Distribution coefficients of polonium between 5% TOPO in toluene and aqueous hydrochloric and nitric acids. Appl. Radiat. Isotopes, 2004, 61, 279. 

Distribution and Diffusion Coefficients of Nitric Acid Complexes of TBP as a Function of TBP Concentration... 

Figure 4. Distribution coefficients of trivalent TPE in the neutral organophos-phorus compound-chloroform-nitric acid systems. The Roman numerals correspond to numbers of reagents in the text.

TABLE III Distribution coefficients of Am [III] and Eu [III] between nitrobenzenic mixtures of 0.25 N 1-10 phe-nanthroline and 0.25 N nonanoic acid as a function of aqueous nitric acid concentration (y = 0.1]... 

The distribution coefficients of UO and Am ions were measured between these solvents and aqueous phases in 0.2 N nitric acid... 

The distribution coefficients have been determined for Cm(III), Am(III), Cf(III), Pu(IV), Pu(VI), Np(IV), Np(VI), and U(VI) between 30 volume % DHDECMP in DIPB and various nitric acid concentrations. Results are shown in Figure 2. Tracers were taken to incipient dryness in concentrated nitric acid several times, then dissolved with the particular nitric acid concentration being studied. After setting the oxidation state, extractions were done using equal volumes of aqueous and organic phases. Contact times were 5 minutes at 23°C. Extractions were done in 10 mL tubes which were agitated with a mechanical wrist shaker. Each data point was obtained by a separate extraction. 

Efforts to determine distribution coefficients for Pu(III) using 0.025M Fe(S03NH2)2 or 0.025M sodium formaldehyde sulfoxylate (NaCH20S02) were successful up to 1.0M nitric acid. Above that concentration, oxidation to Pu(IV) readily occurred. 

Figure 2 shows conclusively that DHDECMP can extract trivalent as well as tetravalent and hexavalent actinides from moderately concentrated nitric acid solutions. The valence (III) actinides, Am, Cm, and Cf, have distribution coefficients greater than one above 1.5M HNO3, while valence (IV) and (VI) actinides have values greater than one above 0.5M HNO3. In addition, DHDECMP shows very favorable back extraction or stripping characteristics below 0.3M HNO3. Pu(IV) polymer formation undoubtedly occurred in low-acid measurements and may account for the low distribution coefficients. 

Figure 3. Distribution coefficients of Pu (IV) in a nitric acid-citric acid mixture...

Calcium(II), which shows no appreciable complexing, has a distribution coefficient of 147 in 0.5 M perchloric acid and 191 in 0.5 M hydrochloric acid. Strelow. Rethc-meyer, and Bothnia [10] also reported data for nitric and sulfuric acids that showed complexation in some cases. Mercury(II), bismuth(III), cadmium(II), zinc(II), and lead(II) form bromide complexes and are eluted in the order given in 0.1 to 0.6 M hydrobromic acid [11]. Most other metal cations remain on the column. Aluminu-m(III), molybdenum(VI), niobium(V), tin(IV), tantalum(V), uranium(VI), tung-sten(VI), and zirconium(IV) form anionic fluoride complexes and are quickly eluted from a hydrogen-form cation-exchange column with 0.1 to 0.2 M HF [12]. 

Anion-exchange distribution coefficients for most metallic elements in sulfuric acid solution have been measured [28, 29], Uranium(Vl), thorium(IV), molybdenum(VI). and a few other elements are retained selectively from such solutions. Thorium(lV) is taken up selectively by anion-exchangers from approximately 6 M nitric acid [30]. 

Table 4.3 gives distribution coefficients for uranyi nitrate between aqueous nitric acid and 40 percent TBP in kerosene observed by Goldschmidt et al. [G3]. At each nitric acid concentration, the uranium distribution coefficient decreases with increasing uranium concentration. This can be attributed to the following overall reaction equilibria [M2] ... 

Table 4.3 Distribution coefficients for uranyi nitrate between aqueous nitric acid and 40 v/o TBP (1.464 M) in kerosenet...

Assuming that at equilibrium all aqueous HNO3 is fully ionized and all organic HNO, is in the form of HNO3 TBP, the distribution coefficient of nitric acid is... 

Uranium extraction by TBP may in some cases become poorer in the presence of other extractable components because of depletion of free TBP by components other than uranium. Such behavior is illustrated by the U02(N03)2-HN03-TBP system analyzed above, as shown by the data [Ml ] in Fig. 4.7 for the distribution coefficient of uranium as affected by nitric acid concentration. For acid concentration less than about 5 M, the uranium distribution coefficient is greater the higher the acid concentration, because of the salting effect of nitrate ion from the acid. At acid concentrations greater than about S M, increasing acid concentration inhibits uranium extraction, because enough nitric acid has been extracted so that less free TBP is available to form the extractable complex with uranium. Smilar effects have been observed in the extraction of other elements with TBP [Ml]. 

In designing multistage extraction systems for extractive separations by TBP, or by other extractants that can change appreciably in noncomplexed concentration as a result of extraction, it is necessary to perform analyses similar to Eq. (4.1 S) through Eq. (4.24) for each of the extractable species present in other than trace quantities to determine the distribution coefficients for each of the species in each of the contacting stages [G6, H2, L3]. Such design procedures are illustrated in Sec. 6.6 for the separation of hafnium from zirconium by TBP extraction from a nitric acid solution. 

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