Extraction of plutonium(IV), uranium(VI) and some fission products by di-n-hexyl sulphoxide

The extraction of nitric acid, plutonium, uranium and fission products such as zirconium, ruthenium and europium has been investigated using di-n-hexyl sulphoxide in Solvesso-100. Results indicate that Pu(IV), U(VI), Zr(IV) and Ru NO(III) are extracted as disolvates, whereas Eu(III) is extracted as the trisolvate. The absorption spectra of the plutonium(IV) and uranium(VI) complexes extracted are similar to those of the species extracted by TBP which indicate the similarity of the species involved. Preliminary studies show that irradiated di-n-hexyl sulphoxide extracts zirconium to a smaller extent than irradiated TBP suggesting the use of long chain aliphatic sulphoxides as promising extractants for the recovery of plutonium in high radiation fields.     

Selective liquid scintillation method of plutonium α-spectrometry

A selective liquid scintillation method is suggested for plutonium determination by alpha-spectrometry in the presence of uranium. The analytical process consists of extracting plutonium from nitric acid solutions using BPHA, TOA and MTOA nitrate as extractants into toluene scintillator. Effect of various extractants and nitric acid concentration on the extraction of Pu(IV) and U(VI) together with scintillations quenching were investigated. A simple and fast two-stage selective scintillation method is also suggested for Pu determination in the irradiated uranioum samples.     

Extraction behavior of uranium,plutonium and some fission products with gamma-irradiated N,N′-dialkylamides

The extraction behavior of uranium(VI), plutonium(IV) and fission products like zirconium, ruthenium and europium from 3.5M nitric acid medium with gamma-irradiated dibutyl derivatives of hexanamide (DBHA), octanamide (DBOA) and decanamide (DBDA) in dodecane has been investigated as a function of absorbed dose up to 184 MRads. The results indicate that the K_d value for extraction of uranium(VI) decreases gradually, while K_d for extraction of plutonium(IV) decreases rapidly with dose up to 35 MRads, increasing thereafter with dose, indicating synergistic effects of radiolytic products at higher doses. Ruthenium and europium are not extracted in the entire dose range up to 184 MRads, while extraction of zirconium(IV) increases steadily up to 50 MRads and increases radiply thereafter, indicating synergistic effect of radiolytic products similar to that of plutonium(IV) beyond a dose of 50 MRads. The extractability of uranium(VI) and plutonium(IV) with 1M dibutyl decanamide (DBDA) in dodecane was studied for uranium loading up to 75 mg/ml and plutonium loading up to 3 mg/ml. The percent extraction was found to vary from 91 to 71 for uranium and 95 to 89 for plutonium, respectively. Quantitative stripping of uranium can be achieved with 0.01M nitric acid and plutonium with 0.5M nitric acid and 0.05M hydroxylamine soluton in two steps from an organic phase loaded with 53.2 mg/ml of uranium.     

Studies on the coulometric determination of uranium and plutonium employing a graphite electrode

Summary Graphite has been employed as a working electrode in the controlled potential coulometric determination of uranium and plutonium. The couples U(VI)/U(IV) and Pu(IV)/Pu(III) employed for analysis have diverse redox potentials and commonly the working electrodes employed are mercury and platinum. A graphite electrode in the shape of a beaker showed satisfactory performance for the quantitative reduction of U(VI) to U(IV) and Pu(IV) to Pu(III) and also for quantitative oxidation of Pu(III) to Pu(IV). Studies on the levels of the background current, blank values and their reproducible behaviour in acid media have been carried out with a view to achieve good precision and accuracy. A software-based predictive evaluation technique of end-point charge has been investigated. The results have shown that the graphite electrode can be used for the determination of both uranium and plutonium in the presence of each other with a precision and accuracy of better than ±0.5%.     

Extractive photometric determination of plutonium(IV) with Aliquat-336 and xylenol orange

A rapid extractive photometric method using Aliquat-336 and xylenol organe for the determination of plutonium(IV) at μg levels has been developed. Quantitative extraction is obtained from ∼4M aqueous HNO₃ medium, affording estimation in the presence of several commonly occurring impurities, viz. iron, uranium, fission products and cladding materials. Effects of acidity, reagent concentration and diverse ions on the estimation have also been invetigated. Unlike the well-known absorptiometric method for determining plutonium(IV) employing Arsenazo III, the procedure presented here tolerates manyfold excesses of uranium(VI) as well as chromium(III), iron(III) and zirconium(IV), which are some of the major contaminants of plutonium during reprocessing.     

Dioctyl butyramide and dioctyl isobutyramide as extractants for uranium(VI) and plutonium(IV)

Two isomeric monoamides, dioctyl butyramide (DOBA) and dioctyl isobutyramide (DOIBA) were synthesized for extracting uranium(VI) and plutonium(IV) from aqueous nitric acid medium into various diluents such asn-dodecane, tertiary butyl benzene and xylene. DOBA extracted uranium(VI) and plutonium(IV) efficiently whereas DOIBA extracted uranium(VI) with negligible extraction for plutonium(IV). Both these cations were extracted as their disolvates. The thermodynamic parameters involved in the extraction determined by the temperature variation method indicated the reactions in all cases to be enthalpy favoured and entropy disfavoured. Possibility of separating micrograms of plutonium(IV) from macroquantities of uranium(VI) using the mixture of these amides was explored.     

Extraction of actinides and fission products by octyl(phenyl)-N,N-diisobutylcarbamoylmethyl-phosphine oxide from nitric acid media

Extraction of promethium(III), uranium(VI), plutonium(IV), americium(III), zirconium(IV), ruthenium(III), iron(III) and palladium(II) has been carried out with a mixture of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) and tributyl phosphate (TBP) in dodecane. The effects of nitric acid, TBP and CMPO concentrations on the extraction of these metal ions have been studied. The nature of the species of the above metal ions extracted into the organic phase has been suggested.     

A spectrophotometric method for the determination of neptunium and plutonium in process solutions

A method is described for the determination of neptunium and plutonium in process solutions. This involves the separation of these elements followed by their spectrophotometric determination as Arsenazo III complexes. Neptunium(IV) and plutonium(IV) are separated using TTA extraction method and the separated Np(IV) and Pu(IV) are then determined as their Arzenazo III complexes in 5M HNO₃. A few solutions obtained by dissolving irradiated fuels were analysed for plutonium and neptunium using this method and the results were compared with those obtained by other methods. An attempt was made to use Arsenazo III to determine uranium in the plant solutions.     

Anion-exchange separation of plutonium in hydrochloric-hydrobromic acid media

Plutonium can be rapidly and selectively separated from the elements that interfere in its radiochemical determination, by the use of hydrobromic acid in a hydrohalic acid anion-exchange separation procedure. Plutonium(IV) and (VI) are adsorbed onto the resin column from 9M hydrochloric acid, interfering elements such as americium and thorium are washed from the column with 9M hydrochloric acid, and the plutonium is reduced to plutoniurn(III) and washed from the column with 11M hydrobromic acid. Interfering elements such as uranium and neptunium, which are adsorbed onto the column from 9M hydrochloric acid, are retained there during the hydrochloric and hydrobromic acid washes. This system would also appear to provide the means for effectively separating plutonium from those elements that commonly interfere in such chemical methods of analysis as redox titration.     

Modeling of Pu(VI) distribution coefficients in 30 % TBP based PUREX process

Hexavalent plutonium (Pu(VI)) is an important solute in the PUREX (plutonium uranium extraction) process. In 30 % TBP based PUREX solvent extraction system, distribution coefficient of Pu(VI) is much lower than that of Pu(IV). This lower distribution coefficient of Pu(VI) may cause unexpected Pu loss during primary HA extraction in low acid flowsheets. An empirical model for Pu(VI) distribution coefficients in 30 % TBP and its temperature dependency has been reported in this paper. Comparison with literature data revealed a reasonably good agreement between the reported experimental and model predicted values.     

Extraction of uranium(IV) from phosphoric acid solutions with 1-phenyl-3-methyl-4-benzoylpyrazolone-5 (PMBP)

The extraction of uranium(IV) from phosphoric acid solutions with PMBP and PMBP-TOPO mixtures has been studied. The synergic extraction with PMBP-TOPO is more effective than the simple chelate extraction with PMBP and both systems are more effective than the synergic extraction of uranium(VI) with DEHPA-TOPO. It is established that the complexes extracted are U(PMBP)(4) and U(PMBP)(4).TOPO for the chelate and synergic extraction respectively. The most probable uranium(VI) species in the aqueous phase (2.9-6.33M H(3)PO(4)) is the neutral complex U(H(5)P(2)O(8))(4). Analytical methods suitable for determination of uranium in phosphoric acid solutions have been developed. The highest sensitivity is achieved by combining the synergic extraction with the uranium(IV)-arsenazo III colour reaction.     

Extraction of uranium(VI) and plutonium(IV) with some aliphatic amides

Extraction of uranium(VI) and plutonium(IV) has been studied with N,N-dibutyl derivatives of hexanamide (DBHA), octanamide (DBOA) and decanamide (DBDA) at various fixed temperatures of 20, 30, 40 and (50±0.1)°C. The equilibrium constants for the uptake of nitric acid (K_h, a measure of their relative basicities) by these amides were evaluated by the usual method. The equilibrium constants for the extraction of uranium as well as plutonium with all the three amides follow their order of basicity (K_h) viz. DBHA (0.09)<DBOA (0.10)<DBDA (0.13) with log K values of 1.31, 1.43 and 1.73 for uranium and 3.55, 3.65 and 4.17 for plutonium, respectively. It has been observed that whereas uranium(VI) is extracted as a disolvate (similar to TBP and sulfoxides), plutonium(IV) has been found to be extracted as a trisolvate. The thermodynamic parameters evaluated by the usual temperature coefficient method indicate that the extraction reactions of uranium as well as plutonium are stabilized by negative enthalpy change only.     

Bestimmung der freien Säure in wäßrigen Uran(IV)-nitrat- und Uran(IV)-perchloratlösungen

Methods described in literature for the determination of free acid in solutions containing plutonium(IV), uranium(VI) and aluminium(III) were investigated for their applicability in the presence of uranium(IV). Most methods turned out to work in the presence of uranium(IV). The simplest procedure was the suppression of the uranium(IV) hydrolysis by complexation with excess of fluoride. No bias was observed in the presence of 0–30 mg of uranium(IV). A variance of 1.4% resulted from the determination of 0.4 millimole of acid in the presence of 26 mg of uranium(IV) and a variance of 0.26% was obtained when 2 millimoles of acid were determined in the presence of 130 mg of uranium(IV). Uranium(IV) from 30–260 mg in 250 ml caused a negative bias, which can be corrected for. — A concentration of potassium fluoride in the titration medium of 10 g/l turned out to be optimum. In 11/2 years more than 750 determinations were carried out with the same glass electrode and no destruction of the electrode was observed. The influence of uranium(VI), iron(III) and aluminium (III) on the determination of the free acid was also investigated.     

Prompt gamma-ray analysis using cold and thermal guided neutron beams

The extraction behavior of uranium(VI), plutonium(IV) and some fission products like zirconium(IV), ruthenium(III) and europium(III) from 3.5M nitric acid with -irradiated organic phase pre-equilibratedn-dodecane solutions of dihexyl derivatives of hexanamide (DHHA), octanamide (DHOA) and decanamide (DHDA) has been investigated as a function of absorbed dose upto 184·10⁴ Gy. The results indicate that the extraction of uranium(VI) decreases gradually with dose upto 72·10⁴ Gy and becomes almost constant thereafter, while, the extraction of plutonium(IV) decreases upto a dose of 20·10⁴ Gy and then increases rapidly up to a dose of 82·10⁴ Gy indicating synergistic effects of radiolytic products formed at higher doses. Extraction of zirconium(IV) increases gradually upto a dose of 72·10⁴ Gy. Europium(III) does not get extracted with any of these amides in the entire dose range (0–184·10⁴ Gy) studied, however, ruthenium shows insignificant increase in extraction with dose. The decrease inD values noticed in the case of plutonium and zirconium after the dose of 72·10⁴ Gy which was attributed to the third phase formation and emulsification. Infrared studies confirm the final products of radiolysis as the respective amines and carboxylic acids. The degraded amide contents have been estimated by quantitative IR spectrophotometric technique. Extraction data obtained for uranium(VI) and plutonium(IV) with TBP/n-dodecane system have also been compared under similar experimental conditions.     

Controlled potential coulometry: the application of a secondary reaction to the determination of plutonium and uranium at a solid electrode

A method is described for the simultaneous determination of plutonium and uranium in mixed oxides by controlled potential coulometry at a gold working electrode in two stages: first a coulometric oxidation, at 0.73 V vs. a silver/silver chloride electrode, of Pu(III) and U(IV) to Pu(IV) and U(VI) by a combination of a direct electrode reaction and a secondary chemical reaction proceeding concurrently, and secondly, a coulometric reduction at 0.33 V of Pu(IV) to Pu(III), leaving uranium as U(VI). The determination is carried out in a mixture of sulphuric and nitric acids, and Ti(III) is used to reduce plutonium and uranium to Pu(III) and U(IV) before electrolysis. The precision (3sigma) of Pu:U ratio results obtained from mixtures containing about 30% and 2% plutonium was 0.5% and 1-5% respectively. The effect of experimental variables on the time taken to complete the coulometric determination is discussed.     

Di(2-ethyl hexyl) butyramide and di(2-ethyl hexyl)isobutyramide as extractants for uranium(VI) and plutonium(IV)

The extraction of uranium(VI) and plutonium(IV) from nitric acid into n-dodecane was studied using two isomeric branched alkyl amides, di(2-ethyl hexyl) butyramide (DEHBA) and di(2-ethyl hexyl) isobutyramide (DEHIBA). The extraction ratios of Pu(IV) at relatively high acidities were higher than the corresponding values for U(VI) in the case of DEHBA. However, with DEHIBA the values for Pu(IV) were negligibly small. Pu(IV) was found to be extracted as trisolvate by DEHBA and as disolvate by DEHIBA. U(VI) was extracted by both the amides. From the study of the extraction reactions at different temperatures, it was shown that all the reactions in the present investigation were enthalpy favoured and entropy disfavoured. Separation of Pu(IV) from bulk of U(VI) was feasible. However, the purity of the separated plutonium was not satisfactory in batch extraction studies.     

Coulometric determination of uranium with a platinum working electrode

Experimental conditions have been established which enable uranium to be determined coulometrically by the reduction of uranium(VI) to uranium(IV) at a platinum working electrode, by controlled-potential or controlled-potential-limit techniques. The procedure has been used successfully as a subsidiary method in the routine determination of uranium in pure uranyl nitrate solutions. The platinum electrode has several important practical advantages over the well established mercury-pool electrode for the coulometric determination of uranium. The consecutive determination of iron(III) and uranium(VI), or plutonium(IV) and uranium(VI) can be carried out with the same working electrode in the same solution and the coulometric oxidation of uranium(IV) to uranium(VT) is practicable. The rate of stirring of the cell liquor is much less critical in the case of the platinum electrode. Two main problems had to be overcome before a practical procedure could be achieved; hydrogen evolution during the uranium(VI)-(IV) reduction had to be eliminated so that 100% current efficiency could be obtained for the desired reaction and electrode-surface poisoning phenomena had to be controlled so that reaction times could be kept reasonably short. It was found that selection of a hydrochloric acid base solution containing a small amount of bismuth(III) enabled hydrogen evolution to be avoided: also electrode-surface poisoning with this base solution was not particularly serious and could be maintained at a satisfactorily low level by occasionally anodizing the electrode in dilute sulphuric acid. Bismuth(III) forms a complex with chloride ions and its presence increases the hydrogen overvoltage at the working electrode: no visible deposit of bismuth metal forms on the electrode during the uranium reduction. Samples containing nitrate can be analysed provided sulphamic acid is added to this hydrochoric acid base solution.     

Indirect determination of uranium by the on-line reduction and fluorimetric detection of cerium(III).

A novel flow injection method has been developed for the indirect determination of uranium by the on-line reduction and subsequent fluorimetric detection of cerium(III). A sample solution containing uranium(VI), prepared as a sulfuric acid solution, was injected into a sulfuric acid carrier solution and passed through a column packed with metal bismuth to reduce uranium(VI) to uranium(IV). The sample solution was merged with a cerium(IV) solution to oxidize uranium(IV) to uranium(VI) and the cerium(III) generated was then monitored fluorimetricaly. The present method is free from interference from zirconium, lanthanides, and thorium, and has been successfully applied to the determination of uranium in monazite coupled with an anion-exchange separation in a sulfuric acid medium to eliminate iron(III). The sample throughput was 25 per hour and the lowest detectable concentration was 0.0042 mg l(-1).     

Extraction of molybdenum(V) as its ferron complex with trioctylamine in chloroform from a sulphuric acid medium

A simple, rapid, and highly selective method for the separation of molybdenum from a large number of elements of analytical importance has been developed. The method is based on the extraction of a Mo(V)-ferron (7-iodo-8-hydroxyquinoline-5-sulphonic acid) complex into trioctylamine-chloroform in a sulphuric acid medium using ascorbic acid as a reductant. Many elements such as Re(VII), W(VI), U(VI), Th(IV), Cr(III), Cr(VI), V(V), Ce(IV), Ru(III), Co(II), Ni(II), Mn(II), Fe(II), Fe(III), Cd(II), Mg(II), Cu(II), Al(III), Zn(II), Pb(II), Ag(I), and As(V) are not extracted under the conditions proposed and, thus, molybdenum can be easily separated without any interference. Sulphate, chloride, nitrate, phosphate, and oxalate anions have no effect on the extraction of molybdenum. However, zirconium and palladium interfere seriously. The ratio of Mo: ferron: TOA in the extracted species is found to be 1: 1: 3 using Job’s method of continuous variations. This value has been further confirmed by the mole-ratio method. The text was submitted by the authors in English.