Separation of boric acid from radioactive wastes by liquid-liquid extraction

The extraction of boric acid from a solution modeling radioactive waste has been studied. Different aliphatic alcohols were used as extractants. Factors affecting the distribution ratio of boric acid and the behaviour of some other components of the solution under conditions of boric acid extraction were investigated. The composition of species extracted was determined from distribution data of n-hexanol and H₃BO₃.     

Physical and chemical aspects of extraction separation of boric acid from the products of nuclear fission

Different aliphatic alcohols were tested for the extraction of boric acid from solutions modeling radioactive waste. In addition to distribution measurements, the number of molecules of extractant per H₃BO₃ molecule in the organic phase was determined assuming extraction by solvation. A method of activity coefficient evaluation in aliphatic alcohols-nonpolar solvent systems is proposed and hydration and solvation effects in these systems are investigated.     

Separation of gram quantities of uranium from fission products by extraction chromatography

The separation of gram quantities of uranium from fission products has been investigated by extraction chromatography. The separation which is based on the difference in distribution coefficients between uranium and the fission products on a tributyl phosphate (TBP) resin in nitric acid medium, was carried out by means of high acidity feed and stepwise elution on a TBP chromatography column. The results show that this technique is capable to separate 5 g of uranium from a large quantity of fission products. The recovery of uranium is more than 99%. The decontamination factors of g- and b-activities were 2.1^.10³ and 2.3^.10³, respectively.     

Separation of strontium from nuclear waste solutions by solvent extraction with crown ethers

The possibilities of strontium separation from medium activity waste (MAW) solutions have been investigated. MAW originates from the PUREX process and contains NaNO₃ and HNO₃ in a large excess. By solvent extraction with the crown ether dicyclohexano-18-crown-6 (DC-18-C-6) in 1,1,2,2-tetrachloroethane, separation is possible. The distribution ratio for Sr²⁺ depends on the concentration of HNO₃, NaNO₃ and Pb(NO₃)₂. The extraction system is employed in a continuous counter-current process. After use, the extraction agent can easily be regenerated by reextraction with pure water.     

Studies of short-lived fission products by means of the multistage solvent extraction system SISAK

The multistage solvent extraction system SISAK is described. The system is used for online studies of nuclides with half-lives down to 1 s. Some of the chemical separation procedures are presented, and a survey is given on the results obtained so far. The possiblity to gain access to nuclides with even shorter half-lives is also discussed.     

Separation of trivalent actinides from lanthanides by solvent extraction

A method is presented for separating the trivalent actinides, mainly Am and Cm, from trivalent lanthanides by the use of only two solvent extractants. The first solvent removes the heavy lanthanides, leaving the Am, Cm and the lighterlanthanides; the second removes the Am and Cm. Because additional complexing agents are not required, waste-disposal and corrosion problems are reduced. Overall separation factors may be as high as several thousand for the separation of Am and Cm from lanthanides in the fission waste products from reactor fuel processing.     

Separation of trace impurities of131I from99Mo obtained by extraction from fission products of uranium

The radioisotope⁹⁹Mo was separated from a mixture of²³⁵U fission products in the presence of Hg²⁺ by sorption on a chromatographic column filled with Al₂O₃ and elution with 1M NH₄OH. Trace impurities of¹³¹I in the molybdenum fraction were eliminated by selective sorption on silver iodide or by repeated sorption of⁹⁹Mo on Al₂O₃.     

Separation of Zr and Hf from strong hydrochloric acid solution by solvent extraction with TEHA

In order to separate Zr(IV) and Hf(IV) from chloride solutions, TEHA (tri 2-ethyl hexyl amine) was used as an extractant. The aqueous phase consisted of 200 ppm of Zr and Hf in strong HCl solution. In our solvent extraction system, the extractability of the constituents by TEHA was found to be in the following order, HCl > Zr(IV) > Hf(IV). The highest separation factor between the two metals was obtained from 8 M HCl solution. Based on the selectivity towards Zr over Hf with TEHA, McCabe–Thiele plot was constructed and batch simulation of counter-current extraction studies has been conducted. Scrubbing results from the loaded TEHA showed that Hf was selectively scrubbed over Zr by strong HCl solution (9 M). Complete stripping of Zr was possible from the organic phase with distilled water after scrubbing of Hf. The extraction behavior of Zr and Hf by TEHA was compared with that by TiOA and TOA. Our results can be utilized in developing a solvent extraction process to separate Zr and Hf from concentrated chloride solutions by using TEHA.     

Separation of zirconium from fission products in silica gel—nitric acid systems

A method for the separation of zirconium from fission products based on the system 100–200 mesh silica gel—2.0 M nitric acid is described. Decontamination factors are over 500 for ⁹⁵Nb, ¹⁰⁶Ru, ¹²⁴Sb, ¹³⁷Cs, molybdate and uranium(VI), and the yield of zirconium is 98 %.     

Separation of95Zr and95Nb from each other and from other fission products by adsorption and desorption on silica gel using hydrochloric acid solutions

The silica gel adsorption behaviour of zirconium, niobium, ruthenium and cerium in hydrochloric acid has been investigated by batch and column techniques. A satisfactory radiochemical separation of zirconium and niobium from each other and from other fission products has been achieved by a two column technique. The recommended procedure consists of sorption of all the nuclides on a primary silica gel column. Fifteen per cent of⁹⁵Nb, all of the zirconium and all of the other fission products are eluted first by washing with 5.5 M HCl. A second elution with concentrated hydrochloric acid then recovers the⁹⁵Nb (free from other products). The solution from the first elution after evaporation to 1 ml is then passed through another silica gel column and successively washed with 0.5M HCl, 5.5M HCl and concentrated HCl to obtain three fractions—other fission products—⁹⁵Zr free from other products—⁹⁵Nb free from other products, respectively.     

The extraction of chromium(VI) from sulphuric acid solutions by 4-(5-nonyl)pyridine and its separation from fission products

4-(5-Nonyl)pyridine, a new liquid anion exchanger, has been studied for the extraction of chromium(VI) from sulphuric acid solutions. The optimal acidity is 0.1–1 M, depending on the concentration of chromium. Common anions have little effect on extraction in concentrations up to 0.1 M. Reducing agents such as ascorbic acid and thiosulphate prevent extraction at concentrations above 0.1 M. Separation of chromium(VI) from fission products was achieved.     

Rapid separations of corrosion and fission products

A separation scheme of a complex mixture of radiohygienically important radionuclides of corrosion and fission products has been worked out. Rapid separation by means of solvent extractions with metal (sodium, antimony, zinc) diethyldithiocarbamates has been achieved. Chloroform containing metal diethyldithiocarbamates has been used as the organic phase. The procedure permits to separate selectively the representative radionuclides. The selectivity of separation was verified by gamma spectrometry.     

Separation and recovery of heavy metals from hydrometallurgical effluents by solvent extraction

Summary The possibility of separating and recovering heavy metals from hydrometallurgical effluents by successive solvent extractions has been investigated by two different procedures with liquid waste from the Espindesa Zinc process. The waste (pH value near to 1.5) includes significant amounts of Zn (1.35), Cu (0.12), Co (0.32) and Mn (0.6 g/l) in the presence of big concentrations of macro-constituents (sulphate, chloride, Na) and Fe [8.8 g/l, mostly as Fe(II) salts]. As extractants, Amberlite La-2 (a secondary ammine, as chlorohydrate) and DEHPA (di-2-ethylhexyl-phosphoric acid) at 25% volume in kerosene were selected. The first method includes two extraction stages with LA-2 for Zn and Cu separation (the last one with 60 g/l of chloride ions) and three stages with DEHPA at pH values near to 1.5, 2.0 and 3.5 for isolating Fe, Mn and Co. The second method separates firstly Fe (as ferric salts) with DEHPA. Afterwards, one stage with LA-2 isolates Zn and three stages with DEHPA at pH values near to 2.0, 3.0 and 3.5 lead to fractions rich in Mn, Cu and Co. Reextractions from organic layers with water or HCl at different concentrations lead to purer solutions of the isolated metals. With both methods, the liquid waste can be converted into a saline solution with lesser problems for disposal.     

Separation of rhenium from molybdenum and other heavy metals by solvent extraction

Summary Two methods are presented for the extractive separation of rhenium from molybdenum and other heavy metals in hydrochloric acid solution. In the first method, Mo(VI) and Re(VII) are reduced by hydrazine in strong hydrochloric acid solution to Mo(V) and Re(IV). The former is then extracted intoiso-amyl acetate. The Re(IV) remaining in the aqueous phase is oxidised to Re(VII) and determined by known procedures. In the second method, Re(VII) and other ions in 1–1.3N HCl are boiled with hydrazine sulphate for 5 minutes. After adding EDTA to complex Mo(V) and adjusting the solution to 0.33N HCl, rhenium is extracted into chloroform containing 1% tribenzylamine, and is recovered by shaking with water having sufficient ammonia to neutralise the acid and a little hydrogen peroxide.

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Zusammenfassung Zwei Arbeitsweisen für die extraktive Trennung des Rheniums von Molybdän und anderen Schwermetallen in salzsaurer Lösung wurden angegeben. Bei dem ersten Verfahren werden Mo(VI) und Re(VII) mit Hydrazin in stark salzsaurer Lösung zu Mo(V) und Re(IV) reduziert. Ersteres wird dann mit Isoamylacetat extrahiert. Re(IV) verbleibt in der wäßrigen Phase, wird zu Re(VII) oxydiert und auf bekannte Art bestimmt. Beim zweiten Verfahren werden Re(VII) und die anderen Ionen in 1- bis 1,3-n Salzsäure 5 Minuten mit Hydrazinsulfat gekocht. Nachdem man ÄDTA zur Komplexierung des Mo(V) zugesetzt und die Lösung auf 0,33-n an Salzsäure eingestellt hat, wird Rhenium mit einer 1%igen Lösung von Tribenzylamin in Chloroform extrahiert. Die Rückextraktion erfolgt mit Wasser, worin Ammoniak (zur Neutralisation der Säure) und etwas Wasserstoffperoxid gelöst sind.

     

Recovery of137Cs from acidic fission products solutions

A procedure for the isolation of¹³⁷Cs from acidic fission products solutions, based on the use of silica gel and zirconium phosphate ion exchangers, is presented. The¹³⁷Cs recovered by the ion-exchange process is converted to powder by coprecipitation of cesium with ammonium molybdophosphate.¹³⁷Cs pellets have been prepared by compression of¹³⁷Cs ammonium molybdophosphate powder using a hydraulic press. An important aspect of this procedure is that it does not require neutralization of the Purex waste.     

Volatility of tellurium and various fission products in heated nitric acid solutions

The volatility of tellurium and some other fission products was radiochemically studied in heated nitric acid solutions. As tracers ¹²¹Te produced by bremsstrahlung of an electron LINAC and other fission products produced by neutron irradiation were used. The distribution rate of radionuclides between the mother solution and the condensate, was considered as volatility, and was determined. The volatility of tellurium was found to be small and close to that of cesium. Volatilization tests were also performed in the presence of large amounts of solutes.The authors wish to thank Mr. Roy Jacobus for his help in preparing this paper.     

Volatility of tellurium and various fission products in heated nitric acid solutions

The volatility of tellurium and some other fission products was radiochemically studied in heated nitric acid solutions. As tracers ¹²¹Te produced by bremsstrahlung of an electron LINAC and other fission products produced by neutron irradiation were used. The distribution rate of radionuclides between the mother solution and the condensate, was considered as volatility, and was determined. The volatility of tellurium was found to be small and close to that of cesium. Volatilization tests were also performed in the presence of large amounts of solutes.The authors wish to thank Mr. Roy Jacobus for his help in preparing this paper.