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.     

Desorption of99Mo from spent99Mo/99mTc generator

A simple method for desorption and purification of⁹⁹Mo from spent⁹⁹Mo/^99mTc generators is described. The alumina column was washed successively with 0.9% saline water, 35% H₂O₂, and then the⁹⁹Mo was eluted with 2M NH₄OH. Ammonia and residual H₂O₂ were removed by heating the eluate. Finally,⁹⁹Mo solution was passed through a 0.2 m membrane filter to remove precipitated aluminium hydroxide.     

Preparation of99Mo,132Te isotopes and99mTc,132I generators

Adsorption and desorption of⁹⁵Zr−⁹⁵Nb,⁹⁹Mo,¹⁰³Ru,¹³²Te and²³⁹Np in a HCl-alumina system were studied in order to purify⁹⁹Mo and¹³²Te obtained by the cation-exchange separation of fission products and to prepare highly pure^99mTc and¹³²I generators.⁹⁹Mo and¹³²Te, of which radionuclidic purity was over 99.99% and 99.999%, respectively, could be obtained by passing the cation-exchange separated Mo and Te fractions through alumina columns, by washing with HCl and finally by eluting⁹⁹Mo with 1M NH₄OH and¹³²Te with 3M NaOH. In order to raise the recovery of⁹⁹Mo and¹³²Te from the alumina columns, they should be eluted as quickly as possible after the adsorption. The direct use of the alumina column containing⁹⁹Mo or¹³²Te as the generator allowed milking of^99mTc or¹³²I, of which radionuclidic purity was over 99.999%. Milking yields of^99mTc with 0.1M HCl and¹³²I with 0.01M NH₄OH were 77% and 90%, respectively. The latter value was much higher than that in usual performance of the generator.     

Elution of 235U fission products through a calcined hydrotalcite-packed column

Calcined hydrotalcite packed columns were utilized to sorb ²³⁵U fission products and their decay products. The elution behavior of some radionuclides was studied after washing the columns, either with distilled water or 0.5% NaCl solution. Afterwards, fission products and their decay products were eluted using 0.5% NaCl solution. It was found that no matter the washing process, ^99mTc, the b^--decay product of ⁹⁹Mo, was easily separated from ⁹⁹Mo which was strongly retained on the hydrotalcite. ¹³²I, the b^--decay product of ¹³²Te, was eluted slowly and was separated from ¹³²Te which was retained on the column. ¹³¹I and ¹⁴⁰Ba were eluted together with ^99mTc and ¹³²I, although in smaller proportions.     

Separation of iodine produced from fission with a porous metal silver column in99Mo production

In Argentina, at the Ezeiza Atomic Center,¹³¹I is produced by wet distillation of natural tellurium dioxide irradiated with thermal neutrons in a pool-type reactor. In order to recover the¹³¹I present in the production process of fission⁹⁹Mo obtained by irradiation of UAL_x/Al targets (with 90% enriched uranium) a separation method was developed. Iodine isotopes can be separated from a sodium hydroxide solution containing fission products using a column filled with alternate beds of glass microspheres and porous metal silver. Tests with tracers were performed in radiochemical laboratory. Following this results, a series of tests with higher activities (3 TBq of⁹⁹Mo and 0.7 TBq of¹³¹I) were carried out in hot cells. Molybdenum passes through the silver column, while¹³¹I retention was 92–97% in tracer test and 90% in optimised hot cell tests. This result depends on several facts that are discussed. An initial separation of iodine isotopes diminishes radiation damage on ion-exchange resin used in the subsequent molybdenum purification, improving its retention and elution yield.     

Chemical states of iodine produced by the spontaneous fission of252Cf

The distributions of the chemical states of¹³¹I,¹³²I,¹³³I,¹³⁴I and¹³⁵I produced by the spontaneous fission of²⁵²Cf were investigated by the method of fractional precipitation separation in 6M NH₄OH solution followed by measurement of the X-ray spectrum of the samples with a Ge(Li) detector. The iodine fission fragments were separately collected in the matrices of NaNO₃, NaCl, dehydrated sodium sulfate, CH₃COONa·3H₂O, Na₃H₂IO₆, KI and NaIO₃ crystals. The results showed that the distribution of the chemical states was the function of the collection time, the nature of matrix materials and the type of iodine isotopes. The relative amount of the reduced states of¹³⁴I decreased with the increase of collection time in the matrix of NaNO₃. The ratio of the amount of reduced states to the total amount of the¹³⁴I was the highest (50.4%) in NaCl matrix and the lowest (9.4%) in Na₃H₂IO₆ matrix. The relative quantities of reduced states of¹³⁵I were the highest (58.5% and 97.7%) and that of¹³⁴I were the lowest (16.9% and 63.1%) in matrices of NaNO₃ and NaCl, respectively.     

Improved processes of molybdenum-99 production

Two improved processes of⁹⁹Mo production have been developed on laboratory scale. The first one allows to purify Mo of natural isotopic composition from tungsten impurities from 64 to <10 ppm by using preferential adsorption of tungsten on hydrated tin(IV) oxide (SnO₂ nH₂O) before irradiation in a nuclear reactor. The second process deals with the separation of pure fission product⁹⁹Mo from²³⁵U irradiated in a reactor. Two versions of separation process for production of fission⁹⁹Mo have been developed. Both versions start with the dissolution of²³⁵U oxide target in nitric acid and are based on sequential use of alumina and anion exchange resin AG® 1-X8 columns. The yield of⁹⁹Mo in both versions is 80–89%.     

Radiochemical separation of110mAg,210Pb,127Te and131I from aqueous nitric acid solution by bis-2-(butoxyethyl ether)

A bis-2-(butoxyethyl ether) (DBC) solvent extraction method has been developed for the radiochemical separation of^110mAg,²¹⁰Pb,¹²⁷Te and¹³¹I in varying concentrations of aqueous HNO₃. Various factors were examined to determine the optimum conditions of extraction. The effect of various masking agents has been studied. The extraction of¹³¹I is enhanced to 99% at 2.4M HNO₃ in the presence of KSCN.¹³¹I was stripped into aqueous sodium hydroxide from the oxygenated organic extractant. The method was then applied for the recovery of¹³¹I from neutron irradiated tellurium metal. The mechanism and reactivity of DBC with metal ions is described.     

Adsorption of fission products on a metal surface in nitric acid solutions: Radiochemical study using a multitracer

Adsorption behavior of fission products in nitric acid solution on various alloys and metals was studied by using a multitracer produced by neutron irradiation of UO₂. The adsorption behavior of the fission products ⁹⁹Mo, ¹³¹I, ¹³²Te, ¹⁴⁰La, and ¹⁴³Ce, and ²³⁹Np was simultaneously studied. Some chemical decontamination tests were also examined. Clear adsorption of ⁹⁹Mo, ¹³¹I, and ¹³²Te was observed, whereas adsorption of ¹⁴⁰La, ¹⁴³Ce, and ²³⁹Np was not. The adsorption characteristics were discussed by considering anion-exchange reaction and surface complexation.     

Separation and preconcentration of131I− and131IO 3 − in a liquid-liquid system

The application of isotope exchange in a liquid-liquid system for the separation and preconcentration of¹³¹I^– and¹³¹IO^3/– from water is described. For this purpose a solution of elemental iodine in tri-n-butyl phosphate diluted with toluene was used. The influence of various factors on the separation efficiency of¹³¹I was investigated. These are: time of the exchange, concentration of a carrier in the aqueous phase, concentration of I₂ in the organic phase, volume ratio of the phases, pH, foreign ions, storage of the organic phase, etc. The method is quite rapid and the selective preconcentration of these chemical forms of radioiodine from water can be accomplished even in the presence of the most important fission products. This method makes also possible to separate these chemical forms from each other under controlled pH conditions. The activity of the separated radioiodine can be measured advantageously, e.g., by homogeneous liquid scintillation counting after decolourization of the organic phase.     

Rapid determination of131I in environmental waters using a liquid anion exchanger

A rapid and specific method for the determination of¹³¹I in environmental water samples in the presence of some of the most important fission products is described. Radioiodine is separated from acidified water using tri-n-octylamine solution in toluene with dissolved iodine by one-stage static procedure with about 90% separation efficiency and 200-fold volume concentration. After the decolorization of the organic phase with NaOH in methanol, radioactivity of¹³¹I is counted by a toluene base liquid scintillator with a counting efficiency of 70%. The method is simple and enables to determine low radioactivity¹³¹I with a detection limit less than 5 pCi/1 in about 1.5 hrs.     

Hydrated titanium dioxide as an adsorbent for99Mo−99mTc generator

The adsorption behaviour of⁹⁹Mo in the form of molybdate and of^99mTc in the form of pertechnetate on hydrated titanium dioxide was investigated at different molarities of hydrochloric acid. The adsorption capacity of molybdate on hydrated TiO₂ is higher than on Al₂O₃. A^99mTc-generator is suggested. This generator is based on the adsorption of (⁹⁹Mo) molybdate on hydrated TiO₂, at acidities of 0.05–0.1M. HCl.^99mTc is eluted with 0.9% NaCl. Radionuclidic, radiochemical and chemical purities of the eluates were checked. This generator seems to have a great potential as compared to the traditional alumina generators.     

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.     

Measurement of absolute intensity of 1001 keV gamma-ray of 234mPa

The sorption behavior of ²³⁵U fission fission products ⁹⁹Mo and ¹³²Te was studied through batch and dynamic experiments when they were dissolved in 1 to 7M HNO₃ solutions. It was found that ⁹⁹Mo is always totally adsorbed on hydrated SnO₂, while ¹³²Te is rather weakly adsorbed, therefore they can be separated from each other although ¹³²Te in the solution still remains contaminated with other radionuclides as well as ⁹⁹Mo does in the solid.     

Determination of99Tc in rain and dry fallout by ICP-MS

Due to the difficulty of⁹⁹Tc analysis, data are insufficient for discussing its behavior in the environment. In this study, we focused on the determination of⁹⁹Tc in rain and dry fallout samples. The samples were collected monthly at Nakaminato, Japan, from June 1993. They were concentrated by heating on a hot plate without any loss of Tc. The solution was filtrated and then a liquid-liquid extraction (LLX) with trioctylamine (TOA), which works as a liquid anion exchanger, was carried out. Technetium was extracted from 5% HNO₃ solution into the organic phase with a high extractability. After being back-extracted from TOA/xylene into 1M K₂CO₃, LLX with cyclohexanone was used to remove ruthenium, which has a stable isotope of mass 99. Technetium was back-extracted into deionized water, and the solution was measured by inductively coupled plasma mass spectrometry (ICP-MS). The average recovery under the experimental conditions was 67% and the instrumental detection limit was 0.04 ppt (0.03 mBq/mL).     

99mTc generator with hydrated MnO2 as adsorbent of 99Mo

An ^99mTc generator with MnO₂ as adsorbent of ⁹⁹Mo was investigated. Through batch experiments the retention of ⁹⁹Mo onto MnO₂was studied as a function of the shaking time and the pH value of the ⁹⁹Mo solution. It was found that ⁹⁹Mo showed a retention of 100% onto MnO₂ at the pH range from 3 to 11, and the equilibrium distribution was reached in less than 10 minutes. In column experiments the retention of ⁹⁹Mo onto MnO₂ was also high: 99.72%. In this case, the pH of the utilized ⁹⁹Mo solution was 5. The ^99mTc could be eluted from the MnO₂-⁹⁹Mo column by using either distilled water with a pH of 5 or an aqueous solution of 0.9% NaCl. With the saline solution, the ^99mTc elution yields were higher than 80%, and only one aliquot of 5 ml was needed to get these yields. The best results were obtained when the column was packed with 1 g of MnO₂. The water and the saline solution were passed through the column at a rate of 1.25 ml/min.     

Separation of technetium(VII) from irradiated MoO3 sample by solvent extraction with tri-iso-octylamine

Summary A solvent extraction method for the separation of technethim and molybdenum is outlined. After irradiation of MoO₃ and dissolution in sodium hydroxide, the short-lived ^99mTc isotope is extracted from 1 M hydrochloric acid into a solution of tri-iso-octylamirie in 1,2-dichloroethane. The percentage of ⁹⁹Mo in organic phase is less than 0.5%.

---

Zusammenfassung Eine Extraktionsmethode zur Trennung von Technetium und Molybdän wird beschrieben. Hierbei wird nach Neutronenbestrahlung von MoO₃ und Auflösung in Natronlauge das kurzlebige ^99mTc-Isotop aus 1 m salzsaurer Lösung in eine Tri-iso-octylaminlösung in 1,2-Dichloräthan extrahiert. Weniger als 0,5% ⁹⁹Mo finden sich in der organischen Phase.

     

Sequential distillation of fission-produced radioiodine and radioruthenium from sulfuric acid solutions

Fission-produced ¹³¹I and ¹⁰³Ru radionuclides have been separated sequentially by distillation from H₂SO₄ of controlled chemical composition. The thermal-neutron irradiated uranium trioxide targets were digested in 2M NaOH solution and then, the supernatant solution was acidified to 20% H₂SO₄ with addition of a few drops of H₂O₂ solution. On boiling for 3.5 hours, ≥99.99%¹³¹I was volatilized, passed through 3M H₂SO₄ traps, and then collected in 0.1M NaOH + 0.01% Na₂S₂O₃ solution with a recovery yield of 73.6%. The product radionuclide had high radiochemical and radionuclidic purities. After separation of ¹³¹I, the fission-product solution was acidified to 40% H₂SO₄ acid containing KMnO₄ as an oxidant and boiled for 40 minutes. Ruthenium nuclides were volatilized and collected in 0.1M NaOH solution. Gamma-ray spectrometry showed that the separation and the recovery yields of ¹⁰³Ru were ≥99.99 and 65%, respectively, with ~92% radionuclidic purity, measured immediately after separation. The radionuclides of ¹³²I and ¹⁰⁶Rh were the main contaminants detected in the obtained ¹⁰³Ru product solution. This revised version was published online in July 2006 with corrections to the Cover Date.     

The determination of molybdenum in geological samples by Neutron Activation Analysis

A metal-silicate extraction technique combined with neutron activation analysis has been developed to determine molybdenum in geological samples. The samples are equilibrated with Femetal powder at high temperatures. Molybdenum is completely extracted into the metal phase because of very reducing conditions in the furnace. The metal spherule is separated from the silicates, irradiated and dissolved in an acid solution. The molybdenum is precipitated as a sulfide and the precipitate is dissolved in aqua regia and counted on a Ge/Li/detector. The radiochemical yield is obtained by irradiation of the solution. The method avoids production of⁹⁹Mo from induced fission of²³⁵U by performing the metal-silicate separation before irradiation. The precipitation step may be necessary to remove the high background from the decay of⁵⁹Fe. Mo concentrations down to 15 ng/g have been obtained using this method.     

A simple and sensitive separation technique of 99Mo and 99mTc from their equilibrium mixture

The present work describes a simple and inexpensive separation method of ⁹⁹Mo from the equilibrium mixture. The liquid–liquid extraction technique has been employed to separate ⁹⁹Mo and ^99mTc using triisooctylamine (TIOA). The ⁹⁹Mo and ^99mTc were quantitatively separated out in 2 M TIOA with tripled distilled water; ^99mTc was back extracted from TIOA organic phase to aqueous phase by 0.1 M DTPA. The species information or indirect speciation of molybdenum was also established by the extraction profile of the molybdenum.