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Abstract  

In order to analyze actinide elements in radioactive metal waste, the dissolution and chemical separation conditions were optimized. The surfaces of a type 304 stainless steel plate and of pipe waste sampled from the prototype advanced thermal reactor (Fugen) were dissolved in mixed acid solution (HNO3:HCl:H2O = 1:1:4). The resulting solution was evaporated to dryness and dissolved with 2 mol/dm3 of HNO3 to prepare sample solutions. In order to analyze trivalent actinide elements in the sample solution containing a large amount of Fe(III) (>0.1 g) using TRU resin, the effect of Fe(III) concentration on the recovery of Am(III) and reduction effect of Fe(III) to Fe(II) with ascorbic acid were studied. On the basis of results of this study, chemical separation scheme was constructed and Pu and Am in the sample solutions were separated. Thorium and U in the sample solutions were separated with UTEVA resin. High recoveries for all experimented elements were obtained from the analysis of spiked sample solutions, the effectiveness of the method was confirmed.

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Abstract  

The colour reaction of Am(III) with Arsenazo III in several hydroorganic media has been examined systematically on the addition of certain polar water-miscible organic solvents in the course of a search for improved and simple spectrophotometric methods for the estimation of americium. Addition of these substances resulted in the stabilization of colour and brought about a drastic enhancement in the absorbance values. The organic additives studied include acetone, acetonitrile, dimethylformamide, dioxane and ethanol. Among the many solvents tested, alcohol and dioxane proved to be the most effective; highest sensitivity is obtained by using a 60% dioxane-ethanol (11) mixture. The apparent molar absorptivity based on Am content is 184616±9931 mol–1 cm–1 at 655 nm which is about 3 times that attained for the reaction in aqueous medium (65178±1243). Strikingly, this is the highest value reported as yet for its determination. Beer's law is obeyed both in mixed as well as aqueous media. The effects of some experimental variables on colour development have also been studied to optimize the conditions for the assay of Am.

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Abstract  

The present paper describes a novel type of extractant for actinides called bis (dioctylcarbamoylmethyl) sulfoxide which neither contains phosphorus nor entails the addition of tributyl phosphate as phase modifier for extraction. This extractant, abbreviated as CMSO, has been found to be freely soluble in dodecane and to form no third phase even with concentrations of nitric acid as high as 10M. The distribution ratios for the extraction of Am(III), Pu(IV) and U(VI) at trace levels have been found to be 13, 220 and 11, respectively, from 5M nitric acid using 0.2M CMSO in dodecane and those for back-extraction have been found to be 2×10–4, 8×10–3 and 5×10–2 using 0.01M nitric acid, 0.1M oxalic acid and 0.35M sodium carbonate, respectively. Similar distribution ratios were obtained with the recycled extractant. Extraction was found to be very rapid. Eu(III) and Sr(II) were found to be moderately extracted with distribution ratios of 2 and 0.77, respectively, while the extraction of Cs(I) was negligible (KD=0.005).

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Abstract  

High-level liquid waste from fast reactor fuel reprocessing stream contains significant quantities of lanthanides and trivalent minor actinides. The lanthanides and minor actinides (MA) have been separated from the fast reactor high-level liquid waste (FR-HLLW) using TRUEX solvent, which is a mixture of 0.2 M octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO)-1.2 M tri-n-butylphosphate (TBP) in n-dodecane. A new stripping composition, 0.1 M HNO3 and 0.1 M citric acid (CA), has been employed for back extraction of them from the TRUEX solvent. In order to separate lanthanides from actinides present in the strip solution, the extraction behavior of 241Am(III) and (152+154)Eu(III) from CA–HNO3 medium by a solution of bis-2-ethylhexylphosphoric acid (HDEHP) in n-dodecane has been studied. Separation factors (SF = D Eu/D Am) has been reported as a function of various parameters such as pH, concentrations of HDEHP, diethylenetriamine-N,N,N′,N′′,N′′′-pentaaceticacid (DTPA), 1-octanol and TBP in this paper.

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Abstract  

In order to develop a direct separation process for trivalent minor actinides from fission products in high level liquid waste (HLLW) by extraction chromatography, a novel macroporous silica-based 2,6-bis(5,6-diisohexyl)-1,2,4-triazin-3-yl)pyridine resin (isohexyl-BTP/SiO2-P resin) was prepared. The content of isohexyl-BTP extractant in the resin was as high as 33.3 wt%. The resin exhibited much higher adsorption affinity for Am(III) in 2–3 M (mol/L) HNO3 solution over U and FP which are contained in HLLW. The kinetic data were analyzed using pseudo-second-order equation. The results suggested that the Eu(III), Gd(III), and Dy(III) adsorption was well explained by the pseudo-second-order equation. Quantitative desorption for adsorbed elements was achieved by using H2O or thiourea as eluting agents. However, the kinetics of adsorption and desorption were rather slow and this drawback needs to be resolved. Stability of the resin against HNO3 was also examined. It was found that the resin was considerably stable against ≤4 M HNO3 solution for the reasons of an extremely small leakage of the extractant into the solution from the resin and the adsorption performance keeping for rare earths in 3 M HNO3 solution.

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Abstract  

Bench-Scale studies on the partitioning and recovery of minoractinides from the actual and synthetic sulphate-bearing high level waste (SBHLW) solutions have been carried out by giving two contacts with 30% TBP to deplete uranium content followed by four contacts with 0.2M CMPO+1.2M TBP in dodecane. The acidity of the SBHLW solutions was about 0.3M. In the case of actual SBHLW, the final raffinate contained about 0.4% -activity originally present in the HLW, whereas with synthetic SBHLW the -activity was reduced to the background level.144Ce is extracted almost quantitative in the CMPO phase,106Ru about 12% and137Cs is practically not extracted at all. The extraction chromatographic column studies with synthetic SBHLW (aftertwo TBP contacts) has shown that large volume of waste solutions could be passed through the column without break-through of actinide metal ions. Using 0.04M HNO3>99% Am(III) and rare earths could be eluted/stripped. Similarly >99% Pu(IV) and U(VI) could be eluted.stripped using 0.01M oxalic acid and 0.25M sodium carbonate, respectively. In the presence of 0.16M SO 4 2– (in the SBHLW) the complex ions AmSO 4 + , UO2SO4, PuSO 4 2+ and Pu(SO4)2 were formed in the aqueous phase but the species extracted into the organic phase (CMPO+TBP) were only the nitrato complexes Am(NO3)3·3CMPO, UO2(NO3)2·2CMPO and Pu(NO3)4·2CMPO. A scheme for the recovery of minor actinides from SBHLW solution with two contacts of 30% TBP followed by either solvent extraction or extraction chromatographic techniques has been proposed.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: Qifeng Liu, Jiali Liao, Ning Liu, Dong Zhang, Houjun Kang, Yuanyou Yang, Bing Li, Haijun Zhu, and Jiannan Jin

Abstract  

As an important radioisotope in nuclear industry and other fields, 241 Am is one of the most serious contamination concerns due to its high toxicity and long half-life. In order to supply useful reference for disposal of 241Am waste with low-medium radioactivity, the adsorption and migration behavior of 241Am on aerated zone soil were investigated by the static experimental method and column experiments. The results showed that more than 98% of the total 241Am could be adsorbed from 241Am solution of 0.32·10−7−1.1·10−7 mol/l by the soil at pH 4–9. The adsorption of 241Am on the soil was a pH-dependent process at pH<4, but for pH>4, the adsorption rate of 241Am on the soil changed minutely. The adsorption equilibrium was achieved within 24 hours and no significant effect on adsorption of 241Am was observed at liquid-solid ratios of 50:1–500:1. The relationship between concentration of 241Am and adsorption capacities of 241Am can be described by the Freundlich adsorption equation. Adsorption of 241Am on the soil can be inhibited by humic acid, ferric hydroxide colloid, or some anions, such as citric acid anion, saturated EDTA solution, C2O4 2− and CO3 2−. It was also noted that the adsorption rate of 241Am drops in solutions containing Eu3+ or Nd3+, even 0.5 times above the 241Am concentration. A migration distance of 8 mm for 241Am(III) is observed only in the aerated zone soil containing ferric colloid, while a migration distance of less than 2 mm is noted in other soil samples after more than 250 days. All these results indicate that the aerated zone soil is an efficient sorbent for 241Am and can inhibit the migration of 241Am.

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Abstract  

Nuclear test explosions and nuclear reactor wastes and accidents have released large amounts of radioactivity into the environment. Actinideions in waters often are not in a state of thermodynamic equilibrium and their solubility and migration behavior is related to the form in which the nuclides are introduced into the aquatic system. Chemical speciation, oxidation state, redox reactions, and sorption characteristics are necessary in predicting solubility of the different actinides, their migration behaviors and their potential effects on marine biota. The most significant of these variables is the oxidation state of the metal ion as the simultaneous presence of more than one oxidation state for some actinides in a solution complicates actinide environmental behavior. Both Np(V)O2 + and Pu(V)O2 +, the most significant soluble states in natural oxic waters, are relatively noncomplexing and resistant to hydrolysis and subsequent precipitation. The solubility of NpO2 + can be as high as 10−4M while that of PuO2 + is much more limited by reduction to the insoluble tetravalent species, Pu(OH)4, (pKsp≥56) but which can be present in the pentavalent form in aqautic phases as colloidal material. The solubility of hexavalent UO2 2+ in sea water is relatively high due to formation of carbonate complexes. The insoluble trivalent americium hydroxocarbonate, Am(OH)(CO3) is the limiting species for the solubility of Am(III) in sea water. Thorium(IV) is present as Th(OH)4, in colloidal form. The chemistry of actinide ions in the environment is reviewed to show the spectrum of reactions that can occur in natural waters which must be considered in assessing the environmental behavior of actinides. Much is understood about sorption of actinides on surfaces, the mode of migration of actinides in such waters and the potential effects of these radioactive species on marine biota, but much more understanding of the behavior of the actinides in the environment is needed to allow proper and reliable modeling needed for disposition of nuclear waste over many thousands of years.

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