Dissolution Behavior of Uranium Oxides with Supercritical CO2 Using HNO3-TBP Complex as a Reactant.

Tomioka, Osamu; Meguro, Yoshihiro; Enokida, Youichi; Yamamoto, Ichiro; Yoshida, Zenko

doi:10.3327/jnst.38.1097

Cited by 36 publications

(39 citation statements)

References 26 publications

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“…The uranium extraction percentage slightly increased with an increase of pressure. Previously, an opposite pressure effect, which was a decrease of the extraction percentage with an increase of pressure, was observed in the extraction of uranium from UO2 powder 19 and from a sea sand sample contaminated with UO2. 12 The negative-pressure effect resulted from a decrease of activity of the HNO3-TBP complex along with an increase of solvation of the CO2 molecules to the HNO3-TBP complex in the supercritical CO2 phase of higher pressure or higher density.…”

Section: Extraction Of Uranium From Uranyl Phosphate Compoundsmentioning

confidence: 99%

“…12 The negative-pressure effect resulted from a decrease of activity of the HNO3-TBP complex along with an increase of solvation of the CO2 molecules to the HNO3-TBP complex in the supercritical CO2 phase of higher pressure or higher density. 19 The pressure effect on the uranium extraction consists of that on the reaction of the extractant with the uranium compound and that on the dissolution of a uranium-TBP complex formed by the reaction into the supercritical CO2.…”

Section: Extraction Of Uranium From Uranyl Phosphate Compoundsmentioning

confidence: 99%

“…In the present study, we investigated the extraction behavior of uranium into supercritical CO2 from uranium compounds, prior to developing a SFE method using CO2 of uranium from these uranium ores. Because we have already shown that uranium can be extracted from uranium oxide into supercritical CO2 including the HNO3-TBP complex, 19 three uranyl phosphate compounds were prepared in this study, and uranium was extracted into supercritical CO2 including the HNO3-TBP complex from them. In addition, a simulated powdered ore including small amount of pitchblende was used to demonstrate the feasibility of the SFE method using CO2 as a uranium separation method.…”

Section: Introductionmentioning

confidence: 99%

“…In the present study, we investigated the extraction behavior of uranium into supercritical CO2 from uranium compounds, prior to developing a SFE method using CO2 of uranium from these uranium ores. Because we have already shown that uranium can be extracted from uranium oxide into supercritical CO2 including the HNO3-TBP complex, 19 The supercritical fluid extraction (SFE) method using CO2 as a medium with an extractant of HNO3-tri-n-butyl phosphate (TBP) complex was applied to extract uranium from several uranyl phosphate compounds and simulated uranium ores. An extraction method consisting of a static extraction process and a dynamic one was established, and the effects of the experimental conditions, such as pressure, temperature, and extraction time, on the extraction of uranium were ascertained.…”

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Extraction of Uranium from Simulated Ore by the Supercritical Carbon Dioxide Fluid Extraction Method with Nitric Acid-TBP Complex

et al. 2006

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Uranium used for the uranium fuel of nuclear power plants is obtained from uranium ores having relatively high uranium content by extraction and separation. However, generally utilized ores, such as monazite, phosphate rock, and titanium ore, are not uranium ores, but include a small amount of uranium. In order to determine uranium content in these ores, uranium is first separated out by leaching ores with mineral acids, and then uranium in the leaching solution is determined by inductively coupled plasma mass spectrometry (ICP-MS). The accuracy of this method is not very high due to a large resultant leaching solution and various associated impurities. Therefore, it is very important to develop a novel and selective uranium separation method from the ores, in which separation processes are simple and wastes are less generated, for ensuring that the analysis of uranium in ores is of high accuracy.Supercritical fluid extraction (SFE) using CO2 as a medium has been widely and practically utilized for the extraction and separation of useful materials in many industries, such as food, medicine, and cosmetic. Recently, much attention has been paid to a separation technology of metals involving SFE using CO2. 1 Several methods of SFE using CO2 as a medium were developed for the separation of metal ions from an aqueous solution using supercritical CO2 instead of an organic solvent. [2][3][4][5][6][7][8][9] It is particularly worth noting that an alternative and more attractive method of supercritical CO2 technology is "direct leaching" of metals from solid samples by utilizing a large penetration force and high diffusivity of supercritical CO2 into the solids. [9][10][11][12][13][14][15][16][17][18] In order to extract uranium from radioactive wastes, the authors have developed a novel extraction method, 12 in which supercritical CO2 containing a reactant is used as a medium to dissolve metal compounds involved in a solid matrix. It was demonstrated that the method using a nitric acid-tri-n-butyl phosphate (HNO3-TBP) complex as an extractant was applicable to the extraction of uranium from simulated radioactive waste samples contaminated by uranium oxides. 12,18 This extraction method is for the direct separation and recovery of metals from a solid sample without using any acid leaching, and shows several attractive properties, as follows: (i) the extraction efficiency and rate are enhanced due to the large penetration force and rapid diffusion of supercritical CO2, (ii) rapid and complete recovery of the extracted substances from the CO2 medium is attained by the gasification of CO2, (iii) the extraction system is easily expanded based on substantial experiences of SFE in general industry, such as the food industry, (iv) the generation of wastes from the process is totally minimized and (v) a solid sample after the extraction treatment is in the form of a dried solid that does not contain an appreciable quantity of an organic reactant and acid.There are many ores that are known as uranium including ores, such as autun...

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Section: Extraction Of Uranium From Uranyl Phosphate Compoundsmentioning

confidence: 99%

Section: Extraction Of Uranium From Uranyl Phosphate Compoundsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…In the present study, we investigated the extraction behavior of uranium into supercritical CO2 from uranium compounds, prior to developing a SFE method using CO2 of uranium from these uranium ores. Because we have already shown that uranium can be extracted from uranium oxide into supercritical CO2 including the HNO3-TBP complex, 19 The supercritical fluid extraction (SFE) method using CO2 as a medium with an extractant of HNO3-tri-n-butyl phosphate (TBP) complex was applied to extract uranium from several uranyl phosphate compounds and simulated uranium ores. An extraction method consisting of a static extraction process and a dynamic one was established, and the effects of the experimental conditions, such as pressure, temperature, and extraction time, on the extraction of uranium were ascertained.…”

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confidence: 99%

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Extraction of Uranium from Simulated Ore by the Supercritical Carbon Dioxide Fluid Extraction Method with Nitric Acid-TBP Complex

et al. 2006

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“…Uranium dioxide in its solid state can be dissolved directly in supercritical CO2 with a TBP-HNO3 complex [14][15][16]. To prepare the reagent (i.e., TBP-HNO3 complex) for extraction, anhydrous TBP and 70% HNO3 were fully mixed in a 1:1 ratio in a beaker using a rotating magnetic stirring bar.…”

Section: Preparation Of the Reagent For Extraction And The Extractionmentioning

confidence: 99%

Decontamination of Uranium-Contaminated Soil Sand Using Supercritical CO2 with a TBP–HNO3 Complex

Park

Jung

Park

2015

Metals

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An environmentally friendly decontamination process for uranium-contaminated soil sand is proposed. The process uses supercritical CO2 as the cleaning solvent and a TBP-HNO3 complex as the reagent. Four types of samples (sea sand and coarse, medium, and fine soil sand) were artificially contaminated with uranium. The effects of the amount of the reagent, sand type, and elapsed time after the preparation of the samples on decontamination were examined. The extraction ratios of uranium in all of the four types of sand samples were very high when the time that elapsed after preparation was less than a few days. The extraction ratio of uranium decreased in the soil sand with a higher surface area as the elapsed time increased, indicating the possible formation of chemisorbed uranium on the surface of the samples. The solvent of supercritical CO2 seemed to be very effective in the decontamination of soil sand. However, the extraction of chemisorbed uranium in soil sand may need additional processes, such as the application of mechanical vibration and the addition of bond-breaking reagents.

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Study on Properties of TBP‐HNO₃ Complex Used for Direct Dissolution of Lanthanide and Actinide Oxides in Supercritical Fluid CO₂

et al. 2007

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The tri-n-butyl phosphate-nitric acid (TBP-HNO 3 ) complex prepared by contacting the pure TBP with the concentrated HNO 3 can be used for direct dissolution of lanthanide and actinide oxides in the supercritical fluid carbon dioxide (SCF-CO 2 ). Properties of the TBP-HNO 3 complex have been studied. Experimental results showed that when the initial HNO 3 /TBP volume ratio was varied from 1∶7 to 5∶1, the concentration of HNO 3 in the TBP-HNO 3 complex changed from 1.95 to 5.89 mol/L, the [HNO 3 ]/[TBP] ratio of the TBP-HNO 3 complex changed from 0.61 to 2.22, and the content of H 2 O in the TBP-HNO 3 complex changed from 2.02% to 4.19%. All of the density, viscosity and surface tension of the TBP-HNO 3 complex changed with the concentration of HNO 3 in the complex, and were higher than those of the pure TBP. The protons of HNO 3 and H 2 O in the complex underwent rapid exchange to exhibit a singlet resonance peak in nuclear magnetic resonance spectra. When the TBP-HNO 3 complex was dissolved in a low dielectric constant solvent, small droplets of HNO 3 were formed that can be detected by NMR.Keywords TBP-HNO 3 complex, supercritical fluid carbon dioxide, property IntroductionReprocessing of the spent nuclear fuel for extraction of plutonium (Pu) and uranium (U) is conventionally carried out by the PUREX process, which involves the dissolution of the spent nuclear fuel in nitric acid followed by solvent extraction of U and Pu from the acidic solution using tri-n-butyl phosphate (TBP) as extractant in kerosene dilutent.1 However, a large amount of high-level liquid radioactive wastes is produced in the PUREX process, and the cost for liquid waste treating is high.Recently, the TBP-HNO 3 complex has been found to be effective for dissolution of solid UO 2 and U 3 O 8 as well as lanthanide oxides in supercritical fluid carbon dioxide (SCF-CO 2 ).2-5 The U(IV) in solid UO 2 is possibly oxidized to U(VI) by HNO 3 in the TBP-HNO 3 complex and dissolves in SCF-CO 2 as UO 2 (NO 3 ) 2 •2TBP. The metallic nitrate complex with TBP is finally recovered by depressurizing to atmospheric pressure. The process does not involve any aqueous solution to dissolve the uranium oxides and leads to minimum generation of the wastes, therefore, it is an attractive process for the spent nuclear fuel reprocessing and decontamination of uranium-contaminated solid waste.6 A super-DIREX (supercritical fluid direct extraction) process has been suggested by Japanese scientists for direct dissolution of actinide and lanthanide oxides and extraction of these elements with SCF-CO 2 containing the TBP-HNO 3 complex. 7A remarkable increase of the dissolution rate with increase of both HNO 3 /TBP molar ratio and the content of H 2 O in the TBP-HNO 3 complex was reported for direct dissolution of uranium oxides in SCF-CO 2 .2 The physical properties of the TBP-HNO 3 complex such as density, viscosity and surface tension are important for the direct dissolution of lanthanide and actinide oxides in SCF-CO 2 . In order to understand the nature and mechani...

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Dissolution Behavior of Uranium Oxides with Supercritical CO2 Using HNO3-TBP Complex as a Reactant.

Cited by 36 publications

References 26 publications

Extraction of Uranium from Simulated Ore by the Supercritical Carbon Dioxide Fluid Extraction Method with Nitric Acid-TBP Complex

Extraction of Uranium from Simulated Ore by the Supercritical Carbon Dioxide Fluid Extraction Method with Nitric Acid-TBP Complex

Decontamination of Uranium-Contaminated Soil Sand Using Supercritical CO2 with a TBP–HNO3 Complex

Study on Properties of TBP‐HNO₃ Complex Used for Direct Dissolution of Lanthanide and Actinide Oxides in Supercritical Fluid CO₂

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Dissolution Behavior of Uranium Oxides with Supercritical CO2 Using HNO3-TBP Complex as a Reactant.

Cited by 36 publications

References 26 publications

Extraction of Uranium from Simulated Ore by the Supercritical Carbon Dioxide Fluid Extraction Method with Nitric Acid-TBP Complex

Extraction of Uranium from Simulated Ore by the Supercritical Carbon Dioxide Fluid Extraction Method with Nitric Acid-TBP Complex

Decontamination of Uranium-Contaminated Soil Sand Using Supercritical CO2 with a TBP–HNO3 Complex

Study on Properties of TBP‐HNO3 Complex Used for Direct Dissolution of Lanthanide and Actinide Oxides in Supercritical Fluid CO2

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Study on Properties of TBP‐HNO₃ Complex Used for Direct Dissolution of Lanthanide and Actinide Oxides in Supercritical Fluid CO₂