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

Abstract

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...

Characterization and remediation of soils contaminated with uranium

“…The supercritical fluid extraction (SFE) method using CO 2 as a medium with an extractant of HNO 3 -tri-n-butylphosphate complex was applied by Dung et al [241] to extract uranium from several uranyl phosphate compounds and simulated uranium ores. They found that uranium could be efficiently extracted from both the uranyl phosphates and simulated ores.…”