Uranium recovery by extraction

Purex [Plutonium and uranium recovery by extraction] A process for the solvent extraction of plutonium from solutions of uranium and fission products, obtained by dissolving spent nuclear fuel elements in nitric acid. The solvent is tri-n-butyl phosphate (TBP) in... 

Purex [Plutonium and uranium recovery by extraction] A process for the solvent extraction of plutonium from solutions of uranium and fission products, obtained by dissolving spent nuclear fuel elements in nitric acid. The solvent is tri- -butyl phosphate (TBP) in kerosene. First operated by the U.S. Atomic Energy Commission at its Savannah River plant, SC, in 1954 and at Hanford, WA, in 1956. Now in operation, with modifications, in several countries. Sites include Savannah River (SC), Cap de la Hague (France), Marcoule (France), Sellafield (England), Karlsruhe (Germany), and Trombay (India). See also Recuplex. 

The essential functions of the reprocessing of spent fuel elements is to separate uranium and plutonium from one another and both of them from the radioactive fission products. For this purpose, the PUREX process (Plutonium and Uranium Recovery by Extraction), based on extractive separation, has become accepted worldwide. It is currently u,sed in all modern reprocessing plants. 

It is used in the mining industry to recover metals such as copper and nickel. Parasite plants, based on solvent extraction, are used in the phosphate industry to recover by-product uranium from crude phosphoric acid. The uranium concentration in phosphoric acid is very low but, because of the high volume of phosphoric acid that is produced to meet agricultural needs, considerable uranium can be recovered using solvent extraction. In the nuclear industry [5], solvent extraction is used to purify uranium and plutonium [using the plutonium and uranium recovery by extraction (PUREX) process], zirconium from hafnium, and for many other applications. It is also used in environmental applications to clean soil, say, to remove polychlorinated biphenyls (PCBs), dioxins, pesticides, and other hazardous pollutants. 

As far as reprocessing in the U/Pu fuel cycle is concerned, several chemical separation techniques have been proposed and developed in the past few decades. The most efficient process to date remains the PUREX process (Plutonium and Uranium Recovery by Extraction). This process uses nitric acid HNO3 and organic solvents to dissolve and extract selectively U and Pu, resulting in two separate product streams (U on one side and Pu on the other side of the process chain). As far as reprocessing in the Th/ U fuel cycle is concerned, THOREX (Thorium Oxide Recovery by Extraction) technology must be used, also based on dissolution in nitric acid and solvent extraction (however, with special care for the extraction of Pa, for the separa-tion of U and U, and for the dissolution of thorium dioxide in pure nitric acid). 

Pilot plant uranium and chromium recovery data for a SLM system was reported by Babcock (65). Polysulfone hollow fibers were used in the module and a tertiary amine in kerosene was the organic phase. Operational costs for the separation of uranium were 0.8/Kg for a 3.8 X 10 m /day plant. This cost estimate was lower than those for uranium recovery by solvent extraction and ion exchange. 

Beginning in approximately 1975, both IMG and Ereeport Minerals operated large uranium recovery plants in the United States using this technology. Several plants continue to mn but a number have been closed because of the depressed uranium prices that resulted when uranium from the former Soviet Union flooded Western markets. A relatively small plant is operated by Prayon in Belgium (40). TOPO is available from Cytec Industries Inc. as CYANEX 921 extractant. D2EHPA is available from Albright Wilson Ltd. and is also sold by Daihachi as DP-8R. 

The O or S atoms in P=0 and P=S groups may act as electron donors although these groups form relatively weak complexes with electron acceptor compounds such as nonpolarizable, more electropositive (ie, hard) acids, including protons (14). Use is made of this property in the recovery of uranium from wet-process phosphoric acid by extractants such as trioctylphosphine oxide [78-50-2] and di(2-ethylhexyl) hydrogen phosphate [298-07-7]. 

Martella, L. L. Navratil, J. D. "Recovery of Uranium from Mixed Plutonium-Uranium Residues by an Extraction Chromatography Process," U.S. DOE Rept. RFP-3289, Rockwell International, Golden, Colorado, May 15,1982. 

A recent and extremely important development lies in the application of the technique of liquid extraction to metallurgical processes. The successful development of methods for the purification of uranium fuel and for the recovery of spent fuel elements in the nuclear power industry by extraction methods, mainly based on packed, including pulsed, columns as discussed in Section 13.5 has led to their application to other metallurgical processes. Of these, the recovery of copper from acid leach liquors and subsequent electro-winning from these liquors is the most extensive, although further applications to nickel and other metals are being developed. In many of these processes, some form of chemical complex is formed between the solute and the solvent so that the kinetics of the process become important. The extraction operation may be either a physical operation, as discussed previously, or a chemical operation. Chemical operations have been classified by Hanson(1) as follows ... 

The possibility of dissolving the mixed hydroxide in HNOs and obtaining direct extraction of thorium (and uranium) from the nitrate solution has been studied [155,156], but does not seem to be too promising, possibly due to the partial oxidation of tripositive cerium to the tetrapositive state. Kraitzer [157] was able to separate thorium from the mixed hydroxide cake by extracting the cake with sodium carbonate buffer at pH 9.5—10. Thorium was found to form a soluble carbonate complex and a recovery of better than 99% of thorium was claimed after only four extractions. 

Hurst, F.J. Crouse, D.J. Recovery of uranium from wet-process phosphoric acid by extraction with octylphenylphosphoric acid, Ind. Eng. Chem. Proc. 13 (1974) 286-291. 

North and Wells (N7) described the design and operation of a rotary-film contactor for the solvent extraction of metals directly from leached ore slurries. It consists of an enclosed rotating assembly of closely spaced disks centrally mounted on a common horizontal shaft. The transfer of the metal to the solvent layer is effected by the rotating disks where a film of slurry is formed on contact with the leached ore at the bottom of the vessel. This contactor gave excellent uranium recovery from sulfuric... 

The achievement of an economically viable process for the extraction of uranium fix>m seawater, however, could be achieved only through use of a sorbent with uranium concentrating factors greater than those provided by titanium oxides [181]. Polyacrylamidoxime sorbents, characterized by D value > 10 ( 10 ) (see Table 5) made an appearance at the end of the 1970s to remove this impediment to the economic recovery of uranium fix>m seawater. Their appearance reoriented research in the field of uranium recovery toward highly selective organic resins [188, 189]. 

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