Tributyl phosphate solvent extraction

Barnard, K.R. and Turner, N.L. (2011) The effect of temperature on hydroxyoxime stability in the LIX 63 - Versatic 10 - tributyl phosphate synergistic solvent extraction system under synthetic nickel laterite conditions Hydrometallurgy 109 245-251... 

An improved solvent extraction process, PUREX, utilizes an organic mixture of tributyl phosphate solvent dissolved in a hydrocarbon diluent, typically dodecane. This was used at Savannah River, Georgia, ca 1955 and Hanford, Washington, ca 1956. Waste volumes were reduced by using recoverable nitric acid as the salting agent. A hybrid REDOX/PUREX process was developed in Idaho Falls, Idaho, ca 1956 to reprocess high bum-up, fuUy enriched (97% u) uranium fuel from naval reactors. Other separations processes have been developed. The desirable features are compared in Table 1. 

In practice, uranium ore concentrates are first purified by solvent extraction with tributyl phosphate in kerosene to give uranyl nitrate hexahydrate. The purified uranyl nitrate is then decomposed thermally to UO (eq. 10), which is reduced with H2 to UO2 (eq. 11), which in turn is converted to UF by high temperature hydrofluorination (eq. 12). The UF is then converted to uranium metal with Mg (eq. 19). 

For solvent extraction of a tetravalent vanadium oxyvanadium cation, the leach solution is acidified to ca pH 1.6—2.0 by addition of sulfuric acid, and the redox potential is adjusted to —250 mV by heating and reaction with iron powder. Vanadium is extracted from the blue solution in ca six countercurrent mixer—settler stages by a kerosene solution of 5—6 wt % di-2-ethyIhexyl phosphoric acid (EHPA) and 3 wt % tributyl phosphate (TBP). The organic solvent is stripped by a 15 wt % sulfuric acid solution. The rich strip Hquor containing ca 50—65 g V20 /L is oxidized batchwise initially at pH 0.3 by addition of sodium chlorate then it is heated to 70°C and agitated during the addition of NH to raise the pH to 0.6. Vanadium pentoxide of 98—99% grade precipitates, is removed by filtration, and then is fused and flaked. 

The separation of basic precipitates of hydrous Th02 from the lanthanides in monazite sands has been outlined in Fig. 30.1 (p. 1230). These precipitates may then be dissolved in nitric acid and the thorium extracted into tributyl phosphate, (Bu"0)3PO, diluted with kerosene. In the case of Canadian production, the uranium ores are leached with sulfuric acid and the anionic sulfato complex of U preferentially absorbed onto an anion exchange resin. The Th is separated from Fe, A1 and other metals in the liquor by solvent extraction. 

Spectrophotometric methods may often be applied directly to the solvent extract utilising the absorption of the extracted species in the ultraviolet or visible region. A typical example is the extraction and determination of nickel as dimethylglyoximate in chloroform by measuring the absorption of the complex at 366 nm. Direct measurement of absorbance may also be made with appropriate ion association complexes, e.g. the ferroin anionic detergent system, but improved results can sometimes be obtained by developing a chelate complex after extraction. An example is the extraction of uranyl nitrate from nitric acid into tributyl phosphate and the subsequent addition of dibenzoylmethane to the solvent to form a soluble coloured chelate. 

Solvent Extraction. A modified, one-cycle PUREX process is used at Rocky Flats to recover plutonium from miscellaneous Pu-U residues (11). The process utilizes the extraction of uranium (VI) into tributyl phosphate (TBP), leaving plutonium (III) in the raffinate. The plutonium is then sent to ion exchange for... 

Dapex [Di-alkylphosphoric acid extraction] A process for the solvent extraction of uranium from sulfuric acid solutions using di-(2-ethylhexyl) phosphoric acid (HDEHP). The HDEHP is dissolved in kerosene containing 4 percent of tributyl phosphate. The uranium is stripped from the organic phase by aqueous sodium carbonate and precipitated as uranyl peroxide (yellow cake). The process was no longer in use in 1988. See also Amex. 

Fuel. The nuclear fuel cycle starts with mining of the uranium ore, chemical leaching to extract the uranium, and solvent extraction with tributyl phosphate to produce eventually pure uranium oxide. If enriched uranium is required, the uranium is converted to the gaseous uranitim hexafluoride for enrichment by gaseous diffusion or gas centrifuge techniques, after which it is reconverted to uranium oxide. Since the CANDU system uses natural uranium, I will say no more about uranium enrichment although, as I m sure you appreciate, it is a major chemical industry in its own right. 

Thorium sulfate, being less soluble than rare earth metals sulfates, can be separated by fractional crystallization. Usually, solvent extraction methods are applied to obtain high purity thorium and for separation from rare earths. In many solvent extraction processes, an aqueous solution of tributyl phosphate is the extraction solvent of choice. 

Finely-ground monazite is treated with a 45% NaOH solution and heated at 138°C to open the ore. This converts thorium, uranium, and the rare earths to their water-insoluble oxides. The insoluble residues are filtered, dissolved in 37% HCl, and heated at 80°C. The oxides are converted into their soluble chlorides. The pH of the solution is adjusted to 5.8 with NaOH. Thorium and uranium are precipitated along with small quantities of rare earths. The precipitate is washed and dissolved in concentrated nitric acid. Thorium and uranium are separated from the rare earths by solvent extraction using an aqueous solution of tributyl phosphate. The two metals are separated from the organic phase by fractional crystallization or reduction. 

Solvent extraction by tributyl phosphate (TBP) (13, 96), dithizone (20, 71, 72), cupferron (89), thenoyl trifluoroacetone (TTA) (55), diiso-propyl ketone (26), mesityl oxide (92), tri-n-benzylamine and methyl di-n-octylamine (99), diisopropyl and diisobutyl carbinol (100) have all found some application on the trace scale. Acetylaeetone and methyl isobutyl ketone extract milligram amounts of polonium almost quantitatively from hydrochloric acid, but the stable polonium-organic compounds which are formed make it difficult to recover the polonium in a useful form from solutions in these ketones (7). Ion exchange (22, 115, 119) and paper chromatography (44, 87) have also been used for trace scale separations of polonium, but the effects of the intense alpha-radiation on organic com-... 

Although tellurium tetrachloride has been reported55 to form a 1 2 complex with acetamide, there appears to be little other information available on the complex. Similarly, the reported tributyl phosphate complex of polonium tetrachloride56 has received little attention. The formation of a polonium(IV) perchlorate complex with tributyl phosphate has been suggested57 in the solvent extraction of polonium from perchloric acid. 

The solvents used vary with die nature of the products involved. Widely used are water, hexane, acetone, isopropyl alcohol, furfural, xylene, liquid sulfur dioxide, and tributyl phosphate. Solvent extraction is an important method of both producing and purifying such products as lubrication and vegetable oils, pharmaceuticals, and nonferrous metals,... 

Z. Kolarik. The formation of a third phase in the extraction of Pu(IV), U(VI) and Th(IV) nitrates with tributyl phosphate in alkane diluents. In Proceeding of the International Solvent Extraction Conference (ISEC-77), 1977. 

Stieglitz, L. 1971. Investigation on the nature of degradation products in the system 20 vol.-% tributyl phosphate-dodecane-nitric acid. I. Enrichment of complexing products and infra-red study. Proceedings of the International Solvent Extraction Conference, 19-23 April, Society of Chemical Industry London, Vol. I, 155-159. 

The uranium and plutonium are recovered for further use by first dissolving the spent fuel in nitric acid and subjecting the resulting solution to a solvent extraction process. Several different processes exist, the best known being the Purex process (Fig. 18), in which tributyl phosphate (TBP) (30% solution in kerosene) is the extractant. Extraction is carried out in compact mixer-settlers or air-pulsed columns fabricated of stainless steel, with about 99.9% removal of uranium and plutonium in the extract. 

Advantage may be taken of these conditions by use of solvent extraction techniques. It is known (25-30) that Am extraction with TBP ( tributyl phosphate) or DBBP (dibutyl butyl phos-phonate) is enhanced by high nitrate salt concentrations in the aqueous phase, particularly at HN03 concentrations below 1.0 N. 

Solvent extraction [tributyl phosphate (TBP)] operations to recover plutonium from unirradiated scrap have been performed at the Hanford Site since 1955. The aqueous raffinate (CAW stream) from the TBP plutonium extraction process contains, typically, <10 mg/L plutonium and 2-10 mg/L 2 1Am. This latter isotope is present in the plutonium scrap as the result of beta decay of Pu (t]/2 = 14.4 y) tri valent americium does not accompany plutonium from the HNO3-HF feed solution into the TBP solvent. 

Solvent Extraction. The yellow cake is dissolved in nitric acid and extracted from this aqueous phase by 5 percent tributyl phosphate (TBP) in a hydrocarbon diluent. The diluent reduces the density and viscosity of the TBP, enhancing the aqueous/solvent phase separation. The extraction is very specific for uranium, with separation factors of 103 to 105. The product thus obtained is an aqueous uranyl nitrate solution (Fig. 21.14). 

The control of the actinide metal ion valence state plays a pivotal role in the separation and purification of uranium and plutonium during the processing of spent nuclear fuel. Most commercial plants use the plutonium-uranium reduction extraction process (PUREX) [58], wherein spent fuel rods are initially dissolved in nitric acid. The dissolved U and Pu are subsequently extracted from the nitric solution into a non-aqueous phase of tributyl phosphate (TBP) dissolved in an inert hydrocarbon diluent such as dodecane or odourless kerosene (OK). The organic phase is then subjected to solvent extraction techniques to partition the U from the Pu, the extractability of the ions into the TBP/OK phase being strongly dependent upon the valence state of the actinide in question. 

Rare earths separation has been achieved by formation of species of the formula Ln(NC>3)3 -3TBP, where TBP is tributyl phosphate. This process is solvent extraction which is widely used at present in the production of rare earths in pure form. 

Chemex [Chemical exchange] A process for separating uranium isotopes, based on the equilibrium between U3+ and U4+ in aqueous solution. U-238 concentrates in the LP+ state and U-235 in the U4+. Uranium in the two valence states is separated by solvent extraction into tributyl phosphate. Developed and piloted in France but not commercialized. 

NPEX A process for removing neptunium and plutonium during the processing of nuclear fuel by solvent extraction. The solvent is tributyl phosphate diluted with n-dodecane. Developed by E.R Howitz at the Argonne National Laboratory, Argonne, IL. See also SREX, UREX+. 

UREX [URanium Extraction] A solvent extraction process for extracting uranium and technetium from used nuclear fuel, while rejecting all the transuranic elements. Based on the Purex process, which uses tributyl phosphate in a hydrocarbon mixture, but incorporating acetohydroxamic acid, which complexes the Pu and Np and thereby prevents them from being extracted. Developed by the Westinghouse Savannah River Company in 2003. Associated processes are NPEX, TRUEX, and Cyanex 301. 

UREX+ A solvent extraction process for separating the components of used nuclear fuel so that the unreacted fraction can be reused in an Advanced Burner Reactor. Based on the Purex process, which uses tributyl phosphate in n-dodecane, but using multistage, centrifugal contactors. Developed by the Argonne National Laboratory, Chicago, IL, from 2003 and proposed for use by 2014. 

Cerium (IV) in solution is obtained by treatment of Ce111 solutions with very powerful oxidizing agents, for example, peroxodisulfate or bismuthate in nitric acid. The aqueous chemistry of CeIV is similar to that of Zr, Hf, and, particularly, tetravalent actinides. Thus Ce gives a phosphate insoluble in 4 M HN03 and an iodate insoluble in 6 M HN03, as well as an insoluble oxalate. The phosphate and iodate precipitations can be used to separate Ce from the trivalent lanthanides. Ce is also much more readily extracted into organic solvents by tributyl phosphate and similar extractants than are the Lnm lanthanide ions. 

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