Plutonium fluoride

Preparation of Plutonium Metal from Fluorides. Plutonium fluoride, PuF or PuF, is reduced to the metal with calcium (31). Although the reactions of Ca with both fluorides are exothermic, iodine is added to provide additional heat. The thermodynamics of the process have been described (133). The purity of production-grade Pu metal by this method is ca 99.87 wt % (134). Metal of greater than 99.99 wt % purity can be produced by electrorefining, which is appHcable for Pu alloys as well as to purify Pu metal. The electrorefining has been conducted at 740°C in a NaCl—KCl electrolyte containing PuCl [13569-62-5], PuF, or PuF. Processing was done routinely on a 4-kg Pu batch basis (135). 

Compounds with Fluorine. The available data on plutonium fluorides and related species are listed in Table I. 

Thermodynamic data associated with the solid plutonium fluorides and oxyfluorides at 298 K. 

Christensen, D. C. Rayburn, J. A. "Pyrochemical Recovery of Plutonium Fluoride Reduction Slag," Los Alamos National Laboratory, In Press. 

Plutonium is recovered from uranium and fission products by solvent extraction, precipitation, and other chemical methods. In most chemical processes, plutonium first is converted to one of its salts, usually plutonium fluoride, before it is recovered in purified metallic form. The fluoride is reduced with calcium metal to yield plutonium. Electrorefining may produce material of higher purity. 

This work was carried on by B. B. Cunningham and L. B. Werner. On August 18, 1942, they isolated about one microgram of a pure compound. This was the first sight of a synthetic element and the first case of the isolation of a weighable amount of an artificially produced isotope (71, 59, 69). In September, 30 micrograms of the element were obtained and the iodate, hydroxide, peroxide, and ammonium plutonium fluoride were prepared in a pure state. 

Knighton, J. B. Auge, R. G. Berry, J. W. Molten Salt Extraction of Americium from Molten Plutonium Metal, Rockwell International Rocky Flats Plant, RFP-2365, March 12, 1976. Mullins, L. J. Morgan, A. N. A Review of Operating Experience at the Los Alamos Plutonium Electrorefining Facility, 1963-1977, Los Alamos National Laboratory, LA 9843, Dec. 1981. Christensen, D. C. Rayburn, J. A. Pyrochemical Recovery of Plutonium Fluoride Reduction Slag, Los Alamos National Laboratory, In Press. 

The two step-fluorination process shown in Figure 9 has been proved to provide a stable recovery of plutonium more than 99 % (34). The retention mechanism of plutonium on alumina fluidizing media is interpreted in terms of the elutriation characteristics of plutonium fluorides (35). 

Plutonium metal is prepared by calcium reduction of plutonium fluorides or oxides in induction-heated MgO crucibles, under an inert atmosphere of helium or argon. The thermodynamics of plutonium reduction are discussed later in this chapter. 

Plutonium trichloride. Although PUCI3 is more hygroscopic than the plutonium fluorides, and although it generates less heat of reaction in subsequent metallothermic reduction to the metal. 

PdF2 PALLADIUM FLUORIDE 1313 PuOF PLUTONIUM FLUORIDE OXIDE 1355... 

Table V-15 Comparison of tetravalent zirconium, uranium, neptunium and plutonium-fluoride interaction coefficients. Uranium data are from [92GRE/FUG], neptunium and plutonium from [2001LEM/FUG].

Comparison of tetravalent zirconium, uranium, neptunium and plutonium-fluoride interaction coefficients.140... 

Barton, C.J. 1960. Solubility of Plutonium Fluoride Mixtures in Fused Alkali Fluoride-Beryllium Fluoride Mixtures. J. Phys Chem 64(3), 306-309. 

Systems containing PuFa. The behavior of plutonium fluorides in molten fluoride mixtures has received considerably less study. Plutonium tetrafluoride will probably prove very soluble, as have UF4 and ThF4, in suitable fluoride-salt diluents, but is likely to prove too strong an oxidant to be compatible with presently available structural alloys. The trifluoride of plutonium dissolves to the extent of 0.25 to 0.45 mole % in LiF-BeF2 mixtures containing 25 to 50 mole % Bel T. As indicated in Chapter 14, it is belie ed that such concentrations are in excess of those required to fuel a high-temperature plutonium burner. 

The many possible oxidation states of the actinides up to americium make the chemistry of their compounds rather extensive and complicated. Taking plutonium as an example, it exhibits oxidation states of -E 3, -E 4, +5 and -E 6, four being the most stable oxidation state. These states are all known in solution, for example Pu" as Pu ", and Pu as PuOj. PuOl" is analogous to UO , which is the stable uranium ion in solution. Each oxidation state is characterised by a different colour, for example PuOj is pink, but change of oxidation state and disproportionation can occur very readily between the various states. The chemistry in solution is also complicated by the ease of complex formation. However, plutonium can also form compounds such as oxides, carbides, nitrides and anhydrous halides which do not involve reactions in solution. Hence for example, it forms a violet fluoride, PuFj. and a brown fluoride. Pup4 a monoxide, PuO (probably an interstitial compound), and a stable dioxide, PUO2. The dioxide was the first compound of an artificial element to be separated in a weighable amount and the first to be identified by X-ray diffraction methods. 

The plutonium extracted by the Purex process usually has been in the form of a concentrated nitrate solution or symp, which must be converted to anhydrous PuF [13842-83-6] or PuF, which are charge materials for metal production. The nitrate solution is sufficientiy pure for the processing to be conducted in gloveboxes without P- or y-shielding (130). The Pu is first precipitated as plutonium(IV) peroxide [12412-68-9], plutonium(Ill) oxalate [56609-10-0], plutonium(IV) oxalate [13278-81-4], or plutonium(Ill) fluoride. These precipitates are converted to anhydrous PuF or PuF. The precipitation process used depends on numerous factors, eg, derived purity of product, safety considerations, ease of recovering wastes, and required process equipment. The peroxide precipitation yields the purest product and generally is the preferred route (131). The peroxide precipitate is converted to PuF by HF—O2 gas or to PuF by HF—H2 gas (31,132). 

Calcium metal is an excellent reducing agent for production of the less common metals because of the large free energy of formation of its oxides and hahdes. The following metals have been prepared by the reduction of their oxides or fluorides with calcium hafnium (22), plutonium (23), scandium (24), thorium (25), tungsten (26), uranium (27,28), vanadium (29), yttrium (30), zirconium (22,31), and most of the rare-earth metals (32). 

Plutonium(lV), Pu+Yagj, forms a complex ion with fluoride ion, PUF+3 ... 

The pattern of iridium halides resembles rhodium, with the higher oxidation states only represented by fluorides. The instability of iridium(IV) halides, compared with stable complexes IrCl4L2 and the ions IrX (X = Cl, Br, I), though unexpected, finds parallels with other metals, such as plutonium. Preparations of the halides include [19]... 

On the basis of these facts, it was speculated that plutonium in its highest oxidation state is similar to uranium (VI) and in a lower state is similar to thorium (IV) and uranium (IV). It was reasoned that if plutonium existed normally as a stable plutonium (IV) ion, it would probably form insoluble compounds or stable complex ions analogous to those of similar ions, and that it would be desirable (as soon as sufficient plutonium became available) to determine the solubilities of such compounds as the fluoride, oxalate, phosphate, iodate, and peroxide. Such data were needed to confirm deductions based on the tracer experiments. 

We solved the first problem by bombarding large amounts of uranyl nitrate with neutrons at the cyclotrons at the University of California and Washington University plutonium concentrates were derived from these sources through the efforts of teams of chemists who used ether extractions to separate the bulk of the uranium and an oxidation-reduction cycle with rare earth fluoride carrier to concentrate the product. I managed to convince chemists trained in the techniques of ultramicrochemistry to join us to solve the second problem—Burris B. Cunningham and Louis B. Werner of the University of California and Michael Cefola from New York University. 

The reason for the ultramicrochemical test was to establish whether the bismuth phosphate would carry the plutonium at the concentrations that would exist at the Hanford extraction plant. This test was necessary because it did not seem logical that tripositive bismuth should be so efficient in carrying tetrapositive plutonium. In subsequent months there was much skepticism on this point and the ultramicrochemists were forced to make repeated tests to prove this point. Thompson soon showed that Pu(Vl) was not carried by bismuth phosphate, thus establishing that an oxidation-reduction cycle would be feasible. All the various parts of the bismuth-phosphate oxidation-reduction procedure, bulk reduction via cross-over to a rare earth fluoride oxidation-reduction step and final isolation by precipitation of plutonium (IV) peroxide were tested at the Hanford concentrations of... 

In the case of the monofluorocomplexes of quadrivalent plutonium, it is obvious that the lower values obtained in chloride and nitrate media are due to complexing by these ions these results will not be discussed further. In HCIO4 media the data for the first two fluoride complexes are quite self-consistent and well within the same order of magnitude as these reported for the other quadrivalent actinides (12, 89). An extensive comparison would extend beyond the scope oT tKTs paper. In the case of PuF3+, extrapolation of bi to zero ionic strength is not warranted as such in view of the limited number of data. However, in the case of ThF3+ where the data extend over a very wide range of ionic... 

Only two complex fluorides of pentavalent plutonium are known, both having been prepared by Penneman et al. ( 1). One of these, Rb2PuF7, appeared to be stable its crystal structure ( 1) and its electronic spectrum (2) have been reported. The other, CsPuF6, appeared to decompose after a few days (J ) and only its crystal structure was reported. Our interest in the bonding and electronic structure of Pu(V) and particularly in Pu(V) fluorides prompted the present study of CsPuFg. 

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