Plutonium processing cationic

A primary goal of chemical separation processes in the nuclear industry is to recover actinide isotopes contained in mixtures of fission products. To separate the actinide cations, advantage can be taken of their general chemical properties [18]. The different oxidation states of the actinide ions lead to ions of charges from +1 (e.g., NpOj) to +4 (e.g., Pu" " ) (see Fig. 12.1), which allows the design of processes based on oxidation reduction reactions. In the Purex process, for example, uranium is separated from plutonium by reducing extractable Pu(IV) to nonextractable Pu(III). Under these conditions, U(VI) (as U02 ) and also U(IV) (as if present, remain in the... 

Electrodeposition could be a pseudo-S-L type process, although definitive proof is lacking. The element to be ionized, uranium [16] or plutonium [17], is coelec-trodeposited with a platinum metal layer, then covered with an additional layer of platinum. The U or Pu is believed to be electrodeposited as an oxide, and platinum is electrodeposited as the metal. Hence there is thought to be a U or Pu oxide buried in the metal matrix. When this deposit is heated, after a sufficient length of time atomic cations of U or Pu begin to sublime from the surface without measurable metal oxide ions. Metal oxide ions should be readily observable if they are present in the matrix. Thermodynamic calculations indicate that the hot platinum matrix will not reduce the U and Pu oxides to the metallic state, and yet the observed species are atomic ions and not oxide molecular ions. 

The process sequence currently used for waste salts (except those containing aluminum for which no process currently exists) is shown in Figure 1. The process includes (1) dilute hydrochloric acid dissolution of residues (2) cation exchange to convert from the chloride to the nitrate system and to remove gross amounts of monovalent impurities (3) anion exchange separation of plutonium (4) oxalate precipitation of americium and (5) calcination of the oxalate at 600°C to yield americium oxide. 

A continuing problem with the cation exchange process as used in production operations is that it has not been sufficiently selective and therefore allows considerable carryover of the MSE salt constituents and impurities with the plutonium and americium. This isn t serious with plutonium since plutonium can be subsequently purified by anion exchange. For americium, however, the subsequent recovery process is oxalate precipitation which is less selective and carries some of the impurities into the final product. 

Plutonium Finishing. The separated plutonium was processed to Pu02 by conventional cation resin exchange, oxalate precipitation, and calcination methods. 

The sorption process and the attainment of apparent equilibrium may be regarded then as involving essentially two kinds of sorbing species. There are a very small number of ionic plutonium species, including monomeric and low-molecular-weight polymeric hydrolysis products (1) which sorb relatively quickly and perhaps are involved in a true equilibrium, such as by ion exchange with silanol sites at the silica surface. There is evidence of such sorption of various types of univalent and multivalent cations on silica, and both chemisorption and physical adsorption processes have been deduced (13, 14, 15). Filtration of the desorbing plutonium with a 15-40-micron porous silica disc indicated that the very first material to desorb was essentially small, unfilterable Pu(IV). 

When an extractable cation, such as Zi, is readily hydrolyzed, reduction of hydrogen ion concentration will reduce the distribution coefficient by increasing the proportion of the element in the form of partially hydrolyzed, nonextractable ions such as ZrO . This principle was used in the Redox process [B2, C7, C8] for the hexone extraction of plutonium from irradiated uranium, wherein the aqueous phase was made sUghtly acid-deficient with ammonium hydroxide, to reduce the extraction of zirconium and rare-earth fission products. 

From the above discussion it follows that tetravalent and hexavalent thorium, uranium, and plutonium can be separated from the trivalent rare-earth fission products by taking advantage of differences in complexing properties. More highly charged cation fission products, such as tetravalent cerium and the fifth-period transition elements zirconium, niobium, molybdenum, technetium, and ruthenium, complex more easily than the trivalent rare-earths and are more difficult to separate from uranium and plutonium by processes involving complex formation. 

Plutonium trifluoride. Plutonium trifluoride can be converted directly to plutonium metal, or it is an intermediate in the formation of PUF4 or PUF4 -PUO2 mixtures for thermochemical reduction, as described in Sec. 4.8. The stabilized Pu(III) solution, produced by cation exchange in one of the Purex process options for fuel reprocessing, is a natural feed for the formation of plutonium trifluoride, as is shown in the flow sheet of Fig. 9.9 [03]. A typical eluent solution from cation exchange consists of 30 to 70 g plutonium/liter, 4 to 5 Af nitric acid, 0.2 Af sulfamic acid, and 03 Af hydroxylamine nitrate. The sulfamic acid reacts rapidly with nitrous acid to reduce the rate of oxidation of Pu(III) to about 4 to 6 percent per day. Addition of ascorbic acid to the plutonium solution just before fluoride precipitation reduces Pu(IV) rapidly and completely to Pu(III). 

The PuFs process does not attain the degree of decontamination from cationic impurities that can be achieved in peroxide or oxalate precipitation, but it is acceptable vriien the plutonium nitrate feed contains no more than a few hundred parts of uranium and aluminum per million of plutonium. This process has been in routine use at the U3. plant at Savaimah River [B6,03]. 

If the plutonium to be fluorinated is the plutonium peroxide cake, as in one of the processes used at the U.S. Savannah River plant, the air-dried cake is reacted with HF gas at 600°C. The reaction time is quite sensitive to sulfate containment in the oxalate cake, which interferes with fluorination and requires a longer time for reaction of the oxalate with HF. The interfering sulfate is that present due to a sulfuric acid wash of the cation-exchange resin prior to peroxide precipitation. 

The PRF also recovers Am from the raffinate of the TBP-solvent extraction plutonium-purification process. The process employs 30 v/o dibutyl butylphosphonate in CCI4 as the solvent to extract both americium and residual plutonium from the high-nitrate feed solution, adjusted to about pH 1 by the addition of NaOH. Americium is selectively stripped from the solvent and purified by a cation-exchange procedure. 

In a second aliquot of the same sample, the concentrations of the burnup monitor Nd and of the gadolinium isotopes in irradiated UO2—Gd20j fuel can also be determined. In this procedure, the rare earth elements are first separated from uranium, plutonium and the fission products by anion exchange from hydrochloric acid solution by addition of known amounts of Nd and Gd spikes to the sample solution, correction for losses of both rare earth elements during the separation process can be made. In the second step, the neodymium and gadolinium fractions are isolated from the other rare earth elements by cation exchange using... 

Chitosan has been widely accepted in the purification process of water by virtue of its metal ion chelating capability and acting as a flocculating agent because of its poly-cationic character. It is also used as an adsorbent for removal of dyes from water. Pesticides and chemicals such as phenols, methyl mercury acetate, plutonium, etc., can be removed from wastewater [170]. 

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