Redox process extractant used

In order to separate the uranium and plutonium the Pu022+ was reduced to Pu3+, which was not extracted by MIBK and was thus held in the aqueous phase. The choice of a reducing agent for plutonium is rather important, and is discussed in more detail below in relation to the Purex process. In the Redox process, 0.05 M aqueous iron(II) sulfamate salted with 1.3MA1(N03)3 was used, the reduction of Pu022+ by Fe2"1" proceeding according to equation (156). The products... 

Metallurgy, the science of extracting and purifying metals from their ores, makes use of numerous redox processes. We ll see in Section 21.2, for example, that metallic zinc is prepared by reduction of ZnO with coke, a form of carbon ... 

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. 

The tendency toward hydroly of some of these elements can be used to advantage in separation processes. For example, in the Redox process for separating uranium and plutonium from fission products, the aqueous feed to the separation plant is made acid-deficient to promote hydrolysis of zirconium to a less extractable species, probably a colloidal hydrate [B5]. 

The solvent used in the Redox process was hexone, methyl isobutyl ketone, an extractant already in use for purifying uranium ore concentrates (Chap. 5)., Hexone is immiscible with water and will extract uranyl nitrate and plutonyl nitrate selectively from fission-product nitrates if the aqueous solution has a sufficiently high nitrate ion concentration. In the Redox process, aluminum nitrate was used as salting agent because high concentrations of nitric acid would decompose the hexone solvent. 

A modification of the Redox process, the U-hexone process, was used at the Idaho Chemical Processing Plant of the U.S. AEC, to recover highly enriched uranium from U-A1 alloy fuel elements irradiated in the Materials Testing Reactor. The aluminum nitrate needed as salting agent was provided when the fuel was dissolved in nitric acid. The plutonium content of the fuel was too low to warrant recovery. Plutonium was made trivalent and inextractable before solvent extraction and thus routed to the aqueous high-level waste. 

An example of the use of the phase shifting technique is demonstrated in Fig. 2.27 [87]. The redox process of adsorbed cytochrome Cs, whose signal is much weaker than that of the simultaneously occurring solution redox process of methyl viologen, is successftiUy extracted at an Ag electrode. 

Another development which should be mentioned was that in purifying the thorium salts, a process was developed at Ames using a liquid—liquid extraction with hexanone, where the thorium went into the hexanone and the impurities stayed in the water phase. While this process was successful and produced pure thorium, it had the disagreeable property that occasionally the apparatus would catch fire, so tributyl phosphate was substituted for the hexanone and this made the process completely satisfactory. It later also formed the basis, being used with uranium, for the Redox Process, which was used widely at Hanford and elsewhere for separating the radioactive fission product impurities from the uranium and plutonium. 

Variants of the Purex (Pu-U Reduction Extraction) process are the most widely used plutonium-reprocessing schemes worldwide. Purex on the industrial scale began at the US Savannah River Plant in 1954 and replaced the Redox process at the Hanford works in 1956 every country that has produced significant quantities of plutonium has exploited the method. In Purex, the organic extractant is tributyl phosphate (TBP). In addition to optimum com-plexation properties for nuclear analytes of interest, TBP has a low aqueous solubility and is chemically and radiolytically stable. The density of TBP (0.98 g/cm ) is so close to that of water that it is common to dilute it in a lower density solvent. It is completely miscible with common organic solvents (e.g., kerosene, n-dodecane) at ordinary temperatures. 

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. 

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