Uranium isolation processes

In 1798 Martin Klaproth, who had earlier discovered and named uranium, isolated the same silvery white metal from the same problematical ore. Klaproth, however, recognized that he and Muller had isolated a new element for which he suggested the name tellurium, meaning earth. He properly acknowledged the prior work of the Baron, who is consequently listed as its discoverer. Later it was found that tellurium does occasionally exist as the free element but more often than not exists as the gold telluride. Oddly, workers who process this ore and the metal derived from it acquire a garUc-Hke odor to their breath, a condition referred to (rather honestly but certainly not flatteringly) as tellurium breath. 

Fig. 6-16. Thorex process, uranium isolation and third cycle flowsheet.

The wastes from uranium and plutonium processing of the reactor fuel usually contain the neptunium. Precipitation, solvent extraction, ion exchange, and volatihty procedures (see Diffusion separation methods) can be used to isolate and purify the neptunium. 

Hydrocarbyl Complexes. Stable homoleptic and heteroleptic uranium hydrocarbyl complexes have been synthesized. Unlike the thorium analogues, uranium alkyl complexes are generally thermally unstable due to P-hydride elimination or reductive elimination processes. A rare example of a homoleptic uranium complex is U(CH(Si(CH2)3)2)3, the first stable U(I11) homoleptic complex to have been isolated. A stmctural study indicated a triganol... 

Since the amount of fissile material in the fuel assemblies is only about 3 percent of the uranium present, it is obvious that there cannot be a large amount of radioactive material in the SNF after fission. The neutron flux produces some newly radioactive material in the form of uranium and plutonium isotopes. The amount of this other newly radioactive material is small compared to the volume of the fuel assembly. These facts prompt some to argue that SNF should be chemically processed and the various components separated into nonradioac-tive material, material that will be radioactive for a long time, and material that could be refabricated into new reactor fuel. Reprocessing the fuel to isolate the plutonium is seen as a reason not to proceed with this technology in the United States. 

When the Plutonium Project was established early in 1942, for the purpose of producing plutonium via the nuclear chain reaction in uranium in sufficient quantities for its use as a nuclear explosive, we were given the challenge of developing a chemical method for separating and isolating it from the uranium and fission products. We had already conceived the principle of the oxidation-reduction cycle, which became the basis for such a separations process. This principle applied to any process involving the use of a substance which carried plutonium in one of its oxidation states but not in another. By use of this... 

The sol-gel-entrapped microbial cells have shown excellent tolerance to different alcohols [99], The immobilized E. coli cells followed the Michaelis-Menten equation when quantified with the (3-glucosidase activity via the hydrolysis of 4-nitrophenyl-(3-D-galactopyranosdie [142], The sol-gel matrices doped with gelatin prevented the cell lysis, which usually occurs during the initial gelation process [143], Microorganisms are now widely used in the biosorption of different pollutants and toxicants. Bacillus sphaericus JG-A12 isolated from uranium mining water has been entrapped in aqueous silica nanosol for the accumulation of copper and uranium [144], Premkumar et al. [145] immobilized recombinant luminous bacteria into TEOS sol-gel to study the effect of sol-gel conditions on the cell response (luminescence). The entrapped and free cells showed almost the same intensity of luminescence (little lower), but the entrapped cells were more stable than the free cells (4 weeks at 4°C). This kind of stable cell could be employed in biosensors in the near future. 

They knew there must be another radioactive element in the pitchblende after the uranium was removed. Marie Curie painstakingly processed a ton of pitchblende to recover only a small amount of uranium. Even so, there was still something radioactive in all that processed pitchblende. As it turned out, there were two radioactive elements that she was able to isolate. One was radium, and the other polonium. They were identified by using piezoelectricity, discovered by her husband Pierre Curie, which could measure the strength of radiation given off by the radioactive elements with which Marie Curie was working. 

The most common isotope of protactinium is Pa (tj/2 = 3.3 x 10 years), which occurs in pitchblende in the amount of 300 mg/ton, about the same as radium. The heroic efforts of British researchers resulted in the isolation of some hundred grams of Pa from the sludge left over from uranium processing without this supply, little or nothing would... 

The first S5m.thetic ventures into actinide and lanthanide organometalhc chemistry were attempted during World War II and were motivated by the need for stable, volatile uranium complexes in the uranium gaseous diffusion process. It soon became apparent that the homoalkyl complexes (MR4) of uranium were extremely unstable and at best could exist only as transient intermediates at low temperatures [128). With the isolation of the tricyclopentadienides of the lanthanides in 1954, the focus of /-transition metal organometaUic chemistry shifted to the n-carbocychc complexes and has remained unchanged until the recent isolation of stable alkyls and aryls of both the lanthanides and actinides. 

The exclusive isolation of uranium at the front-end by an amide extractant (BAMA process using a Branched Alkyl MonoAmide)... 

Fractional crystallization (or differential crystallization) is a process whereby two chemically compounds that form crystals with slightly different solubilities in some solvent (e.g., water) can be separated by a "tree-like" process. One should remember the herculean work by Marie Curie3, who by fractional crystallization isolated 0.1 g of intensely radioactive RaCl2 from 1 ton of pitchblende (a black mixture of many other salts, mainly oxides of uranium, lead, thorium, and rare earth elements). 

Radium is isolated in the processing of uranium ores after coprecipitation with barium sulfate, it can be obtained by fractional crystallization of a soluble salt. 

In the course of processing of uranium ores, appreciable amounts of long-lived radioactive decay products of uranium are obtained, as listed in Table 11.3. With respect to radiation hazards, they have to be handled carefully. Some of them, such as Th, Pa, Ra or Pb, may be isolated for practical use. 

The discovery of nuclear fission in 1938 proved the next driver in the development of coordination chemistry. Uranium-235 and plutonium-239 both undergo fission with slow neutrons, and can support neutron chain reactions, making them suitable for weaponization in the context of the Manhattan project. This rapidly drove the development of large-scale separation chemistry, as methods were developed to separate and purify these elements. While the first recovery processes employed precipitation methods (e.g., the bismuth phosphate cycle for plutonium isolation). 

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