Uranium distribution ratios

Fig. 2.15 Dependency of the uranium distribution ratio, Ku, on TBP concentration in [Ciomim] [NTf2] at constant (3 M) nitric acid concentration (Dietz and Stepinski 2(K)8)...

Distribution ratios and transport were carried out on real HAW arising from dissolution of a mixed oxide of uranium and plutonium (MOX) fuel (burnup 34,650 MW d/tU), where uranium and plutonium have been previously extracted by TBP.86 The experiments were performed in the CARMEN hot cell of CEA Fontenay aux Roses with two dialkoxy-calix[4]arene-crown-6 derivatives (diisopropoxy and dini-trophenyl-octyloxy). High cesium distribution ratios were obtained (higher than 50) by contacting the HAW solution with diisopropoxy calix[4]arene-crown-6 (0.1 M in NPHE). Moreover, the high selectivity observed with the simulated waste was confirmed for most of the elements and radionuclides (actinides or fission products Eu, Sb, Ce, Mo, Zr, and Nd). The residual concentration or activity of elements, other than cesium, was less than 1% in the stripping solution, except for iron (2%) and ruthenium (8%) the extraction of these two cations, probably under a complexed... 

Extraction of Actinides(IV) and (VI). Table VI shows the D s for representative hexa- and tetravalent actinides from 3 M HNO3 at 50 C for DHDECMP, HHDECMP, and 0( )D[IB]CMPO. The same concentration of extractants in DEB were chosen as used to measure the fission product D s. The D for Np(V) was found to be 0.64 from 3 M HNO3 at 50°C using 0.5 M 0(j)D[IB]CMP0 in DEB. The data for U (VI), Np(IV), and Pu(IV) for DHDECMP are in general agreement but somewhat higher than the values reported by Schulz and Mclsaac (1). This disparity is probably due primarily to the lower purity of the CMP extractant used in the earlier work. The trends in distribution ratios for tetravalent actinides and uranium follow the same trends as D for the three classes of CMP extractants. 

The distribution ratios for the extraction of the elements to be recovered (uranium and thorium, for example) may be optimized such that both elements can be efficiently extracted then selectively stripped into HNO3. Optimizing the distribution ratios eliminates the necessity of adding complexing agents to the aqueous phase for selective stripping of the metals. 

Amine Phase ratio, aqueous/organic Uranium distribution coefficient... 

A.l. In a solvent system the distribution ratio, uranium and is 0.003 for cesium. If 99.5% U is to be extracted in a repeated batch fashion (eqn. (A.5)), (a) how much Cs is coextracted If instead a countercurrent process is used with 10 extraction and 2 wash stages, what percentage of (b) uranium and (c) cesium is extracted In an extraction equipment 0.003 cannot be maintained, because droplets are carried over between stages the practical value will be D q, 0.02. (d) How much cesium is extracted in this latter case with the countercurrent equipment Assume equal phase volumes. 

A similar batch ether process was operated on a scale of 1 ton/day by the U.S. Mallinckrodt Works as early as 1942. It was, however, modified in 1946 to a counter-current acid ether process using 40 ft high columns of about four theoretical stages. These columns had centrifugal pumps and jet mixers at 4 ft intervals, and relatively calm zones between. Advantage was taken of the increased uranium distribution coefficient in the presence of excess nitric acid, to reduce the solvent-to-aqueous fiow ratio and achieve a... 

Since all sources of thorium are associated with a certain amount of uranium, the first solvent-extraction cycle is designed solely to eliminate this element. The proportion of uranium to thorium can vary, but is often of the order of 5 per cent. The uranium distribution coefficient into tributyl phosphate is much higher than that of thorium under comparable conditions, e.g. 20 and 0-5 respectively for 40 per cent TBP/xylene or 6 and 0 04 respectively for 5 per cent TBP/xylene. The more highly diluted solvent is used for the uranium separation cycle in view of the higher ratio of the two distribution coefficients, or separation factor . Xylene is chosen in preference to, for example, odourless kerosene owing to the danger of formation of a third phase rich in thorium with the latter diluent. 

For the first purification of plutonium in the processing of irradiated nuclear fuels, an anion-exchange process has been widely used [202]. In this process, complex formation of plutonium(iv) with nitrate is utilized in order to remove the last traces of uranium (present as uranyl(vi)) and fission products (primarily lanthanides). In this system, the maximum sorption of plutonium (iv) occurs at a nitric acid concentration of 7.2 m. The process is run at 60°C. At lower temperatures, the sorption is too slow at higher temperatures, the distribution ratio becomes more unfavorable and the resin is more liable to deteriorate. Under the conditions chosen, neither uranyl(vi) nor lanthanides are sorbed. The elution of plutonium(iv) is readily achieved by dilute (0.7 m) nitric acid. The weak point of the process is the limited resistance of organic ion exchangers to chemical attack and to high doses of radiation, already discussed in Section 21.6.1. These difficulties can be overcome, at least partly, by careful selection of the resin to be used. 

Sometimes, the distribution ratio is referred to as the partition coefficient, which is often expressed as the logarithm. Note that a distribution ratio for uranium and neptunium between two inorganic solids (zirconolite and perovskite) has been reported. In solvent extraction, two immiscible liquids are shaken together. The more polar solutes dissolve preferentially in the more polar solvent, and the less polar solutes in the less polar solvent. In this experiment, the nonpolar halogens preferentially dissolve in the nonpolar mineral oil. 

In all spent researches the received ratio signal / noise and sensitivity for revealed defects, distribution of material density and the weights of high density components (tungsten, lead, uranium) are well agreed with results of alternate physics-chemical methods of analyses... 

Plater AJ, Ivanovich M, Dugdale RE (1995) Ra contents and Ra/ Ra activity ratios of the Fenland rivers and the Wash, eastern England spatial and seasonal trends. Chem Geol 119 275-292 Pliler R, Adams JAS (1962) The distribution of thorium and uranium in a Pennsylvanian weathering profile. Geochim Cosmochim Acta 26 1137-1146... 

The four isotopes, as those of any element, have the same chemical properties. The four are not, however, uniformly distributed in the earth s crust the occurrence of three of them, in minerals and rocks, is associated with the radioactive decay of isotopes of thorium and uranium. In most minerals and rocks the relative amounts (or the isotopic ratios) of the isotopes of lead (often expressed relative to the amount of stable lead-204) are generally within well-known ranges, which are independent of the composition of the mineral or rock they are, however, directly related to the amounts of radioactive thorium and uranium isotope impurities in them. 

Fig. 2. General alteration and geologic features of basement- and sandstone-hosted uranium deposits showing distributions in U and Li isotope ratios.

---