Thorium distribution ratio

Percentage Extraction, % , and, in Brackets, Distribution Ratios, D, for Lanthanides and Thorium Nitrates by Narrow-Rim Calixarenes CMPO from 1 M HN03 into Dichloromethane T = 20°C, CM = 10 4 M... 

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. 

Figure 2. Thorium concentration profile and distribution ratio for Contactor I (%) aqueous phase (O) solvent phase (X) distribution ratio (DTn) (------) calcu-...

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. 

However, column separation performance in the Hanford Thorex campaign correlates better with a Z)u/ Th rstio of 14 (Prob. 10.5). Because the distribution coefficient of thorium is so much less than that of uranium, the Thorex process requires a much higher organic/aqueous flow ratio than the Purex process. 

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. 

Shiraishi et al. [82] studied the distribution of uranium and thorium in freshwater samples collected in Ukraine, Russia, and Belarus. The analytes were detected directly by PN-ICP-MS and the isotope ratios were determined by increasing the signal integration periods to obtain good counting statistics. The isotopic compositions found for uranium were consistent with fallout from the Qiemobyl nuclear accident. Table 3.10 [33,83-93] shows some procedures for the determination of isotopes by ICP-MS. 

---