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Separation factors of lanthanides extracted with dibutylphosphate

Practical significance of the double-double effect

Journal of Radioanalytical and Nuclear Chemistry
Authors: I. Fidelis and J. Krejzler

Abstract  

Extraction coefficients and separation factors of all lanthanides in the diluted aqueous HDBP—HNO3 system were determined in the temperature range 10–50 °C. Essential differences were noticed between the results obtained for light (La—Gd) and heavy (Gd—Lu) lanthanides. It was found that the selectivity of the investigated system, in the case of heavy lanthanides, is as high as that observed for the best organophosphorous extractants: HEHϕP and HDEHP. The sequence of the separation factors shows the pattern of regularities (the double-double effect) within the whole series of lanthanides and within the whole investigated temperature range.

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Abstract  

Extraction coefficients and separation factors of all lanthanides were determined in the system: dibutylphosphoric acid /HDBP/ - 3M NH4NCS, in the temperature range of 15–50 °C. The values for the separation factors for such pairs as: Gd–Tb and Er–Tm, are higher than 4, those for the pair of Tb–Dy are higher than 3, and those for the La–Ce, Pm–Sm, Dy–Ho, Ho–Er and Tm–Yb pairs are higher than 2. The influence of temperature on the separation factors of light /La–Gd/ and heavy /Gd–Lu/ lanthanides is discussed and compared with that observed for the extraction from the nitric acid solutions. The results are also discussed in the light of the double-double effect and outer-, vs. inner-sphere complexation in the lanthanide series.

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Abstract  

Extraction coefficients for all lanthanides have been determined in two systems: 0.2M TBP-3M NaNCS, and 3.6M TBP-0.2M NaNCS. The data have been used for the calculation of relative changes in thermodynamic functions accompanying the investigated extraction process. The compensation of enthalpy and entropy changes is found as a result of dehydration of the lanthanide aquaions.

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Abstract  

Tetra-n-butylammonium iodide (TBAI) forms associations in chloroform and aqueous solutions. A TBAI solution in chloroform extracts hydroiodic acid by addition. From 0.5M hydroiodic acid medium cadmium is quantitatively extracted into a TBAI solution in chloroform. Under these conditions zinc is not extracted. This makes possible the extractive separation of cadmium from zinc in micro-or macroamounts.

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