Solvent Extraction in Radiochemical Separations

Abstract

The last several years have seen a reawakening appreciation of the value of solvent extraction separations processes both on analytical and process scales. Separations by solvent extraction are simple, convenient, clean, and applicable equally well to carrier-free tracer and macro amounts of materials. They usually require apparatus as uncomplicated as a separatory funnel and may readily be adapted to remote handling procedures.A variety of separations techniques have been applied to the problems of isolation and radiochemical purification of nuclides. General descriptions and recent surveys of radiochemical separations can be found in references (1) through (5). Although all of the separation methods mentioned are of great importance to the radiochemist, solvent extraction is particularly well suited to the purification of many radioisotopes since, after several extractions of a substance, the final product is usually relatively free from extraneous im purities which may be present when other separation procedures are em ployed. Also, if the isotope of interest has a short half life, a rapid separation is essential and extraction procedures have proved invaluable. Most of the extractions employed in radiochemistry are based on previously developed conventional analytical extractions, and the recent book by the authors (6) offers a comprehensive treatment of the subject of extraction as applied to inorganic analysis. In addition to covering the principles and practical as pects of the technique, procedures for the extraction of the elements are presented. The review by the authors (7) in Analytical Chemistry surveys the latest developments in the field. CLASSIFICATION OF SOLVENT EXTRACTION SYSTEMSMost metal salts are strong electrolytes that are relatively insoluble in organic solvents and soluble in water because of its ability to solvate the ions as well as because of its high dielectric constant. Since it is usually necessary to transform the hydrated metal ion into an uncharged complex in order to extract it into an organic solvent, it is convenient to classify metal extraction systems on the basis of the nature of the extractable metal 1 The survey of literature pertaining to this review was completed in December, 1958.2 Among the abbreviations used in this chapter are: EDTA (ethylenediamine tetraacetic acid); HDGP (dioctylphenyl orthophosphoric acid); TBP (tributyl phos phate); TTA (thenoyltrifluoracetone).

Perspectives on the Use of Liquid Extraction for Radioisotope Purification

“…It provides a high selectivity even when dealing with very low concentrations, as partition conditions can be easily varied to obtain radioisotope yields relatively free from chemical and radionuclidic impurities. LLE can be performed rapidly (a particularly vital characteristic when isolating isotopes with shorter half-lives), and is relatively simple to automate [61,63]. Typically, LLE is followed by evaporation of the extracting solvent, back extraction in aqueous phase or SPE/chromatography to purify the radionuclide from the organic phase and dissolved into a solution phase appropriate for successive radiolabelling or injection.…”

Biotechnology Processes for Scalable, Selective Rare Earth Element Recovery

“…The well-established 'PUREX' process uses tributyl phosphate (TBP) to sequester actinides against a background of metal cations. An early study indicated that the complexation of TBP to uranyl ion was more than to REE [46]. Hence, TBP was considered as a possible agent to retard removal of UO 2 2+ in the REE-accumulating column to enable later recovery of U(VI) downstream.…”

“…A hypothesis was formulated to widen the flow rate 'window' boxed in Figure 3. This assumes that REE 3+ forms a weaker complex with TBP than does UO 2 2+ [46]; no benefit for REE removal would be anticipated with TBP (Figure 6) if REE 3+ is presumed to be not in close association with TBP or its breakdown products. Rare earth phosphate (REEPO 4 ) formation is rapid and hence occurs at high flow rates while UO 2 2+ requires more time to form a precipitate [21].…”

Investigations concerning the retention of fission products on humic acids

“…According to the paper of H. FREISER ar~d G~ORr H. MORRISON [11], the following elements of the periodic system can be expected as partially extracted together with (UO2) + +: Zr, As, Ce(IV).…”