Radium separation through complexation by aqueous crown ethers and ion exchange or solvent extraction

Abstract

The effect of three water-soluble, unsubstituted crown ethers (1 5-crown-5 (1 5C5), 18-crown-6 (18C6) and 21-crown-7 (21C7)) on the uptake of Ca, Sr, Ba and Ra cations by a sulfonic acid cation exchange resin, and on the extraction of the same cations by xylene solutions of dmonylnaphthalenesulfonic acid (HDNNS) from aqueous hydrochloric acid solutions has been investigated. The crown ethers enhance the sorption of the larger cations by the ion exchange resin, thereby improving the resin selectivity over calcium, a result of a synergistic interaction between the crown ether and the ionic functional groups of the resin. Similarly, the extraction of the larger alkaline earth cations into xylene by HDNNS is strongly synergized by the presence of the crown ethers in the aqueous phase. Promising results for intra-Group IIa cation separations have been obtained using each of the three crown ethers as the aqueous ligands and the sulfonic acid cation exchange resin.Even greater separation factors for the radium -calcium couple have been measured with the crown-ethers and HDWS solutions in the solvent extraction mode. The application of the uptake and extraction results to the development of radium separation schemes is discussed and a possible flowchart for the determination of 226Ra/22sRa in natural waters is presented.

Incorporating Size Selectivity into Synergistic Solvent Extraction: A Review of Crown Ether-Containing Systems

“…11,17,38 (In fact, the aqueous solubility of unfunctionalized crown ethers has led to their use in several different separation schemes. [39][40][41][42] ) Similar studies have employed the more organophilic dibenzo-18-crown-6 (DB18C6, Figure 2) with HTTA in o-dichlorobenzene for partitioning of Ba(II), again for analytical purposes. 36 Cobalt(II) is the best characterized among the transition metals, 20,43 while Mn(II), 44 Zn(II), 45 Cd(II), 45 and Pb(II) 46 have also been examined using combinations of DB18C6 and HTTA for analytical separations.…”

“…Several detailed separation schemes using the solvent extraction approach 41,42 or a sulfonic acid cation-exchange resin are presented. 40,42 In a study of Eu(III) extraction by HDNNS, the addition of DCH18C6, DB24C8, or TOPO was found to have antagonistic effects. 139 By contrast to the previously discussed works in which HDDNS micelles facilitated extraction, submillimolar benzene solutions of HDNNS were employed in this study.…”

Extraction of Alkaline Earth and Actinide Cations by Mixtures of Di(2-Ethylhexyl) Alkylenediphosphonic Acids and Neutral Synergists

“…[6,7] In the H 2 DEH[MDP]=o-xylene system, in contrast, addition of 21C7 leads to strong antagonistic effects for all cations except Ca 2þ . [6,7] In the H 2 DEH[MDP]=o-xylene system, in contrast, addition of 21C7 leads to strong antagonistic effects for all cations except Ca 2þ .…”

“…For systems involving the use of an acidic extractant (e.g., b-diketones, carboxylic and organophosphorus acids), this is accomplished by the extractant itself, which is anionic under appropriate aqueous phase conditions. [6][7][8][9][10] Two useful insights have emerged from this work. While each of these approaches offers certain advantages, each is also subject to significant limitations.…”

“…[11] Because the extraction behavior of dialkyl alkylenediphosphonic acids has been shown to be profoundly affected by the aggregation state of the reagent (which is, in turn, determined by the length of the alkyl chain separating the two phosphoryl groups of the molecule), [12,13] we have also evaluated related systems incorporating the ethylene or butylene analogs of H 2 DEH[MDP] (I, with n ¼ 2 or 4). Because prior reports suggest that barium and radium partitioning may be effectively synergized by larger ring size crown ethers, [6,7] we have examined systems employing H 2 DEH[MDP] or H 2 DEH[EDP] in combination with 21-crown-7 and its dicyclohexano-analog.…”