Fig. 6.
Published distribution coefficients (Kd) of U, Pa, and Nb with strongly basic anion exchange resin using (a) pure HF solution and (b) mixed HCl–HF solutions. A higher Kd indicates stronger adsorption. To separate two analytes, a difference in Kd of at least 100 is generally desired, in which the desorbing element has a Kd of less than 10 [31]. (a) Solids lines are from Faris [32] using Dowex 1-X10 resin in F− form whereas dotted lines are from Caletka and Krivan [33] using Dowex 1-X8 resin in Cl− form. (b) In 9 M HCl, Pa is very weakly adsorbent at every HF molarity, whereas U strongly adsorbs at every HF molarity. Nb strongly adsorbs at very low molarity HF. For > 0.05 M HF in 9 M HCl, Kd for Pa is less than 2, indicating no practical Pa adsorption to the resin. These data are extracted from Kim et al. [34] and Faris [35]. No information was found for the behavior of Th under these conditions in the previous literature