Solvent extraction and separation of hafnium from zirconium using Ionquest 801

Abstract

The solvent extraction (SX) characteristics of Ionquest 801 were investigated to determine if the selective extraction of hafnium (Hf) over zirconium (Zr) is possible. Firstly, Ionquest 801 was screened for its suitability as a function of acid concentration. The solvent consisted of 5wt % extractant, corresponding to a extractant to metal ratio (E:MZr) of 14:1, in cyclohexane with 5% v/v 1-octanol added as modifier. Aqueous solutions of ZrCl4 with 3 wt% HfCl4 were prepared by dissolution of the salts in HNO3 to obtain 1.0 g/l Zr(Hf)Cl4(aq) feed solutions (aged 24 hours). Subsequently, the extractant concentration was varied at optimal acid molarities. The most favourable extraction percentages were attained at 0.7 M HNO3 and an E:MZr ratio of 5:1. Artifices in the form of aqueous additives were used to maximize the Hf selectivity at these optimal conditions. These included the addition of 1.5 M NaCl, NaNO3, Na2SO4, and NaClO4.H2O, as well as tartaric, oxalic, mandelic, and citric acid with and without the addition of 6 wt% hydrogen peroxide (H2O2). Exploratory studies on the influence and usability of the most promising factors such as [SO4-2], [H2O2], and combinations thereof in a SX system were undertaken.