Hafnium/Zirconium Separation Using Cyanex 925

Abstract

The processing of zirconium ores to produce hafnium-free zirconium for nuclear applications requires a hafnium/zirconium separation step. Conventional solvent extraction technology uses methylisobutyl ketone (MIBK) to selectively extract hafnium as its thiocyanate complex from hydrochloric acid solutions of zirconium and hafnium. Use of the organophosphorus extractant Cyanex 925 has been studied as a possible alternative for hafnium/zirconium separation. Cyanex 925 selectively extracts zirconium over hafnium from hydrochloric acid solutions of these metals but without thiocyanate complexation. Advantages offered by Cyanex 925 are a lower aqueous solubility and a higher flash point relative to MIBK, while the avoidance of thiocyanate ions removes the possible formation of hydrogen sulphide, hydrogen cyanide or mercaptans. Cyanex 925 is a trialkyl phosphine oxide containing branched alkyl groups rather than the straight alkyl chains of conventional trialkyl phosphine oxide extractants.Batch contacts between Cyanex 925 in kerosene and single metal solutions of hafnium or zirconium in hydrochloric acid, at up to 6M, showed that zirconium was always loaded preferentially to hafnium. The results were consistent with extraction of both metals by solvation of a chloride complex. Subsequent tests with mixed metal solutions showed that optimum separation was at about 3.5 M. HCl, regardless of metal/extractant ratio. For example, the separation factor was 37 (61% Zr, 4% Hf extractions, O/A = 2) when using 3.6 x stoichiometric extractant addition for complete reaction with 0.10 M. Zr, 0.010 M. Hf. Résumé -Lorsqu'on veut obtenir du zirconium sans la présence de hafnium, pour applications nucléaires par exemple, le traitement de minerais de zirconium requiert une étape de séparation du hafnium et du zirconium. La technologie d'extraction conventionnelle avec solvant utilise de la cétone méthyl-isobutylique (MIBK) afin d'extraire le hafnium sélectivement, sous forme d'un complexe thiocyanate, à partir de solutions d'acide chlorhydrique de zirconium et de hafnium. On a étudié l'usage du solvant d'extraction organo-phosphore Cyanex 925 comme remplaçant possible dans la séparation de l'hafnium et du zirconium. Le Cyanex 925 extrait sélectivement le zirconium du hafnium à partir de solutions d'acide chlorhydrique de ces métaux, mais sans la formation du complexe thiocyanate. Les avantages offerts par le Cyanex 925 incluent une solubilité aqueuse plus basse et un point d'éclair plus élevé par rapport au MIBK. De plus, l'absence d'ions de thiocyanate prévient la formation d'acide hydrosulfurique, de cyanure d'hydrogène ou de mercaptans. Le Cyanex 925 est un oxyde de phosphine trialkyle contenant des groupes alkyles branchés plutôt que les chaînes droites d'alkyles des solvants d'extraction conventionnels d'oxyde de phosphine trialkyle.Les contacts par lot entre le Cyanex 925 dans le kérosène et les solutions à métal unique de hafnium ou de zirconium dans de l'acide chlorhydrique, jusqu'à 6 M, ont montré que le zirconium était toujour...

Selective extraction of Hf(IV) over Zr(IV) from aqueous H2SO4 solutions by solvent extraction with acidic organophosphorous based extractants

“…In addition, among other reported results on the selective extraction of Zr over Hf, use of Cyanex 925 in 3.5 mol L ‐1 HCl solution results in a separation factor of 37 between Zr and Hf . However, in the present study, a similar separation factor of 30 between Hf and Zr was obtained from H 2 SO 4 solution using D2EHPA.…”

“…However, little work has been reported on the selective extraction of Hf(IV) over Zr(IV) . The proposed process has the potential for selective extraction of Hf(IV) over Zr(IV), but suffered from significant drawbacks, such as high aqueous solubility of solvent, low flash point and possible generation of toxic gases . A solvent extraction route recently appeared in the literature for the selective extraction of Hf(IV) over Zr(IV) from dilute solutions (pH 1 to 4) using Cyanex 301 .…”

“…24 da Silva et al reported a separation factor of 37 between Zr(IV) and Hf(IV), obtained by extraction with Cyanex 925 from HCl medium. 25 Karve et al described a selective stripping process to separate Zr(IV) over Hf(IV) from loaded Aliquat 336 using 9 mol L -1 HCl for Hf(IV) stripping followed by Zr(IV) stripping with 2 mol L -1 HCl. 26 McDonald patented the selective extraction of Zr(IV) over Hf(IV) from acidic sulphate solution containing α-hydroxy carboxylic acid as a water soluble complexing reagent using tertiary amine based extractant and decanol modifier.…”

“…38,39,48 The proposed process has the potential for selective extraction of Hf(IV) over Zr(IV), but suffered from significant drawbacks, such as high aqueous solubility of solvent, low flash point and possible generation of toxic gases. 25,37,39 A solvent extraction route recently appeared in the literature for the selective extraction of Hf(IV) over Zr(IV) from dilute solutions (pH 1 to 4) using Cyanex 301. 40 Therefore, developing a new process on the selective extraction of Hf(IV) over Zr(IV) is an attractive subject for many researchers.…”

Design of an Extractive Distillation Column for the Environmentally Benign Separation of Zirconium and Hafnium Tetrachloride for Nuclear Power Reactor Applications

“…Extraction is still the most popular and economic way for commercial Zr-Hf purification [10][11][12][13][14][15][16]. On the other hand, regardless of its main virtue in mass production, the extraction-based Zr-Hf separation requires considerable amounts of relatively expensive, corrosive and environmentally harmful solvent chemicals.…”