Evaluation of novel solvent extraction systems for Zr/Hf separation with MIBK homologues

Zr/Hf separation has always been a great challenge. Although the methyl isobutyl ketone (MIBK)-thiocyanic acid (HSCN) extraction system selectively extracts Hf over Zr and can realize Zr/Hf separation, it has the following disadvantages: it has a strong smell; it is easy to burn; and there is large loss of extractant during extraction due to the low boiling point (115.7 ℃), low flashing point (13 ℃), and high solubility of MIBK in water (1.7% at 25 ℃). In this study, Zr/Hf separation performance by MIBK homologues — of which one side of C=O is isopentyl, isohexyl, n-pentyl, n-hexyl or n-heptyl, while the other side are all methyl — were studied and compared with MIBK. Effects of HSCN pre-extraction, HCl concentration, NH4SCN concentration on Zr, Hf extraction and separation performance were investigated. Relationships between methyl alkyl ketone structure and their Zr/Hf separation performance were revealed. A new Zr/Hf separation system MNPK (methyl n-pentyl ketone)-HSCN was found. MNPK has a higher boiling point (151 ℃), a higher flashing point (47 ℃) and a lower solubility in water (0.43% at 20 ℃) than MIBK. Compared to MIBK, it is safer, more friendly operation environments and less extractant loss during extraction. MNPK has as fast extraction kinetics as MIBK. It also has good anti-emulsification performance. Its maximum βHf/Zr can reach to 12.61. The loaded Zr and Hf in MNPK have very similar stripping behaviors with those loaded in MIBK by HCl and H2SO4 solutions, respectively. MNPK is the most possible candidate to replace MIBK from HSCN media in Zr/Hf separation industry.