Separation of Hf(IV) from Zr(IV) in thiocyanate medium with ionic liquid Aliquat 336

Abstract

Solvent extraction is the key technical link for the preparation of nuclear-grade Hf and Zr for advanced nuclear reactors. In this study, the separation of Hf(IV) over Zr(IV) from the highly concentrated aqueous feed by solvent extraction with ionic liquid Aliquat 336 was investigated. The results indicated that thiocyanate forms of the ionic liquid dissolved in amyl acetate were more conducive to selective extraction of Hf(IV). Under the selected conditions, optimal extraction efficiency of Hf(IV) could be up to 94.5%. The separation factor of Hf(IV) to Zr(IV) was found to be 19.4. The extraction mechanism of Hf(IV) was revealed by slope analysis and FTIR analysis. The extracted complex of Hf(IV) was determined as [(A336+)12(HfO2+)3(H+)(12x-2)(SCN−)(16+12x)]. The extraction isotherm indicated that nuclear-grade Zr(IV) could be recovered from the raffinate via a two-stage extraction. The sulfuric acid solution showed appreciable selectivity in scrubbing of Zr(IV) from the loaded organic phase. The Hf(IV) species in the remaining loaded organic phase could be effectively stripped by 3.0 M (NH4)2CO3 solution. Accordingly, a recyclable process flowsheet for the separation of Hf(IV) from Zr(IV) using Aliquat 336 was developed. It is believed that this process is a promising way for the preparation of enriched Hf and high purity Zr.