The Hafnium-Selective Extraction Fom a Zirconium(Hafnium) Heptafluoride Ammonium Solution Using Organophosphorus-Based Extractants

The suitability of the organophosphorus-based extractants, DiOPA, Ionquest 801 and D2EHPA was evaluated for the selective extraction of Zr and Hf from an (NH4)3Zr(Hf)F7 acidic solution using both dispersive and pertraction solvent extraction (SX). A stock solution of (NH4)3Zr(Hf)F7 was dissolved in either HCl or H2SO4 (0.1–8 M). The following extraction variables were investigated: type and concentration of the acidic solution, the contact time, and extractant to metal ratio. Subsequently, the stripping was investigated using (NH4)2CO3, CaCl2, H2SO4 and C2H2O4 in the concentration ranges of 0–2 M. During extraction, scrubbing and stripping using D2EHPA, CaCl2 and C2H2O4, the Zr purity was increased from 97.2% to 99.0%. When extracting from 4 M H2SO4 with 9 wt% D2EHPA, a Hf selectivity of 32% was observed where after stripping with C2H2O4 resulted in a 98.7% recovery of Zr. With 1.2 M CaCl2 as stripping liquor, almost no Hf and 75% Zr stripping was obtained. During the pertraction 72% Hf and 44% Zr extraction was achieved after 180 min when extracting with 9 wt% D2EHPA from 4 M H2SO4. Pertraction based stripping with 1.2 M C2H2O4 yielded 75% of both Zr and Hf, while stripping with 2 M CaCl2 resulted in 58% Hf stripped with almost no Zr stripping.