Process for synergistic extraction of Hf(IV) over Zr(IV) from thiocyanic acid solution with TOPO and N1923

A novel process for the separation of Hf(IV) over Zr(IV) from thiocyanic acid solution using TOPO and N1923 as the extractant has been developed. It was observed that the mixture of TOPO and N1923 exhibited a synergistic effect on selective extracting the minor element of Hf(IV). Several crucial parameters influencing the separation process have been investigated. The extraction efficiency for Hf(IV) was found to be 86.3% under optimum conditions: TOPO+N1923 total concentration of 16 vol%, TOPO/N1923 ratio of 6/10, HSCN concentration of 2.0 M, ammonium sulfate concentration of 0.5 M and extraction O/A phase ratio of 2/1. Meanwhile, the separation factor for Hf(IV) over Zr(IV) could reach up to 21. Furthermore, the reverse extraction properties of the loaded organic phase were studied systematically. The results suggested that the co-extracted Zr(IV) could be scrubbed by 1.0 M H2SO4 with a separation factor of 24.13. Hf(IV) was then stripped from the loaded organic phase using 2.0 M NH4HCO3. The attractive characteristics of the newly designed process were the use of low thiocyanic acid solution, achieving higher extractability of Hf(IV) over Zr(IV), the recyclable process flow and the potential to prepare high pure Hf and Zr.