Selective Extraction of Hafnium over Zirconium with Dialkylphosphinic Acids from H2SO4 Media

Designing highly efficient dialkylphosphinic acid extractant for zirconium/hafnium separation relies on systematic structure-property studies. In this paper, dialkylphosphinic acids with different substituents at [3-C, gamma-C and 8-C for zirconium and hafnium extraction and separation from H2SO4 media were investigated. The results show that substituents at [3-C, gamma-C and 8-C reduce the extraction ability of dialkylphosphinic acids for both zirconium and hafnium. The substituent effect at [3-C is greater than that at gamma-C and 8-C. The larger steric hindrance of the substituents (ethyl > methyl > H), the weaker extraction ability of the dialkylphosphinic acids. The zirconium and hafnium separation behavior is related to the extraction ability of dialkylphosphinic acids. Dialkylphosphinic acids with stronger extraction ability show better zirconium/hafnium separation performance at higher acidity of 2.0 mol L-1 H2SO4, while those with weaker extraction ability show better zirconium and hafnium separation performance at lower acidity of 0.25 mol L-1 H2SO4. The highest hafnium/zirconium separation factor ([3Hf/Zr) in the current study occurs with (2-ethylhexyl) (2,4,4-trimethylpentyl)phosphinic acid (USTB-1), which reaches 19.2.