Synergistic extraction of zirconium(IV) and hafnium(IV) with 4-acylbis(1-phenyl-3-methyl-5-pyrazolones) in the presence of neutral organophosphorus extractants

Abstract

Various 4-acylbis(1-phenyl-3-methyl-5-pyrazolones), namely, 4-adipoylbis(1-phenyl-3-methyl-5-pyrazolone) (H 2 AdBP), 4-sebacoylbis(1-phenyl-3-methyl-5-pyrazolone) (H2SbBP) and 4-dodecandioylbis(1-phenyl-3-methyl-5-pyrazolone) (H(2)DdBP) were synthesized and examined with regard to the solvent extraction behavior of zirconium(IV) and hafnium(IV) from hydrochloric acid solutions. The results demonstrate that Zr(IV) and Hf(IV) extracted into chloroform with 4-acylbis(1-phenyl-3-methyl-5-pyrazolones) (H2X), as ZrO(HX)(2) and HfO(HX)(2), respectively. The equilibrium constants (K-ex) of the extracted complexes follow an order H2SbBP > H(2)AdBP > H(2)DdBP. The synergistic extraction of Zr(IV) and Hf(IV) was also investigated with mixtures of H2SbBP and tri-n-butylphosphate (TBP), tri-n-octylphosphine oxide (TOPO), and trialkylphosphine oxide (TRPO), where the complexation strength follows the order TOPO > TRPO > TBP. The equilibrium constants of the synergistically extracted complexes have been correlated with the donor ability of the phosphoryl oxygen of the neutral organophosphorus extractants in terms of their P-31 NMR chemical shifts and their basicity values (K-H =nitric acid uptake constant).