EXTRACTION EQUILIBRIA OF SOME TRANSITION-METAL IONS BY BIS(2-ETHYLHEXYL)PHOSPHINIC ACID

Measurements of dimerization constants (K-d,K-HR) and distribution con stants (K-D,K-HR) of bis(2-ethylhexyl)phosphinic acid (PIA-8) in three kinds of organic diluents were carried out by a potentiometric two-ph ase titration technique at 298 +/- 0.1 K. Extraction of iron(III), zin c(II), copper(II), manganese(II), cadmium(II), cobalt(II) and nickel(I I) by PIA-8 from 1.0 mol dm(-3) ammonium sulfate solution into heptane was investigated as a function of pH and extractant concentration. Th e data have been analyzed both graphically and numerically to determin e the stoichiometry of extracted species and their extraction constant s. The extracted metal species were found to be FeR3 . 2HR for iron(II I), ZnR2 and ZnR2 . 3HR for zinc(II), CuR2 . HR and CuR2 . 5HR for cop per(II), MnR2 . 2HR and MnR2 . 3HR for manganese(II), CdR2 . 3HR for c admium(II), CoR2 . HR and CoR2 . 4HR for cobalt(II) and NiR2 . 3HR and NiR2 . 6HR for nickel(II), respectively. (C) 1997 Elsevier Science B. V.