Extraction equilibria of some transition metal ions by bis(2-ethylhexyl)phosphinic acid

Measurements of dimerization constants (K-d,K-HR) and distribution constants (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-phase titration technique at 298 +/- 0.1 K. Extraction of iron(III), zinc(II), copper(II), manganese(II), cadmium(II), cobalt(II) and nickel(II) by PIA-8 from 1.0 mol dm(-3) ammonium sulfate solution into heptane was investigated as a function of pH and extractant concentration. The data have been analyzed both graphically and numerically to determine the stoichiometry of extracted species and their extraction constants. The extracted metal species were found to be FeR3 . 2HR for iron(III), ZnR2 and ZnR2 . 3HR for zinc(II), CuR2 . HR and CuR2 . 5HR for copper(II), MnR2 . 2HR and MnR2 . 3HR for manganese(II), CdR2 . 3HR for cadmium(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.