Abstract

Liquid-liquid extraction of cobalt (II) ions have been carried out using 0.05 M solution of N,N’-ethylenebis (4-propionyl-2,4-dihydro-5-
methyl-2-phenyl-3H-pyrazol-3-oneimine) (H2PrEtP) Schiff base in chloroform. Various parameters for the extraction such as effect of pH,
concentrations of the extractant, cobalt(II) ion , phase ratio and synergistic effect of 4-propionyl-2,4-dihydro-5-methyl-2-phenyl-3Hpyrazol-3-one (HPrP) have been investigated and optimized. Extraction with single ligand was observed to have a pH1/2 of 7.05 with
percentage extraction of 53.24 % corresponding to logD value of 0.0563, and optimum pH of 9.25 with percentage extraction of 98.43 %,
logD value of 1.7971. The synergistic effect of HPrP on the extraction significantly lowered the pH1/2 from pH 7.05 (near neutral) to pH
6.25 (slightly acidic) with percentage extraction of 52.60 % corresponding to logD value of 0.0451. Optimum extraction of 99.30 was
observed at pH 8.26 when the mixed ligands, H2PrEtP and HPrP were used. The extraction of cobalt (II) ions increased rapidly as the
concentrations of the ligands H2PrEtP increased from 2.5×10-3 M to 4.0×10-2 M and that of HPrP from 2.5×10-3 M to to 2.5×10-2
. Variation
of the metal concentration did not have much effect on the extractions, hence the percentage extraction was relatively high over all the
metal concentrations studied.

Key words: distribution, cobalt(II), N,N’-ethylenebis(4-propionyl-2,4-dihydro-5-methyl-2-phenyl-3H-pyrazol-3-oneimine), effect of pH and synergist.