Cobalt-nickel separation: The extraction of cobalt(II) and nickel(II) withbis(2-ethylhexyl) phosphinic acid (PIA-8) in toluene

The extraction behaviour of cobalt(II) and nickel(II) from sulfate solution s with bis(2-ethylhexyl) phosphinic acid (PIA-8) in toluene has been studie d. Quantitative extraction of Co(II) was observed at pH 5.0-5.9 while that of Ni(II) at pH 6.8-7.0 with 0.03 M PIA-8 in toluene. The difference in pH( 0.5) for Co(II) and Ni(II) was 1.9. The stoichiometry of the extracted spec ies were determined by slope analysis method. The extraction reaction proce eds by cation exchange mechanism and the extracted species were Co . R-2(HR )(2) and Ni . R-2 . 2(HR)(2). Temperature dependance of the extraction equi librium constants were determined to estimate the apparent thermodynamic fu nctions (AG, AS and All). The method was used for separation of cobalt(II) and nickel(II). Cobalt(II) was separated from nickel even at 1:20 (Co:Ni) r atio. The separation of cobalt(II) from nickel(II) was favoured with the in crease in temperature.