Thiosulphate as a complexing agent in the separation of cations by anion-exchange chromatography

Abstract

The anion-exchange behaviour of a number of metal ions on Dowex 1-X8 (Cl^– form), in both neutral and alkaline sodium thiosulphate solution (0.02–0.40 M), has been investigated. Cu(II), Zn(II), Cd(II), Ag(I) and Pb(II) form anionic complexes and are selectively adsorbed by the resin, whereas other metal ions remain unadsorbed. The separation factors relative to Cu(II), Zn(II), Cd(II), Ag(I) and Pb(II) have been calculated as a function of sodium thiosulphate concentration following determination of the distribution coefficients. As predicted from the separation factor, column chromatographic separations of a number of synthetic binary mixtures could be achieved. Cu(II), Zn(II), Cd(II), Ag(I), or Pb(II) can be separated from Mn(II), Co(II), Ni(II), Mg(II), Ca(II), Sr(II), Ba(II), La(III) or Ce(III).

Of the sorbable ions, Ag(I) and Pb(II) are firmly held by the resin at high sodium thiosulphate concentrations. Separation of either of these ions from the other sorbable ions, Cu(II), Zn(II) or Cd(II), was achieved and experimental conditions for the separations are described. Also, ternary separations of Ag(I) or Pb(II) from Cu(II), Zn(II) or Cd(II) and from Mn(II), Co(II), Ni(II), Mg(II), Ca(II), Sr(II), Ba(II), La(III) or Ce(III) have been carried out.

The distribution coefficients, column elution behaviour, elution curves and statistical evaluation of the experimental results are presented.