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

Abstract

A batch equilibration technique has been employed using an aqueous and aqueous-alkaline thiosulphate-Dowex 50W-X8 system to separate metal ions. The formation of strong anionic complexes by Cu(II), Cd(II), Ag(I) and Pb(II) lower their distribution coefficients (K) appreciably and they therefore remain in solution while other cations are taken up by the cation exchanger. A critical analysis of the K values indicated the conditions under which a number of binary and ternary mixtures could be resolved by column chromatography. In 0.06–0.10 M sodium thiosulphate solutions, the following binary separations have been achieved: Cu(II), Cd(II), Ag(I) or Pb(II) from Mn(II), Fe(II), Co(II), Ni(II), Zn(II), Mg(II), Ca(II), Sr(II), Ba(II), La(III) or Ce(III); and in 0.28 M sodium thiosulphate solution Sr(II), Ba(II), La(III) or Ce(III) were separated from other metal ions studied. The following ternary mixtures have also been resolved: Cu(II), Cd(II), Ag(I) or Pb(II) from Mn(II), Fe(II), Co(II), Ni(II), Zn(II), Mg(II) or Ca(II) from Sr(II), Ba(II), La(III) or Ce(III). In all of the separations favourable column kinetics have been observed. The distribution coefficients, elution characteristics of metal ions, elution curves and statistical analyses of the results of the resolution of artificial binary and ternary mixtures are reported.