Anion exchange of metal complexes—IV[1]: The cobalt-thiocyanate system

Abstract

Using 60Co, distribution isotherms between a strongly basic anion exchangers, Dowex 1 × 8, and solutions of ammonium, lithium, potassium, and sodium thiocyanate have been determined. No effects attributable to polynucleation were observed with concentrations of Co 2+ up to 8·48 × 10 −8 M. The thiocyanate solutions employed covered the concentration range between 0·05 and 5·0 M. Above 3·25 M, the distribution of the tracer metal as it was influenced by the non-exchange cation of the thiocyanate salt was in the order: K + > NH 4 + > Li + > Na +. These distributions, when corrected for resin invasion and ligand activity, gave distributions as a function of the ligand activity from which the overall complexity parameters related to the neutral complex were evaluated as: k +2 = 1·60×10 −2; k +1 = 5·32; k 0 = 1 (by definition); k −1 = 1·44 × 10 2; and k −2 = 1·38 × 10 2. These values seem to be valid up to Co 2+ concentrations of 0·025 M. Resin sorption is estimated to effect ∼ 3000-fold stabilization of the neutral species over the aqueous phase.