The separation of divalent metal ion mixtures has been investigated chromatographically on columns of either gel or sol forms of alginate polyelectrolyte. Separation was obtained in the form of narrow sharp zones for the metal ions. Ion exchange selectivity indicated that Cu²⁺ ions were most strongly retained among the divalent metal ions studied. The factors which affect the ion exchange selectivity, such as the strength of chelation and the mobility and radii of the metal ions, are discussed. The selectivity coefficient for the separation of a mixture of Cu²⁺ and Co²⁺ ions on columns of calcium alginate gel or sodium alginate sol was determined and found to be 1.9 ± 0.1 in both ion exchangers at 25°C.