Enrichment and separation of holmium and erbium by high-speed countercurrent chromatography

Selective enrichment of rare earth elements and subsequent separation were performed by high-speed countercurrent chromatography (CCC) using a multilayer coiled column filled with a toluene solution of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester as a stationary phase. A large volume of aqueous solution containing adjacent rare earth elements, holmium and erbium, was passed through the column, and then the rare earth elements enriched in the stationary phase were chromatographically eluted by the mobile phase of an appropriate pH value. Mutual separation with sufficient resolution was accomplished, and approximately linear relationship existed between the area of elution peak and the quantity of rare earth element injected.