Countercurrent chromatography and reverse micelles for separation and extraction of metal cations

Countercurrent chromatography (CCC) is a separation technique in which the stationary phase is a liquid. Diethylhexyl phosphoric acid (DEHPA) forms reverse micelles in heptane. Metallic ions, located in an aqueous phase, can be extracted into the aqueous core of the reverse micelles in the heptane phase. A CCC apparatus can be considered as a powerful mixing and extracting machine with efficiency above several hundreds of theoretical plates. La3+, Ce3+, Pr3+, and Nd3+ lanthanide cations were separated using CCC with a DEHPA-containing heptane stationary phase. Studying the retention variations with aqueous mobile phase pH, it was possible to determine the lanthanide extraction constants and separation coefficients. Overloading conditions are described. Frontal chromatography was performed using a Co2+ and Ni2+ solution. The Co2+ ions were concentrated in the heptane + DEHPA stationary phase, a part of the solution was deionized, and another part was enriched in only Ni2+ ions. This method also produced the extraction constants and separation coefficients. The use of CCC with a complexing stationary phase can be applied to any cation for ion filtering and concentration, or for deionization of aqueous phases.