Adsorptive separation of La, Ce and Pr using microcapsules containing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester

• The microcapsules adsorbed well the rare-earth metals: La, Ce and Pr.
• Metal complex formation contributed the overall adsorption process of the metals.
• Feed flow rate, column height and solution pH controlled the metal separation.
• Separation of the metals was achieved in eight repetitions of adsorption–desorption.

The adsorption of lanthanum, cerium and praseodymium onto microcapsules containing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHPNA) was investigated. Through scanning electron microscopy imaging of the microcapsule-surface and neutralization titration estimation of the amount of EHPNA extractant remaining in the microcapsule, the microencapsulated extractant was characterized. As a result, it was found that the microcapsules with a mean particle diameter of 143 μm contained the extractant of 1.63 × 10− 3 mol/g-microcapsule. The adsorption behavior for each of the metals was measured from the metal adsorption equilibrium and the metal adsorption rates, from which it was estimated that the formation of a metal complex contributes to the overall adsorption rate of the metals. The separation of each of the metals was examined using a column packed with the microcapsules. It was found that the separation of the metals was most enhanced under the conditions of the microcapsule-packed column of 10 cm, the flow rate of 0.002 L/min, and the initial metal feed solution at pH 2.0. The separation of lanthanum, cerium and praseodymium from a La–Ce–Pr mixed solution was then examined in detail, with effective separation of these metals achieved within eight repetitions of the adsorption–desorption step.