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

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 143μm contained the extractant of 1.63×10−3mol/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 10cm, the flow rate of 0.002L/min, and the initial metal feed solution at pH2.0. 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. •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.