Formation of W/O Microemulsions in the Extraction of the Lanthanide Series by Purified Cyanex 301

Abstract

ABSTRACTThe formation of water-in-oil (W/O) microemulsions during the extraction of the series of trivalent lanthanides Ln(III) by bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HC301, also known as purified Cyanex 301) was studied. The phenomena in the formation of W/O microemulsions were similar in the extraction of all Ln(III) by HC301 at a high neutralization degree (50%), according to the measurement of the distribution ratios of Ln(III) and the concentrations of Na+ and NO3- in the organic phase, IR spectroscopy, and dynamic light scattering (DLS). W/O microemulsions also formed at a low neutralization degree (15%) for the extraction of heavy Ln(III). The coordination environment of the representative heavy lanthanide Ho(III) in the extracted complexes was monitored by absorption spectroscopy and extended X-ray absorption fine structure (EXAFS). Unlike the light lanthanide, Nd(III) and Ho(III) in the organic phase did not directly coordinate with the HC301 anions regardless of whether W/O microemulsions formed, which further demonstrated the different extraction behavior of HC301 toward the light lanthanides and the heavy lanthanides.