Effect of Temperature on the Synergistic Extraction of Some Lanthanides by 2‐Ethylhexyl Phenylphosphonic Acid and Micelles of Dinonyl Naphthalene Sulfonic Acid

Abstract Synergistic enhancements were observed in the extraction of the lanthanides. Slope analysis and continuous variation methods were used to establish the extraction stoichiometry. The stoichiometry differs between the early and late members of the series. Thermodynamic parameters of the extraction process were determined by the temperature coefficient of extractability. Extractions from HClO4 by dinonyl naphthalene sulfonic acid (HDNNS) and the mixed ligand system are entropy controlled, whereas the process is enthalpy controlled when 2‐ethylhexyl phenylphosphonic acid (HEHφP) is the extractant. These results shed further light on the mechanism of the synergy by the combined extractants.