Complex extraction of rare earth elements from nitrate solutions with a tri-n-octylamine-octanoic acid bifunctional ionic liquid

•The IL based on tri-n-octylamine and octanoic acid was synthesized for the first time.•The physical–chemical properties of the IL was studied.•The synthesized IL was used for the complex extraction of REEs.•The mechanism of extraction of metal salts was studied and confirmed. In this work, a new hydrophobic bifunctional ionic liquid based on tri-n-octylamine and octanoic acid was synthesised and a physicochemical characterisation was performed on it. The extraction of a series of rare earth elements (Y, Eu, Gd, Tb) (REEs) from aqueous nitrate solutions in a system containing the resulting ionic liquid was studied. Extraction isotherms were obtained and regularities of the interphase distribution of REEs were determined as a function of extraction process time, NaNO3 concentration, the pH of the aqueous phase, the concentration of the ionic liquid in the system, the volume ratio, and temperature of the process. It was shown that the extraction of REEs nitrates by the ionic liquid based on tri-n-octylamine and octanoic acid occurred in accordance with the mechanism of binary extraction of salts with the formation of two extractable compounds in the organic phase. In addition, this IL has been shown to exhibit excellent reusability.