Solvent extraction and separation of light rare earths from chloride media using HDEHP-P350 system

Solvent extraction is the most important method for rare earth extraction and separation. Currently, di(2-ethylhexyl) phosphoric acid (HDEHP) and 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (HEH/EHP) are widely used in industrial production, but there are still obvious deficiencies that require further research to resolve. In this paper, the unsaponification extraction of light rare earth ions in a hydrochloric acid medium by di(2-ethylhexyl) phosphoric acid-di(1-methyl-heptyl) methyl phosphonate (HDEHPP350) system was studied. The results show that the addition of P350 reduces the extraction capacity of HDEHP, and also greatly reduces the concentration of acidity required for the back-extraction. It still has a good separation factor for light rare earths without saponification, and the extractant is not easy to emulsify. With an aqueous phase of pH 1/4 2.85, and HDEHP mole fraction X-HDEHP = 0.9 (compared with O/A = 2), the separation effect of light rare earth is the best, resulting in the separation coefficient beta(Ce/La) = 3.39, beta(Pr/Ce) = 1.67 and beta(Nd/Pr) = 1.45, respectively. The loaded light rare earth ions extracted by HDEHP-P350 can be easily stripped when 2 mol/L HCl is used as the stripping agent. Finally, the extraction mechanism is discussed using a slope method, and the final structure of the extracted complex is determined to be RECl[(DEHP)(2)](2)P350((o)), based on a combination of infrared spectra and H-1 NMR and P-31 NMR analyses. (c) 2021 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.

Automated summary

Solvent extraction is a crucial method for rare earth extraction and separation. In this study, the unsaponification extraction of light rare earth ions in a hydrochloric acid medium by the HDEHPP350 system was investigated. The results show that HDEHP-P350 has a good separation effect for light rare earths and is easy to strip. The structure of the extracted complex is determined through analysis and discussion.