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 (HDEHP-P350) 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 = 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 β Ce/La = 3.39, β Pr/Ce = 1.67 and β 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 1 H NMR and 31 P NMR analyses. ReCl 3 ( a ) + 2 ( H 2 A 2 ) ( o ) + B ( o ) ↔ K 12 ReCl [ HA 2 ] 2 ⋅ B ( o ) + 2 H ( a ) + + 2 Cl ( a ) − Adding P350 reduces the extraction capacity of HDEHP and still has a good separation effect for light rare earths without saponification; the structure of the extracted complex was determined to be RECl(DEHP) 2 P350 (o) .