Selective separation of rare earth from acetatesolution containing aluminum by nonequilibrium extraction

The separation of RE(III) and Al(III) is conventionally achieved by solvent extraction, however, typical saponification-based routes suffer from low separation coefficients and generate hypersaline wastewater. In this paper, an efficient process was proposed for the selective separation of RE(III) and Al(III) via nonequilibrium extraction from acetate solution using unsaponified P507. The greater extraction selectivity of RE(III) over Al(III) at the initial stage under kinetically controlled conditions indicates that prior removal of Al(III) is unnecessary in the proposed process. Calculations demonstrated that the mass transfer coefficient of La(III) from the aqueous phase to the organic phase was 15.77 times higher than that of Al(III). After optimizing the conditions, La(III) exhibited an extraction efficiency of 94.04%, with a corresponding separation coefficient (β_La/Al) of 102.8. A mechanism combining cation exchange with neutral complex extraction was proposed to explain the extraction behavior, which was supported by maximum-loading measurements and spectroscopic analyses. The terminal ternary complex in the saturated organic phase was inferred to exhibit the general stoichiometry 1:2:1 ([La³⁺]:[P507]:[acetate]). This acetate separation system enables efficient, non-saponification REEs/Al separation with environmentally benign hydrometallurgical applications.