China Nonferrous Metallurgy

When using liquid-liquid solvent extraction to directly separate low-concentration rare earth ions from leachate, there are problems such as high organic phase dissolution loss and easy emulsification, resulting in a large amount of oily wastewater. In this study, the surfactant Span 80 was added as an interfacial stabilizer in the P507-kerosene extraction system, and the effects of aqueous Er³⁺ concentration, impurity ion (Mg²⁺/Al³⁺) concentration, operating temperature, and the number of organic phase recycling times on Er³⁺ extraction performance and oil content in the raffinate were systematically analyzed. The results show that under optimal conditions, the Er³⁺ extraction rate reached 99.77%, and the oil content in the raffinate was as low as 1.14 mg/L. After three cycles of organic phase reuse, the extraction rate was still above 98%, indicating that this stabilizer significantly improves the reusability and stability of the organic phase. AFM, FTIR and DFT analyses revealed that Span 80 can optimize the molecular arrangement at the interface and enhance the interfacial film strength, thereby effectively suppressing emulsification and reducing organic phase loss. Increasing the Er³⁺ concentration or introducing an appropriate amount of salting-out agent Mg²⁺ can reduce the oil content in the raffinate, whereas Al³⁺, due to hydrolysis to form polynuclear hydroxy complexes, can destroy the interface, resulting in decreased extraction rate and increased oil content.