A green method for the extraction and determination of La³⁺ and Ce³⁺ ions from water and copper solution based on Calix[4]resorcinarene chelation

Green extraction and recovery of rare earth metals is an important and urgent problem for the rare earth industry. To explore a method capable of extracting and enriching rare earth elements in both aqueous and high-copper matrix solutions, a calix[4]resorcinarene chelation-cloud point extraction (CPE)-inductively coupled plasma optical emission spectrometry (ICP-OES) approach was established to achieve the extraction, enrichment, separation, and determination of rare earth elements. In this study, a methylsulfonated derivative of calix[4]resorcinarene (C4RS) was prepared, which is a polydentate ligand with four flexible methylene sulfonate groups. Through UV-vis spectroscopy, it was demonstrated that C4RS exhibits a high complexation ability towards rare earth (RE) ions. During the development of the analytical method, Triton X-114 (TX-114), a nonionic surfactant, was employed as the extractant, while water-soluble C4RS acted as the chelating agent for CPE of La3⁺ and Ce3⁺ ions. The CPE process, including experimental conditions and influencing factors for enriching La3⁺ and Ce3⁺ ions, was systematically investigated and optimized. This study found that the CPE procedure could extract La3+ and Ce3+ ions with high efficiency in water and even from copper solutions with a certain concentration. Then, the La3+ and Ce3+ ions extracted and enriched by CPE are determined by ICP-OES. The detection limits were as low as 0.0002 and 0.0003 for La3+ and Ce3+ ions, respectively, with excellent standard recovery rates and precision.