A synergistic two-stage process for rare earth element extraction from bastnasite leachates in ethylene glycol: The dual role of Cyanex 923 as a purification and process conditioning agent

Artikel i vetenskaplig tidskrift, 2026

The recovery of rare earth elements (REE) using non-aqueous solvents provides a sustainable alternative to conventional hydrometallurgy, while enabling unique extraction mechanisms inherent to organic media. This study examines REE extraction from bastnasite ore leached in an ethylene glycol–FeCl₃ system. Among four different extractants evaluated, D2EHPA demonstrated exceptional selectivity for heavy REE, achieving a Y/Ce separation factor of 270.4. Following the extractant screening step, the loading and stripping conditions for D2EHPA were systematically optimized to maximize Y extraction efficiency. Optimized loading conditions enabled Y extraction to reach 97 % under 30 min. shaking time, 2000 rpm, and 2:1 E/L ratio. Y was stripped back with 3 M HNO₃ at a high recovery rate (87.4 %), but substantial iron co-extraction necessitated an additional purification step. Therefore, a pre-treatment stage using C923 was implemented, achieving an iron scavenging efficiency of over 95 %. Beyond simple purification, this step revealed a novel in-situ chemical conditioning mechanism. As confirmed by FTIR spectroscopy—which showed an intensified free-water band (∼1650 cm⁻¹) resulting from HFeCl₄ solvation and subsequent proton consumption—C923 inherently reduced the extreme acidity of the non-aqueous matrix. This base-free pH modification eliminated the precipitation challenges common in aqueous systems and successfully "unlocked" D2EHPA to co-extract light REE alongside heavy REE. Such an outcome was previously impossible in the raw acidic leachate. Overall, the study establishes two operational pathways: a highly selective Y extraction route using D2EHPA alone, and a synergistic bulk REE recovery route enabled by the dual purification and acidity-conditioning functions of C923.