Synergistic Recovery of Dysprosium(III) from Water via an Emulsion Liquid Membrane at Low Concentrations of Cyanex 272–D2EHPA: Impact of Process Factors and Water Sources

This study reports an investigation of the synergistic extraction of dysprosium (Dy(III)) from aqueous media using a low-concentration, binary carrier mixture of Cyanex 272 and D2EHPA within an emulsion liquid membrane (ELM). Within the tested formulations, the one containing 0.42% (w/w) Cyanex 272 and 0.28% (w/w) D2EHPA yielded the best results. The impact of process factors that maximize recovery efficiency and minimize emulsion breakdown was also examined. A Span 80 loading of 0.75% (w/w) achieved 97.5% extraction with minimal breakage (less than 2.1%). An external phase pH of 5.8 achieves an optimal balance of high-throughput Dy(III) recovery and membrane stability; 0.2 N HNO₃ as the stripping phase strikes the optimal balance, providing strong initial uptake with minimal emulsion degradation. As the initial Dy(III) loading increases, extraction efficiency decreases. Increasing the temperature from 15 to 45 °C accelerates mass transfer, achieving near-complete extraction in under 15 min. However, above 45 °C, emulsion breakage spikes, causing a collapse in efficiency. Similarly, increasing NaCl levels suppresses Dy(III) uptake and promotes coalescence. This reduces recovery from seawater to just over 70%. Nevertheless, the balanced mineral content of Zamzam water preserves emulsion integrity and enables 100% extraction. The activation energy was found to be 26.16 kJ/mol, suggesting that mass transfer, rather than the chemical reaction at the interface, controls the process. The results of this study highlight the synergistic efficiency advantage of the ELM system at lower carrier concentrations, even in complex water sources.