Three-Liquid-Phase Extraction and Separation of Rare Earths and Fe, Al, and Si by a Novel Mixer–Settler–Mixer Three-Chamber Integrated Extractor

Abstract

In the present work, three-liquid-phase extraction and separation of rare earths and Fe, Al, and Si by a novel mixer–settler–mixer three-chamber integrated extractor was investigated. Various three-liquid-phase systems (TLPSs) involving different organic extractants were employed to conduct continuous three-liquid-phase separation of rare earths and Fe, Al, and Si. In the TLPS of PC-88A/PEG 2000/(NH4)2SO4–H2O, light, middle, and heavy rare-earth ions had different distribution behaviors selectively into the organic top phase and salt-rich bottom phase, while most of Fe, Al, and Si were enriched into the poly(ethylene glycol) (PEG)-rich middle phase. Influences from aqueous pH values, agitation speeds, and flow ratios on three-liquid-phase partition behaviors of rare earths and Fe, Al, Si were evaluated. Experimental results indicated that an increase of the aqueous pH value facilitated the extraction of rare earths into the organic top phase and enrichment of Fe, Al, and Si into the PEG-rich middle phase. An increase of the agitation speed in three-phase mixer resulted in a change in the disappearance time of the dispersion band in a three-phase settler. The agitation speeds in a two-phase mixer and flow ratios of the organic phase to an aqueous biphasic mixture resulted in a change in the phase volumes of three-layered liquid flows in a three-phase settler so as to affect the partition behaviors of rare earths and Fe, Al, and Si. On the basis of analysis of the phase-forming behaviors of TLPSs and partition behaviors of rare earths and Fe, Al, and Si, the novel mixer–settler–mixer extractor is recommended for future application of continuous and countercurrent TLPE processes.