Extraction of rare earths using bubbling organic liquid membrane with un-saponified P507

Abstract

Extraction and enrichment of low-concentration rare earths from the in-situ leaching solutions of ion-absorbing type rare-earth ores using bubbling organic liquid membrane with un-saponified P507 was investigated. Experimental results revealed that saponification of P507 extractant are unnecessary for extraction of rare earths using bubbling organic liquid membrane. The equilibrium pH of the aqueous solutions flowing out from the extraction column would not decrease obviously, because the total volume of un-saponified P507 contacting with the aqueous phase in the column was very small, and the aqueous-to-organic phase ratios could be very large. Therefore, the loading capacity of rare-earth ions in the organic phase have no obvious changes, compared to that using saponified P507. Scale-up experiments in the pilot-scale columns connected in cascade for continuous countercurrent extraction of low-concentration rare earths about 100mg/L in the leaching solutions demonstrated that, the final residual concentrations of rare earths remained below 3.0mg/L, while total recovery of rare earths after extraction and stripping processes could reach above 90%. Bubbling organic liquid membrane extraction is in fact an interfacial chemical reaction of rare-earth ions with un-saponified P507 adsorbing at the surface of organic liquid membrane. During countercurrent extraction processes, shearing interaction of the aqueous solutions with dispersed organic bubbles rising in the extraction column would result in continuous exposure of fresh surface of organic bubbles, which is a main driving force to promote the mass transferring and enrichment of rare-earth ions into the organic liquid membrane layer.