This research investigated the recovery of rare earth elements (REEs) from leachates of coal fly ash, a large volume waste material that is enriched in REEs. Leachates of fly ash generally comprise not only the target elements of interest (i.e., REEs) but also are enriched in other major metal ions (e.g., Na, Ca, Fe, Al, Si) such that REE recovery methods must be highly selective for REEs over these other major ions. Here, we investigated the selective recovery and concentration of REEs from coal ash leachates using two types of liquid membrane configurations: liquid emulsion membrane (LEM) and a supported liquid membrane (SLM). The methods are capable of separating REEs from leachates while also reducing the use of organic solvents relative to conventional extractions for REE recovery. The relative selectivity and recoveries of individual REEs were compared between LEM and SLM configurations, as well as other process parameters including solvent type and extraction time. Both SLM and LEM processes demonstrated 3-5 orders of magnitude greater selectivity of individual REEs compared to major ions (e.g., Al, Si, Na). Separation efficiencies with mineral oil-based liquid membrane were similar to separations with kerosene. LEM-based separation and conventional solvent extraction were most efficient for the light REEs (La, Ce, Pr, Nd, Sm, Eu, Gd) while the SLM approach was most efficient for the heavy REEs (Y, Dy, Ho, Er, Tm, Yb, Lu), suggesting different rate limiting steps for REE recovery. Future work will explore the mechanisms of REE recovery and identify key process variables for improving recovery efficiency of selected high value REEs.

Comparison of liquid membranes for selectivity of rare earth elements from coal ash leachates

255th National Meeting (2018)

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