(557a) Understanding the Role of Limited Current Density in the Recovery of Rare Earth Elements and Minerals By Electrodialysis Metathesis

Rare earth elements (REE) have REE have become essential to several technologies due to their use in many current technologies such as touchscreen, cell phones, LED light bulbs, microchips, magnets, and wind turbines, which has shown an increase in REE demand over the past decade, and the demand will continue to increase while supply becomes critically short. This has caused an increased interest in identifying new sustainable methods and sources of obtaining REE. One method is electrodialysis metathesis (EDM), a membrane-based process that combines an electrical current with a metathesis reaction to help selectively and simultaneously separate and concentrate ions without membrane scaling. To ensure the EDM system can efficiently separate REE and minerals while ensuring minimal fouling and energy consumption, a better understanding of the role of the limited current density of the system is needed.

In this study, the limiting current density (LCD), a critical parameter in designing the EDM process, was determined by developing current-voltage curves for various numbers of quads of ion-exchange membranes in the EDM stack exposed to solutions with ions of interest. A stepwise increase in the applied voltage obtained the ohmic, limiting current, and over-limiting current regions. The electrical conductivity (EC), total dissolved solids (TDS), and pH were recorded at regular intervals to understand further the metathesis reaction using the selected salts. Results showed that the LCD decreased as the number of quads increased in the EDM stack. Also, the stack resistance was negligible after a particular applied voltage. The metathesis reaction occurred while varying the LCD of each EDM stack. These results indicated that separating and concentrating elements of interest can be efficiently accomplished while controlling the LCD in the EDM process. Under these conditions, EDM can remain a viable, effective, and sustainable method for separating and recovering REE and minerals present in impaired solutions.