Selective electrochemical recovery of cerium over lanthanum from complex waste feedstocks by alternating current electro-precipitation

Rare earth elements (REEs) are critical for modern society due to widespread industrial demand and supply chain challenges. Efficient technologies for REE recovery and recycling are essential for a sustainable energy transition. Here, we propose a symmetric electrochemical precipitation system which leverages alternating current operation to separate cerium and lanthanum from complex waste streams. Taking advantage of the redox properties of cerium, and the differences in solubility of Ce- and La-hydroxide, we were able to electrochemically recover cerium from lanthanum with high selectivity. The separation efficiency of Ce vs La was assessed by electrochemical parameters such as the the frequency of change for the cell voltage or current direction, applied cell voltage or current, time of operation, as well as solution conditions such as pH and concentration of cerium. The successful recovery of cerium with a purity exceeding 90 wt% was achieved from initially equimolar mixtures of cerium-lanthanum. To validate the approach with real-world feedstocks, leachate from iron slag was used as the waste liquid feedstock, with the electrochemical system achieving a recovery of cerium as high as 95% purity from the complex multicomponent stream. Our work demonstrates the tunability of symmetric electrochemical configurations for the recovery of light rare-earth elements.