Redistributing Fe and REE Loadings in Multi-Column Adsorption Trains: A Dual-Adsorbent Strategy for Fe-Dominated Coal Leachates

The recovery of rare earth elements (REEs) from coal-derived acid leachates is challenged by high iron (Fe) concentrations, which can hinder downstream separation. In this study, a dual-adsorbent, multi-column strategy was evaluated for sequential Fe removal and Nd capture from a synthetic multicomponent solution formulated to model an Fe-rich coal-derived leachate, with Nd as the sole REE and an Fe/Nd mass ratio of approximately 43:1. Phosphinic acid-based TP-272 was used for upstream Fe capture, and D2EHPA-impregnated VP OC-1026 was used for downstream Nd capture. The two-stage batch experiment achieved 99.9% overall Fe removal, with Nd recovery reaching 64.7% at 150 min. Separate single-column experiments characterized breakthrough and desorption under continuous flow. When the columns were connected in series, Fe breakthrough into the downstream Nd-capture column remained substantial. An intermediate TP-272 buffer column with bed heights of 10, 20, and 30 cm was therefore evaluated. In these three-column experiments, increasing the buffer height from 20 to 30 cm reduced the C2 share of total retained Fe from approximately 54% to 15% and increased its share of total retained Nd from approximately 19% to 36%. These distribution fractions describe the allocation of retained metals, rather than feed-based removal or recovery efficiencies. The results illustrate the balance between additional Fe interception and Nd co-adsorption when a buffer bed is added. They reflect the combined effects of resin inventory, nominal contact time, and column configuration and provide a basis for further evaluation with real leachates and mixed-REE feeds.