An automatic and low-maintenance chelator ion chromatography method for rare earth element determination in...

Rare earth element (REE) detections for industrial-scale production from unconventional feedstocks are often cost-prohibitive, high-maintenance, and unsuitable for continuous monitoring in complex industrial process streams. This study developed an automated, low-maintenance, and thus more cost-effective REE chelation ion chromatography (CIC) method, featuring an automated post-column reagent delivery designed for continuous monitoring. Following new hardware configuration, the CIC method was optimized by evaluating dilution matrices, eluent gradient, and coloring agent composition. Calibration for 16 REEs, La, Ce, Pr, Nd, Sm, Sc, Eu, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb, and Lu was established at 0.10 mg/L to 5.0 mg/L range, achieving detection limits of 0.089-0.12 mg/L. Matrix interference evaluations of the optimized method (e.g., Na⁺, Ca²⁺, Al³⁺, Cl^-, SO₄^2-) demonstrated robust performance for REE detection (95.8%-103% recovery) in the presence of NaCl, Na₂SO₄, and CaCl₂ up to 10,000 mg/L concentration. While the method remained robust against high salt backgrounds, Al³⁺ was identified as an interfering ion, with recovery deteriorating for select REEs (Tb, Dy, Y, and Ho) from 81.9 to 110% at 200 mg/L Al³⁺. No measurable REE recovery was observed at 2020 mg/L Al³⁺. The CIC method further quantified REEs in select test processing streams from a continuous membrane solvent extraction experiment, demonstrating 94.4% to 109% recovery compared to ICP-MS for most REEs. Overall, this study demonstrates an automatic, low-maintenance, salt-tolerant, and cost-effective CIC technique, suitable for continuous REE monitoring to support process optimization.