Rare Earth Nanofiltration Review Finds 97% Rejection-but Adjacent Elements Still Defeat Membranes

Highlights

• Reviewed membranes rejected over 97% of neodymium, praseodymium, dysprosium and cobalt from simulated acidic wastewater, but rejection is not the same as separation.
• Commercial nanofiltration membranes achieve separation factors of no more than two between adjacent rare earths, far below high-purity commercial requirements.
• Real mine leachates containing iron, aluminum and organics foul membranes and reduce charge-based separation effectiveness, limiting industrial applicability.
• Complexing agents can improve separation by more than an order of magnitude in lab conditions, but long-duration pilots using genuine feed streams remain scarce.
• Nanofiltration may pre-concentrate rare earths before conventional solvent extraction but is not yet a replacement for China's mature processing systems.

Zhenhua Feng of the Sichuan Provincial Testing Research Center of Natural Resources, working with Wenjie Jiang, Binbin Tang, Xiaojun Yang, Ke Liu and supervisor Guangyong Zeng of Chengdu University of Technology, reviewed nanofiltration as a cleaner way to process rare earth elements. Their conclusion is promising but sober: membranes can capture rare earth ions efficiently, yet cannot reliably separate chemically similar neighbors at industrial scale.

REEx Insight: Catching Rare Earths Is Not Separating Them

This distinction matters. One reviewed membrane rejected more than 97% of neodymium, praseodymium, dysprosium and cobalt from simulated acidic wastewater. But rejecting several elements together does not produce separated, saleable oxides. Commercial membranes typically achieve separation factors of no more than two between adjacent rare earths—well below high-purity requirements.

How the Review Tested the Membrane Promise

Published August 13, 2026, in Membranes, the paper examined commercial, modified and experimental nanofiltration membranes. It compared pore-size screening, electrical-charge effects and complexing agents that enlarge chemical differences between rare earth ions. Complexation can improve separation by more than an order of magnitude under selected laboratory conditions.

The Laboratory Water Is Too Clean

Real leachates are acidic, salty and crowded with iron, aluminum, organics and particles. These foul membranes, weaken charge-based separation and reduce flow. Long-duration data using genuine mine or recycling streams remain scarce. The review created no new data and did not report a systematic search protocol, techno-economic analysis or life-cycle assessment. Its description of nanofiltration as “green” is therefore plausible—not proven.

Nanofiltration may eventually reduce solvent use by pre-concentrating or grouping rare earths before conventional extraction. It is not yet a replacement for China’s mature solvent-extraction systems. Next must come standardized testing, real-feed pilots lasting thousands of hours, acid-resistant modules and independently verified economics.

Citation: Feng, Z., et al. (2026). “Selective Separation of Rare Earth Elements by Nanofiltration Membranes.” Membranes, 16(8), 268. DOI (opens in a new tab)