Membrane processes for lithium recovery from multi-salt-organic waters

RWTH Publications (RWTH Aachen)

Abstract

Lithium-ion batteries (LIBs) used for electric mobility and grid energy storage accelerate the global demand for lithium. To meet the rising demand, primary extraction and secondary recovery necessitate high-yield, mild-conditioned, and sustainable routes. This dissertation experimentally develops and evaluates two complementary membrane-based approaches, polyelectrolyte-multilayer (PEM) nanofiltration (NF) and flow-electrode capacitive deionization (FCDI), to recover, separate, convert, and concentrate lithium from complex aqueous streams arising from salt lake brines and a novel wet-shredding LIB recycling process. To the best of my knowledge, the solution generated by this recycling process has never previously been investigated using membrane-based processes. A PEM-coated NF membrane is fabricated on hollow-fiber substrates by Layer-by-Layer deposition of eight bilayers of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS), resulting in a nanofiltration membrane that enables selective multivalent ion rejection while favoring lithium passage. The (PDADMAC/PSS)8 membrane achieves separation of lithium from magnesium in mimicked brines with selectivities up to 6 and negative lithium rejections down to -56 %. In real multi-salt-organic LIB recycling solutions, the membrane reaches monovalent/multivalent anion separation with selectivities up to 32. Feed engineering via dilution and asymmetric salt addition enhances lithium yield threefold. To convert real multi-salt–organic LIB recycling solutions that are rich in low-solubility lithium fluoride (LiF) into a concentrated, market-relevant lithium product, an electro-driven salt-metathesis process integrated into FCDI is developed. The salt metathesis generates high-purity lithium hydroxide (LiOH) of 100 mol% purity for synthetic feeds and 90 mol% purity for real feeds containing ionic and organic impurities. Lithium is recovered by 92 % and 43 %, respectively, while simultaneously the product is concentrated up to 70-fold and 42-fold, respectively. Stream-recirculation experiments improve lithium recovery. During scale-up, the performance per unit membrane area is preserved, validating the concept's scalability. Together, the two membrane-based processes establish a route from lithium fractionation to electrochemical conversion and concentration, addressing both primary extraction and secondary recovery. The dissertation provides fundamental insight into ion-selective transport in NF and FCDI systems and offers a modular, resource-efficient foundation for future large-scale implementation in a circular lithium economy.

Authors 1

1. Kerstin Wienkamp corresponding Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen