Acid-resistant membranes for efficient metal recovery from acidic wastewater in spent lithium-ion battery recycling

The recycling of spent LiCoO 2 batteries generates acidic wastewater containing Li + and Co 2+ , typically treated using nanofiltration (NF) for wastewater management and metal recovery. However, conventional polyamide membranes (PA-M 0 ) exhibit poor acid resistance, compromising their long-term performance. To address this limitation, acid-resistant membranes PA-M 1 and PA-M 2 were developed by reacting PA-M 0 with 3-aminopropyltrimethoxysilane (APTMS) and ladder-like polyorganosiloxane (POS) synthesized from APTMS, respectively. After 21 days in an acidic medium (pH = 1), PA-M 0 experienced a 91.5 % flux increase and an 11.6 % Mg 2+ rejection decrease, while PA-M 1 showed a reduced flux increase of 45.1 % and a smaller rejection decline of 6.7 %. In contrast, PA-M 2 demonstrated remarkable stability, with minimal performance changes, highlighting its excellent acid resistance. Furthermore, PA-M 2 achieved superior Li + /Co 2+ separation, with Co 2+ rejection consistently above 95.3 % and a Li + /Co 2+ separation factor reaching up to 352. During 36-h NF operation at pH = 1, PA-M 0 suffered signification degradation, whereas PA-M 2 maintained stable separation performance. These findings underscore the critical role of POS, featuring abundant NH 2 groups, a dense Si-O-Si network and an ordered structure, in enhancing membrane acid resistance and selectivity. PA-M 2 presents an effective solution for treating acidic wastewater and recovering metals from spent lithium-ion battery recycling.