High-purity and high-recovery lithium extraction via dual selectivity optimization of ion and water in a batch nanofiltration–RO process for spent LiB leachates

• A batch-type NF–RO process enables selective lithium recovery from spent LiB leachates. • The process achieves 99.8 wt% purity and >99% recovery of lithium with minimal water and acid. • Key innovations: pH control, retentate recycling, and RO permeate reuse as dilution water. • Simulation and material balance support adaptability to both concentrated and dilute leachates. • The process design contributes to resource-efficient lithium recovery technologies. To recover Li⁺ from sulfuric‑acid leachates of spent lithium‑ion batteries, we developed a batch‑type nanofiltration (NF)–reverse osmosis (RO) process with NF retentate recirculation and pH control. The batch configuration enables time‑based tuning of recovery under high overall recovery constraints. A two‑stage NF followed by RO was analyzed experimentally and through process simulation to separate Li⁺, sulfuric acid, and water. Experiments using a Mg²⁺/Li⁺ sulfate model system achieved high Li⁺ purity (>9 9.8 wt%) and overall recovery (> 99 %), although with higher acid consumption than the optimized simulation. Under aligned ≥ 99 % recovery and product concentration targets, simulations show that the batch process and an aligned continuous NF–RO process require comparable external water make‑up owing to RO permeate reuse, whereas the continuous process involves approximately tenfold larger internal RO permeate circulation and sulfuric acid addition. Using Mg²⁺ as a surrogate multivalent cation, further validation with real leachates is required to confirm robustness under complex compositions.