Valorization of battery manufacturing wastewater: Recovery of high-value metal ions through reaction-enhanced membrane cascade

•Reaction-enhanced membrane cascades (REMCs) are proposed for valorizing battery wastewater.•REMCs consist of two sequential ultrafiltration/diafiltration and a nanofiltration process.•REMCs are applied to 16 combinations of transition metal ions and salt impurity ions.•Transition metal ions (Ni2+, Cu2+, and Cd2+) are recovered by 90 % from wastewater.•Transition metal ions are enriched to a 43-fold concentration, achieving 99.8% purity. Leveraging the latent value within battery manufacturing wastewater holds considerable potential for promoting the sustainability of the water-energy nexus. This study presents an efficient method for recovering transition metal ions (Ni2+, Co2+, Cu2+, and Cd2+) from highly saline battery wastewater (Na+, Li+, K+, or Mg2+). Our approach involves the effective utilization of a reaction-enhanced membrane cascade (REMC), comprising a meticulously orchestrated series of selective complexation-decomplexation steps involving polyethyleneimine (PEI) and various transition metal ions. This strategic intervention effectively segregates transition metal ions from salt ions during the fractionation process using an ultrafiltration membrane in a diafiltration process, overcoming osmotic pressure limitations. The ensuing concentration step via nanofiltration achieves an impressive 99 % yield and an extraordinary 215-fold concentration of transition metal ions (>99.8 % purity). The proposed method was validated with 16 different ion pairs to demonstrate its versatility, offering a pragmatic pathway for recycling various transition metal ions from industrial wastewater.