Polyethyleneimine-assisted polydopamine co-deposition for fabricating loose reverse osmosis membranes with enhanced antifouling and selectivity for lithium extraction from geothermal brine

This study presents the fabrication and evaluation of a nanofiltration membrane modified with polydopamine polyethyleneimine (PDAPEI), designed to mimic the characteristics of a loose reverse osmosis (LRO) membrane. The membrane exhibits relatively lower water permeability while providing enhanced selective ion rejection, enabling the effective separation of monovalent ions such as lithium from sodium and potassium, along with efficient rejection of divalent ions like magnesium and calcium in geothermal brine. Surface modification significantly enhanced hydrophilicity, antifouling resistance, and monovalentâ��divalent ion selectivity. The optimal membrane (PDA:PEI = 1:1) demonstrated improved salt rejection and a high selectivity ratio (SFLi⁺/Mg²⁺ 7.8), with enhanced permeability (22.5 L·m²Â·h¹Â·bar¹) and flux recovery (FRR up to 95.3 ) in real geothermal brine. Characterization revealed uniform surface morphology, decreased pore size, and increased negative charge and hydroxyl/amine functionalities that inhibited gypsum and silica scaling. These findings validate PDA PEI modification as a robust strategy for advancing LRO membrane performance in lithium recovery from complex brines. © 2025