Enhancing lithium concentration performance from synthetic geothermal brine through electro-nanofiltration method

Lithium carbonate plays an important role in the battery industry. While lithium extraction has primarily focused on saltlake brines, their high magnesium content presents separation challenges. Geothermal brines, enriched in calcium rather than magnesium, offer a promising alternative to the growing adoption of geothermal energy, particularly in Indonesia. However, the low lithium concentration and the coexistence of calcium remain critical bottlenecks to achieving high-purity lithium carbonate. Electro-nanofiltration (ENF), a nanofiltration membrane separation process enhanced by an electric field. Previous studies have demonstrated its effectiveness in separating lithium from magnesium and magnesium from strontium. In this study, ENF was applied to concentrate lithium from synthetic geothermal brine by evaluating the effects of varying feed compositions (single solute, binary mixtures, and synthetic geothermal brine) and applied voltages (0�4 V). The results indicate that increasing the applied voltage reduces lithium rejection with minimal impact on permeate flux. The presence of coexisting cation ions decreases both lithium rejection and permeate flux. In synthetic geothermal brine, higher voltages resulted in lower monovalent cation rejection but substantially improved calcium rejection, with permeate flux remaining relatively stable. Extended operation under optimal conditions achieved calcium rejection as high as 99.71 at 2.5 V despite a gradual decline in flux. These results highlight ENF as a promising approach for lithium recovery from geothermal brines, particularly through total calcium rejection, thereby enabling the production of high-purity lithium carbonate.