This study concerns the feasibility of extracting lithium and separating aluminum from lepidolite leaching solution by nanofiltration. Four commercial nanofiltration (NF) membranes (DK, DL, NF270, and Duracid NF) were chosen to investigate ion separation performance in simulated lepidolite leaching solution. Membranes were characterized according to FT-IR, hydrophobicity, zeta potential, morphology, thickness, pore size, and hydraulic permeability to reveal the effect of membrane properties on separation. NF membranes were investigated including the retention ratio of SO₄²⁻ and Li+, the separation efficiency of Li⁺/Al³⁺, and the effect of other cations (K⁺, Na⁺, Ca²⁺) on the separation of Li⁺/Al³⁺. The results show that DK membrane displayed the appropriate permeate flux and extremely high Li⁺/Al³⁺ separation efficiency with a separation factor of 471.3 compared with other NF membranes owing to its pore size, smooth membrane surface, and appropriate zeta potential. Overall, it is found that nanofiltration has a superior separation efficiency of lithium and aluminum, which may bring deep insights and open an avenue to offer a feasible strategy to extract lithium from lepidolite leaching solution in the future.

The recovery and leaching kinetics of lithium from lepidolite by sulfuric acid method were investigated in this study, and a new method of nanofiltration to separate Al/Li from lepidolite leaching solution was coupled. The results indicated the optimal conditions about leaching lithium from lepidolite: leaching at 433 K for 4 h with the agitation rate of 120 r min⁻¹, sulfuric acid concentration of 60 wt%, liquid-solid mass ratio of 2.5:1, under which the Li yield could reach at 97%. The kinetics observations revealed that the leaching process was controlled by the hybrid control of solid product layer diffusion and the chemical reaction, and dominated by chemical reaction step, which improved the conclusion of single-step control in the previous literature. A successful attempt was made to couple nanofiltration separation with sulfuric acid extraction of lithium, and DK membrane was used to separate Al/Li from lepidolite leaching solution. DK membrane has shown excellent retention of Al³⁺ and Ca²⁺ and also can effectively permeate Li⁺, which may bring a new inspiration for lithium extraction from lepidolite in the future.