In the current study, the applicability of nanofiltration membrane for recovering lithium from salt lake brine with a high magnesium-to-lithium mass ratio was evaluated under different operating pressure, temperature, multi-ion presence, and concentration ratio conditions. The results showed that the yield of lithium and its separation from magnesium increase with pressure, with the rejection of magnesium reaching 92% at 3.5 MPa. The maximum membrane flux of 50 L/m(2) h is achieved at 313 K, while the separation efficiency decreases with increasing temperature. Furthermore, the existing sodium and potassium compete with lithium to pass through the nanofiltration membrane. The yield of lithium reaches 99% when the concentration ratio is 4. However, membrane flux and separation efficiency decrease with increasing concentration ratio. Ionic fractionation is found to be governed by the special properties of the ions, dielectric exclusion, and steric hindrance. Our results indicate that DK membrane shows considerable promise as a means to separate magnesium and lithium and to recover lithium from salt lake brine with high magnesium-to-lithium mass ratios.