Fig. 4: Ion separation performance of cyclodextrin membranes under crossflow filtration conditions using synthetic real lithium-bearing brines.

a Experimental single ion observed rejection, water permeance (A), and separation factor (SF) of LiOH-Am7CD-0.05 TMC membranes. Filtration conditions: 5 bar, 10 bar, and 18 bar applied pressure using simulated salt-lake brine as feed solution³⁵ (the ionic composition of the feed solution is reported in Supplementary Table 4); b Schematic flow diagram of the cross-flow laboratory scale filtration system. c–e Experimental single ion observed rejection and f–h water flux of M1-M6 membranes (all LiOH-Am7CD-0.05 TMC membranes) plotted as a function of the recovery using three different synthetic brine solutions with various Li⁺ levels, namely, concentrated seawater³⁶, Lungmu Co salt-lake brine³⁷, and Imperial geothermal brine³⁸; here, the filtration conditions were: 70 bar for concentrated seawater (pH 7.5), and 60 bar for Lungmu Co salt-lake brine (pH 7.9) and Imperial geothermal brine (pH 6) (the ionic compositions of the feed solutions are listed in Supplementary Table 5); A is the intrinsic water permeability. The observed rejection and the retentate stream ionic concentrations as a function of the recovery are presented in Supplementary Figs. 30–32; Experimental i, Li⁺/Mg²⁺ and j, Li⁺/Ca²⁺ mass ratios in the synthetic feed solutions (at 0% recovery and at the end of recovery, respectively) and in the final collected permeate. Error bar standard deviation.