## 4 Conclusions  
Lithium-sodium separation by the ED process using a Lithium Composite Membrane (LCM) composed of 50.5 wt.% of LICGC, 25.5 wt.% of PECH-DABCO, 18 wt.% of PES-NH\({}_{2}\) and 6 wt.% of BRIJ76 was the purpose of this study. We were interested both in determining the selectivity coefficient of this membrane towards Li\({}^{+}\) (S(Li/Na)) and in measuring its recovery rate (RR(Li\({}^{+}\)) as a function of two parameters, which were the applied current density and the concentrations of these two cations in the feed compartment. ED operations took place in a two-compartment cell known to be simple to implement or in a four-compartment cell allowing the feed and receiver compartments to be isolated from the electrode compartments, thus, avoiding the telescoping of electrodes reactions with the phenomena studied. In both ED cells, the increase of the current density led to a reduction in the selectivity coefficient; however, this reduction was less pronounced in the four-compartment cell thanks to its protection from redox reactions on the electrode surfaces and the partial \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Membranes** & **Feed Composition** & **S(Li/Na)** & **RR(Li\({}^{+}\)) (\%)** & **Reference** \\ \hline IL-i-OM membrane & \(\left[\text{Li}^{+}\right]_{\text{F}}\) = 170 ppb [Na\({}^{+}\)]\({}_{\text{F}}\) = 10,500 ppm & \
\begin{tabular}{c} Very \\ selective \\ \end{tabular} &
\begin{tabular}{c} 5.94 \\ 22.2 \\ \end{tabular} & [34] \\ \hline PET track-etched membrane & \({}^{*}\) [K\({}^{+}\)]\({}_{\text{F}}\) = 0.13 mol\(\cdot\)L\({}^{-1}\), [Li\({}^{+}\)]\({}_{\text{F}}\) = 0.07 mol\(\cdot\)L\({}^{-1}\) & 0.20 & - & [41] \\ \hline Polymer inclusion membrane (PDT-PIM) & \(\left[\text{Li}^{+}\right]_{\text{F}}\) = [Na\({}^{+}\)]\({}_{\text{F}}\) = 20 mg\(\cdot\)L\({}^{-1}\) & 6.41 & 9.02 & [60] \\ \hline Sulfonated poly (ether ether ketone) composite CEM & \(\left[\text{Li}^{+}\right]_{\text{F}}\) = [Na\({}^{+}\)]\({}_{\text{F}}\) = [K\({}^{+}\)]\({}_{\text{F}}\) = [Mg\({}^{2+}\)]\({}_{\text{F}}\) = 500 ppm & 2.17 & 84 & [61] \\ \hline CR67-MK111 (Homogenous polystyrene/Dvinyl benzene) & \(\left[\text{Li}^{+}\right]_{\text{F}}\) = 27,800 mg\(\cdot\)L\({}^{-1}\) [Na\({}^{+}\)]\({}_{\text{F}}\) = 1350 mg\(\cdot\)L\({}^{-1}\) & 3.54 & 27.53 & [62] \\ \hline Monovalent- cation exchange membrane & \(\left[\text{Na}^{+}\right]/\left[\text{Li}^{+}\right]\) = 0.75 mol\(\cdot\)L\({}^{-1}\), & 1.25 & 21.47 & [63] \\ \hline Lithium selective cation exchange membrane & Feed: (LiOH-H2O = 1.9857 mol\(\cdot\)L\({}^{-1}\), & \\ NaOH = 0.0587 mol\(\cdot\)L\({}^{-1}\)) & 32.2 & - & [35] \\ \hline Supported liquid membrane based on a fluorinated molecule. & LiCl = NaCl = 15.10\({}^{-3}\) mol\(\cdot\)L\({}^{-1}\) & 400 & 99 & [64] \\ \hline Monovalent selective ion exchange membrane & LiCl = NaCl = 0.05 mol\(\cdot\)L\({}^{-1}\) & 7.5 & 74.31 & [65] \\ \hline LCM & \(\left[\text{Li}^{+}\right]_{\text{F}}\) = 200 mg\(\cdot\)L\({}^{-1}\) [Na\({}^{+}\)]\({}_{\text{F}}\) = 2000 mg\(\cdot\)L\({}^{-1}\) & 112.3 & 10.05 & This work \\ \hline \hline \end{tabular} \({}^{*}\)Counter-current electromigration (combined ED and NF processes).  
\end{table} 
Table 4: Comparison between the ED performances of LCM and other reported membranes. decrease of generated proton transfer. We therefore maintained this cell for the rest of our work. The effect of \([\text{Na}^{+}]_{\text{F}}/[\text{Li}^{+}]_{\text{F}}\) ratio in the feeding compartment on membrane selectivity was also tested at 0.5 mA\(\cdot\)cm\({}^{-2}\) for the current density. It was shown that, even at a relatively high concentration ratio, the membrane preserves its selectivity and separation performances towards Li\({}^{+}\). For very high ratio values, this selectivity and recovery rate of Li\({}^{+}\) decreases. For \([\text{Na}^{+}]_{\text{F}}/[\text{Li}^{+}]_{\text{F}}=10\) and after 4 h of ED operation, we successfully recovered 10% of Li\({}^{+}\) with a high selectivity coefficient around 112.