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Membranes 2022, 12, 343 11 of 27 The application of the external electric field during ED promotes the migration and depletion of ions from the feed side across the membrane stack. The enrichment of ions across the membranes and on the permeate side results in a strong polarization. This mechanism, which creates electro-convection at the membrane surface but also water stripping, may lead to changes in ion selectivity. Such limiting considerations in designing Li-ion-selective membranes are created due to the high diffusivity and response rate in Li to variations in current densities (Figure 3d) [72]. 3.1.2. Li extraction Case Studies with ED Lithium extraction from brines by ED has been demonstrated from model solutions, industrial wastewaters, and natural lake waters. The impact of the Mg2+/Li+ ratio, feed temperature (15 to 30 ◦C), feed flow rate, solution residence time, and current densities across the membrane stack (5.9–13.8 A/m2) were systematically investigated. The spe- ciation between Li+ and Mg2+ was achieved at high Mg2+/Li+ ratios. The Mg/Li mass ratio decreased as high as 21.8 times for the mixture with initial mass ratio of a Mg/Li of 400 [79]. In this research the commercial ion exchange membranes Asahi Glass Selemion CSO and ASA were applied. The influence of cations other than lithium ones affected the separation efficiency at different concentrations of Na+, Mg2+, and sulfates. The specific transfer mechanism of lithium could be related to the presence of sulfate ions. The mass transfer through the ion-exchange membrane of each ion species was determined by its dominant existing form [80]. The influence of the presence of coexisting species on the speciation of Li ions across cation exchange membranes was studied. Neosepta CIMS membranes were used for selective extraction of Li ions in mixed liquors containing other ions. The results showed sequences of coexisting cations, in the series K+ > Na+ > Ca2+ > Mg2+, directly affected separation behaviors of lithium. Interestingly, the higher the concentration of the mixed competing monovalent cations, the lower the selectivity for Li-ion was reported. The presence of sulfate and carbonate anions promoted Li over Mg fractionation. Furthermore, the presence of the coexisting anions affected the migration of Mg2+ [4]. The extraction of Li+ ions from lithium bromide solutions contaminated with Na+ ions was demonstrated for industrial liquors where lithium bromide is used as a working liquid within absorption chillers [81]. Although the feed solution contained ~13 g/L of Li ions and 1.35 g/L of Na ions, concentration factors of 88 were achieved for Li/Na. The ratio for fresh and unpolluted lithium bromide solution was 58 [81]. The separation of Mg2+ from Li+ ions was evaluated in terms of separation efficiency and economic benefit, with monovalent ion-exchange membranes. At an optimal applied ED cell voltage of 5 V and a pH range of 4–5, the Li-ions recovery reached 75.44% [82]. The modification of commercial membranes to improve lithium transport with ionic liquids (N,N,N-trimethyl-N-propylammonium– bis(trifluoromethanesulfonyl) imide (TMPA–TFSI) the Selemion CMV) was evaluated [83]. The application of selective cation exchange membranes was also evaluated. The electro- dialysis voltage was 2–3 V, and the process was run for up to 15 h. After this time, 63% of the lithium was separated from the Li, Na, Mg, and K ions mixture [84]. Spent battery effluents were treated by ED to support Li-ions extraction [85]. The solution was first purified and lithium precipitated with phosphate to obtain Li3PO4. The selective separation of lithium over phosphor was achieved [85]. Li-ion recovery from spent battery effluents containing Co ions was performed with multi-stage metal-ion chelation and the ED process. Ethylenediaminetetraacetic acid (EDTA) was added to cause the selective chelation of Co ions and to increase the concentration of Li ions in the permeate stream [86]. Lithium and cobalt separations with monovalent selective ion exchange membranes such as PC-MVK were demonstrated. The value of the applied potential did not influence significantly the separation efficiency: the rise in voltage from 5 V to 15 V turned the separation factor from 98.6 to 99.4% [87]. The cobalt ion concentration in the feed solution affected the selectivity of the monovalent ion exchange membrane. Some reports on the use of electrodialysis for lithium recovery are summarized in Table 7.PDF Image | Electro-Driven Materials and Processes for Lithium
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Product and Development Focus for Infinity Turbine
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