Effects of chloride ions present in brines on lithium recovery by electrodialysis

Field: Chemical Engineering (Physical Sciences)

Introduction Demand for lithium is increasing with the spread of electric vehicles. Lithium supplies primarily come from salt lakes and mines. The solar evaporation method is a method used for collecting from salt lakes. Although this method is low cost, it requires a long construction period and cannot be applied to salt lakes that contain high concentrations of SO 4 2- . Extracting from mines has the problem of short construction times but high costs. There is a need to develop candidate technologies that can solve these problems. Electrodialysis is one of the candidate technologies, and because it can obtain high-purity lithium, it is also expected to be a technology that can comply with European battery regulations (1). We solved the problem of electrodialysis method, which is the slow sampling speed, by developing a unique electrodialysis cell structure that increased the speed by more than three orders of magnitude. However, there are concerns that the collection speed will slow down due to the effects of elements other than lithium in the brine. The research results that I have already reported show that the coexistence of the typical ions Na + and K + , which exist in brine water, has no effect on the rate of lithium transfer (2). In this study, we will clarify the effect of the presence of Cl - , a typical anion found in salt lakes, on the lithium transfer rate. Previous research has shown that the pH of the primary solution, which is the solution from which lithium is recovered, affects the lithium transfer rate, so in this study, experiments were conducted under conditions where the pH was fixed (3). Experimental method The cell used in the experiment used a lithium-ion conductive solid electrolyte La 0.57 Li 0.29 TiO 3 (LLTO) for the diaphragm. By screen printing and baking Pt paste, grid-like Pt electrodes with lines/spaces = 0.5 mm/0.5 mm were formed on the front and back sides of LLTO. Since the chemical potential difference affects the Li + transfer rate, the primary solution was a mixture of lithium hydroxide and lithium chloride so that the Li + concentration was 0.1 mol/L. Sodium hydroxide solution was added to the primary solution to fix the pH. A 0.1 mol/L lithium hydroxide solution was used as the secondary solution that stores the recovered lithium. When a constant voltage of 2.0 V was applied, the current value and bipolar and triode AC impedance were measured. The current measurement was carried out for about 20 hours, during which time the AC impedance was measured every 5 hours. The volume of the primary solution was set to 1 L, which was sufficiently large to avoid a shortage of lithium supply, and the solution was circulated between the subtank and the cell tank using a liquid feed pump. The secondary solution volume was 130 mL. The concentrations of Li + and Na + in the solution after electrodialysis were analyzed using high-frequency inductively coupled plasma optical emission spectroscopy (ICP-OES). The Cl - concentration of the solution after electrodialysis was analyzed by ion chromatography (IC). Results and discussion Fig. 1 is a graph showing the dependence of Li + transfer rate on Cl - concentration. As the Cl - concentration increased, the Li + transfer rate decreased. In ICP-OES, movement with Na+ was not confirmed, but movement of Li + was confirmed. No movement of Cl - could be confirmed by IC. The ICP-OES and IC results confirmed that electrodialysis is a promising lithium extraction and recovery technology. Therefore, within the range of the experimental conditions this time, it is thought that increasing the Cl - concentration has the effect of decreasing the Li + transfer rate. References (1)Regulation (EU) 2023/1542. Official Journal of the European Union, L 191/1EN (2023/7/28) (2)Kitada, Effect of typical ions present in salt lakes on electrodialysis lithium collection rate(3B02), The Ceramic Society of Japan, 2023/3/14-16 (3)National Institutes for Quantum Science and Technology (https://www.qst.go.jp/site/press/20210616.html) Figure 1