High-value conversion of Na2SO4 wastewater by a continuous electrodialytic metathesis process: Effects of coexisting ions

Process for Producing Lithium Iodide Cleanly through Electrodialysis Metathesis

Lithium iodide is commonly used in the production of batteries and drugs. Currently, the neutralization method is the primary means of producing lithium iodide. This method involves using hydriodic acid as a raw material, adding lithium carbonate or lithium hydroxide, and obtaining lithium iodide through evaporation and concentration. However, hydriodic acid is chemically unstable. Its preparation can lead to explosive accidents and encountering high temperatures generates toxic iodine vapors. These limitations restrict its industrial production. The study evaluates the impact of membrane stack configuration, operating voltage, and initial concentrations and volume ratios of reactants on the production process. Electrodialysis metathesis, characterized by a simpler process flow, lower energy consumption, and environmental benefits, emerges as an effective technique for electrically driven membrane separation in lithium salt production and purification. Under the specific conditions of a C-C-A-C-A-C membrane stack configuration, operating voltage at 25 V, initial potassium iodide concentration at 0.4 mol/L, initial lithium sulfate concentration at 0.2 mol/L, and a 1:1 volume ratio of product liquid to raw material liquid, the method achieves a lithium iodide purity of 98.9% with a production cost of approximately 0.502 $/kg LiI.

Highly Ion-Permselective Porous Organic Cage Membranes with Hierarchical Channels

Membranes of high ion permselectivity are significant for the separation of ion species at the subnanometer scale. Here, we report porous organic cage (i.e., CC3) membranes with hierarchical channels including discrete internal cavities and cage-aligned external cavities connected by subnanometer-sized windows. The windows of CC3 sieve monovalent ions from divalent ones and the dual nanometer-sized cavities provide pathways for fast ion transport with a flux of 1.0 mol m^-2 h^-1 and a mono-/divalent ion selectivity (e.g., K⁺/Mg²⁺) up to 10³, several orders of magnitude higher than the permselectivities of reported membranes. Molecular dynamics simulations illustrate the ion transport trajectory from the external to internal cavity via the CC3 window, where ions migrate in diverse hydration states following the energy barrier sequence of K⁺ < Na⁺ < Li⁺ ≪ Mg²⁺. This work sheds light on ion transport properties in porous organic cage channels of discrete frameworks and offers guidelines for developing membranes with hierarchical channels for efficient ion separation.