Converting softening nanofiltration brine into high-solubility liquid salts (HSLS) via electrodialysis metathesis: Effect of membrane type

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.

Developing a reclamation strategy for softening nanofiltration brine: A scaling-free conversion approach via continuous two-stage electrodialysis metathesis

A significant amount of concentrated, scaling-prone brine can be generated during the conversion of unconventional water resources to freshwater, thus necessitating the zero discharge of concentrated brine to meet environmental and resource requirements. In this study, a two-stage feed-and-bleed electrodialysis metathesis (FB-EDM) process was implemented to reclaim softening nanofiltration (SNF) brine. To determine the optimized process parameters, experiments were conducted with various initial diluate to concentrate volume ratios (V_D:V_C), applied voltages, replenishment flow rates (Q_rp), and initial diluate compartment concentration ratios (C_D1:C_D2). The results indicated that these parameters (except for the initial volume ratio) significantly influenced the FB-EDM process. The optimized conditions included a V_D:V_C of 2:1, voltage of 1.5 V per repeating unit, Q_rp of 4 L/h, and C_D1:C_D2 of 1.5:1. The two-stage FB-EDM process operating under the optimized conditions achieved an energy consumption of <0.9 kWh/kg salt, and the total dissolved solids (TDS) in terms of Cl-type and Na-type salts reached 199.1 and 224.4 g/L, respectively; the corresponding overflow rates were 1.17 and 1.14 L/h, respectively. The developed system thus demonstrated approximately 85% TDS removal and ionic conversion of the brine; additionally, the self-crystallization of CaSO₄·2H₂O was realized by blending the Cl-type and Na-type salts. This process therefore represents a suitable method for converting SNF brine into highly-concentrated liquid salts, and provides a reclamation strategy for miscellaneous salts.

Sustainable disposal of seawater brine by novel hybrid electrodialysis system: Fine utilization of mixed salts

Sustainable seawater brine treatment demands an essential paradigm shift for effective recovery of resources and high value utilization of mixed-salts. Here, a novel hybrid electrodialysis (ED) system was proposed that integrated an innovative hybrid selective ED (HSED) and a developed selective bipolar membrane ED (SBMED). The HSED process allowed simultaneous recovery of major divalent cations and anions from seawater brine when NaCl was selectively enriched. Then, the impure NaCl-rich stream was fed directly into the SBMED process for acid/base preparation without any purification pretreatment. Detailed analysis of the HSED process showed that increasing unit voltage from 2.33 V to 2.67 V would improve the removal ratio of Ca²⁺, Mg²⁺ and SO₄^2- from 54.7%, 41.4% and 13.3% to 78.9%, 76.6% and 32.1%, respectively. In addition, the increment of initial concentration of product streams promoted the transport of various ions from the feed and middle compartments. The fine utilization performance, in terms of ionic removal ratio and fractionation ratio of divalent ions in the HSED process, was more limited by the initial concentration of product streams. Furthermore, the SBMED stack was found to have nearly identical performance over five cycles, indicating that the presence of a trace amount of hardness cations did not induce scaling. The current study thus provided a novel suitable strategy with a perspective of fine utilization for practical applications in sustainable disposal of seawater brine.