Development of an Integrated Electrolysis-Based Process for Separating Rubidium from Mixed Solutions

This paper introduces a novel and environmentally friendly electrolysis-based process integrating five-compartment bipolar membrane electrolysis coupled with electrodialysis (FBME-ED) and direct air stripping (DAS) to separate rubidium (Rb) from solutions produced by the treatment of saline lake brines. Electrolysis was applied to remove Mg2+ and detach monovalent cations, generating HCl instead of Cl2. The electrolysis process was optimized by tuning the configuration and operating parameters. FBME-ED performed better than three-compartment bipolar membrane electrolysis. The lowest energy consumption and highest Rb+ recovery rate were obtained under currents of I1 = 1 A and I2 = 0.5 A (I1/I2 = 2:1) and a flow rate of 113.2 mL/min. Decreasing the initial NH4Cl concentration improved the removal of Mg2+ but increased energy consumption. The optimized FBME-ED process achieved a maximum Rb+ recovery rate of 99.38% and an Mg2+ removal rate of 99.73%. DAS was implemented to eliminate NH4+, resulting in an NH4+ concentration of less than 0.01 mol/L (removal rate >90%). The final solid product was confirmed to be Mg(OH)2 by X-ray diffraction, laser granulometry, and scanning electron microscopy. The results demonstrate that the integrated electrolysis-based process is a promising approach for separating Rb+ from mixed solutions.