Quartz Sand-Mediated Ion-Directed Electromigration for High-Salt Wastewater Recycling in Preparative Vertical Free-Flow Electrophoresis.

Electrochemical methods are promising for treating high-salt wastewater. However, their reliance on expensive membranes increases operational costs and introduces membrane-related challenges. To address this, our laboratory has developed a preparative vertical free-flow electrophoresis (PVFE) technique using cost-effective quartz sands instead of expensive membranes. This innovative technique has effectively produced acids and bases from industrial high-salt wastewater. However, a comprehensive understanding of the underlying mechanisms and mass transfer is essential to enhancing the design and performance of the developed PVFE. Herein, the effects of voltage, flow rate, and feed concentration on ion migration in PVFE were systematically examined, providing detailed insights into its driving mechanisms. Results revealed that quartz sand packing effectively suppresses ion diffusion while ensuring a proper ion orientation during electromigration and convection. Additionally, both simulation and empirical models validate the mass-transfer mechanisms and quantify the effect of key operational parameters on the ion transfer capacity. Economic analysis further highlights that PVFE operates within the limiting current, achieving ∼100% current efficiency at low operating costs (5.94 yuan/kg for base and 6.87 yuan/kg for acid). This study provides a comprehensive understanding of mass-transfer mechanisms in PVFE and offers valuable guidance for optimizing its practical application in high-salt wastewater recycling.