Electrochemical Desalination and Recovery of Lithium from Saline Water upon Operation of a Capacitive Deionization Cell Combined with a Redox Flow Battery

With the drastic growth in the demand for lithium, recovery technologies that remove Li ions from a brine solution are attracting more interest. In this field, capacitive deionization (CDI) has been suggested in various studies because it is energy efficient, economical, and environmentally friendly. These selective processes, however, have not been accompanied by desalination, which is a nonselective process by which salt ions are removed from the brine. In this work, a new-concept system has been designed for the simultaneous desalination and recovery of Li from the brine, in which the two different ion-exchange membranes separate the two electrochemically active spaces of desalination and lithium recovery. It is originally based on the combination of a redox flow battery (RFB) and CDI. The CDI cell has been sandwiched between two electrodes of a RFB, which has been operated and desalinates the brine simultaneously with the charging step of the RFB. In addition, an ion sieve (λ-MnO₂) has been utilized in the anolyte tank of the RFB cell, which selectively captures the lithium ions during desalination in CDI and charging in RFB. This combined system has been operated successfully with good desalination performances along with high selectivity in lithium-ion capture.