Ion-selective separation by shock electrodialysis

A method for ion-selective separation by shock electrodialysis utilizing a system that includes at least one liquid conduit with at least one inlet port, at least one outlet port for a dilute stream, and at least one outlet port for a concentrated stream, wherein the system also includes a first electrode and a second-electrode-and-ion-selective-boundary configuration selected from (a) a second electrode and at least one distinct ion-selective boundary and (b) a second electrode that also serves as an ion-selective boundary, wherein the at least one distinct ion-selective boundary or the second electrode has a charge and is contained in the at least one liquid conduit adjacent to a porous medium or that functions as the porous medium, wherein the porous medium defines pore channels that are filled with a liquid including a plurality of species having a charge of the same sign, wherein the pore channels have a surface charge, and wherein the charge of the ion-selective boundary and surface charge of the pore channels share a sign, the method comprising:

• flowing the liquid into the inlet port and through the pore channels, forming a thin diffuse electrochemical double layer at an interface of the liquid and the charged surface of the pore channels in the porous medium with a liquid bulk volume beyond the double layer in the pore channels;
• applying a voltage differential between the electrodes across the porous medium, wherein the voltage differential has a magnitude set to selectively draw a first of the species in the liquid toward at least one of the electrodes to a greater extent than an extent to which a second of the species is drawn toward the same electrode, wherein the species are dissolved ion species, and wherein the first species has a higher valence than the second species;
• via the application of the voltage differential, producing current at the electrodes by either Faradaic reactions or by capacitive charging and discharging and creating a shock in the charged-species concentration in the bulk volume of the liquid within the pore channels, wherein the concentration of the first species in a depleted zone of the liquid bulk volume between the shock and the ion-selective boundary is substantially lower than the concentration of the second species in the liquid bulk volume between the shock and the first electrode, and wherein electric current flows primarily through the double layers or micropores in the region between the shock and the ion-selective boundary, while electric current flows primarily through the liquid bulk volume in the region between the shock and the first electrode;
• extracting the dilute stream from the depleted zone of the bulk volume in the porous medium by flow to the at least one outlet port for the dilute stream between the shock and the ion-selective boundary;
• and
• flowing the first species in the concentrated stream on an opposite side of the shock from the depleted zone, wherein the at least one outlet port for the concentrated stream is separated across the porous medium from the at least one outlet port for the dilute stream by the shock and not by a membrane.