Highly Selective Electrochemical Separations of Metals

The selective separation of metals from aqueous solutions is a critical challenge for many problems in energy, health and sustainability. This talk will describe two classes of highly selective separation methods for metal ions, based on differences in either electrokinetic or electrochemical properties. The first involves the propagation of deionization shock waves through charged porous media. Shock electrodialysis can separate trace amounts of toxic lead from drinking water or radionuclides from nuclear wastewater with minimal energy consumption. Shock ion extraction integrates ion-exchange resins to amplify the separation of multivalent metal ions, such as cobalt, zinc, mercury, nickel and manganese. Further control of these separations is afforded by pH swings, which allow heavy metal cations to be separated by selectively forming oxyanions, as illustrated by chemical-free continuous separation of vanadium, molybdenum, tungsten, cobalt and nickel. The second method involves selective electrosorption of metal cations in capacitive electrodes. Functionalized nanoporous carbon electrodes can separate multivalent from monovalent cations with applications to transition metal recovery in Li-ion battery recycling. Intercalation electrodes can provide extreme chemical selectivity for lithium with applications to extraction from lithium brines and battery recycling leachates, eliminating the need for harsh reagents in traditional hydrometallurgical processes.