Dual-purpose membranes have been developed to desalinate and filter potable water while recovering valuable metals for reuse. The adsorptive membranes engineered by researchers from the University of California Berkeley, the U.S. Lawrence Berkeley National Laboratory and the U.S. Sandia National Laboratories were demonstrated in a one-step ion-capture electrodialysis strategy.

Porous aromatic framework nanoparticles that target specific metal ions are embedded in flexible polymer Polymer membranes with embedded nanoparticles that selectively remove ionic compounds (top) are employed in electrodialysis (bottom) to remove not only salt but also metals, producing clean water and a non-toxic brine that is easier to dispose of. The membranes (green and red) can be flushed and reused many times, while valuable metals could potentially be salvaged. Source: Adam Uliana/ University of California Berkeleymembranes. The membrane can incorporate a single type of tuned nanoparticle if the metal is to be recovered. Several different types, each tuned to absorb a different metal or ionic compound, can be deployed if multiple contaminants need to be removed in one step. Salts are removed with a series of cation and anion exchange membranes in a process that allows for the simultaneous desalination and decontamination of water.

With the inclusion of thiols to capture mercury, a kilogram of the polymer membrane could strip essentially all of this toxin from 35,000 liters of water containing 5 ppm of the metal without the need for membrane regeneration. The treatment proved effective when tested with highly saline groundwater and industrial wastewater.