Industrial wastewater from electronics manufacturing, metal processing and other sectors often contains two difficult pollutants at once: high levels of salt and toxic heavy metals. Current treatment methods typically address those problems separately, creating costly, complex systems that can produce hazardous brines or metal-laden sludge. Now a group of researchers at Rice University and Vanderbilt University have created an electrochemical platform that could do both jobs at once.
A team led by Shihong Lin , associate professor of civil and environmental engineering at Rice, has shown that electrochemical ion pumping, or EIP, can be programmed to desalinate wastewater while selectively recovering dissolved metals such as copper. The approach, published in Nature Water , could offer a new path toward water reuse and resource recovery from industrial brines. Longqian Xu, a postdoctoral researcher at Rice, is the study's first author.
"Conventional desalination technologies such as reverse osmosis can remove salts, but they do not selectively separate valuable or toxic metal ions from background salts," said Lin, who is also part of the research team at the Rice WaTER Institute . "Meanwhile, chemical precipitation can remove metals, but it relies on added chemicals and often produces hazardous sludge."
The key innovation is using electrode potential as a programmable control parameter that determines whether a metal ion passes into the receiving stream or remains captured on the electrode. EIP works by moving ions from one water stream into another. It does this with special electrodes that act almost like temporary holding stations: They capture ions from the wastewater, then release them into a separate receiving stream.
The new study builds on three earlier advances by Lin and his collaborators: the initial demonstration of EIP and its theoretical framework , both published in Nature Water, and a ring-shaped EIP architecture for redox-free desalination published in Nature Chemical Engineering. The latest work extends the platform from desalination to simultaneous desalination and selective metal recovery.
"Conventional electrosorption systems typically require the feed and receiving solutions to be switched between adsorption and regeneration steps," Lin said. "Our method replaces that physical solution switching with rapid changes in the electrical circuit, allowing ions to move continuously in one direction through the system."
Because the system moves only small amounts of ions during each short cycle, the researchers maintain the electrode potential within a very narrow and stable range. That stability is important because it gives them more precise control over what happens at the electrode surface.
In one mode, the system removed both sodium and copper ions from the wastewater and moved them into the receiving stream. In this case, the system acted like a desalination process only, and copper did not build up on the electrode.
But when the researchers shifted the electrode potential below the point where copper begins to react, the system behaved differently. It still removed salt from the water, but it also selectively trapped copper on the electrode surface.
"In tests with synthetic wastewater containing sodium and copper, the system removed 90% of the salt while keeping nearly all of the copper on the electrode instead of sending it into the brine," Lin said.
The researchers also tested the system with a more complex mixture containing copper, nickel and sodium. Using a five-electrode EIP stack, they tuned the electrode voltage so that copper would be captured while nickel and sodium would continue moving through the system.
After four hours, the system removed 85% of the salt and more than 92% of both copper and nickel from the wastewater. But the metals ended up in different places: Nearly all of the copper stayed on the electrode, while almost all of the removed nickel moved into the receiving stream. The copper collected on the electrode was about 96% pure relative to nickel.
"Our results showed that EIP can be tuned to decide where different ions go during treatment," Lin said. "Some metals can be captured on the electrode, while salts and other ions can continue through the normal desalination pathway."
These results could make the technology especially useful for industrial wastewater, where companies often need to both reuse water and recover valuable metals. By keeping target metals out of mixed brine streams, the approach could reduce downstream purification and hazardous waste-management burdens and, after electrode regeneration, produce a metal-enriched recovery stream.
This research was supported by the National Science Foundation (CBET 2530333) and the Office of Naval Research (N000142612042).
