New ion-pumping system strips salt from industrial wastewater, and traps copper, too

Industrial wastewater from electronics manufacturing, metal processing, and other sectors can be especially difficult to treat because it often contains both high salt levels and toxic metals, and current methods usually handle those problems separately. 

Researchers led by Shihong Lin, associate professor of civil and environmental engineering at Rice University, say they may have found a way to address both in a single electrochemical system while recovering copper.

What's happening?

At Rice University, researchers created an electrochemical ion pumping platform that can remove salts from wastewater and selectively separate dissolved metals, including copper, as spotlighted in Tech Xplore.

The study appeared in Nature Water, with Rice University postdoctoral researcher Longqian Xu as first author, and presents the method as a possible new option for treating salty industrial wastewater.

The platform is guided by electrode potential, which can be adjusted to determine whether a metal moves into a receiving stream or stays on the electrode surface. That allows the same system to desalinate water and sort metals at the same time.

"Conventional desalination technologies such as reverse osmosis can remove salts, but they do not selectively separate valuable or toxic metal ions from background salts," Lin said. "Meanwhile, chemical precipitation can remove metals, but it relies on added chemicals and often produces hazardous sludge."

In experiments with synthetic wastewater containing sodium and copper, the device removed 90% of the salt and kept nearly all of the copper on the electrode. When the researchers moved to a more complicated mix of copper, nickel, and sodium, the system removed 85% of the salt and more than 92% of both metals.

Why does it matter?

That kind of dual-purpose treatment could be especially useful for industries such as electronics manufacturing and metal processing, which produce some of the hardest wastewater to manage.

Many companies currently depend on separate processes to deal with salts and heavy metals, which adds cost and can create extra waste streams such as hazardous brine or sludge containing metals.

A system that can clean water and recover metals in one step could help facilities reuse more water instead of continually drawing fresh supplies. That is becoming more important as drought and water stress keep putting pressure on communities and businesses alike.

There is also an economic upside. Copper and nickel are useful industrial materials, so keeping them out of mixed brine streams could make them easier to reclaim rather than discard.

From a public health and environmental standpoint, better control of heavy metals in wastewater can lower the risk of those contaminants ending up in waterways or soils, where they can harm ecosystems and create cleanup problems.

What's being done?

The researchers based this latest system on earlier ion-pumping work, including prior demonstrations of the technology and a ring-shaped design for redox-free desalination.

With this study, the team moved beyond basic salt removal and into simultaneous treatment paired with targeted recovery. Instead of physically exchanging solutions between adsorption and regeneration steps, the system keeps ions moving in one direction by rapidly changing the electrical circuit.

"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," Lin said.

That operating approach keeps the electrode potential tightly controlled within a narrow, stable range, which is what enables selective recovery.

Using a five-electrode version of the platform, the researchers found that almost all of the copper stayed on the electrode while nearly all of the removed nickel entered the receiving stream, producing copper that was about 96% pure relative to nickel.

If the technology can be scaled up, it could give manufacturers a new tool to cut treatment costs, reduce hazardous waste burdens, recover valuable materials, and produce water better suited for reuse.

"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."

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