A new battery system removes toxic metals from wastewater and generates electricity in the process, offering a low-cost, power-positive alternative to conventional treatment.
(Nanowerk Spotlight) Industrial pollution has deposited toxic metals into water systems, creating an environmental challenge that resists simple solutions. These contaminants—manganese, cobalt, nickel, zinc, chromium, and lead—do not degrade and instead accumulate in organisms, becoming more concentrated and harmful as they move through the food chain.
Engineers have explored many ways to extract these metals, but each has drawbacks. Activated carbon adsorbers saturate quickly. Chemical precipitation yields sludge requiring costly disposal. Membrane filters clog easily. Electrochemical removal, while effective, typically consumes significant power—often 5 volts for hours—to extract ions. These demands undermine sustainability by trading one environmental cost for another.
The conceptual link between battery chemistry and wastewater treatment has been largely overlooked, even though both involve ion transport. Traditional batteries store energy through ion movement between electrodes; metal removal similarly requires selective ion capture. The difficulty has been designing a system that performs purification without needing external power.
The battery uses a two-chamber design separated by an anion-selective membrane. In one chamber, contaminated water flows past an electrode containing copper hexacyanoferrate (CuHCF), a porous material with a crystal lattice large enough to accommodate hydrated metal ions. The opposing chamber contains a metal electrode (zinc, iron, or copper). When connected, the inherent voltage difference between the two drives heavy-metal ions into the CuHCF framework, releasing electric current in the process.
Instead of using electricity to extract metals, the system produces it during cleanup.
Schematic illustration: a) Various electrochemical technique for heavy-metal ion removal from wastewater. b) Application outlook of the heavy-metal removal battery. c) Heavy-metal ion adsorption and electrode recycling mechanisms of the heavy-metal removal battery. (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
Tests showed consistent performance across multiple contaminants. The system removed over 96% of manganese, cobalt, nickel, and zinc ions from mixed-metal solutions. When processing water with 100 ppm zinc—a common industrial pollutant—the battery reduced levels below 2 ppm, surpassing environmental discharge standards.
The adsorption capacity reached 61 milligrams of zinc per gram of CuHCF, outperforming activated carbon (typically under 36 mg/g). Adsorption completed in under 4 minutes at higher flow rates, with performance holding even at zinc concentrations as low as 5 ppm. Importantly, the technology maintained efficacy even in the presence of competing ions like sodium—common in wastewater—though zinc uptake was somewhat reduced to 38.25 mg/g in that case. Only in highly acidic water (pH ~1) did adsorption efficiency decline significantly.
Beyond removal, the system resolves the long-standing problem of electrode regeneration. Traditional methods either consume additional energy to recharge or create toxic byproducts. In contrast, the researchers developed a rapid, energy-free method using hydrogen peroxide to oxidize the CuHCF and release the trapped metals. This not only restores the electrodes but converts the extracted metals into usable salts.
In one test, zinc was recovered as Zn₄SO₄(OH)₆·4H₂O by adding sodium hydroxide to the desorption solution. Sodium sulfate, a benign industrial salt, was also recovered after further processing. The electrodes retained over 80% of their original capacity after 25 cycles, suggesting long-term durability.
During operation, the batteries delivered approximately 50 milliampere-hours per gram of electrode material. Output varied with the metal used in the counter electrode: zinc produced the highest voltage (1.42 V) and energy density (71.9 Wh/kg CuHCF). Though not comparable to commercial batteries, the energy output exceeds that of traditional metal-removal systems, which consume electricity rather than generate it.
The system scales well. The researchers connected nine battery units in series to power LEDs with 14 volts. This configuration processed 3.8 liters of contaminated water per hour—suitable for industrial application. A redox-flow configuration could further extend capacity for continuous, high-volume treatment.
Economic analysis favors the design. When accounting for regeneration and electricity generation, the effective cost of metal removal is just $0.024 per gram—less than half that of commercial activated carbon. The recovery of valuable salts instead of toxic sludge improves the financial and environmental profile.
This technology addresses multiple problems at once. It removes a range of persistent metal pollutants without external power, generates electricity, avoids hazardous waste, and yields reusable materials. It reframes wastewater treatment as not just a necessity, but a potential asset.
Ongoing development may enable selective removal of specific metals and improved energy output. But as it stands, heavy-metal removal batteries offer a promising tool for industries confronting tighter regulations, rising energy costs, and the demand for closed-loop systems that minimize waste and maximize value.
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
