Electrifying heavy metal ion recovery and reuse from wastewater

The ever-increasing demand for metals across various industries has resulted in fast-track, large-scale mining and processing operations that create substantial volumes of wastewater. Left untreated, this wastewater rich in highly acidic and toxic heavy metals poses risks to humans, aquatic life and the environment.

“In addition to reducing costs and environmental footprint, the method enables continuous operation and long-term sustainability.”

^{Fawzi Banat}

Traditional techniques developed to prevent the release of heavy metals into the environment include chemical precipitation, ion exchange and membrane filtration. However, these techniques are costly, offer limited recovery efficiency and can generate secondary contaminants.

Now, a team led by Fawzi Banat and Mohammad Abu Haija from Khalifa University has devised a capacitive deionization method to selectively and effectively remove metal ions, such as copper and iron, from wastewater using electrically charged electrodes. Negatively charged cathodes made of a highly porous activated carbon derived from date seeds attract and immobilize the positively charged metal ions on their surface, once a voltage is applied.

Using a thermochemical treatment, the researchers went on to find ways to reuse the recovered metal ions. They transformed them into metal oxide using a thermochemical treatment, and turned the activated carbon support into carbon fibers, creating a photoactive electrode to convert ambient carbon dioxide into value-added chemicals, such as formic acid. 

“The process is energy-efficient and allows electrode regeneration,” Banat says. “Utilizing date-seed-derived activated carbon, an eco-friendly material obtained from agricultural waste, aligns with circular economy principles. In addition to reducing costs and environmental footprint, the method enables continuous operation and long-term sustainability, offering a solution for mining industries looking to improve waste management practices and maximize resource recovery efficiency.”

“Utilizing date-seed-derived activated carbon, an eco-friendly material obtained from agricultural waste, aligns with circular economy principles.”

^{Fawzi Banat}

To improve performance, the researchers modified the cathode surface using polyaniline, generating a composite with multiple functional groups that readily bind metal ions. This enhances the catalytic activity, number of adsorptive sites and electrochemical properties of the cathode. The composite removed much of the metal ions from model mining wastewater solutions, outperforming its unmodified precursor. It also effectively trapped mixtures of metal ions from more complex mining and industrial wastewater.

The team plans to scale up the technology to validate its real-life effectiveness and explore advanced regeneration methods, Banat says. Further work will investigate the catalytic potential of the recovered metal oxides in converting CO₂ into valuable chemicals further to support sustainability and resource recovery efforts.

Reference:

Bharath, G., Hai, A., Rambabu, K., Abu Haija, M. & Banat, F. Sustainable electrochemical process for recovery of metal ions in synthetic mining wastewater and their utilization in photocathodic CO₂ reduction into formic acid. Resources, Conservation & Recycling 190, 106778 (2023). | Article