Electrochemical methods support the nitrogen circulation economy

Imagine a world where industrial waste has not only been reduced, but has been transformed into something useful. This kind of circular economy is already working for carbon. Now, researchers at Washington University in St. Louis have developed a promising route to convert harmful nitric oxide, a key component of acid rain, into valuable nitric acid.

Fen Ziao, Lauren and Lee Fikel are well-known professors at McKelbay School of Engineering in Wash, and collaborators have developed a method to convert nitric oxide (NO) emissions into high-purity concentrated nitric acid (HNO3).

The new process operates on almost ambient conditions with minimal infrastructure and provides an economically viable solution for industrial nitrogen waste with economic and environmental benefits. This work is featured in Nature Catalyst.

“We have developed an electrochemical approach to convert NO, a toxic waste gas, into valuable nitric acid,” Jiao said.

“Our main motivation is not to address waste gas from mining sites, which are used to dissolve metal ores using large quantities of nitric acid, leading to significant emissions. Our technology allows on-site conversion for immediate reuse, creating a more sustainable and cyclical process.”

An innovative electrochemical process uses low-cost carbon-based catalysts without oxidation. When combined with a single metal oxygen reduction catalyst developed by Gang Wu, an energy professor in environmental and chemical engineering at McKelvey Engineering, the process operates at low energy consumption and converts NO to HNO3 without the need for chemical additives or special purification steps.

The electrochemical oxidation system is designed to be “plug and play,” and Jiao was built on-site without major investment in expensive raw materials such as infrastructure and precious metals. It is flexible and customizable for small or medium-sized operations, and operates near room temperature, significantly reducing energy usage, cost and environmental impact, and reduces environmental impact compared to the most common treatment methods that require an increase in operating temperature.

This system achieves more than 90% Farada efficiency when using pure no. Even with low concentrations of NO, the system retains farada efficiency of over 70%, allowing it to adapt to a variety of industrial waste streams.

Without electrolyte additives or downstream purification, the direct synthesis of concentrated high purity HNO3 – 32% per weight.

Beyond mining, Jiao said this approach could have a wider range of industrial applications and strong commercial potential. This was demonstrated in a detailed techno-economic analysis that Jiao and his collaborators boast lower energy consumption and reduced costs compared to traditional HNO3 manufacturing methods.

Turning industrial pollutants into valuable chemicals is not only environmentally friendly, but also a good business, Jiao said.

“The nitric acid output from our system can be used directly in mining applications or other chemical processes,” Jiao said.

“We have already achieved very impressive efficiency and purity in our output. We are working to expand these numbers further in the future, while further improving them. We are looking at how this technology can be built into a nitrogen cycle economy that opens doors to more efficient and sustainable agriculture, manufacturing and many more.”