Researchers are exploring the use of the Earth’s natural heat and geological forces to produce ammonia for fertilizer, instead of depending on energy-intensive reactors that require high temperatures and pressures. In a groundbreaking study featured in the Cell Press journal Joule on January 21, scientists successfully produced ammonia by combining nitrogen-rich water with iron-based rocks—without consuming any energy or emitting CO2. This innovative approach could pave the way for a more environmentally friendly alternative to conventional methods, potentially generating enough ammonia for 2.42 million years.
Researchers are exploring the use of the Earth’s natural heat and geological forces to produce ammonia for fertilizer, rather than relying on energy-intensive reactors that require high temperatures and pressures. In a groundbreaking study featured in the Cell Press journal Joule on January 21, scientists successfully produced ammonia by combining nitrogen-rich water with iron-based rocks—without consuming any energy or emitting CO2. This innovative approach could pave the way for a more environmentally friendly alternative to conventional methods, potentially generating enough ammonia for 2.42 million years.
This concept originated from a unique geological occurrence seen in the 1980s in Mali, West Africa, where locals discovered a well that emitted hydrogen gas. Scientists traced this phenomenon back to a chemical reaction between water and rocks happening below the Earth’s surface.
“It was an ‘aha’ moment,” explains senior researcher Iwnetim Abate from the Massachusetts Institute of Technology (MIT). “We could potentially use the Earth as a factory, utilizing its heat and pressure to create valuable chemicals like ammonia in a cleaner way.”
Ammonia plays a vital role in fertilizers and has the potential to become a clean fuel source in the future. However, current methods of ammonia production in industry are energy-heavy, consuming about 2% of the world’s energy and producing approximately 2.4 tons (5,291 pounds) of CO2 for every ton (2,204 pounds) of ammonia created, making it the largest CO2 emitter in the chemical sector.
To examine their “Earth factory” concept, Abate and his team developed a rock-water reaction system that simulates the conditions found beneath the Earth. They exposed artificial iron-rich minerals to nitrogen-infused water, initiating a chemical reaction that oxidized the rocks and generated ammonia—termed “geological ammonia” by the team. This process required no energy input, produced no CO2, and functioned effectively under normal conditions.
The team then substituted the synthetic mineral with olivine, a naturally occurring iron-rich rock, to better reflect real-world applications. They refined the process further by introducing a copper catalyst and increasing the temperature to 300°C (572°F). Within 21 hours, they obtained about 1.8 kg (4 lb) of ammonia for each ton (2,204.6 lb) of olivine used, demonstrating both the feasibility and sustainability of this method.
“These types of rocks are widespread across the globe, so this technique could be adapted in many locations,” Abate notes. However, he acknowledges that “there’s an additional layer of complexity that we will need to navigate.” This implementation will involve drilling into iron-rich rocks deep underground, injecting nitrogen-infused water, and managing the complexities of how the rocks fracture, expand, and interact with gases and liquids.
The economic prospects for this idea are promising. The cost to produce geological ammonia is approximately $0.55 per kilogram (2.2 lb), which is comparable to traditional methods that range from $0.40 to $0.80. This research may also offer fresh strategies to tackle wastewater pollution.
“Nitrogen sources are often seen as pollutants in wastewater, and getting rid of them costs both money and energy,” states Yifan Gao, the first author of the study from MIT. “However, we may be able to transform that wastewater into ammonia, creating a win-win situation.” Combining wastewater treatment with ammonia production could produce an additional profit of $3.82 per kilogram of ammonia.
“Ammonia is crucial for life,” emphasizes senior author Ju Li, also from MIT. Aside from microbial processes, the only other natural method for ammonia production on Earth occurs through lightning striking nitrogen gas. “This makes geological ammonia production particularly fascinating when we consider the origins of life.”
This research received funding support from the National Science Foundation.
