MIT scientists have developed a new method to cut emissions from ammonia production, a key component of fertilizers. This innovative approach relies on the high temperatures and pressure found deep within Earth, and has the potential to be much more sustainable than any other ammonia production methods used today.

“Our work establishes a foundation for utilizing Earth’s subsurface as a natural reactor, leveraging abundant rocks, heat, and pressure as resources […] with minimal environmental impact,” stated the researchers in their study.

Industrial ammonia production amounts to about 2% of the world’s total energy consumption, with most of this energy being generated using fossil fuels. This makes it the top carbon emitter of the chemical industry, releasing twice and four times more carbon dioxide into the atmosphere every year than steel and cement production, respectively.

As the global population keeps growing, the demand for more fertilizers and therefore ammonia will only increase — and with it the need for sustainable alternatives.

The new method could completely slash these numbers by taking the whole process underground, potentially requiring no energy input and producing minimal carbon emissions while being cost-competitive with traditional ammonia synthesis. 

An underground alternative

The most common way of making ammonia relies on hydrogen, which is produced using coal or natural gas. It is estimated that hydrogen production is responsible for up to 80% of the carbon emissions of industrial ammonia production.

In efforts to make the process more sustainable, scientists have developed alternative approaches to hydrogen production using electrochemical reactions. However, this approach demands enormous energy. Even if fully powered by renewables, meeting global ammonia production needs would require all current renewable energy — plus the environmental costs of manufacturing vast new wind turbines and solar panels.

Iwnetim Abate and his colleagues at MIT were inspired to develop a geological phenomenon that was reported in Mali, West Africa back in the 1980s, where a chemical reaction between rocks and water caused a local well to stream with hydrogen gas.

“It was an ‘aha’ moment,” stated Abate in a press release. “We may be able to use Earth as a factory, harnessing its heat and pressure to produce valuable chemicals like ammonia in a cleaner manner.”

Their method consists of exposing minerals rich in iron that are naturally found under the Earth’s surface to water laced with nitrogen. The high temperature and pressure in this environment can trigger a reaction between the iron in the rocks and the water that produces hydrogen, which then reacts with the nitrogen to form ammonia.

To prove the feasibility of this approach, the researchers simulated the underground conditions of temperature and pressure in the lab. The process was successful at producing ammonia both when using a synthetic mineral and when using olivine, an iron-containing rock found within Earth. In their laboratory setting, they were able to produce 1.8 kg of ammonia per ton of olivine.

“These rocks are all over the world, so the method could be adapted very widely across the globe,” said Abate.

Implementing this process at scale will require drilling into olivine rocks and injecting water into them. If successful, the scientists estimate this method could produce 40,000 tones of ammonia in a single olivine well.

While the drilling of wells and the purification of the resulting ammonia would still result in carbon emissions, the reaction itself requires no external energy input and generates no emissions. The scientists estimate this would still result in carbon emissions 30 times lower than those of conventional ammonia production, but a full assessment will be required to better understand the environmental impact of their approach.

Industrial scale-up

The team have been the first to show that it is possible to produce ammonia using their underground approach. However, experiments have only been completed in a lab up to this point, and more work will be needed to prove whether it works as predicted in the actual conditions found deep under the Earth’s surface.

The researchers plan to run a pilot scale test several kilometers underground by 2026. If successful, they anticipate it may eventually be possible to use wastewater as a source of nitrogen-rich water, since it is common for industrial wastewater and agricultural runoff to contain high levels of nitrogen. This would allow integrating wastewater treatment and ammonia production into a single process.

“Nitrogen sources are considered pollution in wastewater, and removing them costs money and energy,” said Yifan Gao, first author of the study. “But we may be able to use the wastewater to produce ammonia. It’s a win-win strategy.”

A key advantage to producing ammonia underground is that it has potential to be cost-competitive with conventional ammonia production. The researchers estimate that their approach would result in a cost of about $0.55 per kilogram of ammonia, while conventional methods are typically priced between $0.4 and $0.8. Integrating wastewater treatment in the process could yield an additional profit of $3.82 USD per kilogram of ammonia.

Ultimately, implementation at scale will require scientists and engineers to deal with the complexities of how rocks crack, expand and interact with gases and liquids.

“Engineering designs to implement this work in the real world represent fertile ground for new concepts and methods at the intersection of the chemical, mining, and oil and gas industries,” said Abate.

“Understanding the complex interface between rocks and reacting fluid is a rich area to explore, achieved by combining advanced computational and experimental methods to push our knowledge in this field.”

Reference: Yifan Gao et al., Geological ammonia: Stimulated NH3 production from rocks, Joule (2025). DOI: 10.1016/j.joule.2024.12.006