Ammonia fertilizer may very well be produced underground, utilizing Earth’s pure warmth to considerably cut back the trade’s carbon footprint.
MIT scientists have developed a brand new technique to chop emissions from ammonia manufacturing, a key element of fertilizers. This modern method depends on the excessive temperatures and stress discovered deep inside Earth, and has the potential to be far more sustainable than another ammonia manufacturing strategies used in the present day.
“Our work establishes a basis for using Earth’s subsurface as a pure reactor, leveraging plentiful rocks, warmth, and stress as sources […] with minimal environmental affect,” acknowledged the researchers of their study.
Industrial ammonia manufacturing quantities to about 2% of the world’s complete vitality consumption, with most of this vitality being generated utilizing fossil fuels. This makes it the top carbon emitter of the chemical trade, releasing twice and 4 occasions extra carbon dioxide into the ambiance yearly than metal and cement manufacturing, respectively.
As the worldwide inhabitants retains rising, the demand for extra fertilizers and due to this fact ammonia will solely enhance — and with it the necessity for sustainable alternate options.
The brand new technique might fully slash these numbers by taking the entire course of underground, doubtlessly requiring no vitality enter and producing minimal carbon emissions whereas being cost-competitive with conventional ammonia synthesis.
An underground different
The most typical approach of constructing ammonia depends on hydrogen, which is produced utilizing coal or pure gasoline. It’s estimated that hydrogen manufacturing is answerable for as much as 80% of the carbon emissions of commercial ammonia manufacturing.
In efforts to make the method extra sustainable, scientists have developed different approaches to hydrogen manufacturing utilizing electrochemical reactions. Nevertheless, this method calls for monumental vitality. Even when totally powered by renewables, assembly world ammonia manufacturing wants would require all present renewable vitality — plus the environmental prices of producing huge new wind generators and photo voltaic panels.
Iwnetim Abate and his colleagues at MIT had been impressed to develop a geological phenomenon that was reported in Mali, West Africa again within the Eighties, the place a chemical response between rocks and water prompted a neighborhood properly to stream with hydrogen gasoline.
“It was an ‘aha’ second,” acknowledged Abate in a press release. “We might be able to use Earth as a manufacturing unit, harnessing its warmth and stress to supply useful chemical substances like ammonia in a cleaner method.”
Their technique consists of exposing minerals wealthy in iron which might be naturally discovered beneath the Earth’s floor to water laced with nitrogen. The excessive temperature and stress on this surroundings can set off a response between the iron within the rocks and the water that produces hydrogen, which then reacts with the nitrogen to type ammonia.
To show the feasibility of this method, the researchers simulated the underground situations of temperature and stress within the lab. The method was profitable at producing ammonia each when utilizing an artificial mineral and when utilizing olivine, an iron-containing rock discovered inside Earth. Of their laboratory setting, they had been in a position to produce 1.8 kg of ammonia per ton of olivine.
“These rocks are everywhere in the world, so the strategy may very well be tailored very broadly throughout the globe,” stated Abate.
Implementing this course of at scale would require drilling into olivine rocks and injecting water into them. If profitable, the scientists estimate this technique might produce 40,000 tones of ammonia in a single olivine properly.
Whereas the drilling of wells and the purification of the ensuing ammonia would nonetheless end in carbon emissions, the response itself requires no exterior vitality enter and generates no emissions. The scientists estimate this is able to nonetheless end in carbon emissions 30 occasions decrease than these of typical ammonia manufacturing, however a full evaluation will probably be required to raised perceive the environmental affect of their method.
Industrial scale-up
The staff have been the primary to point out that it’s attainable to supply ammonia utilizing their underground method. Nevertheless, experiments have solely been accomplished in a lab up so far, and extra work will probably be wanted to show whether or not it really works as predicted within the precise situations discovered deep beneath the Earth’s floor.
The researchers plan to run a pilot scale check a number of kilometers underground by 2026. If profitable, they anticipate it might ultimately be attainable to make use of wastewater as a supply of nitrogen-rich water, since it’s common for industrial wastewater and agricultural runoff to include excessive ranges of nitrogen. This might permit integrating wastewater remedy and ammonia manufacturing right into a single course of.
“Nitrogen sources are thought of air pollution in wastewater, and eradicating them prices cash and vitality,” stated Yifan Gao, first writer of the research. “However we might be able to use the wastewater to supply ammonia. It’s a win-win technique.”
A key benefit to producing ammonia underground is that it has potential to be cost-competitive with typical ammonia manufacturing. The researchers estimate that their method would end in a value of about $0.55 per kilogram of ammonia, whereas typical strategies are sometimes priced between $0.4 and $0.8. Integrating wastewater remedy within the course of might yield a further revenue of $3.82 USD per kilogram of ammonia.
Finally, implementation at scale would require scientists and engineers to take care of the complexities of how rocks crack, develop and work together with gases and liquids.
“Engineering designs to implement this work in the true world signify fertile floor for brand new ideas and strategies on the intersection of the chemical, mining, and oil and gasoline industries,” stated Abate.
“Understanding the advanced interface between rocks and reacting fluid is a wealthy space to discover, achieved by combining superior computational and experimental strategies to push our data on this discipline.”
Reference: Yifan Gao et al., Geological ammonia: Stimulated NH3 production from rocks, Joule (2025). DOI: 10.1016/j.joule.2024.12.006
