One of the chemical industry’s biggest polluters, ammonia manufacturers, may soon get an eco-friendly, cost-saving overhaul with sub-terranean production. This is because scientists from MIT have shown that ammonia can be produced deep underground by mixing nitrogen-laced water with iron-rich minerals.
According to the researchers, the inspiration for this discovery, “… stems from an unusual geological phenomenon observed in the 1980s in Mali, West Africa. [When] Locals discovered a well streaming with hydrogen gas, which scientists later traced to a water-rock chemical reaction beneath the Earth's surface.”
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“It was an 'aha' moment,” recalls Iwnetim Abate of MIT who was the study’s senior author. “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.”
Official data on the issue paints the ammonia producers as the chemical industry’s worst carbon emitters, with the chemical’s production consuming about 2% of global energy, while emitting as much as 2.4 tons of CO2 for every ton of ammonia produced. Yet it remains a vital global raw material, feeding the world as a feedstock for the manufacture of fertilizer. It also has the potential to power the future as a clean fuel. If the chemical industry could make it cleaner and cheaper, then many of humankind’s environmental, industrial, and transport problems could be solved in a stroke.
As MIT’s Ju Li, another of the study’s authors, notes, “Ammonia is pretty important for life.”
To test their alternative ammonia sourcing concept, the MIT team built a rock-water reaction system which copied the Earth's subsurface environment. As the journal Science Daily reports, “They exposed synthetic iron-rich minerals to nitrogen-laced water, triggering a chemical reaction that oxidized the rock and yielded ammonia, which the team dubbed ‘geological ammonia.’”
To better replicate real-world situations, the team then substituted olivine, a naturally occurring rock that is rich in iron, for a synthetic mineral. By adding a copper catalyst and raising the temperature to 300°C, they further refined the procedure. This allowed them to prove both the viability and sustainability of the process as they produced 1.8 kg of ammonia per ton of olivine over the course of 21 hours.
According to the researchers the process emitted no carbon dioxide, required no energy input, and was conducted under ambient conditions.
“These rocks are all over the world, so the method could be adapted very widely across the globe,” says Abate. Before adding the caveat that there is still, “a whole other level of complexity that we'll need to work through.”
The challenge will be to create a system of drilling into deep-seated iron-rich rocks, injecting them with nitrogen-laced water, and navigating the complexities of how rocks expand, fracture, and interact with gasses and liquids.
Yet the reward to ammonia manufacturers for this hard work and expense is a process that is just as cheap if not cheaper than conventional methods, making geological ammonia at an estimated $0.55 per kilogram compared to the current price of $0.40-$0.80.
Moreover, the process could also be used as an approach to solving water pollution, as many rivers and lakes suffer from a build-up of nitrogen, which leads to algal blooming which kills wildlife.
“Nitrogen sources are considered as pollution in wastewater, and removing them costs money and energy,” observes the study’s author Yifan Gao of MIT. “But we may be able use the wastewater to produce ammonia. It's a win-win strategy.”
If a viable way of integrating wastewater treatment with the new geological approach to ammonia production can be found, then the researchers believe this would add an estimated additional income to ammonia companies of $3.82 per kilogram of ammonia.
Currently, the use of ammonia as a raw material for fertilizer is seen as a necessary evil to feed the world, but this new underground technology could provide low-cost, almost limitless amounts.
As the researchers highlight in the study published in the journal Joule, “Our work paves the way for using Earth’s subsurface as a reactor, with abundant rocks as feedstock, to theoretically produce enough NH3 for 2.42 million years while minimizing environmental impact and achieving sustainability and decarbonization in the chemical and energy sectors.”
“When I first produced ammonia from rock in the lab, I was so excited,” recalls Gao. “I realized this represented an entirely new and never-reported approach to ammonia synthesis.”
The chemical industry is often blamed for creating a toxic, polluted world, full of PFAS, plastic waste, and carbon emissions. Yet it also holds the solution to all of humanity’s challenges. Whether it is finding clean water for everyone, feeding everyone, or making medical innovations and sustainable fuels.
With discoveries like the geological ammonia process, then maybe the chemical industry can do even more to improve its image by providing clean fuel and carbon emission-free fertilizer.
Photo credit: Flickr, Richard Hurd, Stockvault, Vectorportal, & Flickr
