Geological ammonia: Stimulated NH3 production from rocks

Abstract

Although ammonia production is crucial for global agriculture, it comes with substantial carbon footprints. Here, for the first time, we propose and demonstrate a different method for stimulated (proactive) and in situ geological ammonia (Geo-NH₃) production directly from rocks. Our approach demonstrated that NH₃ can be efficiently generated by reacting natural (Fe,Mg)₂SiO₄ (olivine) minerals with nitrate-source water at 130°C–300°C and 0.25–8.5 MPa, and even at ambient temperature and pressure. Using both actual rocks and synthetic mineral Fe(OH)₂, we investigated mechanisms and optimized conditions through experiments and theoretical calculations. We revealed the basic chemistry enabling Geo-NH₃ production: Fe²⁺ contained in rocks reduces the nitrate source to NH₃. Our approach, involving only the injection of nitrate-source water into the subsurface to utilize in situ subsurface heat and pressure, requires no external H₂ or electric current and emits no direct CO₂, offering a feasible alternative to sustainable NH₃ production at scale.