Chemical sorbents and contactors extract CO2 directly from ambient air. Current facilities operate at the scale of thousands of tons per year, with next-generation plants targeting hundreds of thousands. The energy requirement is significant: 6-10 GJ per ton of CO2 captured.
Spreading crushed silicate rocks on agricultural land accelerates natural weathering processes that consume CO2. Basalt and olivine react with atmospheric carbon dioxide, producing bicarbonates that are carried to the ocean. The approach leverages existing agricultural infrastructure and may improve soil health as a co-benefit. Scaling requires massive mining and distribution logistics.
Injecting CO2 into reactive basalt formations converts it to solid carbonate minerals within two years. Iceland's CarbFix project demonstrated 95% mineralization. The storage is effectively permanent -- measured in geological time.
Heating biomass in the absence of oxygen produces biochar -- a stable form of carbon that can persist in soil for hundreds to thousands of years. Applied as a soil amendment, it improves water retention and nutrient availability while locking carbon underground.
Adding alkaline minerals to ocean water increases its capacity to absorb CO2 while counteracting acidification. The ocean already absorbs roughly a quarter of human emissions; alkalinity enhancement amplifies this natural process. Field trials are underway, but ecological impacts at scale require careful study. The potential is enormous: the ocean's surface area provides unmatched contact with the atmosphere.
Electrochemical systems use electricity to drive CO2 separation, potentially offering lower energy costs and modular scalability. pH-swing methods, molten salt electrolysis, and electrochemical membranes represent diverse approaches to electrical carbon capture.