Iron oxide is a general term for chemical compounds of iron and oxygen. These are abundant in nature and are the main component of iron ore. Familiar forms include reddish-brown rust (hematite, Fe₂O₃) and black rust (magnetite, Fe₃O₄).
The relationship between iron oxide and CO₂ emissions is central to steelmaking. To extract pure iron from iron ore (iron oxide), the oxygen atoms must be removed through a process called reduction. This is traditionally done in a blast furnace using carbon from coke. This chemical reaction, which combines carbon and oxygen, is the main cause of CO₂ emissions during steel production. This is why the industry's carbon footprint is so significant, and why reducing the reliance on iron ore is a key goal for decarbonization.