Steel and CO2: the basics
Carbon dioxide(CO2) is unavoidable in the current mainstream method of producing hot metal. In chemical terms, the raw material used – iron ore – is an iron oxide, i.e. a compound of iron and Oxygen(O2). To extract metal it is necessary to separate these components. The scientific name of this chemical process taking place in the blast furnace is reduction. Carbon is used as a reducing agent: it combines with the Oxyden(O2) to form Carbon monoxide(CO) and eventually Carbon dioxide(CO2). The main carbon-bearing material used for this is coal, sometimes transformed into coke, which also serves to generate the high temperatures needed to smelt the iron ore.
The most modern steel plants today operate very close to the limits set by physics. This means that further reducing the amount of carbon used for making steel is not possible without technological change.