section_path: Production of metallic iron/Main industrial route/Blast furnace processing
section_name: Blast furnace processing
paragraph_text: Blast furnace processing
  
  The blast furnace is loaded with iron ores, usually hematite Fe O or magnetite Fe O, along with coke (coal that has been separately baked to remove volatile components) and flux (limestone or dolomite). "Blasts" of air pre-heated to 900 °C (sometimes with oxygen enrichment) is blown through the mixture, in sufficient amount to turn the carbon into carbon monoxide:
  
  This reaction raises the temperature to about 2000 °C. The carbon monoxide reduces the iron ore to metallic iron:
  
  Some iron in the high-temperature lower region of the furnace reacts directly with the coke:
  
  The flux removes silicaceous minerals in the ore, which would otherwise clog the furnace: The heat of the furnace decomposes the carbonates to calcium oxide, which reacts with any excess silica to form a slag composed of calcium silicate CaSiO or other products. At the furnace's temperature, the metal and the slag are both molten. They collect at the bottom as two immiscible liquid layers (with the slag on top), that are then easily separated. The slag can be used as a material in road construction or to improve mineral-poor soils for agriculture.
  
  Steelmaking thus remains one of the largest industrial contributors of CO emissions in the world.