The gas leaving the furnace is known as flue gas. It contains nitrogen,
carbon monoxide, carbon dioxide and fine solid particles including carbon particles. The emission of flue gas into the atmosphere tends to damage the environment and is a source of environmental pollution.
The molten metal obtained from the blast furnace is run into sand moulds where it cools down to solid blocks called pig iron, because its ingots on solidification look like pigs. Pig iron is about 96% iron (Fe), and 4% carbon (c) with small amounts of other impurities such as silicon, sulphur, phosphorus and manganese.