Thermodynamics applied to iron smelting techniques

Thermodynamics allows us to understand the chemical reactions occurring inside an experimental archeometallurgical shaft furnace for iron smelting. The production of an iron bloom, with the so-called direct process, is described in a daily pyrometallurgical cycle. The experiences suggest that, as higher and better blown furnaces were built for improving the production, different reactions have been involved and a new material, pig iron, has been obtained. Iron is the fourth most abundant element and the second metal in the Earth’s crust; it appeared late in the history of extractive metallurgy because its smelting techniques were more difficult than those already developed for the common, and less abundant, non-ferrous metals. Differently from these more or less easily malleable and castable metals, a solid-state technology had to be developed for iron and its alloys, due to the limited temperature performances of ancient furnaces. Many iron ores have been and are still used in metallurgy, and the standard free energy change is usually adopted in pyrometallurgy to predict the thermodynamic feasibility of a reaction. The Gibbs free energy allows us to evaluate the spontaneity of the reaction.