Reduction of Iron Oxides by Carbon and Water Vapor

Abstract: The complete reduction of iron oxide on heating the initial Fe3O4–H2O–C system with isothermal holding is subjected to thermodynamic analysis. (Note that the initial system contains eo moles of Fe3O4 and bo moles of H2O, with excess carbon.) The processes in the system may be divided into four stages. First, the gasification of carbon by water vapor at temperatures below 880 K activates the reaction of the water gas and the dissociation of CO with the formation of lamp black (solid carbon). The composition of the H2–H2O–CO–CO2 gas mixture obtained depends only on the temperature. The carbon consumption at 880 K is ~0.445 mole per mole of water. The second stage, in the range 880–917 K, is the reduction of Fe3O4 to wustite FeO1 + x with different degrees of oxidation. Hydrogen reduces the oxide at temperatures above 888 K. The proportion of the oxide reduced by hydrogen in this temperature range increases from zero to ~63%. The total quantity of Fe3O4 reduced to wustite at 917 K is ~123 moles per mole of water. This is only possible with repeated regeneration of the reducing agents CO and H2 as a result of the gasification of carbon by water vapor and carbon dioxide CO2. The carbon consumption is approximately 78 moles. In the third stage, the wustite FeO1.092 is reduced solely by carbon monoxide CO in the range 917–955°C to wustite FeO1.054, with a lower degree of oxidation. The carbon is only gasified by CO2; the carbon consumption is around 18 moles. In the fourth stage, with isothermal holding at ~955 K, the wustite is reduced to iron by carbon monoxide alone. The carbon consumption is around 257 moles. In a closed system at 1 atm, 1 mole of water is sufficient for the complete reduction of around 123 moles of Fe3O4 in a mixture with excess carbon. The total carbon consumption is ~353 moles, with the production of 368 moles of Fe; that is, the carbon consumption is ~0.21 kg/kg of iron. © 2019, Allerton Press, Inc.