Thermodynamic analysis was performed for complete reduction of iron oxide during heating the initial system «Fe3O4 (eo mol) – H2O (bo mol) – C (excess) » with isothermal exposure. By the nature of ongoing reactions, processes in the system can be divided into four stages. Carbon gasification by water vapor at temperatures below 880 K activates water gas reaction and CO dissociation to form black carbon. Composition of the resulting H2 – H2O – CO – CO2 gas mixture depends only on the temperature. The consumption of carbon at 880 K is ~0,4446 moles on 1 mole of water. Reduction of Fe3O4 to wustite FeO1+x with varying degrees of oxidation occurs in the temperature range 880 – 917 K. Hydrogen reduces oxide at temperatures above 888 K. The percentage part of a whole oxide Fe3O4 reduced by hydrogen into this temperature range increases from zero to ~63 %. The total number of Fe3O4, reduced to wustite at 917 K is ~123 moles for 1 mole of water. It is possible only with repeated regeneration of reductants CO and H2 according to the reactions of carbon gasification by water vapor and by dioxide CO2. The carbon expense is about 78 moles. Wustite FeO1.092 formed at 917 K can be reduced by monoxide CO only at temperatures of 917 – 955 K to wustite FeO1.054 with a lower degree of oxidation. Carbon is gasified only by dioxide CO2, the carbon expense is approximately 18 moles. When isothermal exposure is ~955 K, wustite is reduced to iron. Wustite can be reduced only by carbon monoxide. The carbon expense is approximately 257 mol. For full reduction of 123 mol of Fe3O4 in a mixture with an excess of carbon in a closed system at 1 atm, 1 mole of water is sufficient. The total carbon consumption is ~353 moles for obtaining 368 moles of Fe, or ~0.21 kg/kg iron.
