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.

Thermodynamic analysis of chromium reduction from its oxide in gas phase Н2 – Н2О – СО – СО2 in contact with carbon was performed. Oxidation potential (pO2 ) was determined by two nomograms in the coordinates and taking into account condition normalizations xH2O + xH2 + xCO2+ xCO = 1. In calculations, possible parameters of reduction of chromium from Cr2O3 oxide were determined by ratio of dissociation elasticity of the oxide and oxidation potential of the gas phase. In the СО – СО2 – С system, chromium is reduced at temperature of 1505 K if xCO > 0.9995. At this temperature, Cr2O3 compound is reduced in water gas of the following composition xH2 = 0.0186, xH2O = 0.28·10–4, xCO = 0.9809, xCO2 = 4.86·10–4, for which the oxidation potential is equal to dissociation elasticity of oxide With an increase in hydrogen concentration from 0.0186 to 0.99, oxidation potential of water gas in contact with carbon decreases by four orders of magnitude to This should lead to a significant increase in reduction rate. In such a gaseous atmosphere, it is possible to reduce chromium at temperature of 1230 K. It is technologically simple to obtain reducing water gas and at the lowest cost, for example, by heating water vapor in contact with carbon. It is shown that at temperature of 1500 K water gas is obtained with traces of Н2О and СО2 compounds with parameters xH2 = 0.4999, xCO = 0.4996,  Oxidizing potential of such a gas is less than that of chromium oxide, and this difference significantly increases with increasing temperature.