Abstract:This paper presents the calculation and analysis of the important mononuclear complexes in the Fe-H2O system. Based on the thermodynamic data So298 K, ΔGo298 K and C0p of each reaction substance, the Gibbs free energy of reactions ΔGoT at different temperatures were calculated to construct the dissolved species predominance diagram and Pourbaix diagram of Fe-H2O system at temperatures of 298, 373, 473 and 573 K, respectively. The results show that both Fe2+ and Fe3+ ions can stably exist in the strongly acidic solutions. As the pH increases, Fe2+ and Fe3+ ions are sequentially converted to FeOH+、Fe(OH)20 and Fe(OH)3-, and FeOH2+、Fe(OH)2+、Fe(OH)30 and Fe(OH)4-, respectively. In the high potential regions, Fe2+ is oxidized to Fe3+ and further oxidized to FeO42-. As the temperature increases, the stable regions of Fe2+ and Fe3+ decrease and shift towards the acidic pH regions. Iron phases can be precipitated in the form of FeOOH/Fe2O3 by controlling the reaction potential and pH values. As the temperature rises up to 373 K or above, the dominant region of Fe(OH)4- appears under alkaline conditions, causing corrosion of elemental iron. The stable regions of Fe, FeOOH/Fe2O3 and Fe3O4 in solid phases gradually decrease with the increase of temperature, especially the solid region of Fe2O3 markedly reduces, while the aqueous phase regions continue to expand. Therefore, the higher the temperature in thermodynamic, the more unfavorable it is for the anticorrosion of Fe metal and the precipitation of iron from the aqueous solutions.