Electrochemical Equilibrium Fe-H2SO4-H2O

When processing metal containing aqueous solutions by metal winning electrolysis it is very useful to know the species distributions near the electrodes as a function of the electrode potential Eh for a given concentration.

  • What is the distribution of di- and trivalent iron for 1 g/l of iron in a sulfuric acid solution? 
  • Using the classical approach, a stoichiometric reaction between Fe2+, Fe3+ and an electron, the Nernst equation yields the result given in Figure 1
  • By applying complex equilibrium thermochemistry a far more detailed and correct answer can be obtained taking simultaneously into consideration Fe2+, Fe3+, FeOH+, FeOH2+, Fe2(OH)2+, Fe2(OH)24+, FeSO4+, and Fe(SO4)2-. The distribution of these species is given in Figure 2.