Process of Magnetite Dissolution in Orthophosphoric and Sulfuric Acid Solutions According to Kinetic and Electrochemical Methods

The kinetics of dissolution and the electrochemical features of the behavior of magnetite (in cathodic polarization) in solutions of sulfuric and orthophosphoric acids are studied. Two independent experimental methods establish that the rate and current of dissolution in H₃PO₄ are higher than in H₂SO₄. This pattern is explained based on the stronger complexing properties of various kinds of phosphate anions in comparison with sulfate anions in solution with iron(III) ions. In the range of studied concentrations of orthophosphoric and sulfuric acids, as well as Fe(II) and Fe(III) ions, the reaction orders for orthophosphoric and sulfuric acids are 1.3 ± 0.1; for iron(II) ions, 0.25 ± 0.1; and for iron(III) ions, –0.25 ± 0.1.