AN ELECTROCHEMICAL INVESTIGATION OF THE DISSOLUTION OF MAGNETITE IN ACIDIC ELECTROLYTES

The electrochemical behavior of magnetite was investigated in perchloric acid and ethylenediaminetetra-acetic acid (EDTA). The potential dependence of the total dissolution flux is similar for both acids; the form of this dependence indicates that ion-transfer reactions are rate determining. In EDTA-containing electrolytes, equilibrium is established by electron-transfer between the magnetite and the Fe2+/Fe3+ species liberated by dissolution. This process defines the open-circuit potential of magnetite (E(oc)) in this electrolyte. A similar process does not determine E(oc), in perchloric acid; the nature of the processes defining this potential in perchloric acid remains uncertain. The open-circuit dissolution of magnetite in EDTA is much more rapid than that in perchloric acid. This eff ect is attributable to the difference in the values of E(oc), and not to any influence of electrolyte speciation upon the kinetics of the rate determining ion-transfer reactions. Under strong reducing conditions hydrogen evolution occurs and the reduction of magnetite to metallic iron is suspected.