The effect of Fe3+ ions on the electrochemical behaviour of ocean manganese nodule reduction leaching in sulphuric acid solution.

The effect of Fe3+ ions on the ocean manganese nodule reductive leaching in imitated sulphuric acid solutions was investigated. This work is presented in two courses, including the influence of Fe3+ ions on valuable metal extraction and the electrochemical reductive dissolution of manganese nodules. The results show that the beneficial effects of Fe3+ ion can be interpreted based on two aspects: the first is the acceleration caused by the active transformation of Fe3+/Fe2+ pair, and the second is the hydrogen ion buffer action generated by Fe3+ ion hydrolysis on the surface. On one side, Fe3+ ion could lessen the hydrogen consumption happening at the interface layer of the nodule supported by the leaching test and cyclic voltammetry results. On the other side, Fe3+ ions could be converted into Fe2+ ions and then preferentially reduce manganese oxide leading to an acceleration of the charge transfer reaction of the manganese nodule based on cyclic voltammetry, polarization, and impedance analysis results. The reduction leaching of manganese nodules in sulphuric acid solution is mainly controlled by the electrochemical interface reduction corresponding to manganese oxide dissolution, and the active conversion of the Fe3+/Fe2+ couple affects the dissolution of high valence manganese oxide.